Determining the parameters of the flood hydrograph model WBNM for urban catchments

Transcription

1 University of Wollongong Research Online University of Wollongong Thesis Collection University of Wollongong Thesis Collections 1998 Determining the parameters of the flood hydrograph model WBNM for urban catchments Petar Milevski University of Wollongong Recommended Citation Milevski, Petar, Determining the parameters of the flood hydrograph model WBNM for urban catchments, Doctor of Philosophy thesis, Department of Civil and Mining Engineering, University of Wollongong, Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library:

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3 DETERMINING the PARAMETERS of the FLOOD HYDROGRAPH MODEL WBNM for URBAN CATCHMENTS A thesis submitted in fulfilment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY from The UNIVERSITY of WOLLONGONG by Petar Milevski BE(Hons) Department of Civil, Mining and Environmental Engineering 1998

4 11 ACKNOWLEDGMENTS I would like to thank the following people for their help in the preparation of this thesis: The University of Wollongong for granting me an Australian Postgraduate Award scholarship. Associate Professor Michael Boyd, my thesis supervisor, for all the excellent advice and guida technical details involved in running WBNM and analysing the results. Mr. Fabian Magrini for helping me with all my computing problems. Without his help I would stil trying to start up my computer. My family and friends for supporting and encouraging me.

5 Ill A. ABSTRACT A.1 Introduction The aim of the thesis is to determine values of the rainfall losses and calibration parameter urban catchments using the upgraded version of the Watershed Bounded Network Model, WBNM Version 2.1. A related part of the study is to determine if WBNM is correctly modelling both the pervious and impervious areas within a catchment and if it is correctly modelling the catchment's watercourse sections. The thesis contains a detailed description of runoff routing models, the way in which they mo rural and urban catchments, and the hydrologic principles which they use. These include RAFTS-XP, RORB and WBNM. The urban stormwater model ILSAX was also reviewed. The principles the models use to calculate runoff from rainfall are very similar. Catchment an rainfall data are entered into the computer for each subcatchment. Appropriate rainfall losses are then subtracted from the rainfall data. The excess rainfall is routed through the overland flow surface, which is also known as storage routing. From this procedure, the model calculates a runoff hydrograph at the outlet of the subcatchment. As this runoff hydrograph travels through the next subcatchment, the computer model routes it through the channel section. Storage routing and channel routing can either be linear or nonlinear. Additionally, the upstream hydrograph can be lagged through the channel section by a specified time. Time lagging of a hydrograph is only applicable when the subsidence of the hydrograph peak is not significant. A.2 Catchments and Rainfall and Data rainfall and streamflow data from catchments in Sydney, Canberra and Melbourne were used in the study. A total of 144 storm events was used in the study. The catchments were initially modelled with one subcatchment. This was found to produce quite acceptable hydrographs. Curtin catchment was also subdivided into 4, 5, 11 and 19 subcatchments to study the effect of catchment subdivision on the results. The catchment and storm data were obtained from the doctoral thesis by Bufill (1989), with additional checking of the validity of the data by the author. Table A.l summarises the catchment sizes and amount of urbanisation.

6 IV Table A.1 - Summary of Catchment Characteristics Catchment Area (km 2 ) Urban Fraction Curtin Mawson Long Gully Ck Giralang.94.7 Maroubra.57 1 Strathfield Fisher's Ghost Ck Jamison Park.21 1 Vine Street.64 1 Impervious surfaces, including roads and house roofs ranged from 5% to 52% of the catchment area. Three methods for determining imperviousfractions were investigated in the study to determine which gave the best estimates of the catchment imperviousfraction. These were: 1. An impervious fraction calculated from orthophoto maps which takes into account all impervious areas. 2. A directly connected imperious fraction calculated from orthophoto maps which includes only the impervious areas that are connected to the drainage system. These are difficult to determine as they require detailed inspections of the catchment. 3. A directly connected imperviousfractiondetermined from rainfall and runoff data collected for a catchment. This method requires the total rainfall runoff depth to be plotted against the rainfall depth for a number of events. Boyd et al. (1993) found that when this was done, the data plotted as a straight line with the slope of this line being the effective directly connected impervious fraction. A.3 Linear and Nonlinear Modelling WBNM was initially run with a nonlinearity of.23 (equivalent to m=.77 for RAFTS and RORB) for both the pervious and impervious areas. This was found to overestimate the calibration parameter C. Studies by Sobinoff et al (1983) and Boyd et al (1987) on natural catchments show parameter C has a value of 1.29 to 1.8. In this study, modelling on seven urban catchments produced a value of Further research was then undertaken to determine the reason for the increase. WBNM was modified to run linearly for the impervious areas and remained nonlinear on pervious areas. Modelling was done using two different rainfall loss models (initial loss-constant loss rate LR and initial loss-runoff proportion RP). Baseflows were not modelled as WBNM does not have a soil

7 V infiltration model. The pervious and impervious parts of the catchments were also modelled using two different methods. The methods were: 1. Split catchment modelling where the pervious and impervious areas are treated separately (Boyd and Bufill, 1992) 2. Lumped catchment modelling where the pervious and impervious areas are modelled together and parameter C is adjusted to compensate for the amount of impervious area on the catchment. The method used to adjust parameter C is discussed in chapter 5. A.4 Split and Lumped Catchment Modelling Split catchment modelling was found to be an accurate way of representing urbanised catchment Parameter C was found to decrease slightly with the changes made to WBNM. Table A.2 shows the results from chapter 7. Note the slight reduction over the results of chapter 4 (C=2.24). Table A.2 - Split Catchment Results from Chapter 7 Rainfall Loss Model LR RP Parameter C (excluding Jamison Pk & Vine St) Parameter C (including all catchments) The initial loss-runoff proportion model was particularly suited to those events where very little pervious area contribution occurred. The main reason for this was that unlike the initial loss-constant loss rate model, the runoff proportion model retained the temporal pattern of the rainfall hyetograph in the pervious area runoff hydrograph. WBNM was able to calculate some excess rainfall for the pervious area and this helped improve the fit of the calculated and recorded hydrographs. In these types of events, there were apparent problems when the initial loss-constant loss rate model was used because the high loss rate subtracted most of the rainfall, giving a distorted pervious area excess rainfall hyetograph. Lumped catchment modelling was found to give poor calibration on urban catchments for multi-p rainfall events, but performed very well for single peak rainfall events. Table A.3 shows the results from the lumped modelling performed in chapters 5 and 6. Note that parameter C has reduced about 4 % over the split modelling (Table A.2).

8 VI Table A.3 - Lumped Catchment Results from Chapter 5 and 6 Rainfall Loss Model Parameter C Parameter C (excluding Jamison Pk & Vine St) (includingall catchments) LR LOfj L35 RP 676" OM Sections A3 and A4 indicate that the lag parameter of a rainfall runoff model can vary significantly, depending on the particular rainfall loss and routing functions. This is discussed further in chapter 2. A.5 Investigating High Parameter C Values High parameter C values were found to occur on the three smallest catchments, and also for the smaller storm events on all catchments. Analysis of the results uncovered three reason for these high values. One reason was that the impervious fraction was possibly too high, and needed to be modified f small events. When a plot of the rainfall data against the runoff data was prepared for small storm events (up to 4 mm of rainfall) using the method by Boyd et al (1993), the effective impervious fraction halved. Modelling with this modified imperviousfractionslightly reduced the parameter C values (Table A.4). Table A.4 - Results from Modified Impervious Fraction Modelling Catchment Maroubra Jamison Park C«, for IMP DC C ave forlmp MOD Vine Street The second reason may be due to a change in the loss behaviour of the catchment. Some of the directly connected impervious area probably has depression storage and some does not. As modelling was performed using one subcatchment, the rainfall losses assigned may not be representative of the entire catchment, and more accurate results may be possible by subdividing into a number of subcatchments and assigning different rainfall losses to different areas. This was investigated in chapter 9 and 11. The third reason was that the area exponent used to model impervious areas may be too high. The area exponent for both the pervious and impervious areas was set at.57 in the original version of the model, (equation A-1).

9 vn K = IMPFACT. C. A "Q" 23 (original impervious area lag equation) equation A-l K = IMPFACT.C.A 25 (final impervious area lag equation) equation A-2 However this study showed that a trend between parameter C and the catchment size suggested a lower area exponent should be used. Using linear regression, the new impervious area exponent was calculated to be.25 (equation A-2). Note that from work done in this study, thefinallag equation is also linear (the discharge coefficient was changed from -.23 to ). Testing with the new area exponent confirmed that the real cause of the problem was the way W was modelling impervious areas. Subsequent modelling with this value eliminated the trend between C and catchment size. The average parameter C values reduced to 1.63 for LR modelling and 1.43 for RP modelling, which are similar to parameter C values calculated by Boyd (1985) for rural catchments (C= 1.7). Final adjustment to the factor IMPFACT was performed to make the parameter C values close to those for rural catchments. The old value of IMPFACT was.111 and this was adjusted to.1. This had the effect of increasing parameter C to 1.7 for LR model and to 1.5 for RP model. A.6 Catchment Subdivision Finally, WBNM was applied to the Curtin catchment when it was subdivided into 4, 5, 11 and 19 subcatchments. Modelling showed that different amounts of subdivision did not significantly affect the calculated hydrograph, indicating that WBNM was satisfactorily modelling both overland and watercourse runoff. Nonlinear routing of storm runoff in watercourses was found to be satisfactory. When modellin watercourse sections with WBNM, a routing factor of.6 is applied to watercourses in a natural state. The lined watercourse sections in the Curtin catchment were found to have a Manning's roughness of approximately one third of channels in a natural state, indicating that a watercourse factor of.2 should be used. After detailed testing a watercourse factor of.15 was applied to the lined watercourse sections. The results obtained were very good, with calculated peak discharges in good agreement with the recorded.

10 viii The study showed that it is important to correctly represent the stream network when the catchment is divided into subcatchments. The actual number of subcatchments into which the catchment is divided is not critical. It was also discovered that the watercourse factor WCFACT was very sensitive to parameter C. If applied watercourse factor was too high, WBNM would underestimate the peak calculated discharge and vice versa. A.7 Summary To summarise the work in this thesis, WBNM has been applied to 144 storm events on nine urban catchments located in Canberra, Sydney and Melbourne. The catchments ranged from.21 to 27 km 2 in size, with directly connected impervious fractions from.5 to.31. Two rainfall loss models were used in the study, to determine which was better suited to model catchments. They were the initial loss-constant loss rate (LR) and initial loss-runoff proportion (RP) models. Both performed well, but it was found that the RP model was better for urbanised catchments. Modifications to the impervious area lag equation were made. It was found that better hydrograp reproduction was achieved when the impervious areas were modelled linearly with an area exponent of.25. The pervious areas performed satisfactorily with a nonlinearity of.23 and area exponent of.57. The impervious area factor IMPFACT was set at.1. The channel routing was performed using the nonlinear channel routing equation and was found to be satisfactory. The final lag equations were: K^ = OAjJ^Q-* 23 equation A-3 K imp =.1.C.A iinp - 25 equation A-4 K wc = WCFACT.C.AJ "Q^23 equation A-5 where K^ = pervious area lag time (hours) Kj^p = impervious area lag time (hours) K wc = watercourse lag time (hours) A per = A tot.(l-imp)(km 2 ) A iinp = A tot.imp(km 2 ) A tot = total subcatchment area (km 2 ) IMP = directly connected impervious fraction

11 IX WCFACT = relative lag time for runoff from impervious and pervious surfaces WBNM was used to model catchments undivided and subdivided to determine its performance on both. It was found that for an undivided catchment, parameter C is to be set at 1.7 for modelling with the initial loss constant loss rate model and 1.5 with the initial loss runoff proportion rainfall loss model. For a subdivided catchment, the parameter C values were found to reduce by about 25 %. Thus, parameter C is to be set at 1.29 for modelling with the initial loss constant loss rate model and 1.14 with the initial loss runoff proportion rainfall loss model.

12 X PUBLICATION Boyd, M.J. and Milevski. P. (1996) 'Modelling from Pervious and Impervious Surfaces Urban Catchments.', Proceedings of the Seventh International Conference on Urban Stormwater Drainage, Vol.2, pp

13 TABLE OF CONTENTS A. ABSTRACT in A.1 INTRODUCTION i A.2 CATCHMENTS AND RAINFALL AND RUNOFF DATA i A.3 LINEAR AND NONLINEAR MODELLING iv A.4 SPLIT AND LUMPED CATCHMENT MODELLING V A.5 INVESTIGATING HIGH PARAMETER C VALUES vi A.6 CATCHMENT SUBDIVISION vii A.7 SUMMARY VIII 1. INTRODUCTION ] BACKGROUND AIM GENERAL SUMMARY LITERATURE REVIEW OF URBAN RUNOFF ROUTING PROCEDURES 2^ 2.1 INTRODUCTION LITERATURE REVIEW INTRODUCTION MODELLING OF RURAL AND URBAN CATCHMENTS Infiltration and Impervious Fraction Shape METHOD OF CALCULATING FLOWS Introduction The Unit Hydrograph The Kinematic Wave RUNOFF ROUTING LUMPED AND SPLIT MODELLING RAINFALL RUNOFF MODELS INTRODUCTION RSWM / RAFTS PROGRAM ORGANISATION HYDROGRAPH GENERATION MODULE RAINFALL ROUTING METHOD 2-15

14 Xll STORAGE DISCHARGE RELATIONSHIP RAINFALL LOSS MODULE Initial and Continuing Loss Model RORB INTRODUCTION STORAGE-DISCHARGE RELATIONS RELATIVE DELAY TIME Coefficient Kc ROUTING METHOD ILSAX INTRODUCTION HYDROLOGIC METHODS Treatment of Rainfall Catchment Definition Hydrograph Generation WBNM INTRODUCTION EARLIER VERSIONS OF WBNM WBNM VERSION DESCRIPTION OF WBNM RAINFALL LOSS MODELS MODELLING WATERCOURSES MODELLING STORAGE RESERVOIRS MODELLING URBANISED CATCHMENTS MODELLING OVERLAND FLOW FLOW DIVERSION MODELLING CATCHMENT DIVISION INTO SUBCATCHMENTS APPLICATION OF WBNM TO CATCHMENTS WBNM COMPUTER PROGRAM Input Data Files Output Files Graphic Displays CATCHMENTS AND STORM EVENTS INTRODUCTION CATCHMENT AREA MEASURES OF URBANISATION SURFACE SLOPE RAINFALL DATA WODEN VALLEY CATCHMENTS INTRODUCTION 3-7

15 xiii CURTIN LONG GULLY CREEK MAWSON GIRALANG CATCHMENT MAROUBRA CATCHMENT STRATHFIELD CATCHMENT FISHER'S GHOST CREEK CATCHMENT JAMISON PARK CATCHMENT VINE STREET CATCHMENT NONLINEAR SPLIT MODELLING WITH THE LOSS RATE MODEL INTRODUCTION RESULTS FOR THE CANBERRA CATCHMENTS CURTIN MAWSON LONG GULLY CREEK GIRALANG RESULTS FOR THE SYDNEY CATCHMENTS MAROUBRA STRATHFIELD FISHER'S GHOST CREEK DISCUSSION OF RESULTS CONCLUSIONS LUMPED MODELLING WITH THE CONSTANT LOSS RATE MODEL INTRODUCTION PROCEDURE FOR ADJUSTING THE CALIBRATION PARAMETER RESULTS FOR THE CANBERRA CATCHMENTS CURTIN MAWSON LONG GULLY CREEK GIRALANG RESULTS FOR THE SYDNEY CATCHMENTS MAROUBRA STRATHFIELD FISHER'S GHOST CREEK JAMISON PARK RESULTS FOR THE MELBOURNE CATCHMENT VINE STREET 5-28

16 XIV 5.6 DISCUSSION OF RESULTS CONCLUSIONS LUMPED MODELLING WITH THE RUNOFF PROPORTION MODEL INTRODUCTION RESULTS FOR THE CANBERRA CATCHMENTS CURTIN MAWSON LONG GULLY CREEK GIRALANG RESULTS FOR THE SYDNEY CATCHMENTS MAROUBRA STRATHFIELD FISHER'S GHOST CREEK JAMISON PARK RESULTS FOR THE MELBOURNE CATCHMENT VINE STREET DISCUSSION OF RESULTS AND CONCLUSIONS SPLIT MODELLING WITH THE LOSS RATE AND RUNOFF PROPORTION MODELS INTRODUCTION INITIAL LOSS-CONSTANT LOSS RATE RESULTS (LR) RESULTS FOR THE CANBERRA CATCHMENTS Curtin Mawson Long Gully Creek Giralang RESULTS FOR THE SYDNEY CATCHMENTS Maroubra Strathfield Fisher's Ghost Creek Jamison Park RESULTS FOR THE MELBOURNE CATCHMENT Vine Street INITIAL LOSS-RUNOFF PROPORTION RESULTS (RP) RESULTS FOR THE CANBERRA CATCHMENTS Curtin Mawson Long Gully Creek 7-36

17 XV Giralang RESULTS FOR THE SYDNEY CATCHMENTS Maroubra Strathfield Fisher's Ghost Creek Jamison Park THE MELBOURNE CATCHMENT Vine Street DISCUSSION OF FULLY NONLINEAR MODELLING AGAINST NONLINEAR PERVIOUS AND LINEAR IMPERVIOUS MODELLING USING LOSS RATE MODEL DISCUSSION OF RUNOFF PROPORTION MODELLING WITH NONLINEAR PERVIOUS AND LINEAR IMPERVIOUS USING RP CONCLUSIONS MODIFYING THE IMPERVIOUS FRACTION INTRODUCTION MODIFIED IMPERVIOUS FRACTION INTRODUCTION MAROUBRA JAMISON PARK VINE STREET DISCUSSION OF RESULTS CONCLUSIONS MODIFYING THE CATCHMENT LAG ON IMPERVIOUS AREAS INTRODUCTION THE IMPERVIOUS AREA LAG EQUATION INITIAL LOSS-CONTINUING LOSS MODELLING (LR) RESULTS FOR THE CANBERRA CATCHMENTS Curtin Mawson Long Gully Creek Giralang RESULTS FOR THE SYDNEY CATCHMENTS Maroubra Strathfield Fisher's Ghost Creek Jamison Park 9-22

18 XVI RESULTS FOR THE MELBOURNE CATCHMENT Vine Street INITIAL LOSS-RUNOFF PROPORTION MODELLING (RP) THE CANBERRA CATCHMENTS Curtin Mawson Long Gully Creek Giralang THE SYDNEY CATCHMENTS Maroubra Strathfield Fisher's Ghost Creek Jamison Park THE MELBOURNE CATCHMENT Vine Street DISCUSSION OF RESULTS Loss RATE MODELLING RUNOFF PROPORTION MODELLING CONCLUSIONS FINAL MODIFICATIONS TO WBNM VERSION INTRODUCTION ADJUSTMENT OF THE FACTOR IMPFACT INITIAL LOSS-CONTINUING LOSS MODEL THE CANBERRA CATCHMENTS RESULTS FOR THE SYDNEY CATCHMENTS RESULTS FOR THE MELBOURNE CATCHMENT RESULTS USING THE RUNOFF PROPORTION MODEL THE CANBERRA CATCHMENTS THE SYDNEY CATCHMENTS THE MELBOURNE CATCHMENT DISCUSSION OF RESULTS FINAL ANALYSIS OF RESULTS STATISTICAL ANALYSIS OF RESULTS RECOMMENDATIONS FOR USING WBNM VERSION APPLICATION OF WBNM TO A SUBDIVIDED CATCHMENT INTRODUCTION 11-2

19 XV WATERCOURSE SECTION - DATA COLLECTION AND ANALYSIS SUBDIVISION OF THE CURTIN CATCHMENT INTRODUCTION SUBDIVISION INTO 4 SUBCATCHMENTS SUBDIVISION INTO 5 SUBCATCHMENTS SUBDIVISION INTO 11 SUBCATCHMENTS SUBDIVISION INTO 19 SUBCATCHMENTS MODEL CALIBRATION METHODOLOGY STORM EVENTS RAINFALL LOSSES AND PARAMETER C MODELLING THE WATERCOURSE SECTIONS MODELLING METHOD RESULTS FOR 4 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 5 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 11 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 19 SUBCATCHMENTS WITH MODELLING METHOD MODELLING METHOD RESULTS FOR 4 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 5 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 11 SUBCATCHMENTS WITH MODELLING METHOD RESULTS FOR 19 SUBCATCHMENTS WITH MODELLING METHOD DISCUSSION OF RESULTS EFFECT OF CATCHMENT SUBDIVISION ON PARAMETER C VALUES EFFECT OF WCFACT ON PARAMETER C VALUES FOR VARIOUS DEGREES OF SUBDIVISION VALIDITY OF MODELLING WITH METHOD 1 AND METHOD CONCLUSIONS 11-43

20 12. FINAL DISCUSSION AND CONCLUSIONS INTRODUCTION TOTAL IMPERVIOUS FRACTION AND DIRECTLY CONNECTED IMPERVIOUS FRACTION RAINFALL LOSS MODELS MODIFIED IMPERVIOUS FRACTION THE FACTOR IMPFACT SPLIT CATCHMENT MODELLING OR LUMPED CATCHMENT MODELLING THE WATERCOURSE FACTOR WCFACT MODELLING CATCHMENTS WITH ONE SUBCATCHMENT AND SUBDIVIDED INTO SEVERAL SUBCATCHMENTS SUMMARY REFERENCES 13-2 A. APPENDIX A A2 A. 1 OLD WBNM INPUT DATA FILE FORMAT A-2 A.2 INPUT DATA FILE FORMAT FOR WBNM VERSION 2.1 A-5 A.3 SAMPLE INPUT DATA FILE A-1 A.4 CD WITH INPUT AND OUTPUT DATA FILES A-14

21 XIX LIST OF FIGURES Figure Number and Description Figure 2.1- Simplified Representation Of RSWM/RAFTS (RAFTS-XP V 4. Manual, 1993) Figure Schematic of RORB Model (AR&R, 1987) Figure Construction of Hydrograph by Time Area Method Figure Construction of Pervious and Impervious Area Hydrographs Figure WBNM Schematic (Boyd et al. 1987) Figure Schematic of WBNM Version 2.1 (Boyd et al., 1994) Figure Hydrographs on Natural and Urban Catchments (Boyd et al.1994) Figure Rainfall and s (Boyd et al, 1993) Figure Calculation of ARI for Giralang (Bufill, 1989) Figure Hyetographs and Hydrographs for Curtin (IMP =.17) Figure Plot of Parameter C against Peak Flow and Ratio for Curtin (IMP=.17) Figure Plot of Parameter C against Peak Flow and Ratio for Mawson (IMP =.21) Figure Plot of Parameter C against Peak Flow and Ratio for Mawson (IMP=.26) Figure Hyetographs and Hydrographs for Mawson (IMP =.21) Figure Hyetographs and Hydrographs for Long Gully Creek (IMP =.5) Figure Plot of Parameter C against Peak Flow and Ratio for Long Gully Creek (IMP =.5) Figure Parameter C against Peak Flow and Ratio for Giralang (IMP =.22) Figure Parameter C against Peak Flow and Ratio for Giralang (IMP =.35) Figure Hyetographs and Hydrographs for Giralang (IMP =.22) Figure Hyetographs and Hydrographs for Maroubra (IMP =.16) Figure Plot of Parameter C against Peak Flow and Ratio for Maroubra (IMP =.16) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.18) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.29) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.5) Figure Hyetographs and Hydrographs for Strathfield (IMP =.29) Figure Plot of Parameter C against Peak Flow and Ratio for Fisher's Ghost Creek (IMP=.25)

22 XX Figure Plot of Parameter C against Peak Flow and Ratio for Fisher's Ghost Creek (IMP=.36) Figure Hyetographs and Hydrographs for Fisher's Ghost Creek (IMP =.25) Figure Plot of Average Parameter C against Catchment Area and Impervious Fraction Figure Plot of Parameter C against Qrec and Ratio for all Catchments Figure Plot of URB against IMP (from RAFTS-XP, 1994) Figure Plot of Cnj r against Flowrate for Curtin Figure Hydrographs for Curtin Figure Plot of Cmr against Flowrate for Mawson Figure Hydrographs for Mawson Figure Plot of Cnjr against Flowrate for Long Gully Creek Figure Hydrographs for Long Gully Creek Figure Plot of Cmr against Flowrate for Giralang Figure Hydrographs for Giralang Figure Plot of Cnjr against Flowrate for Maroubra Figure Hydrographs for Maroubra Figure Plot of Cnjr against Flowrate for Strathfield Figure Hydrographs for Strathfield Figure Plot of Cnjr against Flowrate for Fisher's Ghost Creek Figure Hydrographs for Fisher's Ghost Creek Figure Plot of Cnjr against Flowrate for Jamison Park Figure Hydrographs for Jamison Park Figure Plot of C m r against Flowrate for Vine Street Figure Hydrographs for Vine Street Figure Plot of Cmr against Flowrate for all Catchments Figure Plot of Average Cmr against Catchment Area for all catchments Figure Plot of C m r against Flowrate for Curtin Figure Hydrographs for Curtin Figure Plot of Cmr against Flowrate for Mawson Figure Hydrographs for Mawson Figure Plot of C m r against Flowrate for Long Gully Creek Figure Hydrographs for Long Gully Creek Figure Plot of C m r against Flowrate for Giralang Figure Hydrographs for Giralang Figure Plot of C m r against Flowrate for Maroubra Figure Hydrographs for Maroubra Figure Plot of C m r against Flowrate for Strathfield Figure Hydrographs for Strathfield Figure Plot of C m r against Flowrate for Fisher's Ghost Creek Figure Hydrographs for Fisher's Ghost Creek Figure Plot of Cmr against Flowrate for Jamison Park

23 XXI Figure Hydrographs for Jamison Park Figure Plot of C m r against Flowrate for Vine Street Figure Hydrographs for Vine Street Figure Plot of C m r against Flowrate for all catchments Figure Plot of C m r against Catchment Area for all catchments Figure Plot of C against Flowrate and Ratio for Curtin (LR) Figure Single Peak Events for Curtin (LR) Figure Plot of C against Flowrate Ratio for Mawson (LR) Figure Hydrographs for Mawson (LR) Figure Plot of C against Flowrate and Ratio for Long Gully Creek (LR) Figure Hydrographs for Long Gully Creek (LR) Figure Plot of C against Flowrate Ratio for Giralang (LR) Figure Hydrographs for Giralang (LR) Figure Plot of C against Flowrate and Ratio for Maroubra (LR) Figure Hydrographs for Maroubra (LR) Figure Plot of Parameter C against Flowrate and Ratio for Strathfield (LR) Figure Hydrographs for Strathfield (LR) Figure Plot of Parameter C against Flowrate Ratio for Fisher's Ghost Creek (LR) Figure Hydrographs for Fisher's Ghost Creek (LR) Figure Plot of C against Flowrate and Ratio of Ratio for Jamison Park (LR) Figure Single Peak Events for Jamison Park (LR) Figure Plot of Parameter C against Flowrate and Ratio for Vine Street (LR) Figure Single Peak Events for Vine Street (LR) Figure Plot of Parameter C against Flowrate and Ratio for Figure Hydrographs for Curtin (RP) Figure Plot of Parameter C against Flowrate and Ratio for Mawson (RP) Figure Hydrographs for Mawson (RP) Figure Plot of Parameter C against Flowrate and Ratio for Long Gully Creek (RP) Figure Hydrographs for Long Gully Creek (RP) Figure Plot of Parameter C against Flowrate and Ratio for Giralang (RP) Figure Hydrographs for Giralang (RP) Figure Plot of Parameter C against Flowrate and Ratio for Maroubra (RP) Figure Hydrograph for Maroubra (RP) Figure Plot of Parameter C against Flowrate and Ratio for Strathfield (RP)

24 XX11 Figure Hydrographs for Strathfield (RP) Figure Plot of Parameter C against Flowrate and Ratio for Fisher's Ghost Creek (RP) Figure Hydrograph for Fisher's Ghost Creek (RP) Figure Plot of Parameter C against Flowrate and Ratio for Jamison ark (RP) Figure Hydrographs for Jamison Park (RP) Figure Plot of Parameter C against Flowrate and Ratio for Vine Street (RP) Figure Hydrographs for Vine Street Figure Plot of Parameter C against Flowrate for all Catchments with Loss Rate Model Figure Plot of Parameter C against Ratio for all Catchments with Loss Rate Model Figure Plot of Parameter C against Flowrate for all Catchments for Proportion Model Figure Plot of Parameter C against Ratio for all Catchments for Proportion Model Figure Trend between Parameter C and Catchment Area Figure Plots of against Rainfall for Maroubra Figure Plot of Parameter C against Peak Flowrate and Ratio for Maroubra Figure Hydrographs for Maroubra with Modified IMP Figure Rots of against Rainfall for Jamison Park Figure Plot of Parameter C against Peak Flowrate and Ratio for Jamison Park Figure Hydrographfitfor Jamison Park with Modified IMP Figure Plots of against Rainfall for Vine Street Figure Plot of Parameter C against Qrec and Ratio for Vine Street Figure Some Hydrographs for Vine Street with Modified IMP Figure Plot of Parameter C against Qrec and Ratio Figure Plot of Mean Parameter C against Catchment Area Figure Plot of Parameter C against Qrec and Ratio for Curtin (LR) Figure Hydrographs for Curtin (LR) Figure Plot of Parameter C against Qrec and Ratio for Mawson (LR) Figure Hydrographs for Mawson (LR) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek Figure Hydrographs for Long Gully Creek (LR) Figure Plot of Parameter C against Qrec and Ratio for Giralang (LR) Figure Hydrographs for Giralang (LR) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (LR) Figure Hydrographs for Maroubra (LR)

25 xxiii Figure Plot of Parameter C against Qrec and Ratio for Strathfield (LR) Figure Hydrographs for Strathfield (LR) Figure Plot of Parameter C against Qrec Ratio for Fisher's Ghost Creek Figure Hydrographs for Fisher's Ghost Creek (LR) Figure Plot of Parameter C against Qrec Ratio for Jamison Park (LR) Figure Hydrographs for Fisher's Ghost Creek (LR) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (LR) Figure Hydrographs for Vine Street (LR) Figure 9.2- Plot of Parameter C against Qrec and Ratio for Curtin (RP) Figure Hydrographs for Curtin (RP) Figure Plot of Parameter C against Qrec and Ratio for Mawson (RP) Figure Hydrographs for Mawson (RP) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Figure Hydrographs for Long Gully Creek (RP) Figure Plot of Parameter C against Qrec and Ratio for Giralang (RP) Figure Hydrographs for Giralang (RP) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (RP) Figure Hydrographs for Maroubra (RP) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (RP) Figure Hydrographs for Strathfield (RP) Figure Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Figure Hydrographs for Fisher's Ghost Creek (RP) Figure Plot of Parameter C against Qrec and Ratio for Jamison Park (RP) Figure Hydrographs for Jamison Park (RP) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (RP) Figure Hydrographs for Vine Street (RP) Figure Plot of Mean Parameter C against Catchment Area after modelling with Figure Plots of Parameter C against Peak Discharge and Figure Plots of Parameter C against Peak Discharge and Figure Plot of Mean Parameter C against Catchment Area after modelling with Figure Plot of Parameter C against Qrec and Ratio for Curtin (LR) Figure Plot of Parameter C against Qrec and Ratio for Mawson (LR) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (LR) Figure Plot of Parameter C against Qrec and Ratio for Giralang (LR) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (LR) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (LR) Figure Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Figure Plot of Parameter C against Qrec and Ratio for Jamison Park (LR) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (LR) Figure Plot of Parameter C against Qrec and Ratio for Curtin (RP) Figure Plot of Parameter C against Qrec and Ratio for Mawson (RP) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (RP)

26 XXIV Plot of Parameter C against Qrec and Ratio for Giralang (RP) Plot of Parameter C against Qrec and Ratio for Maroubra (RP) Plot of Parameter C against Qrec and Ratio for Strathfield (RP) Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Creek (RP) Plot of Parameter C against Qrec and Ratio for Jamison Park (RP) Plot of Parameter C against Qrec and Ratio for Vine Street (RP) Plots of C against Qrec for Loss Rate Modelling Plots of C against Qrec for Proportion Modelling Plot of C a ve against Catchment Area for Loss Rate modelling Plot of C a ve against Catchment Area for Proportion modelling Comparison C ur b and C m r against Catchment Area Frequency Distribution of Individual Loss Rate values Frequency Distribution of Individual Proportion values Typical Channel cross section Detail Typical Channel Long Section Detail 1.3- Flow against Area at various locations WBNM Model Structure for 4 Subcatchments WBNM Model Structure for 5 Subcatchments WBNM Model Structure for 11 Subcatchments WBNM Model Structure for 19 Subcatchments 1.8- Mass Curves for all Storm Events Parameter C values for various WCFACT Parameter C values for various WCFACT Parameter C values for various WCFACT Parameter C values for various WCFACT Parameter C values for WCFACT = Parameter C values for WCFACT = Parameter C values for WCFACT = Parameter C values for WCFACT = Effect of Fineness of Subdivision on Average Parameter C Effect on Model Subdivision on Model Response (Boyd, 1979) Effect of WCFACT on Parameter C for various Degrees of Subdivision Comparison between Method 1 and Method 2 Parameter C

27 LIST OF TABLES Table Number and Description Table Summary of Some Lag Relations for Rural and Urban Catchments Table Relation Between Impervious And Urbanisation Table Reach Types (RORB Version 3 User manual, 1983) Table Division of catchments into subcatchments (Boyd, 1985) Table Summary of Catchment Details Table Example of IFD Table for Canberra Catchments (Bufill, 1989) Table Summary of Storm Event Details Table Curtin Catchment Events (Bufill, 1989) Table Mawson Catchment Events (Bufill, 1989) Table Long Gully Creek Catchment Events (Bufill, 1989) Table Giralang Catchment Events (Bufill, 1989) Table Maroubra Catchment Events (Bufill, 1989) Table Strathfield Catchment Events (Bufill, 1989) Table Fisher's Ghost Creek Catchment Events (Bufill, 1989) Table Jamison Park Catchment Events (Bufill, 1989) Table Vine Street Catchment Events (Bufill, 1989) Table List of Storm Events Table Summary of Results for Curtin (IMP=.17) Table Summary of Results for Mawson (IMP=.21) Table Summary of Results for Mawson (IMP=.26) Table Summary of Results for Long Gully Creek (IMP=.5) Table Summary of Results for Giralang (IMP=.22) Table Summary of Results for Giralang (IMP=.35) Table Summary of Results for Maroubra (IMP=.16) Table Summary of Results for Maroubra (IMP=.52) Table Summary of Results for Strathfield (IMP=.18) Table Summary of Results for Strathfield (IMP=.29) Table Summary of Results for Strathfield (IMP=.5) Table Summary of Results for Fisher's Ghost Creek (IMP=.25) Table Summary of Results for Fisher's Ghost Creek (IMP=.36) Table Relation between Impervious and Urbanisation (from RAFTS-XP, 1994) Table Urban Fractions using RAFTS-XP Method Table Summary of Results for Curtin Table Summary of Results for Mawson Table Summary of Results for Long Gully Creek Table Summary of Results for Giralang

28 Table Summary of Results for Maroubra Table Summary of Results for Strathfield Table Summary of Results for Fisher's Ghost Creek Table Summary of Results for Jamison Park Table Summary of Results for Vine Street Table Summary of Results for Curtin Table Summary of Results for Mawson Table Summary of Results for Long Gully Creek Table Summary of Results for Giralang Table Summary of Results for Maroubra Table Summary of Results for Strathfield Table Summary of Results for Fisher's Ghost Creek Table Summary of Results for Jamison Park Table Summary of Results for Vine Street Table Summary of Results for Curtin (LR) (IMP=.17) Table Summary of Results for Mawson (LR) (1MP=.21) Table Summary of Results for Long Gully Creek (LR) (IMP=.5) Table Summary of Results for Giralang (LR) (IMP=.22) Table Summary of Results for Maroubra (LR) Table Summary of Results for Strathfield (LR) Table Summary of Results for Fisher's Ghost Creek (LR) Table Summary of Results for Jamison Park (LR) Table Summary of Results for Vine Street (LR) Table Summary of Results for Curtin (RP) Table Summary of Results for Mawson (RP) Table Summary of Results for Long Gully Creek (RP) Table Summary of Results for Giralang (RP) Table Summary of Results for Maroubra (RP) Table Summary of Results for Strathfield (RP) Table Summary of Results for Fisher's Ghost Creek (RP) Table Summary of Results for Jamison Park (RP) Table Summary of Results for Vine Street (RP) Table Parameter C values for Differing WBNM Models Table Summary of Results for Maroubra Table Summary of Results for Jamison Park Table Summary of Results for Vine Street Table Summary of Results for Curtin (LR) Table Summary of Results for Mawson (LR) Table Summary of Results for Long Gully Creek (LR)

29 xxvii Table Summary of Results for Giralang (LR) Table Summary of Results for Maroubra (LR) Table Summary of Results for Strathfield (LR) Table Summary of Results for Fisher's Ghost Creek (LR) Table Summary of Results for Jamison Park (LR) Table Summary of Results for Vine Street (LR) Table Summary of Results for Curtin (RP) Table Summary of Results for Mawson (RP) Table Summary of Results for Long Gully Creek (RP) Table Summary of Results for Giralang (RP) Table Summary of Results for Maroubra (RP) Table Summary of Results for Strathfield (RP) Table Summary of Results for Fisher's Ghost Creek (RP) Table Summary of Results for Jamison Park (RP) Table Summary of Results for Vine Street (RP) Table Parameter C values for Different Loss Models Table Summary of mean Parameter C and Median Loss Rates for Canberra Catchments Table Summary of Results for Curtin (LR) Table Summary of Results for Mawson (LR) Table Summary of Results for Long Gully Creek (LR) Table Summary of Results for Giralang (LR) Table Summary of mean Parameter C and Median Loss Rates for Sydney Catchments Table Summary of Results for Maroubra (LR) Table Summary of Results for Strathfield (LR) Table Summary of Results for Fisher's Ghost Creek (LR) Table Summary of Results for Jamison Park (LR) Table Summary of Results for Vine Street (LR) Table Summary of mean Parameter C and Median Proportion for Canberra Catchments Table Summary of Results for Curtin (RP) Table Summary of Results for Mawson (RP) Table Summary of Results for Long Gully Creek (RP) Table Summary of Results for Giralang (RP) Table Summary of mean Parameter C and Median Proportion for Sydney Catchments Table Summary of Results for Maroubra (RP) Table Summary of Results for Strathfield (RP) Table Summary of Results for Fisher's Ghost Creek (RP) Table Summary of Results for Jamison Park (RP) Table Summary of Results for Vine Street (RP) Table Comparison between Parameter C in Chapter 4 and 1 (LR) Table Mean and Standard Deviation of Errors between the two Loss Models Table Recommended Watercourse Factors (Boyd et al., 1994)

30 Table Cross Section and Long-Section Data Dimensions Table Channel Bed Slopes at Various Locations Table Stage-Discharge at location 1 Table Stage-Discharge at location 2 Table Stage-Discharge at location 3 Table Stage-Discharge at location 4 Table Stage-Discharge at location 5 Table Stage-Discharge at location 7 Table Stage-Discharge at location 8 Table Stage-Discharge at location 9 Table Stage-Discharge at location 1 Table Subdivision data for Curtin with 4 Subcatchments Table Subdivision data for Curtin with 5 Subcatchments Table Subdivision data for Curtin with 11 Subcatchments Table Subdivision data for Curtin with 19 Subcatchments Table Estimation of WCFACT Table Parameter C Results for Curtin with 4 Subcatchments, WCFACT =.15 Table Results for Curtin with 5 Subcatchments, WCFACT =.15 Table Results for Curtin with 11 Subcatchments, WCFACT =.15 Table Results for Curtin with 19 Subcatchments, WCFACT =.15 Table Results for Curtin with 4 Subcatchments, WCFACT =.15 Table Results for Curtin with 5 Subcatchments, WCFACT =.15 Table Results for Curtin with 11 Subcatchments, WCFACT =.15 Table Results for Curtin with 19 Subcatchments, WCFACT =.15 Table Subdivision Modelling Results for Modelling Method 1 Table Subdivision Modelling Results for Modelling Method 2 Table Summary of Suggested Parameter C values

31 LIST OF MAPS Map Number and Description 3.1 Woden Valley Catchments 3.2 Giralang Catchment 3.3 Maroubra Catchment 3.4 Strathfield Catchment 3.5 Fisher's Ghost Creek Catchment 3.6 Jamison Park Catchment 3.7 Vine Street Catchment 11.1 Curtin Subdivided into 4 Subcatchments 11.2 Curtin Subdivided into 5 Subcatchments 11.3 Curtin Subdivided into 11 Subcatchments 11.4 Curtin Subdivided into 19 Subcatchments

32 XXX LIST OF PHOTOGRAPHS Photograph Number and Description 11.1 Channel at Curtin Gauging Station, Outlet of Woden Valley Catchment (Location 1 on Map Appendix E) 11.2 Channel Section Yarralumla Creek, U/S of Curtin Gauging Station (Location 2 on Map in Appendix E) 11.3 Drop in Channel Section Yarralumla Creek, U/S of Curtin Gauging Station (Location 2 on Map in Appendix E) 11.4 Merging of Yarralumla Creek and Long Gully Creek (Location 3 and 7 on Map in Appendix E) 11.5 Yarralumla Creek, Mawson Reach (Location 4 on Map in Appendix E) 11.6 Yarralumla Creek, Mawson Gauging Station (Location 5 on Map in Appendix E) 11.7 Pipes Draining Mawson Catchment into Yarralumla Creek, Just U/S of Mawson Gauging Station (Location 6 on Map in Appendix E) 11.8 Pipe and Culvert Draining Mawson Catchment into Yarralumla Creek, Just U/S of Mawson Gauging Station (Location 6 on Map in Appendix E) 11.9 Yarralumla Creek in Natural State, U/S of Mawson Gauging Station (Location 6 on Map in Appendix E) 11.1 Long Gully Creek, Just D/S of Long Gully Gauging Station (Location 8 on Map in Appendix E) Long Gully Creek, State of Newly Channelised Section (Location 9 on Map in Appendix E) Upper Reaches of Long Gully Creek, in the new Isaacs Residential Subdivision (Location 1 on Map in Appendix E) Start of Piped Section, Draining Upper Reaches of Long Gully, Isaacs Residential Subdivision (Location 1 on Map in Appendix E)

33 XXXI LIST OF SYMBOLS AND ABBREVIATIONS Symbol and Description A Aj Aj C Ajmp Aper ARI ARR(1987) B C C L C per Cimp C ur b Gnat CBD f F F2 F5 g G H IFD IMP IMPDC IMPDCmaps IMPDCrainfall IMP maps Kt) kc kri K KB KC K catchment area (km 2 ) impervious areas not directly connected to piped drainage (km2) impervious areas directly connected to minor drainage (km 2 ) impervious portion of subcatchment (km 2 ) pervious portion of subcatchment (km 2 ) average recurrence interval (years) Australian Rainfall and (1987) calibration coefficient in RSWM/RAFTS WBNM model calibration parameter linear storage calibration parameter for WBNM WBNM pervious area calibration parameter WBNM impervious area calibration parameter lumped urban catchments parameter C lumped natural catchment parameter C Central Business District friction factor and/or watershed shape factor type of reach factor (see table 2.2) 2 year duration factor 5 year duration factor acceleration due to gravity (m/s 2 ) regional skewness flow depth (m) intensity frequency duration subcatchment impervious fraction directly connected impervious fraction directly connected impervious fraction calculated from orthophoto maps directly connected impervious fraction calculated from rainfall and runoff data total impervious fraction calculated from orthophoto maps inflow into a subcatchment (m 3 /s) empirical coefficient applicable to the entire catchment and the stream network (RORB) dimensionless ratio called the relative delay time, applicable to individual reach storage relative delay time of storage i subcatchment lag time (hours) overland flow lag time (hours) principal parameter of RORB model watercourse flow section lag time (hours)

34 per imp KWC L Li L m LR P or P(t) q Q Q* Qp Qpav Qs m n R RP S Sc Sm So Std Dev *P k At URB IMPFACT WCFACT pervious area lag time (hours) impervious area lag time (kours) watercourse lag time (hours) contour length (m) length of reach represented by storage i (km) channel sub-length (m) initial loss-constant loss rate rainfall loss model outflow discharge from detention basin (m 3 /s) rainfall hyetograph (mm/hour) distributed inflow (m 2 /s) streamflow or flowrate (m 3 /s) first approximation of the attenuation peak (m 3 /s) peak discharge (m 3 /s) average peak discharge along the reach (rn 3 /s) spillway discharge (m 3 /s) nonlinearity coefficient in lag and storage-discharge equations Manning's roughness hydraulic radius (m) initial loss-runoff proportion rainfall loss model volume of water temporarily stored on the catchment surface (m 3 ) main drain average slope of catchment (m/m) slope of channel sub-length (m/m) average slope of reach (m/m) standard deviation time to peak flow (minutes) travel time (minutes) rainfall hyetograph and runoff hydrograph time step (min) urbanisation fraction impervious area calibration parameter (default as.1 in WBNM Version 2.1) relative lag time for runoff from impervious and pervious surfaces v a valley shape coefficient attenuation parameter channel improvement factor

35 Chapter 1 Introduction

36 Chapter 1 - Introduction _2 1. INTRODUCTION 1.1 Background Three versions of the Watershed Bounded Network Model WBNM have been developed and they all are physically based rainfall hyetograph-runoff hydrograph computer models based on geomorphologic and hydrologic relations observed on real catchments (Boyd, 1978). The first two versions (Boyd, Pilgrim and Cordery, 1979; Boyd, Bates, Pilgrim and Cordery 1987) modelled rural catchments (ie. with no impervious areas). The second version released in 1987 incorporated a piecewise linear form of model response (Bates and Pilgrim, 1983, 1986). WBNM has been found to successfully model rural catchments ranging from.1 to 1 km 2 in size. With the initial WBNM model, the modelling of urban catchments was not possible. The 1987 model allowed for urbanised catchments, but it was not a userfriendly computer model. Also, the above versions of WBNM could not be applied to urban catchments with any confidence. This encouraged the development of the latest version of WBNM (Boyd, Rigby, Sharpin and Van Drie, 1994). This version of WBNM was specifically designed to allow the user to model both rural and urban catchments. Research by Boyd and Bufill (1993) showed that to accurately model urban catchments, the pervi and impervious areas required different treatment to allow for the different ways water runs off them. It was thought that the pervious areas could be treated in a similar fashion to those of rural catchment, but for impervious areas a factor (called IMPFACT) was introduced into the model to account for the faster travel time of water on impervious surfaces. WBNM was written to calculate runoff hydrographs from pervious and impervious areas using two separate storages. The runoff hydrograph for an urban subcatchment is calculated by adding the hydrograph calculated for the pervious part of the subcatchment to the hydrograph calculated for the impervious part of the subcatchment. 1.2 Aim As the older versions of the WBNM model did not specifically allow modelling of urbanised catchments, the aim of the thesis is to apply the updated version of WBNM (Version 2.1) to a number of urban catchments. In theory, using two parallel storages to model the pervious and impervious parts of a catchment to calculate a runoff hydrograph is justifiable. But, the new version

37 Chapter 1 - Introduction 1_3_ of WBNM has not been tested. The assumed lag equations within the model must be applied to recorded data to determine parameters which others can use. The parameter C values determined by Sobinoff et al (1983) and Boyd et. al (1987) for rural catchments range between 1.29 and 1.8. Amendments will be made to WBNM to ensure that the average parameter C for urban catchments is consistent with parameter C for rural catchments. 1.3 General A summary of tasks performed in each chapter will be presented. In chapter 2, a literature review of urban catchment modelling is presented. It considers the which other researchers have treated the difference between pervious and impervious areas. That is, lumping the pervious and impervious areas together and modelling with one storage, or split modelling where pervious and impervious areas are treated separately. The general lag equations and parameters, and how the lag parameter reduces on urbanised catchments. A review of three of the most popular runoff routing models available in Australia (RAFTS-XP, RORB and WBNM) is presented. The review contains details of the way in which the models calculate runoff hydrographs from rainfall data. The equations used to do this are presented and differences in the methods used by each model are compared. A larger emphasis is given to WBNM, as it was used in the current study. The ILSAX model (O'Loughlin, 1988) which was developed to simulate stormwater drainage systems is also reviewed. Although ILSAX is not strictly a runoff routing model, it is also considered in the chapter because it specifically deals with urban catchments, and it provides useful insights into the treatment of pervious and impervious runoff. Chapter 3 introduces the nine urban catchments used in the study, along with a brief descripti each catchment and a catchment map. Catchment details are provided giving information about their size, amount of urbanisation and average stream slope. Three different methods for determining imperviousfractions were investigated for each catchment. Over the years, different methods of determining impervious fractions have been developed. Initially, a total impervious fraction determined from orthophoto maps was used (IMP maps ). This considered all the impervious area in a catchment. As research continued, it was found that not all of the impervious areas contributed runoff directly into the watercourse, and assuming all the impervious areas do so is incorrect. To overcome this overestimate of impervious areas, a directly connected impervious fraction was introduced. Initially, a value was obtained from orthophoto maps and site inspection (IMP maps ). Recently, Boyd et al (1993) used a method to determine directly connected impervious fractions from rainfall and

38 Chapter I - Introduction 1_4 runoff data ^MP^,^,,,,). All three methods were tested in the study to determine which gives bette calibration results. Chapter 3 also provides information about the storm events that were used in the study. The total rainfall, rainfall excess, peak recorded flowrate, average rainfall intensity, rainfall duration and average recurrence intervals are provided for each event. In chapter 4, seven urban catchments, three located in Sydney and four in Canberra were used to te the new model. Ten storm events were selected for each catchment and calibration of the calculated and recorded hydrographs was achieved. This procedure was repeated for a range of impervious fractions for each catchment, to test whether the method Boyd et al (1993) developed to determine directly connected imperviousfraction without the use of orthophoto maps, was justifiable. WBNM was run as a nonlinear model for both pervious and impervious surfaces. The model was run using split catchments and initial loss-constant loss rate rainfall loss model. Rainfall hyetographs and runoff hydrographs for some events are plotted to give a visual indication of the performance of WBNM. Parameter C for urban catchments was determined to be approximately 3 % higher than for rural catchments (C=2.27). It was found that parameter C was too high for small catchments and too low for the larger catchments. High parameter C values were also found to exist for events where the impervious area contributed more runoff. In chapters 5 and 6, a detailed examination of the model was carried out, concentrating on split v lumped runoff and the effects of different rainfall loss models. A further two catchments (another in Sydney and one from Melbourne) and morerainfallevents were added. The catchments were modeled in a lumped state where both the pervious and impervious areas were combined. After calibration, parameter C was adjusted to give the equivalent natural or rural catchment calibration parameter. See chapter 5 for the adjustment procedure. Split modelling was found to be better than lumped modelling. Lumped modelling was found to be a poor way of representing urban catchments because it did not allow the pervious and impervious areas to be represented properly. In Chapter 7, WBNM was modified to run linearly for the impervious areas. Split catchment modelling with the initial loss-constant loss rate (LR) and initial loss-runoff proportion (RP) rainfall loss models is presented. Comparisons between the results for LR and RP rainfall loss models are made to determine which is more appropriate for urbanised catchments. The LR model removes an initial rainfall loss from the rainfall hyetograph which takes into consideration losses due to the initial wetting of catchment pervious surfaces. A constant loss rate (in mm/hr) is then assigned which takes into consideration infiltration losses into the ground for the remainder of the event. The RP model

39 Chapter 1 - Introduction 1-5 also removes an initial loss, but instead of a constant loss rate, a proportion of all the rainfall is removed. This model retains the shape of the rainfall temporal pattern in the pervious area excess rainfall hyetograph, whereas the LR does not, depending on the value of the loss rate. The study found that both LR and RP produced acceptable results but, because it retained the effect of all ordinates in the rainfall temporal pattern, the RP may be better for urban catchments. The results obtained in chapters 4 and 7 are compared to determine if there are improvements in results between the fully nonlinear WBNM model and the nonlinear pervious and linear impervious WBNM. It was found that there was a slight reduction in parameter C. But of greater importance was the improved fit of the hydrographs over those in chapter 4, indicating the modifications to WBNM to be justified. Throughout the study, parameter C was found to be very high on three catchments (Maroubra, Jamison Park and Vine Street). High parameter C values need to be assigned when the calculated discharges are too high. By increasing parameter C, the calculated discharges are reduced because the lag time is increased. It was thought imperviousfractions which are too high for the catchment was the reason for high parameter C values. In chapter 8, the study investigates the reason for these high parameter C values. Further investigation showed that a significant trend existed between parameter C and the impe area. In chapter 9, this trend was eliminated by reducing the area exponent in the impervious lag equation from.57 to.25. Not only was there a reduction in parameter C on all the catchments, but the amount of scatter reduced significantly and the average parameter C values were similar to those for rural catchments. In chapter 1, further adjustments are made to the model. The final modified version of WBNM wa then used to model all nine catchments for a final time. The mean standard error of the calculated and recorded peak discharges was calculated to be 31 percent. WBNM was found to estimate peak discharges within +15 percent of the recorded value, in 6 percent of events. It was found that parameter C was 1.7 for LR modelling and 1.5 for RP modelling. In chapter 11, WBNM was used to model one of the nine catchments when subdivided. This was done to see if the modifications made to WBNM in chapters 4 to 1 were valid for a subdivided catchment. For this part of the study, the Curtin catchment was subdivided into 4, 5, 11 and 19 subcatchments. Modelling was performed using the RP loss model. Boyd (1979) found there was a trend for parameter C to be higher for catchments modelled with one subcatchment. This trend reduced as the number of subcatchments increased, until there was no trend between the parameter C values and the number of subdivisions. A similar trend was found to exist in this study. Parameter C for a subdivided catchment was found to be about 25% lower than for a catchment modelled with one subcatchment.

40 Chapter 1 - Introduction 1_6 1.4 Summary The results of this thesis enable WBNM to be applied to urban catchments for flood studies. The validity of separate calculation of runoff from pervious and impervious surfaces was verified. For best results, runoff from impervious surfaces was calculated linearly with the lag time related to the impervious area raised to the power of.25. The reduction factor IMPFACT for lag time on impervious surfaces was found to be.1. Both LR and RP were found to give good results, but RP produced slightly better results.

41 Chapter 2 Literature Review of Urban Routing Procedures

42 Chapter 2 - Literature Review of Urban Routing Procedures LITERATURE REVIEW of URBAN RUNOFF ROUTING PROCEDURES 2.1 Introduction Since the introduction and subsequent development of the personal computer, many difficult mathematical calculations in all fields of engineering can now be made. This has paved the way for more complex and accurate models to be developed to simulate natural processes. In the field of Water Engineering, numerous models have been developed to simulate different hydrologic and hydraulic processes. This thesis considers only those models which calculate flood hydrographs from storm rainfall hyetographs on a regional basis. The major models developed in Australia are: 1. RSWM/RAFTS 2. RORB 3. ILSAX 4. WBNM In this section of the study, a literature review concentrating on the way others have modelled urbanised catchments will be presented. The aspects that will be looked at are lumped and split catchment modelling, the use of linear or nonlinear lag equations for use in runoff routing, general catchment lag equations and how the lag parameter is reduced in urbanised catchments. The manner in which these are implemented will be discussed with reference to the four runoff routing models quoted above.

43 Chapter 2 - Literature Review of Urban Routing, Procedures Literature Review Introduction As urbanised areas expand, the lack of planning to cater for even small storm events may prove t have disastrous effects with respect to flooding. For example, a small storm on an urbanised area may create flood damage to buildings constructed on the flood plain, but backwater effects caused by the flow restriction in the flood plain may causefloodingin areas where there originally was no problem. A similar thing may happen at a road culvert, where inadequate culvert sizing may cause the roadway to be washed away. Long term streamflow records covering the periods before and after urbanisation (VanSickle, 1962 Sawyer, 1963) and comparison of adjacent urban and rural catchments show thatfloodingis increased by urbanisation (Codner et al, 1988). Codner et al (1988) studied Giralang and Gungahlin catchments (two adjacent catchments in the Australian Capital Territory (ACT)). The catchments are similar in size (94 ha and 112 ha, respectively), but Giralang is 22 percent impervious and Gungahlin is totally rural. A reduction by a factor of thirty in the volume of channel storage and in the time lag between the rainfall excess and runoff was observed for the urban catchment. An average annual rainfall of 565 mm and 535 mm for Giralang and Gungahlin, respectively, was calculated. The average runoff depth from Giralang was 231 mm, compared to Gungahlin which produced 41 mm of runoff (six times more from the urban catchment). Crippen (1966) and Wiitala (1961) observed similar occurrences on adjacent catchments in the United States Modelling of Rural and Urban Catchments Before hydrologic models for urban catchments can be set up, there needs to be a better understanding of the factors which are changed by urbanisation. These in turn will affect surface runoff. Quantitative measure of these effects must be related to the degree and type of urbanisation. This means that urban areas need to be categorised using criteria such as population density, the amount of impervious area, the degree of industrialisation, the density of the storm water drainage system and the number of dwellings per square kilometre. The maximum discharge produced by an intense storm is the result of two relatively independent phases of the runoff process. One controls the volume of the surface runoff, and the other establishes the shape of the surface runoff hydrograph. The volume of the surface runoff resulting from a storm is equal to the total rain falling on the catchment minus the infiltration (into soil) and permanent retention of water (on vegetation and into the ground water table).

44 Chapter 2 - Literature Review of Urban Routing Procedures Infiltration and Impervious Fraction Infiltration varies from catchment to catchment. If the catchment being studied is large in size, infiltration may also vary at different locations within the catchment. For most soils, the infiltration may vary greatly from time to time and is dependent mainly on the moisture content of the soil at the start of the storm and on the degree and nature of the vegetation cover. The impervious portion of the catchment is one of the results of urbanisation. The amount of impervious area may be estimated from orthophoto maps. It cannot be assumed that all of the impervious parts contribute 1 percent runoff, and for this reason, the concept of a 'directly connected impervious area' has been introduced. This quantity can be derived from hydrograph analysis and represents the percentage of the area which contributes a runoff equal to the total rainfall. Initial rainfall losses are known to be small on impervious surfaces (Melanen and Laukkanen, 1981; Pratt et al, 1984; Jensen, 199), and plots of runoff depth against rainfall depth have been used in many studies to determine initial rainfall losses and the directly connected impervious fraction of a catchment (Miller, 1978; Miller et al, 1978; Jacobsen and Harremoes, 1981; Pratt et al 1984; Boyd and Bufill, 1992, Boyd et al, 1993). As the impervious area is increased by urbanisation this factor may be considered as one of the important effects of urbanisation. But its importance varies with the type and condition of the soil and with the intensity of the rainfall. For example, if the pervious portion of the catchment is very permeable (sandy soil), then most of the surface runoff will be closely related to the amount of directly connected impervious area. This would also be true for rain falling at an intensity less than the infiltration capacity of the soil. On the other hand, if the soil is such that its infiltration capacity is so low that the amount of surface runoff from the pervious parts of the catchment is close to the total rainfall, no noticeable change in the volume of surface runoff will occur when the catchment is urbanised. Wiitala (1961) concluded that for adjacent urbanised and rural catchments, the difference in peak discharges was due entirely to the shape of the hydrograph, with no difference in the surface runoff volumes. Due to the faster flow travel times in urbanised catchments, the time to the peak discharge has decreased, causing the peak discharge to be higher.

45 Chapter 2 - Literature Review of Urban Routing Procedures Shape Factors which determine the shape of the surface runoff hydrograph depend on the time distributio of the rainfall excess and on certain physical characteristics of the catchment. The problem is essentially one of unsteady, spatially varying flow hydraulics in a complex system of nonprismatic channels. The equations of motion for the system are so complicated that an analytical solution is possible, only if assumptions which greatly simplify these equations, are introduced. In runoff routing, the surface runoff hydrograph is made up of the product of two factors. They a the rainfall excess entering the catchment storage and the catchment storage itself. General runoff routing procedures have provisions for: 1. allowing variations in rainfall excess (temporal and areal variation), 2. passing different elements of rainfall excess through different amounts of storage, 3. catchment storages being distributed rather than concentrated, 4. the relationship between stream discharge and catchment storage is non-linear. The relationship between a rainfall hyetograph of continuously varying intensity and the resulti time varying runoff hydrograph is not apparent from the comparison of the two. So to eliminate these rainfall factors, simple hydrographs produced by one short period of rainfall excess are used. This hydrograph can easily be converted to a unit hydrograph. This is done by changing its total volume to one millimetre or by changing the hydrograph ordinates in terms of a percentage of the total volume. This idea wasfirstpresented by Sherman (1932) and can be used as a basis for comparison with other catchments as its shape is dependent mainly on the physical characteristics of the catchment. Since Sherman's idea, many others have shown the unit hydrograph's applicability to rural and urbanised catchments. Horner and Flynt (1936), Brater (194), Gray (1961), Eagleson (1962), March and Eagleson (1965) and Viessman (1968) have all implemented the unit hydrograph idea Methods of Calculating Flows Introduction One of the main physical characteristics of the catchment is its area. Wisler and Brater (1959) p the peak values of the unit hydrograph against catchment area for a number of catchments. A consistent relationship for all catchments was observed. For a given catchment area, the hydrograph shape was found to depend on parameters which represent the stream or channel length, the water velocity in the stream, the shape of the drainage basin and the nature of the stream network.

46 Chapter 2 - Literature Review of Urban Routing Procedures The Unit Hydrograph Another method of calculating runoff from rainfall excess hyetographs (rainfall excess is the ra remaining after all losses area removed from the rainfall hyetograph) is to derive the unit hydrograph. The unit hydrograph procedure assumes that the catchment response to rainfall is linear. In linear theory, the discharge from a single burst of rainfall of a given duration is proportional to the amount of rainfall. For example, if a 1 hour burst of rainfall which produces a 1 mm rainfall excess produced a hydrograph with peak discharge of 1 m 3 /s, then a 1 hour burst of rainfall that produced 2 mm of rainfall excess would produce a hydrograph with a peak discharge of 2 m 3 /s. This rule applies to every ordinate in the runoff hydrograph. Thus if a unit hydrograph is available for a 1 hour burst of rainfall, then a hydrograph can be generated for any storm of 1 hour duration by multiplying the ordinates of the unit hydrograph with the ratio of the rainfalls. Hydrographs of longer durations can also be calculated from the 1 hour unit hydrograph using arithmetic methods, as long as the duration is divisible by the duration of the unit hydrograph. To do this, the storm is divided into separate 1 hour increments and multiplied by the unit hydrograph by the rainfall occurring in each 1 hour increment. A hydrograph is then calculated for each 1 hour increment. The timing of the hydrograph generated for the second rainfall period is delayed by 1 hour; the hydrograph for the third period is delayed by 2 hours and so on before summing the hydrographs from each rainfall period to produce a total flood hydrograph. This method has been investigated by Clark (1945), Nash (1957), Dooge (1959), Singh (1964) and Viessman (1968). Tholin and Kiefer (196), Willeke (1962), and Holton and Overton (1965) routed rainfall excess through storages without using the unit hydrograph. Laurenson (1964) and Crawford and Linsley (1966) used the time-area curve which is related to the catchment shape and overland travel time to calculate runoff hydrographs. One method which is used to determine the influence of urbanisation on the shape of the runoff hydrograph is to establish relationships between parameters that define unit hydrograph shape and drainage basin characteristics. Snyder (1932), Taylor and Schwartz (1952), O'Kelley (1955), Nash (196), Gray (1961), Carter (1961), Eagleson (1962), Wu (1963), Espey, Morgan and Masch (1965) all used this procedure with satisfactory results. Wu (1963) used 21 small catchments which were less than 26 square kilometres. Five to six single rainfall burst storm events with a smooth recession curve were used on each catchment. Wu found that the time to the peak tp did not vary much for the same catchment, so could be used as one parameter, tp is a function of the storm pattern and the catchment characteristics. Wu plotted the dimensionless hydrograph for all the catchments (discharge divided by the peak discharge versus time divided by the time to peak discharge) and found the hydrographs retain a similar shape for a given catchment.

47 Chapter 2 - Literature Review of Urban Routing Procedures 2_7 Five measurable watershed characteristics were determined for all the catchments from topograp maps. These were the catchment area A, length of the main stream L, slope of the main stream S, watershed shape factor f, and valley shape coefficient v. Wu found that the catchment shape factor f and the valley shape coefficient v did not improve the correlation. Due to the difficulty of measurement of these, the three main variables of area, stream length and stream slope were used. Table 2.1 shows the lag equation developed by Wu. Espey, Morgan and Masch (1965) used the above procedure to determine the effect of urbanisatio peak discharges on a particular catchment. A relationship between the period of rise of the unit hydrograph and length and average main stream slope for both rural and urban catchments was developed. For urban catchments, a term for the amount of impervious area on the catchment was included as well as a term to allow for channel improvements and the degree of urbanisation. The peak discharge was then related to the catchment area and period of unit hydrograph rise. Work by Espey, Airman and Graves (1977) has produced a similar equation (see Table 2.1). Many studies of lag time have been made and Table 2.1 summarises some of these lag relations for catchments. Table Summary of Some Lag Relations for Rural and Urban Catchments Researchers No. Catchment URB Lag or Storage Linear or Equivalent Askew (197) Cordery et al (1981) Nash (196) Aitken(1975) Espey etal (1974) Espey et al (1977) NERC(1975) Rao etal (1972) Schaake et al (1967) Viessman (1968) Falk etal (1978) Wu(1963) Catchments Size Range Range Discharge Nonlinear Lag Relation (km2) Relation (L or N).4-9 A.i/Q-.23 N.5-15 L -57 L AO.3OS-*>.3 L A.52 S -.5(i +URB)-1-97Q-.28 N - - Q_AO.8_vipO.27sO.43Rl.75^,-1.2 L L.23 S-.25IMP-.18 ( )1.57 L _.14S-.38(I +_RB)-1.99 L A.46p-.27_).37(i + URB)-1.66 N _.24 S -.16_vtp-.26 L m2 1. no relation L m2 1. SaQO-67 N A.937_-l.474s-I.473 L AU.iV A.32 A.41 A.71 - A.32 A.22 A.46 A The Kinematic Wave Application of the Kinematic Wave theory to the runoff process by Brakensiek and Onstad (1968) shown some promising results. The use of the Kinematic Wave theory for calculating runoff hydrographs is both simple and physically accurate. It allows input to be introduced as a distributed variable, avoiding errors caused by lumping of the rainfall excess. The model can be calibrated by adjusting only one parameter called the n-parameter. This parameter is similar to Manning's roughness coefficient, with calibration being performed on peak discharges. The model uses a linear

48 Chapter 2 - Literature Review of Urban Routing Procedures 2_8 relationship between the drainage area and stream length (Wooding, 1966). Hypsometric and contour length geomorphic relations are used in deriving a one-dimensional flow system. These relationships are preserved in the transformation process which means the flow system has the same hypsometric and contour length relationship as the original catchment. The total catchment is divided into increments to define the hypsometric and contour length curves by a series of line segments. This is done starting at the top of the catchment (highest point). The areas between elevation increments are then calculated, and the lengths of the upper and lower bounding contour lengths are measured. The average distance between bounding contours is then calculated. Using this information, the average slope between bounding contours is calculated. By using this method of transforming the catchment for modelling, topographical detail of the catchment is lost. However, Wooding (1966) mentioned that there is a lack of sensitivity of topographical detail to the runoff problem, thus the detail lost is of no significant importance. The general Kinematic Equations for one-dimensional flow is: dq/dx + da/dt = q (conservation of mass) equation 2-1 Q = Q(H) (flow rating function) equation 2-2 where Q = flow rate (m 3 /s) A = flow area (m 2 ) q = distributed inflow (m 2 /s) H = flow depth (m) x,t = space and time coordinates. Calculation using the above equations and the flow system are performed as follows: 1 The flow area is equal to the contour length (L) times the flow depth (H). 2. Distance between routing sections (Ax) corresponds to the calculated average distance between contours (x). 3. The distributed inflow (q) corresponds to the rainfall excess. 4. The ground slope (So) is the calculated intracontour slope (S). In some of the above models, the rainfall excess is routed through overland flows before introduct into the stream network. The catchments ranged in size from less than.4 hectares to more than 16 hectares, with the imperviousfractionsranging from to 1. A linear relationship between the storage and discharge has been used, which explains why linear procedures used in unit hydrograph applications give satisfactory results. The storage coefficient is closely related to the lag time with it

49 Chapter 2 - Literature Review of Urban Routing Procedures 2-9 nearly being equal to the period of rise of the unit hydrograph. The lag time is defined as the ti distance between the centroid of the rainfall excess hyetograph and the centroid of the surface runoff hydrograph. The period ofrise of the unit hydrograph is the time from the commencement of surface runoff to the peak discharge. The method used has been to examine the runoff under different degrees of urbanisation. This shows the effects on other parameters and the shape of the unit hydrograph. Adjustments to these parameters is then made to remove any trends present due to urbanisation Routing In runoff routing models, the runoff hydrograph is calculated from the excess rainfall hyetograph using two equations, a conservation of mass and storage-discharge relation. The two equations are: I(f)-Q(f) = ds/dt equation 2-3 S = 36.K.Q" 1 equation 2-4 where I = inflow to the catchment surface from the rainfall excess hyetograph (m 3 /s) Q = outflow from the catchment(m 3 /s) S = volume stored on the catchment surface at time t (m 3 ) K = lag time for the catchment (hours) m = storage-discharge nonlinearity (m=l for linear relation) The lag time depends on the size of the catchment, and is smaller for impervious surfaces than for pervious ones. The reason for this is that pervious surfaces possess natural damping factors (grass, trees, shrubs etc.) which slow the velocity of the runoff. Thus the time taken for runoff to dissipate from the catchment is longer. Impervious surfaces, for example, consist of paved roadways, footpaths and house roofs. These are relatively smooth when compared to the pervious area surfaces. They possess little ability to slow the runoff velocity, and lag times on such surfaces are shorter. If the lag time on a catchment remains constant for all sizes of storm events, the catchment resp linear, with the lag times remaining constant for varying discharges. The lag time often varies with event size and becomes smaller for larger events. This catchment behaviour is nonlinear. Examples of linear runoff routing approaches are those of Nash (196), Schaake et al (1967), Viessman (1968), NERC (1975), Espey et al (1977) and Cordery (1981). Nonlinear runoff routing approaches are those of Laurenson (1964), Aitken (1975) and Falk et al (1978).

50 Chapter 2 - Literature Review of Urban Routing Procedures 2-1 A common nonlinear relationship between the lag time K and the discharge Q is: K = a Q equation 2-5 a depends on the size of the catchment and the type of surface, b denotes the degree of nonlinearit b=, the catchment response is linear. If b<, the response is nonlinear. The following general runoff routing equation is obtained by solving equation 2.3,2.4 and 2.5. Qz = (ft + l2)-.5.at + Qj.fK, -.5At))/(K 2 +.5At) equation 2-6 where 1,2 denote the values at the start and end of each time step At = time step (minutes) In nonlinear catchments, K, and K 2 are different at the start and end of the time step, depending on discharge Q at these times. For nonlinear catchments, equation 2.6 must be solved iteratively at each time step. The lag time is an indicator of flow travel time and is related to flow path or stream length, L. St lengths are related to the catchment area A raised to the power near to.55 (Hack 1957, Gray 1961 and Leopold et al 1964). Lag time is sometimes related to the stream slope S. This is also related to the catchment area raised to the power of near to -.4, Gray (1961). The lag time may also be related to discharge in a continuously nonlinear equation (Aitken, 1975 and Askew, 197). It is sometimes related to an index of overall event size (for example, storm rainfall P and duration D) in a quasinonlinear relation (Rao et al 1972). The lag relations cannot be compared directly because they use different combinations of different independent variables. Interrelationships established by Gray (1961) between the main stream length L, catchment slope S, and catchment area A can be used to transform the various lag equations in terms of catchment area. The interrelationships adopted for this were L a A 57 and S a A 56. The transform can be seen in the last column in Table 2.1. As can be seen, the power of area A is larger for nonlinear studies (average.58) than for linear studies (average.29). The reason for this is that larger catchments have larger discharges, and these larger discharges reduce the lag time calculated from nonlinear relations. Therefore the larger power in the nonlinear relations compensates for this.

51 Chapter 2 - Literature Review of Urban Routing Procedures 2-11 The lag times on urban catchments are lower than for equivalent rural catchments. The relations of Aitken (1975), NERC (1975) and Rao et al (1972) show that fully urbanised catchments (ie. URB=1.) should have lag times only 25 percent of the rural ones. It is possible that the use of the urban fraction (URB) as an indicator of the amount of urban development is poor. For example, central business districts (CBD's) and low density residential housing estates are both considered as being completely urbanised (URB=1.). But, the amount of directly connected impervious fraction (IMP) is much higher for the CBD as there is a larger proportion of paved surfaces than on a residential subdivision. A better indicator is to use an imperviousfraction (IMP) or better still, a directly connected impervious fraction (IMPQC). IMPDC is the total amount of impervious area that is connected to the channel or stream section in a catchment Lumped and Split Modelling Lumped modelling is performed when the pervious and impervious areas in an urbanised catchment are combined and modelled as one. Modelling is performed by applying weighted average rainfall losses and a single lag parameter. The lag equations in Table 2.1 can be used to calculate the lag time on a catchment, depending on the urban fraction or imperviousfraction.apart from nonlinear variations of the lag with discharge, this value will be fixed for a particular catchment, thus the same lag parameter would be applied over a range of storm events. But some events may produce only impervious area runoff and others may have both pervious and impervious area runoff contribution. Impervious runoff events will produce lag times that are shorter than for combined pervious and impervious events, but with lumped modelling, these different contributions are not considered. The average lag parameter assigned in lumped modelling will be too large for events with predominantly impervious area runoff, with excessive damping occurring and underestimation of the discharges. The lag will be too small for events with predominantly pervious area runoff and the calculated discharges will be too high. Split modelling (or separate modelling of pervious and impervious surfaces) avoids this problem. appropriate lag times for pervious and impervious surfaces can be assigned to these surfaces. For events that are predominantly impervious, the smaller lag time will dominate the catchment response, and for predominantly pervious events, the larger lag time will be dominant. Diskin et al (1978, 198) proposed a parallel cascade model where the pervious and impervious area were separated and modelled independently as two separate systems operating in parallel. The two areas receive the same rainfall, but due to the differing hydrologic responses of the areas, calculation of runoff hydrographs of these areas uses different procedures. The runoff hydrographs from the two areas are then added to produce the total outflow from the system. The urban cascade model is made up of three elements. The first element produces two rainfall excess hyetographs from the total

52 Chapter 2 - Literature Review of Urban Routing Procedures 2-12 rainfall hyetograph for use as input into the model. The other two elements, which are in paralle convert the rainfall excess into surface runoff hydrographs. These are represented by a cascade of linear reservoirs. The two surface runoff hydrographs are then added at the end to produce the total surface runoff hydrograph from that subcatchment. Similar models were proposed by Wittenberg (1975), and more recently, by Bufill and Boyd (1992). Bufill and Boyd (1992) studied the runoff routing process for the impervious areas separately fr the pervious areas. Small rainfall events were chosen to study the hydrograph recession and it was found that they exhibited similar shapes to one another. Recessions for impervious runoff events were plotted on semi-log graph paper and it was noticed that a straight line could be drawn in the upper part of the recession for all catchments studied, indicating that the storage discharge relationship for impervious areas to be linear (equation 2.4). The slope of this line for all events in a particular catchment was similar, again indicating the same lag for all events which suggests impervious area response was linear. Rao et al (1972) lumped the pervious and impervious areas together and modelled the runoff routi process on urban catchments using quasilinear reservoirs in which the parameters vary with storm duration and total rainfall excess. Rao et al found that for larger catchments, nonlinear modelling produced better results, but for small catchments (less than 8 square kilometres), a single linear reservoir model could be used to analyse the effects of urbanisation. NERC (1975) and Kidd (1976) also lumped the pervious and impervious areas together, but Kidd proposed a single nonlinear reservoir and NERC used a linear unit hydrograph. Of the urban flood hydrograph models commonly used in Australia, RORB is a lumped model and RAFTS, ILSAX and WBNM are split catchment models. But all the models can be set up to model any catchment with pervious areas and impervious areas split (as parallel storages) or lumped (one storage for both pervious and impervious areas). The above four models are considered in more detail in the following section. 2.3 Rainfall Models Introduction The following section will briefly describe four of the most widely used rainfall based runoff r models in Australia. The major models developed in Australia are: 1. RSWM/RAFTS

53 Chapter 2 - Literature Review of Urban Routing Procedures RORB 3. ILSAX 4. WBNM All the models utilise mathematical relationships to simulate the catchment respons following are the factors and processes most of the models account for: * spatial distribution of rainfall throughout the catchment for a given storm event, * temporal distribution of rainfall for a given rainfall event, * infiltration into the soil (rainfall losses), * interception of rainfall by vegetation, with the effect of antecedent moisture conditions (before rainfall), changing soil water content during the storm and soil properties, evaporation and drying of the soil (RAFTS-XP only), * water movement through soil to groundwater, or as baseflow which eventually returns to the main stream (RAFTS-XP only), * movement of water overland and along main streams accounting for factors such as slope, roughness, storage effects, size of the catchment, * storage routing effects of weirs, dams, reservoirs, etc., * modelling the effects of urbanisation. Rainfall runoff models require data to describe the catchment characteristics and r data is usually determined from topographic maps, aerial photographs and site inspections. Rainfall data can be obtained from Meteorological Departments and consists of daily read rainfall gauging stations and pluviograph data. Generally, all runoff routing models include a number of parameters which must be c recorded storm events and streamflows. Calibration is achieved by adjusting the various parameters until the model can accurately reproduce the recorded discharge hydrograph from the input rainfall. The calculated hydrograph should reproduce the peak discharge, time to rise, slope of the rising and falling limbs, recession curve and runoff volume of the recorded hydrograph for successful calibration. The number of storm events one selects to calibrate a model is dependent on the ava reliable rainfall data, the requirements of the project and the time and other resources available. But if no rainfall and runoff data are available for a particular catchment, rainfall and runoff data for another site within the catchment or a hydrologically similar catchment may be used to determine the required parameters for use on the subject site.

54 Chapter 2 - Literature Review of Urban Routing Procedures RSWM/RAFTS RSWM (Regional Stormwater Model) was originally developed by Willing and Partners Pty Ltd and the Snowy Mountains Engineering Corporation (Goyen and Aitken, 1976 ; Black and Codner, 1979). The latest version of RSWM, now called the Analysis and Flow Training System Model (RAFTS-XP) is windows oriented Program Organisation A simplified representation of the model is shown in Figure 2.1. The computer program is organised as a series of modules each addressing a particular component of the rainfall-runoff routing process. The separate modules are called in a particular sequence according to the way the input data is coded. The program consists of five modules: 1. A library module which manages the overall operation of the program and controls data entry, program execution and output format for the arrangement of subcatchments, channels and storage reservoirs. The latest version of the model allows all this to be done at the keyboard with the help of a mouse. Subcatchments are denoted by nodes and they are joined to other nodes by links. The program is userfriendlyin that it allows the operator to draw the nodes and link them to other nodes and storage reservoirs. 2. A hydrograph generation module which estimates a runoff hydrograph from either actual rainfall data or a design storm using Laurenson's nonlinear runoff routing method (1964). The pervious and impervious portions of the subcatchments can be routed separately and then combined at the outlet of the subcatchment. The subcatchments are represented by a nonlinear model which consists of a series of nine equal nonlinear concentrated storages, followed by a tenth storage that has half the delay time of the other storages. The subcatchments providing input to these storages are defined by ten isochrones at equal increments of travel time. 3. A loss model using the Australian Representatives Basins Model (Body and Goodspeed, 1979 ; Black and Aitken, 1977) and the Philip infiltration equations to calculate both urban and rural excess Tainfall. An initial loss constant loss rate loss model as well as an initial loss runoff proportion loss model are available. 4. A reservoir module to route an inflow hydrograph through a storage reservoir or series of reservoirs, allowing for backwater effects from downstream reservoirs. Tidal effects on back water can also be modelled when considering catchments near the ocean. The module also handles hydraulically interconnected basins. 5. A channel or river module which routes a hydrograph along a channel or river system using the Muskingum Cunge method.

55 Chapter 2 - Literature Review of Urban Routing Procedures 2-15 The runoff routing method used by RAFTS will be looked at in detail in the following section. ^ teochrones \ Nods Point - ttefining locations of hyd/oo/aphs Figure 2.1- Simplified Representation Of RSWM/RAFTS (RAFTS-XP V 4. Manual, 1993) Hydrograph Generation Module This module estimates the subcatchment runoff hydrographs. As described above, the Laurenson nonlinear runoff-routing method is used in RAFTS. The main reasons for this are: 1. It allows both rural and urban catchments to be modelled. 2. It allows for nonlinear response from catchments over a large range of event magnitudes. 3. It considers time-area and catchment shape details which are important natural factors. Data for this model consists of catchment area, slope, degree of urbanisation, model losses and rainfall information. 4. Its efficient mathematical procedure Rainfall Routing Method Routing for a subcatchment is carried out using the Muskingum method. The storage, however, is a nonlinear function of the discharge (see equation 2.8)

56 Chapter 2 - Literature Review of Urban Routing Procedures 2-16 S = K(Q).Q equation 2-7 The storage function in finite difference form is: S 2 -Si = (I 1 +I 2 ).At/2 - (Q, + Q_).At/2 equation2-8 Substituting Sj and S 2 in equation 2.8 from equation 2.7 gives the routing equation: Q 2 = CoI 2 + Ql! + C_Q, equation 2-9 where C = C, = At / (2K 2 + At) equation 2-1 C 2 = (2K, - At) / (2K 2 + At) equation 2-11 To solve the equations, an iterative procedure is required and RAFTS uses the Newton Raphson procedure Storage Discharge Relationship Each subcatchment is treated as a conceptual storage and has a delay time: ^-gnm equation 2-12 where B = storage delay time coefficient m = nonlinearity coefficient In RAFTS, m has a default value of -.285, but it may be altered by the user. A nonlinearity coefficient of zero means the catchment is linear. The coefficient B is estimated using equation 2.13 which was derived by Aitken (1975). B =.285.A 52 (1 + URB)- 1 w Sc" 5 equation 2-13

57 Chapter 2 - Literature Review of Urban Routing Procedures 2-17 where B = mean value of coefficient B for subcatchment URB = urbanisedfraction of catchment (see Table 2.2) Sc = main drain average slope of catchment (m/m). RAFTS-XP relates the urban fraction of a catchment to the impervious fraction by a simple linear relationship (Table 2.2). If lumped modelling of a catchment is performed, the storage delay time coefficient is calculated using equation Depending on the impervious fraction of the catchment, a corresponding urbanfractionis assigned from Table 2.2. For example, if the catchment impervious fraction IMP is.3, then the URB=.7 and equation 2.13 becomes: B =.285.A 52.(1.7)- 197 Sc- 5 =.1.A 52.Sc- 5 equation 2-14 If split modelling is used, two coefficient B values would be calculated. One is for the pervious the other for impervious surfaces. For example, if IMP=.3, then for the pervious areas IMP=, and URB=, ie: B per =.285A per (l+)- 197 Sc- 5 = O^SS-Ap^Sc- 5 equation 2-15 For the impervious surfaces, assuming IMP=1., then URB=2. (Table 2.2), ie: B imp =.285.A per (l+2)- 197 Sc- 5 =.33.A imp.sc- 5 equation 2-16 where A per = A 1,(l-IMP) A imp = A_ t.imp Note the large decrease in coefficient B for impervious areas (equation 2.16) compared to equatio 2.14.

58 Chapter 2 - Literature Review of Urban Routing Procedures 2-18 Table Relation Between Impervious And Urbanisation (RAFTS-XP Version 4. Manual, 1993) Impervious fraction (IMP) Urbanised fraction (URB) _ Rainfall Loss Module RAFTS accepts either initial and continuing losses, or infiltration parameters to suit Ph infiltration equation using the Australian Representative Basin Model (ARBM) to simulate excess runoff. The Australian Representatives Basin Model will not be discussed as it is beyond the scope of this study. The initial loss-continuing loss rate and initial loss-runoff proportion rainfall loss models will be discussed and used throughout the study Initial and Continuing Loss Model This is the most widely used method to remove losses from rainfall. It requires an initia which simulates initial catchment wetting when no runoff is produced, followed by a constant continuing loss rate (in mm/hour) to account for infiltration once the catchment is fully saturated. Recommended values for initial and continuing losses are difficult to specify because soil and vegetation types vary. Initial losses can vary from 5 to 1 mm and continuing losses from to 25 mm/hr. For impervious areas, RAFTS recommends an initial loss of 1.5 mm and continuing loss of mm/hr. 2.5 RORB Introduction RORB Version 3 is another of the more popular runoff and streamflow routing models availa calculatingfloodhydrographs from rainfall data and other channel inputs. The basic principles of the model are similar to RAFTS/RSWM and WBNM and will be described briefly using Figure 2.2. A new windows version of RORB was released in 1995.

59 Chapter 2 - Literature Review of Urban Routing Procedures 2-19 Legend. subarea boundary o node <} model storage o subarea inflow / Figure Schematic of RORB Model (AR&R, 1987) The model operates in the following manner: 1. Deduction of losses from the rainfall hyetograph. Two loss models are provided, an initial loss and constant loss rate as well as an initial loss and runoff coefficient. 2. Routing of the rainfall excess starts at the uppermost point in the catchment and proceeds down to where the stream meets another tributary. The calculated hydrograph is then stored and modelling of the other tributary commences. Once this is modelled, the two hydrographs are added and modelling then commences for areas downstream of this point. This continues until the outlet of the catchment is reached. Hydrographs at each specified node in the model are calculated and stored for later use. The following sections will describe in detail the way in which RORB represents the reach storag storage reservoirs and detention basins Storage-Discharge Relations Reach storages represent the storage effects of channel reaches and include the effects of over flows. In RORB, the storage-discharge relation is in the form: S = 36.K.Q m equation 2-17 where m = catchment nonlinearity K = dimensional empirical coefficient

60 Chapter 2 - Literature Review of Urban Routing Procedures 2-2 Parameter m is usually fitted in calibration runs, but is subsidiary to K. The nonlinearity, m, range of.6 to 1. and a value of.8 is recommended for ungauged catchments or for initial calibration. The coefficient K is formed as a product of two factors: K = K...K,. equation 2-18 where K,. = empirical coefficient applicable to the entire catchment and the stream network. K, = dimensionless ratio called the relative delay time, applicable to individual reach storage Relative Delay Time For catchment studies, the relative delay time of a storage is calculated as follows in the pro K ri = F.(L i /d av ) equation 2-19 where Krj = relative delay time of storage i F = type of reach factor (see Table 2.3) L; = length of reach represented by storage i (km) d av = average flow distance in channel network of subcatchment inflows (km). This is calculated by the program from the reach length data. Table Reach Types (RORB Version 3 User manual, 1983) Reach Type Code Description of Channel Reach 1 Natural 1. 2 Excavated but unlined 25 1/3S C 3 Lined or piped 1/9S C 5 4 Drowned (by reservoir). Note: S c slope of channel reach (%)

61 Chapter 2 - Literature Review of Urban Routing Procedures Coefficient^ The empirical coefficient K c is the principal parameter of the model. K,. is strongly dependen nonlinearity factor, m and when a K,. factor is determined with one value of m, it cannot be validly used with another value. When using the RORB model, K,. is adjusted by a factor of (q p / 2) S - m '. For catchment studies, the calculation of K. is iterative and the following equation is used: K, = 2.2A 5 (Q p / 2) 8 - m ' equation 2-2 where Q p = peak discharge of hydrograph (m 3 /s) m' = new value of exponent Routing Method Routing of a hydrograph through a model reach storage is performed by a nonlinear storage routi procedure based on continuity and equation A linear storage function may be adopted by assuming m=l. For m not equal to one, the routing computation for each time increment is an iterative one in which the outflow discharge at the end of the time increment is adjusted until the change in storage calculated from the storage discharge relationship is equal to the difference between inflow and outflow assuming linear variation of the hydrograph over the time increment. The Regula Falsi convergence algorithm is used and a limit on iteration is programmed so that if convergence does not occur, the user has an option to use the last two discharge estimates or to abort. 2.6 ILSAX Introduction The ILSAX computer program is an extension to other similar programs dating back 25 years. ILSA is based on the TRRL, United Kingdom Transport and Road Research Laboratory program (1963), and ILLUDAS, Illinois Urban Stormwater Area Simulator (1974), by Terstriep and Stall. Watson (1981), from South Africa, introduced an improved version, ILLUDAS-SA. O'Loughlin (1988) developed ILSAX by adding enhancements and alterations to ILLUDAS-SA. This was done to make the program suitable for drainage design and analysis in Australia.

62 Chapter 2 - Literature Review of Urban Routing Procedures 2-22 ILSAX is not purely a runoff routing model. It performs calculations on urban or semi-urban catchments subdivided into several subcatchments associated with a drainage system of pipe and channel sections. ILSAX converts rainfall hyetographs into runoff hydrographs and allows for the effects of evaporation, infiltration and routing across catchments surfaces. It also deals with surface flows, points of entry to a pipe drainage system and flows within that system. Pure runoff routing models (such as RAFTS, RORB and WBNM) only calculate runoff hydrographs from rainfall hyetographs. The method ILSAX uses to generate hydrographs will be discussed in detail Hydrologic Methods Treatment of Rainfall Three forms of rainfall input can be entered into ILSAX. They are: 1. Rainfall intensities in mm/hr over specific time periods. 2. Rainfall depths in mm over time steps. 3. Standard design storms from ARR( 1987), chapter Catchment Definition As in runoff routing models, the catchment needs to be divided into subcatchments draining to ea entry point on the pipe and channel system. The subcatchments then need to be divided into subcatchments with the following surface and drainage characteristics (split catchments). 1. Paved areas, impervious surfaces which are directly connected to the pipe system. These include roads, house roofs and driveways, etc. 2. Supplementary areas, impervious areas which are not directly connected to the pipe system, but which drain onto pervious surfaces which connect to the pipe system (eg. house roofs which drain onto afrontyard lawn which then drains to the street kerb.) 3. Grassed areas, pervious areas directly connected to the pipe system (eg, bare ground and porous pavements as well as lawns.) There may also be impervious or pervious areas that do not connect to the pipe system. Thus, ILS cannot be used to model totally rural catchments where there are no pipe drains.

63 Chapter 2 - Literature Review of Urban Routing Procedures Hydrograph Generation ILSAX uses the time area method to calculate runoff hydrographs. In this method, the rainfall hyetograph is combined with a time area diagram, similar to unit hydrograph calculations. A time of concentration for the drained area needs to be calculated. The rainfall hyetograph and time areas diagram is divided into time steps of At, which is based on lines of equal time of travel (isochrones) to the catchment outlet. For times greater than the time of concentration, the area contributing equals the total area of the catchment. Seefigure2.3. When a storm commences on a catchment which has a time of concentration of 5At, the initial discharge Q is zero. At time At, only subcatchment Al contributes to flow at the subcatchment outlet. from the upstream areas will still be travelling towards the outlet and is not considered. Thus theflowrateat the end of the first time step is: Q! = CAj.1, equation 2-21 where C = conversion factor from mm/hr to m 3 /s I, = average rainfall intensity during thefirsttime step (mm/hr) At the end of the second time step, 2At, there are two contributing flows, Q 2, due to the second b of rainfall on the subcatchment nearest to the outlet, C.A,.^, and runoff from thefirstrainfall block on the second subcatchment, CA^I,. The process continues and can be seen in figure 2.3. The hydrograph builds up to a peak and then recedes when the rainfall stops and the catchment drains. A hydrograph of Q values is calculated using the above procedure for the various surfaces on the subcatchment. Losses must then be subtracted from the hydrographs to represent hydrological processes such as interception, depression storage, evaporation and infiltration. ILSAX does not allow for storage effects that may occur on the catchment surfaces such as in other linear or nonlinear reservoirs models or as in Kinematic wave calculations. The impervious area hydrograph is calculated as follows: 1. The paved area depression storage is subtracted from the rainfall hyetograph. 2. This is then combined with the time area diagram to give a runoff hydrograph. The pervious area hydrograph is calculated as follows:

64 Chapter 2 - Literature Review of Urban Routing Procedures The rainfall hyetograph (mm/hr) is adjusted by a factor of grassed plus supplementary area divided by grassed area. This is to allow for rainfall on supplementary impervious areas not directly connected to the pipe system. From the adjusted hyetograph, the grassed area depression storage is removed. The rainfall hyetograph is then combined with the grassed area time area diagram. Horton infiltration is used to subtract infiltration losses. The remaining hyetograph values are scaled by area divided by 36 to convert intensities to flowrates (in m 3 /s) and to form a hydrograph. See figure 2.4 for an illustration of the construction of hydrographs on different areas. < ' \ \ \ l \ t *J ' \ \ 1 1 / 1 / 1 / W i CKTCWENT OR SUB-AKH WITH XSOCHPONES Contributing ftraa Ch-I I AC -t" ^ ^*^*- -*», i A! "! "! st J1B» of Entry j_,v TilK DIAGRAM Q - O i c 'Vi o 2 - ccv 2 <h- V 2 J emji,., '^2 V, =4 - ccv 4» ^ 3 * V 2 -Vi 5 - c< V«' V 3 " M 2* Vi> QG-C< V** Vl* SV 7-C( V4- Qe - c( V4> Intan.lCy "*^~\^ N, 2 l 1" ie 1 At HYETOGRAPH '4 1 *! Figure Construction of Hydrograph by Time Area Method

65 Chapter 2 - Literature Review of Urban Routing Procedures 2-25 Paved Area contributing (ha)... convolved; with... Tune [hi *i paveo*" Borton Infiltratioc curve Rainfall Byetograph Grae&ed Area contributing (ha) convolved witl«... Tine(h) grassed Intensities multiplied by factor : (Graised * Supplementary Area Grassed Area Grassed Area Depression Storage ^ p... which total... Ccnfcined Paved + Grassed Area Flovrates ( Vs) r "\ V 1/ IM OndralMd Area Figure Construction of Pervious and Impervious Area Hydrographs 2.7 WBNM Introduction The Watershed Bounded Network Model (WBNM) was originally developed by Boyd et al (1979). The model was revised further by Boyd et al (1987). Due to increased knowledge of hydrologic processes, improvements in urban stormwater management strategies, and developments in computing technology and quality control, it was possible to improve on the existing WBNM models. This has led to the upgrade, WBNM Version 2.1 (Boyd et al, 1994). A detailed description of the workings of both the old and new versions of WBNM will be given Earlier Versions Of WBNM There were two WBNM models originally developed by Boyd et al. (1979a,b; 1987a). The 1979 and 1987 versions are essentially the same, the major differences being the incorporation offloodrouting through detention basins and a switch from the main frame to personal computer version in 1987.

66 Chapter 2 - Literature Review of Urban Routing Procedures 2-26 The models were designed to have a realistic model structure in which the stream network and subcatchments of the catchment are individually represented. The models conform to geomorphological and hydraulic relations observed on real catchments (Boyd, 1978). The structure of the WBNM models is very similar to that of RORB, but WBNM considers the geomorphological relations of the catchment in more detail. The main difference is that WBNM has two types of storages for two different types of subcatchment. It considers Ordered Basins (now called overland flow OL types), in which no water flows into these subcatchments across watershed boundaries. Rainfall excess hyetographs in these basins are transformed into runoff hydrographs at the outlet of the subcatchment. Interbasins (now called watercourse WC types) are subcatchments where upstream tributaries flow through them. These not only transform the rainfall hyetograph to a runoff hydrograph, but they also route the upstream runoff through the stream in the subcatchment. As this model considers these two different characteristics of catchments, storage delay times for the two types of runoff are different, which is a physically realistic assumption. Figure 2.5a shows a schematic of the watershed bounded network model. szo Ordered basins ta) Catchment Structure J^A 9 O Ordered basins Interbasins (b) Model Structure Figure WBNM Schematic (Boyd et al. 1987) In WBNM, each subcatchment and major stream is represented by a concentrated storage element (Figure 2.5b). For each of these elements, the following equations apply: Continuity I(t)-Q(t) = ds(t)/dt equation 2-22 Storage-Discharge S = 36.K.Q equation 2-23

67 Chapter 2 - Literature Review of Urban Routing Procedures 2-27 Inflow into a subcatchment I(t) = A.P(t)/3.6 (m 3 /s) equation 2-24 Equation 2.24 transforms rainfall excess into runoff. Solving equations 2.22 and 2.23 gives the routing equation for each subcatchment equation 2.25: Qi = [flu + Ii)At + Q i. 1.(2K i. 1 - At)]/(2Ki + At) equation 2-25 where i and i-1 are At apart. The 1987 version of WBNM by Boyd et al (1987) incorporates spatial variability of rainfall, loss and lag parameters as well as optional forms of nonlinearity and reservoir routing. Nonlinearity is modelled using a power function where the lag parameter varies with discharge Q. Equation 2.26 was developed by Askew (1968) based on studies of catchment lags. K B = C.A 57.Q m equation 2-26 In WBNM a reduction factor of.6 is used for transmission lag times, ie. transmission of upstre runoff Kj =.6K B. The nonlinearity parameter m was set at -.23 for the 1979 version of WBNM. In the 1987 version, the user can define m, but m will usually lie between and In WBNM Version 2.1 (described in detail in the next section), m is defaulted at -.23 and only parameter C needs to be evaluated. In the 1987 version, nonlinearity can be modelled using a Piecewise Linear response. This option assumes that catchment response is nonlinear at low flows, but close to linear at high flows. This option has been omitted from WBNM Version 2.1.

68 Chapter 2 - Literature Review of Urban Routing Procedures WBNM Version Description Of WBNM WBNM Version 2.1 is the upgraded version of the Watershed Bounded Network Model. The workings of the model are the same as for earlier versions of WBNM, but the upgraded version has more functions, is more userfriendly, and has better quality control in that it uses one input data file whereas the old version requires separate data files for the catchment, rainfall and storage details. The major differences between the old and new version of WBNM are: I. Use of one data file in which catchment parameters, rainfall losses, storage reservoirs, rainfall data, and streamflow data are entered. This is for quality control purposes, and also allows fast and efficient data input. The date of the model run is also saved along with the output data for reference purposes. 2. User friendliness of the new graphical display of the catchment. This allows the user to see the catchment with the links and nodes. 3. The graphical interface allows for the processing of output data into plots of hydrographs and hyetographs. 4. Summary tables of peak outflows, time of peak flow and runoff volumes for subcatchments can be viewed and printed for report generation purposes. 5. File handling - data required for use with other modelling packages can be extracted and saved for use. 6. ARR(1987) rainfall intensity,frequency and duration (IFD) data can be created for any area in Australia with an in built function. All design storm temporal patterns are provided in the new model, which allows fast and accurate design storm calculations. 7. Built in weir and culvert hydraulics. 8. A range of rainfall loss models. 9. A range of channel routing options. 1. Detention basin routing. These are the improvements made on the old WBNM model and some of the above will be discussed in more detail in the following sections.

69 Chapter 2 - Literature Review of Urban Routing Procedures Rainfall Loss Models WBNM allows various modelling options to be performed. Four rainfall loss models are provided, these being: 1. Initial loss-constant loss rate. 2. Initial loss-loss rate varying in steps. 3. Initial loss-runoff proportion. 4. Horton continually time varying loss rate. Once the desired loss model is chosen, the model calculates the rainfall excess hyetograph for eac subcatchment Modelling Watercourses WBNM also allows three watercourse options, thus allowing natural streams and man-made channels to be modelled. These are: 1. Nonlinear routing, using a lag parameter K,=.6K_, but allowing the ratio to be varied to model any channel conditions. 2. For short watercourse segments where the hydrograph is translated without attenuation, the hydrograph can be delayed by a user specified time. 3. Muskingum Cunge routing where both attenuation and translation are modelled Modelling Storage Reservoirs WBNM allows storage reservoirs of any type to be modelled. These include: 1. Storage basins in urbanised areas. 2. Detention basins with pipe, culvert or weir outlets. 3. Dams with spillways. Puis' level pool routing is used for these calculations. By giving the number, size, type and inve elevation of combined culverts and weirs, WBNM will calculate the height-discharge relation for the reservoir. The model also calculates the hydrograph for flows into and out of the reservoir. Allowance for dead storage of a reservoir can be modelled, allowing the reservoir tofillto a certain level before

70 Chapter 2 - Literature Review of Urban Routing Procedures 2-3 outflow commences. The reservoir can be part full at the start of the storm. RAFTS and RORB also use this method to model storage reservoirs Modelling Urbanised Catchments The ability of WBNM to model the effects of urbanisation is a large improvement on older versions Modelling of urban catchments requires the runoff from pervious surfaces and impervious surfaces to be treated separately (Boyd and Bufill, 1992,1993; Sharpin 1993). Urbanisation affects the flood hydrology of a catchment in three ways: 1. Due to increased impervious areas (roads, concrete driveways, house roofs) an increase in rainfall excess depth and runoff volume occurs. 2. Reduction in overland flow travel times on impervious surfaces and overland flow drainage paths, and increased flow velocities, due to the reduction of surface roughness (Manning's n). 3. Increased flow velocities and reduced travel times in man-made channels. In WBNM, these effects are modelled in the following ways: 1. An initial loss of mm and continuing loss of zero mm per hour are default rainfall loss for impervious surfaces, thus requiring losses to be assigned only to the pervious part of the catchment. Losses on impervious surfaces also occur due to depression storage effects. Open jointed pipes in sandy catchments may discharge directly into the soil. Thus the rainfall losses on impervious areas may also vary. WBNM allows for the user to define the impervious area initial loss for such situations. 2. The lag parameter for the impervious part of the catchment is automatically set by WBNM, based on research of Rao et al (1974), Aitken (1975) and NERC (1975). 3. Any modifications to the watercourses in a catchment can be modelled using nonlinear routing, Muskingum Cunge or the delayed hydrograph methods described earlier Modelling Overland Flow In all versions of WBNM, overland flows are modelled on each subcatchment using a nonlinear reservoir with lag equation based on research by Askew (197): K B = CA^.Q" 23 equation 2-27

71 Chapter 2 - Literature Review of Urban Routing Procedures 2-31 In WBNM, the pervious and impervious portions of the catchment are modelled separately and the runoff hydrographs are then combined at the outlet of the subcatchment to give one combined runoff hydrograph. WBNM divides each subcatchment into a pervious and impervious part, where the size of each is: Ap_. = A.(l-IMP) equation 2-28 A imp = A.IMP equation 2-29 These areas are then used in equation 2.3. The pervious part is assumed to be zero impervious (IMP =.) and the impervious part is assum be 1% impervious (IMP = 1.). WBNM calculates the lag times for a subcatchment as follows: For the pervious part of the subcatchment: K^ = C. A _ ".Q- * equation 2-3 For the impervious part of the subcatchment of the catchment: Ki mp = IMPFACT.C.A imp ".Q" 23 equation 2-31 Note that equation 2.31 was originally proposed for WBNM Version 2.1 by Boyd et al (1994), however the present study has shown that the impervious area lag equation should be as shown in equation Chapters 4, 7 and 9 show how this equation was modified and the reasons for the changes. Ktap = IMPFACT.C.A irap 25 equation 2-32 IMPFACT represents the relative lag times for runoff on impervious and pervious surfaces. Based on studies by Rao et al (1974), Aitken (1975) and NERC (1975) and also on overland travel times (ARR(1987) chapter 14), the original value of IMPFACT was.111. The present study has shown the value to be.1 (see chapter 1).

72 Chapter 2 - Literature Review of Urban Routing Procedures Flow Diversion Modelling WBNM allows the user to model flow diversions from a point of surcharge to a downstream point. This allows surcharging flows from the piped drainage system to be diverted to any node, or to be diverted out of the drainage system. These flows can also be delayed by a specified time or routed though the drainage system channels or storage reservoirs. Again, both RAFTS and RORB allow for flows to be diverted. Seefigure2.6 for details Catchment Division into Subcatchments The amount of division of a catchment is dependent on the size of the catchment. Studies by Boyd (1985) indicate that the larger the catchment, the more division is required. Table 2.4 shows the minimum and maximum number of subcatchments required in a catchment when modelling with respect to the catchment size. The allowable range is quite large, but the number of subcatchments adopted will normally lie near the minimum value. It must be also noted that table 2.4 is only recommended for use on natural catchments, and this study is dealing with urban catchments. Table Division of catchments into subcatchments (Boyd, 1985) Catchment Size (km 2 ) Minimum No. Subcatchments Maximum No. Subcatchments For small urban catchments, less than approximately 2 km 2, where lag times are quite short and fluctuations in the runoff hydrograph closely reflect those in the rainfall hyetograph, a single storage element may be used to represent the total catchment without dividing into any subcatchments. The model requires the catchment to be broken up into subcatchments. This break up depends on the stream network and topography of the catchment. In general, for small urbanised catchments one subcatchment may be satisfactory. Up to fifty subcatchments or more may be required for large rural catchments. Figure 2.6 shows a typical catchment divided into subcatchments. Headwater subcatchments (OL type) (1, 3, 6 and 8) transform excess rainfall into overland flow at the subcatchment outlet. Watercourse subcatchments (WC type) (2, 4, 7, 1 and 11) transform rainfall excess into runoff as well as routing runoff from upstream subcatchments though the watercourse. Subcatchments 5 and 9 are storage reservoirs which may be either dams with spillways or detention basins with culvert or weir outlets. These can be placed at any point in the catchment. Dummy subcatchments can be placed at any point in the catchment so that runoff hydrographs at any point can be calculated. Dummies can also be used to divert flows to or from any point in the stream network.

73 Chapter 2 - Literature Review of Urban Routing Procedures 2-33 In Figure 2.6, flows which exceed the channel capacity immediately downstream of storage reservoir 5, are diverted to the channel in subcatchment 11. (a) Schematic Model Structure v_v diversion O n «>de watercourse <~ overland flow <3 storage reservoir from routed through subarea 4 subarea 2+3 watercourse 4 local overland flow K\M routed though storage reservoir S diverted to subarea 11 (b) Schematic Hydrograph Operations Figure Schematic of WBNM Version 2.1 (Boyd et al., 1994) outflow from S after diversion Application of WBNM to Catchments WBNM is quite general, with many options, and can be used to model a wide variety of catchments. However it is also a very simple model to use, requiring a minimum of data. In its simplest application to a natural catchment, all that is necessary is to divide the catchment into subcatchments and measure the size of each subcatchment, specify the rainfall loss model and values, and specify a single model parameter C. In the simplest application to an urban catchment in which some subcatchments have been urbanised but stream channels have not been modified, all that is needed is the size and imperviousfraction of the subcatchments, the rainfall losses (for the pervious areas only), and a single model parameter C (also for the pervious subcatchments). WBNM automatically calculates rainfall losses and lag parameters for the impervious surfaces. Figure 2.7 shows the results

74 Chapter 2 - Literature Review of Urban Routing Procedures 2-34 for the same storm on adjacent natural Gunghalin and urban Giralang catchments located in Canberra, with the only adjustment for the urban Giralang catchment being the specification of the subcatchment impervious fractions SO so 4 Giralang Urban IMP=Q22 Ca Ic u lata d ^ 1 1 SO 2 Gungahlin Rural Ca Ic u la ted ^ 1 15 Tim e (min ute s ) Figure Hydrographs on Natural and Urban Catchments (Boyd et al.1994) WBNM Computer Program Input Data Files WBNM uses one data file only, thus ensuring faster program execution due to the fact that the program only calls data from one file. The datafilecontains information on the catchment such as the number of subcatchments, storm rainfall, rainfall losses, parameter values, information on storage reservoirs, associated culvert and weirs as well as storage details. The recorded hydrograph at the outlet of a catchment can also be entered, which allows the recorded hydrograph to be compared to the calculated hydrograph. This is useful for model calibration, to obtain rainfall losses and the parameter C value. A standard template is used for the data file and this can be edited using any text editor. A data file format template and a list of all the filenames used in this thesis are given in Appendix A (on CD).

75 Chapter 2 - Literature Review of Urban Routing Procedures Output Files The output file of WBNM has been developed to satisfy quality control requirements. Thus the ability to quickly identify key results from model runs is available. The outputfileprints the following: 1. Input filenames and the date the file was created. 2. Key input data parameters so as to provide a check on input data. 3. Rainfall and runoff depths and volumes as well as a balance of runoff volume from each subcatchment. 4. Peak flowrate and time to peakflowratefor subcatchment overland flow. 5. Peak flowrate and time to peak flowrate for watercourse and storage reservoir inflows and outflows, as well as for diversions and total flows from the subcatchment. 6. Maximum flows for all ARI's modelled and automatic indication of the critical storm duration required for design purposes. The program allows the user to indicate which of the output preferences is to be printed for any nominated subcatchment. Files can be created for the overland flows and total area hydrographs for use in open channel hydraulics programs such as MIKE-11. This is a handy utility as large data files can easily be transferred to other programs, saving time and money and more importantly, making tasks easier to accomplish with better quality control Graphic Displays WBNM has the added feature of displaying useful plots, which are important mainly for model calibration. Plots give better indications of results than tables of numbers, and this is helpful for presentation purposes. In model calibration, hydrographs are calculated from one or a number of rainfall hyetographs in a catchment. These can then be compared to recorded hydrographs for calibration purposes. Plots of the calculated and recorded hydrographs can be constructed, making this easier. Hydrographs can also be plotted at the inlet or outlet of a subcatchment. A scheme of the entire catchment can be drawn, which is automatically scaled to fit the computer screen. Other plots include the rainfall hyetograph data at each rain gauge and weighted rainfall hyetograp for each subcatchment. Also, for each storage reservoir, plots of the height-discharge-storage are available. Future upgrades of WBNM will include the ability to produce these outputs in DXF format which would be very useful for use in AUTOCAD, CIVILCAD and other drawing packages.

76 Chapter 3 Catchments and Storm Events

77 Chapter 3 - Catchments and Storm Events CATCHMENTS and STORM EVENTS 3.1 Introduction This thesis utilised recorded rainfall and runoff data from nine catchments located in Sydney, Canberra and Melbourne which are listed below. These catchments varied in characteristics and the selection included fully rural, partially urbanised and fully urbanised catchments. 1. Canberra Curtin Mawson Long Gully Creek Giralang 2. Sydney Maroubra Strathfield Fisher's Ghost Creek Jamison Park 3. Melbourne Vine Street Mawson and Long Gully Creek are located within the Curtin catchment and these are known as the Woden Valley catchments. This section of the thesis will describe the catchments used, giving information such as the size o catchment, the impervious fraction and directly connected impervious fraction, land uses in the catchment, and the dates of the storm events which were used to calibrate the model. A summary of catchment characteristics is given in Table 3.1.

78 Chapter 3 - Catchments and Storm Events 3-3 Table Summary of Catchment Details Catchment National Area Urban IMP ^ IMPcc^ MPQC^M Slope Station (km 2 ) Fraction (m/m) No. Curtin Mawson Long Gully Ck. Giralang Maroubra Strathfield Fisher's Ghost Ck. Jamison Park Vine Street NA * * Changed to.22 after modelling (see chapter 4), NA - not applicable, monitoring done by other agencies Catchment Area Orthophoto maps were obtained by the author from the Department of Environment Land and Planning from Canberra, Sydney and Melbourne for all nine urban catchments. The catchment boundaries were then carefully sketched onto the orthophoto maps following the watershed lines. The area inside the catchment boundary was measured several times with a planimeter to determine an average catchment area. The areas obtained were compared to values determined by others to check that the values were consistent Measures of Urbanisation The effective impervious fraction was determined as well as the degree of urbanisation. Three methods for determining the effective imperviousfraction were investigated. The three methods are: 1. IMP maps - A total impervious fraction calculated from orthophoto maps. The total impervious fraction can be determined from orthophoto maps. The above total imperviousfractions were obtained from Bufill (1989) and checks on the validity of the total imperviousfractiondata were made by the author. The total lengths of all the streets and highways within each catchment were measured, and the total number of houses were also counted from the orthophoto maps. Shopping centres, schools, offices and other commercial properties were also measured. An average street width measured on the catchment was used to give a total area of roadway while the average imperviousfraction of a typical lot was determined and multiplied by the number of lots counted from the orthophoto maps. The total impervious fraction of the catchment was then calculated from the above information.

79 Chapter 3 - Catchments and Storm Events IMPocmaps - A directly connected imperviousfractiondetermined from orthophoto maps and plans showing the piped drainage system within the catchment. This is the impervious fraction directly connected to the watercourse which includes roads, house and garage roofs, etc. This is a difficult method of evaluating the directly connected impervious fraction because some houses and garages may not be directly connected to the watercourse. For example, in many suburbs, roof water is discharged to absorption trenches which flow onto pervious areas before entering the watercourse. Thus these area cannot be considered a directly connected impervious areas. This data was obtained from Boyd et al (1993). 3. IMPUGN.,]! - A directly connected impervious fraction determined from rainfall and runoff data by plotting the rainfall depth against the runoff depth (seefigure3.1). The slope of the plotted line then gives the effective impervious fraction of the catchment. This is a far more accurate method of measuring the effective impervious part of the catchment. This data was obtained from Boyd et al (1993). The question of impervious and directly connected impervious fractions has to be examined more closely. Studies by Miller (1978), Miller et al. (1978), Jacobsen and Harremoes (1981), Pratt et al. (1984), Bufill and Boyd (1992) and Boyd et al. (1993) show that urban catchments are made up of three types of surfaces, namely: 1. Pervious or semi-pervious areas (A p ) which consist of lawns, gardens and parks, 2. Impervious areas (A ic ) which are directly connected to the drainage system such as roads, parking areas and in some cases building roofs, and 3. Impervious areas (Aj) which are not directly connected. Thus the total catchment area is: A_ t = A p + A ic + Ai equation 3.1 from the directly connected impervious area A ic flows straight into the drainage system and into the catchment watercourse. It has a quick response and minimal distributed storage. On the other hand, runoff from the impervious area A ; flows over pervious surfaces before reaching the drainage system. These areas have slower response and greater distributed storage and behave in a similar manner to pervious catchments. The total impervious fraction is the sum of the directly connected impervious fraction (A ic ) plus imperviousfractionnot directly connected (Aj).

80 Chapter 3 - Catchments and Storm Events 3-5 The use of the correct imperviousfractionis of utmost importance for correct modelling. The three impervious fractions described will be modelled for all the catchments. Results will be compared and conclusions drawn about the effect of the imperviousfractionused in modelling. Rot of against Rainfall Rainfall 2 Maroubra IMP Total of 58 events Figure Rainfall and s (Boyd et al, 1993) Surface Slope The average surface slope is given to show the differences in the topography in each of the catchments being studied. It is measured along the longest flow path within the subcatchment, starting at the outlet, running up the main channel and then branching off at the furthest tributary all the way to the top of the subcatchment. It is not used in the modelling process but is shown to give some indication of the topography of the catchment Rainfall Data The storm duration, average intensity, and ARI was taken from the doctoral thesis by Bufill (1989 is not used in the modelling process, but is included to give an indication of the size of the event. The duration of the largest rainfall burst in the storm is shown. The number of storm bursts in each event varies, but by looking at the rainfall hyetograph for each event, one can see the number of bursts for a particular storm. A burst is a high intensity period of rainfall, followed by a less intense period. Some events may have only one burst and others many. In these events, only the duration of the largest burst is given because little or no rainfall occurs between bursts. Some events may have many bursts with continuous rainfall between each burst. For these events, the duration given is the total duration of the event.

81 Chapter 3 - Catchments and Storm Events 3-6 The intensity of the storm (mm/hour) is the average intensity of the storm or of the most intense burst and the value is dependent on the duration of the event. Finally, the average recurrence interval (ARI) in years is given to show the size of the storm. calculation method for ARI's is given in ARR(1987) in volume 1, chapter 2. Intensity-Frequency- Duration (IFD) tables were prepared by Bufill (1989) for the Canberra, Sydney and Melbourne catchments. It must be noted that the ARI values are approximate, and are only used to give some indication of the size of the storm. See Table 3.2 andfigure3.2. Table Example of IFD Table for Canberra Catchments (Bufill, 1989) ARI (Years) Duration min hr hrs hrs.9 I.I Skewness G =.24, F2 = 4.28, F5 = #i[r>^ Figure Calculation of ARI for Giralang (Bufill, 1989)

82 Chapter 3 - Catchments and Storm Events 3-7 Another important factor in the modelling process is the time step At. The time step should b enough to adequately define therisinglimb and peak of the runoff hydrograph as well as defining the rainfall hyetograph. A value of At less than onefifth of the hydrograph time ofriseis recommended. The time step for each of the catchments can be seen in Table 3.3. For Jamison Park, the time varied between 2 and 1 minutes. Table Summary of Storm Event Details Catchment Time Step At Smallest Event ARI Largest Event ARI Name (min) (years) (years) Curtin 6 <1 >1 Mawson Long Gully Creek 6 <1 >1 Giralang 6 <1 3 Maroubra 3 <1 1 Strathfield 3 <1 6 Fisher's Ghost Creek 3 <1 8 Jamison Park 2-1 <1 4 Vine Street 6 < Woden Valley Catchments Introduction The Woden Valley catchments are located in the southern suburbs of Canberra. The main catchmen is Curtin, with the other two catchments (Mawson and Long Gully Creek) lying within it. See Map 3.1. The main stream in the valley is Yarralumla Creek, which runs from south to north and finally into the Molongolo River. Yarralumla Creek is gauged in a section close to the township of Curtin. Maps for the catchment were compiled in 1992 by the Department of Environment, Land and Planning. Rainfall and runoff data are available for the catchment from 1971 to As the catchment has undergone constant urbanisation between 1983 and 1992, the amount of urbanisation and impervious area has increased. Imperviousfractionvalues obtained from the more recent maps should not be used in modelling as the rainfall and runoff data was collected between 1971 and Gauging of the Woden Valley catchments commenced in 1971 and data up to the end of 1983 was used in this study. A total of 14 storm events were available for Curtin and Long Gully Creek and 11 events for Mawson.

83 Chapter 3 - Catchments and Storm Events 3-8 The top soil consists of fine graded materials which vary in thickness, underlain by clay and weathered rock. This clay and weathered rock probably contributes to high runoffs due to low permeability. Tables 3.4 to 3.6 shows the storm event details. It must be noted that the catchment areas in were used in modelling Curtin The catchment area of Curtin is reported to be 26.9 km 2 and was measured by the author to be 26. km 2. The urbanised fraction of the catchment was.57 in 1983 (measured by Bufill, 1989) and measurements by the author on maps dated 1992, have found it to have an urbanfraction of Long Gully Creek Long Gully Creek has had the largest impact on the overall urban and impervious fraction on the Curtin catchment. Long Gully Creek catchment lies at the upper reaches of Woden Valley, south south east of the Curtin township. Originally, the catchment was covered by a pine plantation, but now most of it is residential. The catchment is just 4.94 km 2 in size and was only.16 urbanised in Measurements performed by the author have found that the catchment now has an urban fraction of.59. The highest points on the boundaries of the catchment have elevations of 8 metres. The ground then slopes steeply in a northerly direction towards the Curtin township where elevations at the outlet of the catchment are in the order of 6 to 7 metres. Urbanisation was initially in the northern part of the catchment, which is not very steep (up to 5%). At present, urbanisation has reached the boundaries of the catchment at the southern and western ends where the slopes are up to 7.5%. Due to the very steep terrain at the east of the catchment (slopes of 3%), further urbanisation has not commenced and the land use is solely for pine plantations Mawson The Mawson catchment lies next to, and to the west of Long Gully Creek. It is drained by the up Yarralumla and gauging of the catchment occurs in Mawson township, where elevations are around 6 metres. Mawson is 5.21 km 2 in size, including the unurbanised area between Mt. Taylor and the

84 Chapter 3 - Catchments and Storm Events 3-9 residential development. Studies done by the ACT Flood Management Trust indicated that a cut off drain exists at the boundary of the residential development, which diverts overland flows that occur west of the drain, out of the catchment. The size of this unurbanised area was measured by the author to be.76 km 2, thus reducing the overall size of the Mawson catchment to 4.45 km 2. Table Curtin Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 26/1/71 5/2/71 1/2/71 13/2/72 21/3/74 5/11/74 14/1/77 6/4/77 2/3/78. 23/3/78 9/1/78 5/2/81 6/1/ > < /1/ <1

85 Chapter 3 - Catchments and Storm Events 3-1 Table Mawson Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 13/2/72 21/3/74 5/11/74 14/1/77 6/4/77 2/3/78 23/3/78 9/1/78 5/2/81 6/1/81 15/1/ Table Long Gully Creek Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 26/1/71 5/2/71 1/2/71 13/2/72 21/3/74 5/11/74 14/1/77 6/4/77 2/3/78 23/3/78 9/1/78 5/2/81 6/1/ > /1/ <1

86 Chapter 3 - Catchments and Storm Events 3-11 Map 3.1 -Woden Valley Catchment

87 Chapter 3 - Catchments and Storm Events Giralang Catchment Giralang is located in the Canberra suburb of Belconnen and has an area of.94 km 2. Before subdivision of the catchment occurred in 1974, the land was used for grazing, and it was grassed with no trees. By 1976, the construction of roads, drainage and other facilities (telephone, electricity gas, water, sewerage) was complete, and housing development commenced. By late 1977, lawn and tree regeneration was completed to stop erosion on the disturbed soil. No further urbanisation of Giralang has taken place to date. Gauging of the catchment commenced after completion of urban development in 1976 and data up to 1984 was used. The soil in this catchment is similar to that in the Woden Valley catchment. The Giralang catc boundaries were drawn on orthophoto maps and used to determine the size, urban and impervious fractions. The total lengths of road inside the Giralang catchment measured to be approximately 8. km with a total of 515 residential allotments. Table 3.1 shows the Giralang catchment details and Table 3.7 the storm events. Map 3.2 shows the Giralang catchment. Table Giralang Catchment Events (Bufill, 1989) Event 27/3/76 14/1/77 6/4/77 2/2/8 6/1/81 9/1/78 23/3/78 27/1/78 2/3/78 5/2/81 24/3/82 15/1/83 13/12/83 Total Rain Surface Peak Flowrate (m 3 /s) Average Intensity (mm/hr) Duration of Largest Burst (min) Approx. ARI (years) <1 <1 <1 <1 <1 <1 <1 3 6 <1 3 25/3/

88 Chapter 3 - Catchments and Storm Events 3-13 Map The Giralang Catchment

89 Chapter 3 - Catchments and Storm Events 3.4 Maroubra Catchment The suburb of Maroubra is located north of Botany Bay in south eastern Sydney. The catchment has an area of.57 km 2 and is part of the Bunnerong main drain. The outlet of the catchment is at the Nagle Park gauging station (No.2133) on Maroubra drain. The gauging station is operated by the school of Civil Engineering, University of New South Wales. Gauging commenced at the beginning of 1977 and a total of 39 storm events were available between 1977 and Table 3.8 shows the twenty events chosen for use in the modelling process. The subdivision on which the catchment is located is about fifty years old with medium to high density housing development. The drainage system was built at the time of the urbanisation. The drainage from roofs and paved areas from the older buildings is diverted to absorption pits built in the highly pervious sandy soils which are predominantly found in the south eastern Sydney area. Only some impervious areas are connected to the drainage system. Note the large difference between the total imperviousfraction (IMP maps ) and directly connected imperviousfraction (IMPD^,^,) in table 3.1, because the imperviousfractionis measured from orthophoto maps while the directly connected imperviousfractionis measured from rainfall data. The sandy soil is highly pervious and is able absorb most of the runoff, thus the difference in the two imperviousfractiontypes. The catchment boundaries were marked on an orthophoto map to determine the land usage of the Maroubra catchment. Checks were made and compared to the values obtained by Bufill (1989). The catchment is predominantly residential (61%) with the roads making up 3% of the catchment. A small part of the catchment is parkland (2%) and the rest of the catchment is composed of shopping centres and other commercial properties. Table 3.1 shows the Maroubra catchment details and Map 3.3 shows the Maroubra catchment.

90 Chapter 3 - Catchments and Storm Events 3-15 Table Maroubra Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 1/3/77 5/3/77 3/3/78 17/3/78 27/3/78 13/4/78 18/5/78 19/6/79 2/6/79 17/3/83 18/6/83 6/11/84 8/11/84 11/12/84 1/5/85 12/4/86 3/7/87 4/1/87 2/4/ <1 <1 <1 <1 <1 <1 <1 <1 <1 2.5 <1 <1 1 <1 <1 <1 <1 < /4/ "

91 Chapter 3 - Catchments and Storm Events 3-16 Vt«A- * \x:.~ 1 \ \ * T< "LiT-«< Map The Maroubra Catchment

92 Chapter 3 - Catchments and Storm Events Strathfield Catchment Strathfield is a fully urbanised 2.31 km 2 catchment located west of Sydney. The catchment and drainage was developed early in the twentieth century. The impervious fraction of the catchment indicates that it is predominantly residential, with medium to high density housing development. The catchment boundaries were marked on an orthophoto map to determine the land usage. Checks were made and compared to the values obtained by Bufill (1989). The catchment is predominantly residential (76%) with the roads making up 21% of the catchment. A small part of the catchment is parkland (1%) and the rest of the catchment is composed of shopping centres and other commercial properties. The soil in the catchment is shallow to moderately deep (up to 15 cm) red podzolic soil and brown podzolic soil. The upper slopes of the area are well drained. In the lower lying areas where natural drainage depressions occur, yellow podzolic soil 15 to 3 cm deep are found. The soils in the area are moderately reactive, highly plastic and have very little fertility. Strathfield has the second largest available sample of storm data of all the catchments. A total events have been recorded between the beginning of 1977 and the end of The catchment has a fully piped drainage system which flows into a U shaped concrete lined channel at the outlet of the catchment. Other details of the catchment are outline in Table 3.1. Table 3.9 shows the twenty events chosen for modelling. Map 3.4 shows the Strathfield catchment and its boundaries.

93 Chapter 3 - Catchments and Storm Events 3-18 Table Strathfield Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 3/9/77 4/9/78 2/3/81 2/4/81 4/4/81B 4/4/81 3/12/82 25/3/82 3/9/83 16/3/83 21/5/83 7/4/84 8/1/84 8/11/84 1/5/85 3/4/85 4/8/86 13/2/88 3/4/88 28/4/ <1 <1 <1 <1 <1 <1 <1 <1 <1 15 <1 <1 <1 4 <1 < <1 5 Note: The letter B at the end of the event date denotes that the event is the second of two events that occurred on that day.

94 Chapter 3 - Catchments and Storm Events rw<u:-?'j\\ ' V^. \ : \Of=iC.-*.--ii>v\^.jjK>«FSO..Vi M«-;47 /, 1 : 'l r! «it." ; VJ--.-T-".- JCTT?>-....J^l ii il,v < T&; : Map The Strathfield Catchment

95 Chapter 3 - Catchments and Storm Events ^ Fisher's Ghost Creek Catchment The Fisher's Ghost Creek catchment is located in the suburb of Bradbury in the Campbelltown area, south west of Sydney and has an area of 2.35 km 2. The catchment is residential with low to medium density housing. The catchment boundaries were marked on an orthophoto map to determine the land usage. Checks were made by the author and compared to the values obtained by Bufill (1989). The catchment is predominantly residential (75%) with the roads making up 12% of the catchment. A small part of the catchment is parkland (11%) and the rest of the catchment is composed of shopping centres and other commercial properties. The upper half of the catchment is fully piped and the main stream is not lined. The stream runs through parkland and is vegetated. This may have been done to slow down the flow velocities in the main channel in flood periods. The highest parts of the catchment are at the boundaries and reach elevations of up to 15 metres. The catchment outlet is at a height of 75 metres above sea level. Surface slopes of up to 12% occur near the catchment boundaries and are up to 5% in the lower parts of the catchment near the main stream. The soil in the catchment is composed of medium red clays and shale with top soil having a typica depth of 2 cm. Below the top soil is a base of sandstone (Hawkesbury Sandstone) which outcrops in the stream bed. The soil characteristics are very similar to those described for the Strathfield catchment. Storm data for Fisher's Ghost Creek from 1981 to 1988 has been used, with a sample of 23 events. Table 3.1 shows the twenty events chosen for modelling. Table 3.1 shown the details of the catchment and Map 3.5 details the boundaries of the Fisher's Ghost Creek catchment.

96 Chapter 3 - Catchments and Storm Events Table Fisher's Ghost Creek Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 2/11/81 4/5/81 19/1/81 25/12/81 17/3/83 2/3/83 5/3/83 27/11/83 13/12/83 26/1/84 7/2/84 8/11/84 9/11/84 8/12/85 15/1/86 6/8/86 18/11/86 24/1/87 5/6/ <1 <1 <1 < <1 <1 <1 <1 <1 <1 <1 3 3 < /5/ <1

97 Chapter 3 - Catchments and Storm Events 3-22 Ml UTU1EIT MIU1IT in-utuinr nnoitr M '«t irci CIEEX m m A. uotiitmrai fifn iiiiiitt runsnm MO loi-cirtiicn II«EI limit a u m lectmic m it tuna Dim n n «i tiiuu. MUI IF cmr n» m-urciien um irmui m n unnni rat ami a a ~ iwnui itmu miairru M f in nt in us CATCHHEKT CONf 1EUBATIN Map Fisher's Ghost Creek Catchment

98 Chapter 3 - Catchments and Storm Events Jamison Park Catchment Jamison Park is a fully urbanised catchment with an area of.21 km 2 located approximately two kilometres south of the Penrith railway station in western Sydney. The catchment has been gauged by the University of Technology, Sydney since Jamison Park was developed about 15 years ago and consists of low to medium density residential housing. It possesses wide streets and unpaved footpaths, which are common to modern residential subdivisions. The total imperviousfractionis.36 with the directly connected impervious fraction being.21. The catchment boundaries were traced onto an orthophoto map and used to confirm the data obtained from Bufill (1989). The total length of roadway inside the subdivision was 2.4 km with a total of 191 allotments. The catchment is predominantly residential (89%), the roads make up another 9% of the catchment, with the rest of the catchment being parkland (2%). The catchment has no commercial areas. The soil characteristics of this catchment are similar to those of Strathfield and Fisher's Gho which were discussed earlier. Due to constant monitoring of the catchment by the University of Technology, Sydney, over ninety storms were available for modelling. Table 3.11 shows the twenty events chosen for modelling. Map 3.6 details the boundaries of the Jamison Park catchment.

99 Chapter 3 - Catchments and Storm Events 3-24 Table Jamison Park Catchment Events (Bufill, 1989) Event Total Surface Peak Average Duration of Approx. Rain Flowrate Intensity Largest Burst ARI (m 3 /s) (mm/hr) (min) (years) 21/3/83 7/11/84 3/6/86 3/1/86 4/1/86 1/1/87 1/3/87 1/12/87 6/9/87 1/1/88 1/4/88 21/1/88 2/1/88 4/1/88 4/4/88B 6/4/88B 7/2/88B 8/2/88 8/5/88 9/4/ <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 Note: The letter B at the end of the event date denotes that the event is the second of two events that occurred on that day.

100 Chapter 3 - Catchments and Storm Events 3-25 Map Jamison Park Catchment

101 Chapter 3 - Catchments and Storm Events Vine Street Catchment Vine Street catchment is located on the western side of Melbourne. The total catchment area has quoted as.7 km 2 by Maksimovic and Radojkovic (1986). Measurements by the author on two catchment maps has shown the area to be.64 km 2. The catchment is mainly residential with low to medium density housing and flats. Most of the dwellings are directly connected to the drainage system. Other impervious areas such as footpaths are graded to drain across pervious areas and are therefore not connected. The catchment boundaries were traced onto an orthophoto map and used to confirm the data obtaine from Bufill (1989). The total length of roadway inside the subdivision was 1.3 km with over 7 allotments. The catchment is predominantly residential (72%), the roads make up another 13% of the catchment and 5% parkland. The rest of the catchment consists of commercial areas (1%). The directly connected imperviousfraction of the catchment is.31, with a total imperviousfraction of.37. The average surface slope of the catchment is.41 with the soil within the catchment being primarily quaternary basalts and volcanic clays. These types of clays are able to absorb large quantities of water and thus swell and shrink on drying, which causes foundation problems. In hot, dry weather, cracks in the ground are known to develop and the soil infiltration capacity varies seasonally because of this. A total of eleven storm events were used for this catchment. Table 3.12 shows the storm details Table 3.1 the details of the catchment. Map 3.7 gives the boundaries of the Vine Street catchment.

102 Chapter 3 - Catchments and Storm Events 3-27 Table Vine Street Catchment Events (Bufill, 1989) Event Total Rain Surface Peak Flowrate (m 3 /s) Average Intensity (mm/hr) Duration of Largest Burst (min) Approx. ARI (years) 15/2/ /2/ /5/ /1/ <1 29/12/ /11/ /4/ /1/ /9/ /12/ /11/ Map Vine Street Catchment

103 Chapter 4 Nonlinear Split Modelling with the Loss Rate Model

104 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model NONLINEAR SPLIT MODELLING with the LOSS RATE MODEL 4.1 Introduction In this chapter, we examine the performance of WBNM incorporating a split catchment option, nonlinear storage routing for both the pervious and impervious areas combined with a loss rate rainfall loss model. Calibration is also performed with three different imperviousfraction (IMP maps, IMPrxmaps and IMPix;^^, table 3.1) for each catchment. As can be seen for some catchments (eg. Curtin, Long Gully Creek and Vine Street) the imperviousfractioncalculated from the three different methods are the same or similar and for these catchments, modelling was only performed once. At this stage of the study, all the catchments are modelled using one subcatchment. This has been shown to be satisfactory for catchments up to approximately 13 km 2 by Rao et al (1974), Diskin (198) and Bufill and Boyd (1992). Modelling utilised observed rainfall and streamflow data from seven urban catchments. The catchments studied were; Curtin, Mawson, Long Gully Creek, Giralang, Maroubra, Strathfield and Fisher's Ghost Creek. The date of storm events used are listed in Table 4.1 for each catchment. It must be noted at this stage that not all the hydrographs are shown for each catchment. Only some of the hydrographs are shown and the rest are on the CD in the appendices. Table List of Storm Events Curtin Mawson Long Gully Ck Giralang Maroubra Strathfield Fisher's Ghost Ck 26/1/71 21/3/74 26/1/71 27/3/76 1/3/77 25/3/82 2/11/81 5/2/71 5/11/74 5/2/71 14/1/77 3/3/78 16/3/83 5/3/83 1/2/71 14/1/77 1/2/71 6/4/77 19/6/79 21/5/83 2/3/83 21/3/74 6/4/77 21/3/74 27/1/78 17/3/83 7/4/84 27/11/83 5/11/74 9/1/78 5/11/74 2/3/78 5/11/84 8/11/84 15/1/86 14/1/77 2/3/78 6/4/77 5/2/81 8/11/84 4/8/86 6/8/86 9/1/78 23/3/78 9/1/78 24/3/82 11/12/84 13/2/88 24/1/87 2/3/78 6/1/81 2/3/78 15/1/83 1/5/85 3/4/88 28/4/88 5/2/81 5/2/81 5/2/81 13/12/83 2/4/88 28/4/88 24/5/88 15/1/83 15/1/83 15/1/83 25/3/84 28/4/88 4/7/88 5/6/88 The model was calibrated for each storm event by modifying the pervious area initial losses, pervious area continuing losses, and the pervious area calibration parameter C until good agreement was obtained (if possible) between the calculated and recorded hydrographs. For all impervious areas, a default initial loss of 1 mm and loss rate of mm/hour was adopted. The parameter C for the impervious areas was computed automatically by WBNM. Chapter 2 shows the equations used to do this. The results from the modelling for each catchment is described in the following sections.

105 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4.2 Results for the Canberra Catchments Curtin After running WBNM with the data files for Curtin, Table 4.2 was prepared. The rainfall hyetograp and runoff hydrographs for all events were plotted and can be seen infigure4.1. By looking at the shape of the calculated and recorded runoff hydrographs, it can be seen that overall calibration was successful. The rest of the hyetographs and hydrographs for this catchment and all other catchments are in Appendix A on diskettes. The timing of the calculated hydrographs was satisfactory, indicating that a pervious area initial loss of mm is an adequate assumption. For this data, the initial loss was satisfied by prior rainfall before the main storm. This also applies to the other catchments. It may seem odd that the impervious areas were assigned an initial loss higher than pervious areas. The reason for this is that because the storm events used were quite large events, the pervious areas of the catchment were already saturated, thus initial losses were Omm. As impervious areas dry faster than pervious areas, an initial loss of 1 mm is used to allow for the initial wetting of the impervious areas. But as the storm events are quite large, an initial loss of 1 mm will have little or no effect on the final runoff volumes calculated by the model. In some events the rainfall losses on the pervious areas were so high that no pervious area runof occurred. In these events runoff was generated only on the impervious surfaces. This happened on the 21/3/74 and 9/1/78. The event on the 21/3/74 was omitted from the final results because the calculated runoff volume did not balance with the recorded runoff volume (see Table 4.2). This lack of volumes balancing also occurred in some other catchments, and the events in which this happened were also omitted from the study.

106 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4.4 Table Summary of Results for Curtin (IMP=.17) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (thoum 3 ) (thoum 3 ) (m 3 /s) (m % ls) 26/1/ /2/ /2/ /3/ /11/ /1/ /1/ /3/ /2/ /1/ Mean 1.85 Std Dev.84 Curtin IMPuG^i,^ =.17, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

107 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-5 I Hydrograph I I Hydrograph I I Hydrograph I 1.15 B too Aw 1 2 R*(frin) f TVrB(rrtn) 15 _ 1 4 BOO 7to»(n*i) TVm(rrtn) Curth CXrUn 1 Subt/u Bf «r* Curtin-l&utwma Brant Tm(rrin) Hyetograph "T>r»(rrin) Hyetograph I Tbm(irin) S1 1 5 it. T«T»(mn] *»«yllllfflh,, CUrtn-ISutana Curth -1 Subaraa Curtin -1 Subaru &ant Evtrt Brant 1 Hydrograph 1 ~ 4 i- * 2 _Odcukttd ft_ ) 1 2 J Tbm(irtn) n I 3-2 1, " J ' J L Tkm(irin) I afawk I Curtin -1 Subana i S-1-83 Brant Figure Hyetographs and Hydrographs for Curtin (IMP =.17)

108 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-6 Figure 4.2 was produced to determine if there is any trend between parameter C and storm size. In this case the data is not conclusive. Figure 4.2 b was produced to determine if there is any trend between parameter C and the runoff volume ratio. It can be seen that parameter C reduces as the runoff volume ratio approaches 1. Fully pervious catchments have a lower parameter C than fully impervious catchments. If WBNM was correctly modelling both pervious and impervious runoff, there should be no trend of C with the runoff volume ratio. Therefore, this result indicates that the way WBNM models the impervious part of the catchment needs further investigation. Note, however, that there are not a lot of events to make firm judgment. For this reason the study was extended in the later chapters to include more catchments and more events. Event 21/3/74 produced only impervious area runoff and this can be clearly seen in table 4.2 (the pervious area volume is zero for this event). It produced a parameter C value that was much higher than any of the other events (5.41). The reason for this is that the runoff volume from the impervious surfaces exceeds the recorded runoff volume, and parameter C needs to be increased to reduce the calculated flowrate. This may also indicate that the model overestimates runoff from impervious surfaces. This event was omitted from the study. The mean value of parameter C was found to be 1.85 and the standard deviation was.84. A larger sample of events needs to be studied to see if there are any trends, but from this small sample, it could safely be said that there are no strong trends between the size of the storm and the calibration parameter for the Curtin catchment. I Plot of Parameter C against Qrec I 1 Plot of Parameter C against Vper/Vtotl O 3 > I 2 S 1 C fourth IMP Qrac(rrfVa) (a) O 3 & V 4 1 ( fourth IMP Vpar/VM (b) Figure Plot of Parameter C against Peak Flow and Ratio for Curtin (IMP-.17) Note: Vper/Vtot = volume of runoff from pervious areas / volume of runoff from total area

109 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Mawson There were two different impervious fractions to test for the Mawson catchment (see table 3.1) 4.3 shows the results for IMPD^^,, =.21 and table 4.4 for IMP^^ =.26. Rainfall hyetographs and runoff hydrographs for four events can be seen in figure 4.5. The plots are for the impervious fraction of.21 because generally better calibration was achieved with this value. The average parameter C value for IMP =.21 was 1.36, compared to 1.53 for IMP =.26. For IM =.26, WBNM calculated more impervious area runoff, and this required higher parameter C values to calibrate the peak discharges. Figures 4.3 shows the plot of parameter C for each event against the corresponding peak record flowrate and runoff volume ratio for Mawson with IMP of.21. Figures 4.4 shows the plot of parameter C for each event against the corresponding peak recordedflowrate and runoff volume ratio for Mawson with IMP of.26. The mean parameter C value for IMPu^^i =.21 is 1.36 with a standard deviation of.53. The mean parameter C value for IMP^,,,^ =.26 is 1.53 with a standard deviation of.94. There is a larger scatter for the larger impervious fraction, but a similar trend as in the results for Curtin is present which shows further investigation is required to determine the reason WBNM overestimates discharges for events producing more impervious area runoff. (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Mawson (IMP =.21), O 5 > V S 1 a I Plot of P arameter C against Qrec I 1 D 2 M«w«on IMP».26 a a Q,«c (rrgrt) O ' k V 4i 1 Plot of Parameter C against Vper/Vtotl a a {Mawaofl MP-.26 [ Vpar/Vtot (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Mawson (IMP=.26)

110 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model I Hydrograph I I Hydrograph] I Hydrograph I r T2 2 a «1 _C*tuatod _R*eora*d Thn>(frtn) Tlmi(mln) 1 Hyetograph j lomnfal I ec f» ^ Mmraon Brarrl n Tkm(rrtn) Tbm(rrfci) Tkra(rrfn) Hyetograph I 5 JOO Thni(rrin) Mwton 9-l-78».r Tam(irin) 1 ISO 2 25 nrr»(«*)) 1 Hyetograph 1 I Hyetograph 6 - r LBI L_ Tlwfirtn) R*<«Tyynsnn Hydrograph T2L J 1. I ^ 3 6 Ttai(n*Q I 4 * I. 3 2 K 1 Hyetograph 1 ~JL.., L Mmrson Branl lafwnm Figure Hyetographs and Hydrographs for Mawson (IMP =.21)

111 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4_ Table Summary of Results for Mawson (IMP=.21) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 5 ) (thoum 3 ) (thoum 3 ) (m 3 /s) (m 3 /s) 21/3/ /11/ /1/ /4/ /1/ /3/ /3/ /1/ /2/ /1/ Mean 1.36 StdDev.53 Mawson IMP^xainm =.21, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear Table Summary of Results for Mawson (IMP=.26) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (thoum 3 ) (thoum 3 ) (m 3 /s) (m 3 /s) 21/3/ /11/ /1/ /4/ /1/ /3/ /3/ /1/ /2/ /1/ Mean 1.53 StdDev.94 Mawson IMPcc,^ =.26, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

112 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Long Gully Creek After running WBNM with the data files for Long Gully Creek, Table 4.5 was compiled. The rainfall hyetographs and runoff hydrographs for four events can be seen infigure4.6. Event 26/1/71 produced one large rainfall burst, followed by two very small bursts. The peak inten of the first burst was just on 1 mm/hr and the duration of the burst was about 2 minutes. The overall fit of the calculated and recorded hydrographs was poor with WBNM overestimating the discharges on the catchment after the peak flowrate. This event had Vper/Vtot =.87 indicating runoff was almost entirely from the pervious area and therefore the recession fell slowly (see figure 4.6). For the events on the 21/3/74, 5/11/74, 6/4/77 and 9/1/78, WBNM underestimated the calculated discharges after the peak discharge. Because these had larger proportions of impervious area runoff, this may indicate there is a problem with the way the impervious area is being modelled. At this point in the study, the pervious and impervious area lag times are being calculated with a nonlinearity coefficient of negative.23. These results indicate the impervious area modelling procedure may need further investigation. Table Summary of Results for Long Gully Creek (IMP=.5) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (thoum 3 ) (thoum 3 ) (m 3 /s) (m 3 /s) 26/1/ / /2/ /3/ /11/ /4/ /1/ /3/ /2/ O /1/ Mean 2.52 Std 2.31 Dev Long Gully Creek IMPOQ^^ =.5, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

113 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-11 Hydrograph I Hydrograph I 12 1 S «_C*leunrtad _R»cordad SO 1 ISO 2 Tlm»(rrin) 2 4 T*m<rr*i) 1 I * - S 8 I - a» Lang Guly Craak 26*1-71 &anl 11 J*._. TVn(rrtn) nmnfm Lang Guly Craak Ev art 1 Hydrograph] Tbn(rrin) 4 f 2 i- a AV k _C«lcuWad Tir»(rrtn) _.R»coriad Long Gut/ Craak 5-t 1-74 Bant Long Gua/Craak Event 1 ISO 2 Tn»<rrin) T)ma(rrai) I Hyetograph] Tkm(nt>) LengQJyQaak &ant T*m(rrin) Long Guly Craak Brant 71rm{frtn) 2 1 Long Guly Cr««k S-2-61 Eveot L- DR** r 2 c I Hydrograph I /v\ I 4 BOO 12(X Tkm(rrai) 1 Hyetograph _Ctleuktod _Ftoeora«d 1 M *2 I" - "j_l Long out/crmk B/ant Tlm(rrin) L o*w««figure Hyetographs and Hydrographs for Long Gully Creek (IMP =.5)

114 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-12 Figure 4.7 shows the plots of parameter C for each event against peak recorded discharge and runoff volume ratio. For discharges above 6 m 3 /s there is no trend between the parameter C and discharge. The amount of scatter is very small and one can conclude that the results are very good. Below 6 m 3 /s, the scatter in the parameter C values increases by a large amount, ranging from.5 to almost 8. The average parameter C for this catchment was the highest for all the Canberra catchments studied, having a value of The scatter is definitely very high and events 6/4/77 and 9/1/78 contributed to this, with the latter event having the highest parameter C of 7.9. Event 6/4/77 produces twice as much pervious runoff volume than impervious. Event 9/1/78 produced the same pervious and impervious runoff volume. The only similarity between the two events is that their pervious area rainfall losses were very high compared to the other events. The most evident trend that can be seen from the plots is that runoff from the catchment is predominantly from the pervious areas. The reason for this is that Long Gully has the smallest imperviousfraction (IMP=.5) of all the catchments, and one can say that it is essentially a natural catchment. It would be expected even before modelling such a catchment that the majority of the runoff would come from pervious areas. A trend similar to Curtin and Mawson can be seen for Long Gully Creek. That is a slight increase i parameter C for events where there is more impervious area runoff contribution. Again, this trend will need to be further investigated. I Plot of Parameter C against Qrec I 2 «I 4 i, V * * J_ 5 1 IS 2 Qrac(nti/s) [Long Guly CwklMP-o.oT] LonflGul»Ci klmp-q.t] Vper/vtot (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Long Gully Creek (IMP =.5)

115 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Giralang Table 4.6 shows the results for IMP maps =.22 and Table 4.7 shows the results for IMPDC^^, =.35. Note that IMPDC,^ is similar to IMP raaps, and modelling was only performed with IMP maps as the results would have been similar. The rainfall hyetographs and runoff hydrographs can be seen in figure 4.1. IMP =.35 produced poorer results than IMP =.22. The reason for this was that the larger imperviousfraction produced large calculated runoff volumes, which exceeded the recorded runoff volumes in five out of ten events. To try to balance the calculated and recorded volumes, the rainfall losses on the pervious surfaces were forced to be very high. In some cases (14/1/77, 6/4/77, 2/3/78, 24/3/82 and 15/1/83), the rainfall losses were so high that there was zero calculated runoff volume from the pervious surfaces, but the volume of runoff from the impervious surfaces still exceeded the recorded runoff volumes. IMP =.22 value was therefore adopted as the corrected imperviousfraction and was used throughout the study. The IMP value of.25 was not modelled because it is close to the adopted value of.22, and even.22 overestimated runoff volumes in one event Figures 4.8 shows the plot of parameter C for each event against peak recorded runoff and runoff volume ratio for IMP =.22. Figures 4.9 shows the plot of parameter C for each event against peak recorded runoff and runoff volume ratio for IMP =.35. The results for IMP =.22 are better than those for IMP =.35 because all events calibrated successfully with little trends in the results. The average parameter C for IMP =.22 is 1.43 with a standard deviation of.9, compared to for IMP =.35. Five events for IMP=.35 were omitted from the study due to calculated and recorded volumes unable to be balanced because of IMP =.35 being too high.

116 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-14 I Plot of Parameter C against Qrec I I Plot of Parameter C against VperrVtot I O 3 B I a 1 12 Qrec (rrij/s) Vper/Vtot OUfcHBlMP-.22 IGMkng II (a) (b) Figure Parameter C against Peak Flow and Ratio for Giralang (IMP =.22) O 2 1" 3 1 < JGImang IMP-.35 I Plot of Parameter C against Qrec I a 1 12 Qrec (n-q/s) (a) O 2 S _ 1-5 «1 ' ( 1 Plot of Parameter C against VperA/tot jglnling IMP S.6 VperA/tot (b) Figure Parameter C against Peak Flow and Ratio for Giralang (IMP =.35) Table Summary of Results for Giralang (IMP=.22) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 27/3/ S/4/ /1/ /1/ /3/ /2/ /3/ /1/ O.OO /12/ /3/ Mean 1.43 StdDev.9 Giralang lmp mlfi =.22, Split Catchment Initial Loss-Constant Loss Rate Pervious -Non-Linear Impervious - Non-Linear

117 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-15 Table Summary of Results for Giralang (IMP=.35) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 27/3/ /4/ /1/ /1/ /3/ B /2/ /3/ /1/ /12/ /3/ Mean 1.51 StdDev.5 Giralang IMPooatefcn =.35, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

118 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-16 I Hydrograph I [Hydrograph) r 7, 2 A,.5 * S 1 k..5 - ft A\, T1rra(rrtrt) I Holograph I Hyetograph I t nmrmrv. Glrchng Z7J-76&«nt _RIW.I GMUng Tti»(n*i) 2 a io S & «W-77&enl A irrtu Tlmifmh) O M «5 1 ISO 2 25 Itm(nvi) Hyetograph I: Hydrograph n»(rrin) Eii TH»(n*i) Qnlug M-78 E>eM I QRlWil J Gmimg 2D-3-78 Evert k_ lotewm [ Gtifeng Enit Hydrograph J _CMcuW»d S 2 - I, _*Wv Ai. 4 8 TVmlrrin) I Hyetograph] Ikra(rrtn) foo 15 2 Thm<rrin) ? ol_ji JL, l Thm(rrin) Giralang Brant Glnfcng Event Gkafcng t Brant - a I. * s * 1. % 6 i- 1 Hydrograph 1 i. V>^ ) ! J Gtafeng 2M-84E».f» Tkm(nln) 1 Hyetograph 1 L_nm._,, Th»(mn) fv, _Cncu««1 _Rtcorft*l 1 o«*l«1 Figure Hyetographs and Hydrographs for Giralang (IMP =.22)

119 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Results for the Sydney Catchments Maroubra Two different impervious fractions were obtained for the Maroubra catchment. IMPD^^, was calculated to be.16 and IMP maps was.52. The reason for such a difference in impervious fraction values is that Maroubra is a very highly unbanised catchment with half of the catchment being made up of impervious surfaces. But not all these surfaces are directly connected to the piped drainage system. The directly connected impervious fraction is much lower. As Maroubra is located on sandy soils, impervious surfaces which are not connected to the piped drainage system do not directly contribute runoff to the watercourses located within the catchment. from these surfaces flows onto pervious surfaces and is absorbed into the ground. These flows are then passed to the ground water table as baseflows. As WBNM does not model the baseflows, the rainfall losses assigned to his catchment are very high because the baseflow component is assumed not to contribute to runoff. After running WBNM with the data files for Maroubra, two results tables were compiled. Table 4.8 shows the results obtained when the model was run with an imperviousfraction IMP =.16 and Table 4.9 with IMP =.52. Figure 4.11 shows the rainfall hyetographs and runoff hydrographs obtained for only IMP =.16 because an IMP =.52 produced calculated runoff volumes greater than the recorded runoff volumes, indicating that an imperviousfraction of.52 is too high for this catchment. For IMP =.52, a balance in the calculated runoff volumes and recorded runoff volumes was not achieved for any of the events. The calculated runoff volume was three times higher than the recorded in some events, and to calibrate the peak discharges required excessively high parameter C values. For IMP =.16, better results were obtained, but four in ten events still produced a greater calculated runoff volume than recorded. This indicates that IMP =.16 may still be slightly too high. Note the very small runoff contribution from the pervious areas in this catchment. This is a very common feature on small, sandy soiled catchments where the runoff from the pervious areas is absorbed into the sand, and runoff contribution is mainly from the impervious surfaces. Most of the dwellings located within Maroubra do not discharge to the street, but rather to absorption trenches. Thus a large proportion of the impervious areas within Maroubra are not directly contributing to surface runoff, but rather to baseflow. As the piped drainage system within Maroubra is old, the pipes draining the street may also be broken and stormwater is released to the ground water table, and again there is a loss in runoff to the ground water table.

120 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-18 Table Summary of Results for Maroubra (IMP=.16) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 1/3/ /3/ /6/ /3/ /11/ /11/ /12/ / /4/ /4/ Mean 3.6 StdDev 2.96 Maroubra IMPu^^y, =.16, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear Table Summary of Results for Maroubra (IMP=.52) Event Pervious Pervious c Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 1/3/ /3/ /6/ /3/ / /11/ /12/ /5/ /4/ /4/ X Maroubra IMP-,, =.52, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

121 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-19 I Hydrograph I I Hydrograph T*r»(rrin) t 1 o.s - IN fu - is\ A \\ J J, I v_ l>^_, Hrr»(rrtn) 1 2 Tkr»(n*i) 1 2 I- ama hkraubn IS-S-79&mt Tm(Mn) Hn»(n*i) 1 Hyetograph 1 [Hyetograph] 15 i 1 1 E 5 fl IE m_ nr»w- Dl^ili Maroubra 8-ll-e4Ew«rt Brant "nma(ftin) Thnafirtn) Hyetograph ^ Ikmira _«*<«" Maroubra f s so I - s 2 ^ Maroubra 1.III a 1 ****" B/anl Brant 1 Hydrograph 1 1" i ^ _catuwoo.hkokm «1 I: 1 Hyetograph 1 Z l kllaalmi jnr»r««j TH»(irtn) Mroubri 28-4^8 6.. Figure Hyetographs and Hydrographs for Maroubra (IMP =.16)

122 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-2 Figure 4.12 shows the plot of parameter C for each event against peak recorded runoff and runoff volume ratio. The parameter C values are fairly high and scatter by a large amount. There are five events where the parameter C values were very high and these events are 3/3/78, 17/3/83, 5/11/84, 8/11/84 and 28/4/88. The events on the 5/11/84 and 8/11/84 produced totally impervious runoff, while the other events recorded a small amount of pervious area runoff. The average parameter C for the events which calibrated was found to be 3.6 with a standard deviation of Another important finding was that half of the events studied produced totally impervious area runoff while for the other half, some pervious area runoff was produced, but in all cases the impervious runoff was much higher. o s 1" S. 2 1 Plot of Parameter C against Qrec 1 4> 4> Qrec (rrfl/s) 1 Maroubra IMP O 6 l 4 I2 < I Plot of Parameter C against VperA/tot I ]Maroubra IMP Vpw/Vtrt (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Maroubra (IMP =.16) The impervious fraction finally adopted was IMPu^,^! =.16. This value is still high compared to the other catchments which indicates that the impervious fraction is still too high or mat the model overestimates runoff from impervious surfaces and needs a high parameter C value to compensate for this. The problem with the Maroubra catchment is that it is an old urban catchment which was developed in the early 19's. Due to its highly pervious soils, runoff from house roofs (which is a major contributor to urban runoff) has been diverted to seepage ponds under the residential dwelling. The runoff is essentially diverted to the ground water table and which reduces streamflows. Another reason for these high values was that in some events on Maroubra, a portion of the high flows exceeds the drainage system capacity and is diverted out of the catchment. The recorded rainfall data is correct, but the recorded streamflow data is incorrect in that the recorded flows at the gauge are lower than they should be due to flow diversion. WBNM calculated "correct" streamflows, but high parameter C values were required to reduce the calculated streamflows to equal the low recorded flows. The data for event 5/11/84 was found to be incorrect. Information obtained after the calibration of this event confirmed that the gauge measuring the flows was faulty, and this event has been omitted from further study and another event (3/7/87) has been added to replace it. As the catchment is 1% urbanised, we may be inclined to accept the high imperviousfraction of.52, but this would be incorrect. A good example of this is the modelling using IMP=.52. In all

123 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-21 events, the calculated runoff volume was more than three times greater than the recorded runoff volume, which is a clear indicator of an incorrect imperviousfraction (Table 4.8 and 4.9) Strathfield Table 4.1 shows the results using IMPm^ =.18, table 4.11 shows the results using IMP^^i =.29 and table 4.12 shows the results using IMP maps =.5. The results for IMP maps =.5 (Table 4.12) show this value to be incorrect because in half of the events, WBNM calculated more runoff than was recorded. Even after applying very high rainfall losses, a balance in the calculated and recorded runoff volumes does not occur. This indicates an IMP =.5 is too high for this catchment. To determine the correct impervious fraction, figures 4.14,4.15 and 4.16 were prepared and the plot of the hydrographs (figure 4.13) were examined. IMP =.5 can immediately be rejected because of the high calibration parameters (C was ) and a lot of scatter. For the impervious fractions of.18 and.29, the average parameters C were and , respectively. As can be seen, there is an obvious trend that if the imperviousfractionis increased, the value of the calibration parameters increases. The reason for this is that the larger runoff volumes require a larger lag parameter to reduce the calculated peak discharge down to the value of the recorded peak discharge. After studying the hydrographs, IMP =.29 was chosen to represent the impervious fraction of Strathfield rather than IMP =.18. IMP =.29 gives a better fit of calculated and recorded hydrographs, even though parameter C was higher than for IMP =.18. For example, the event on the 16/3/83 clearly demonstrates a very good fit between the calculated and recorded hydrographs (figure 4.13) for this event, whereas for the same event but with IMP =.18, WBNM underestimated the discharges after the peak discharge. This is also evident on a number of the other events, but it is not as clear as for this event. Again, this indicates a problem with WBNM's ability to model impervious areas.

124 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-22 Table Summary of Results for Strathfield (IMP=.18) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 25/3/ /3/ /5/ /4/ /11/ /8/ /2/ B /4/ /7/ /4/ Mean 1.88 Std Dev 1.2 Strathfield IMP^,^ =.18, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear Table Summary of Results for Strathfield (IMP=.29) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 25/3/ /3/ /5/ /4/ /11/ /8/ /2/ B /4/ /7/ /4/ Mean 3.16 Std Dev 1.99 Strathfield IMPocnMaii = -29, Split Catchment Initial Loss-Constant Loss Rate Pervious -Non-Linear Impervious - Non-Linear

125 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-23 Table Summary of Results for Strathfield (IMP=.5) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mmm) (thoum 3 ) (m'/s) (m 3 /s) 25/3/ ZOO /3/ / /4/ /11/ /8/ /2/ /4/ /4/ /7/ Mean 4.28 Std Dev 1.39 Strathfield IMPa g =.5, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear I Plot or Parameter C against Qrec I I Plot of Parameter C against VpertVtot I o 3 E o 3 S i Qrec (rro/s) IStntMWdlMP-O.iaJ Vper/VtOt [StnthDtldlMP-Q.16 (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.18) I Plot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtot I o «i Cm (rrtvs) [swtt.fidmp.jz91 StntfifieW IWP- 23 Vrw/vtot (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.29)

126 er 4 - Nonlinear Split Modelling with the Loss Rate Model I Plot of Parameter c against Qnse 1 1 Plot of Parameter C against VpeoVtot 1 9 e is «I 4 i i i i i 6» ie 16 2 Qrec(nflfc) t s Vper/Vtot Sti.inr»ldlMP-.S jstnmn»utmp>o.so (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Strathfield (IMP=.5) [Hydrograph I I Hydrograph I Hydrograph i" BO N W 1.OfctMad.FteconM _L _R»cord*J 5 1 ISO 2 25 TTrr»(mhj Tkm(rrin) n-ra(rrtn) Strwffrf r_b MM). T Evrt StnWMd & «StratMMU &«rrt mm(irtr)) Tirn»(irin) IOC Thm<n*.) fhyetograph I StritMWd 21-S-83 &-«rt Tlrr»j<rrfn) StrattifWd Event J a*""* 11 : Hydrograph I 1 Hydrograph 1 1 Hydrograph 1 I F J 1 fjn, J\jy 2 4 KK Tkm(n*i) _C»Cuttiwa _ * 1 CfeuMad A _RKorttod a too 2 3( Kt Tbm(rrtn) ^ 1 l 5 JUJl C TVni(rrtn) _GtUitMl? 12 f 1 i so 3 " 2 «2 Stnthftau 4446 Enrt 1 Hyetograph 1 7ln»<irtn) jamnfab 1 1 Hyetograph 1 A 1 1 j- Urmfnin) StntMMd &«ot 1 MMil I" fl 4 i- StrathfMU br wit 1 Hyetograph _ Temfrrin) fo*fh

127 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model StrttMMd Bvant Tlmi(rrtn] f: i --..-ill. ill SMMWd E»M Dn»(n*i) Figure Hyetographs and Hydrographs for Strathfield (IMP =.29) Fisher's Ghost Creek Table 4.13 shows the results for IMPDCrainfaii = -25 and table 4.14 shows the results for IMP maps =.36. Note that IMPocmaps i s similar to IMP maps and this value was not modelled. The results for IMP =.36 show that in three out of ten events the calculated runoff volume did not balance with the recorded runoff volume, even with high rainfall losses. This indicates the impervious fraction is too high. Better results were obtained with IMP =.25. The rainfall hyetographs and runoff hydrographs for four event were plotted and can be seen infigure4.19. The correct impervious fraction was adopted to be.25. Event 5/3/83 was the only event that did not calibrate, producing a calculated runoff volume four times larger than the recorded. The same happened with IMP =.36 for the same event, so it can be assumed that the data for this event may be incorrect and it was not used in the study. For IMP =.25, the average parameter C was 2.55 with a standard deviation of.94. For IMP =.36, the mean was 3.25 and standard deviation was The amount of scatter definitely reduced with the smaller imperviousfraction. See figures 4.17 and There is a slight tendency for parameter C to be higher for events which produce more impervious area runoff. Figure 4.17 clearly shows this, but a similar trend has occurred for all the catchments studied in this chapter.

128 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-26 I Plot of Parameter C against Qrec I 1 Plot of Parameter C against VperA/tot 1 o < h L a S Qrac(nOs) Fowl's Ghon CrMk IMP-.25 O 4 I * Vper/Vtot jfr»h«r«gr>o«cr»«hlmp«.2s (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Fisher's Ghost Creek (IMP=.25) I Plot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtot I» 4 I 3 «2 Qrec (mis) [ F*t*f» Ghort Cwk IMP-.3 FMWG*M«tCl klmp-.36 (a) (b) Figure Plot of Parameter C against Peak Flow and Ratio for Fisher's Ghost Creek (IMP=.36) Table Summary of Results for Fisher's Ghost Creek (IMP=.25) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 2/11/ /3/ /3/ /11/ /1/ S 678/ /1/ /4/ /5/ / , Mean 2.55 StdDev.94 Fisher's Ghost Creek IMPncnfoiai =.25, Split Catchment Initial Loss-Constant Loss Rate Pervious - Non-Linear Impervious - Non-Linear

129 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-27 Table Summary of Results for Fisher's Ghost Creek (IMP=.36) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Lass Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 2/11/ /3/ /3/ /11/ /1/ /8/ /1/ /4/ /5/ / , Mean 3.25 Std Dev 1.25 Fisher's Ghost Creek IMP Pervious - Non-Linear Impervious - Non-Linear, =.36, Split Catchment Initial Loss-Constant Loss Rate Hydrograph I Hydrograph I Hydrograph I 1 2 3O 2 4 SO BO Th»(nfrt) Tfcm(irin) n _ClteU*_ttKl i^aj 2 4 Tkm(nin) [ Hyetograph Hyetograph I _ Ftthen Ghost CreeK Event Ftatwrs Ghost Cresk Evert Tm(n*i) Fishers Ghost Crssk &«* T»r»(n*i) Th»{nsn) TVnBfnin) Hyetograph Fkshsfi Ghost Crssk Evsnt _JL^_ 2. UteEnK

130 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Tkm(nto) TlrT»<R*i) [Hyetograph I SOO Tlm(irtn) C. 4 1 X 2 I _H»W«> so 4 5 _r*hm Ewrt Fklwft Ghost &Mfc &»rt FtohtnGhoktCrMk 2454 Ertflt I Hydrograph I!" TiT»(rrtn) Fls hers Ghost Crssk Evsri Figure Hyetographs and Hydrographs for Fisher's Ghost Creek (IMP =.25) 4.4 Discussion of Results The average parameter C value for all the catchments was calculated to be 2.27 with a standard deviation of This value is higher than the average calculated by Boyd et al, 1987 for 33 rural catchments and 248 storm events which produced an average parameter C of 1.7. Figure 4.2 shows the average parameter C value for each catchment plotted against catchment characteristics. As can be seen, there is a large amount of scatter in the data. Note the trend between C and the catchment area. The same trend is present in the plot of parameter C against the impervious area, these trends indicate problems with the way WBNM models impervious areas. The trend of parameter C with these catchment characteristics partly explains the high standard deviation (1.71). One reason why parameter C is higher for events which produce more impervious area runoff (in figure 4.21) is that the lag equations WBNM uses to calculate runoff are possibly underestimating the lag time on the impervious surfaces. WBNM then uses the shorter travel times to calculate the runoff hydrograph and the discharges are overestimated. A higher parameter C is then required to reduce the lag time on the impervious areas.

131 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-29 Another reason could be that the factor IMPFACT introduced into the impervious areas to factor down parameter C is incorrect. In this chapter, IMPFACT is default at.111 which means that parameter C on the impervious surfaces is nine times smaller than that for pervious surfaces. This factor was introduced into the model to compensate for the faster flow travel times on impervious surfaces _ ( Cav against Impervious Fraction ) Impervious Fraction 4 > 8 1 Plot of Cav against Total Area 1 i Total Area (krrc) Plot of Cav against Impervious Area hpervious Area (knfi) Figure Plot of Average Parameter C against Catchment Area and Impervious Fraction Figure 4.21 are plots of parameter C against the peak recorded discharge and the runoff volume ratio. These graphs show the parameter C values for all events on all catchments. As can be seen, there is a trend for high C values for the smaller and for the more impervious events. These figures show that further investigation is required for events which produce more impervious area runoff as well as for events with small discharges. Note that the large parameter C values for very small discharges in figure 4.21 are mainly from the small catchments (particularly Maroubra). 1 o 8 6 i 4 2 Plot of Parameter C against Qrec mi u* Qrec(m3/s) ISplit Modelling, Al Catchments! O o 6 I 4 S. 2 Plot of Parameter C against VperA/tot t **&& VperA/tot Split Modelling. AD Catchments t* < o.a Figure Plot of Parameter C against Qrec and Ratio for all Catchments

132 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model Conclusions The results of this chapter show that WBNM could give reasonable reproduction of flood hydrographs on urban catchments, however some features need to be improved. The following conclusions were drawn from this stage of the study: 1. The directly connected impervious fraction should be used in modelling rather than the total impervious fraction. 2. The study showed that the effective directly connected imperviousfraction IMPucrainfaii, (Boyd et al, 1993) is a better way of obtaining imperviousfractions. The method requires the plotting of total runoff depth against rainfall excess depth for a number of events. The slope of the plotted line gives the IMPD^,,^, for the catchment (see figure 3.1). After modelling all catchments with IMP maps, IMPcc,^ and IMPD^,,^,, the present study showed that the best values agreed with IMP^^f-m, except for Giralang where a value of IMP maps =.22 was found to be better. 3. A trend for larger values of parameter C to be associated with smaller catchments was evident. Measures to reduce this trend will be undertaken. 4. The parameter C values did not show a strong trend when compared to peak recorded flowrates, except for small events on Maroubra. 5. The parameter C values showed slight trends when compared to the ratio of pervious runoff volume and total runoff volume (runoff volume ratio, Vper/Vtot). There was a tendency for parameter C to be high when Vper/Vtot was low, which indicates the way in which WBNM models impervious runoff needs to be further investigated. The following points will be investigated to determine if better calibration can be achieved with WBNM for urban catchments. 1. Both the pervious and impervious areas were being modelled with a nonlinearity of negative.23. This may not be an adequate assumption because pervious and impervious areas behave very differently. Assuming that they both have the same nonlinearity could be incorrect. A better assumption may be to modify WBNM to model impervious areas linearly. Researchers such as Nash (196), Schaake et al (1967), Viessman (1968), NERC (1975), Espey et al (1977) and Cordery (1981) have modelled catchments linearly with success. 2. It has been suggested that split modelling is better for urban catchments (Boyd and Bufill, 1992), never the less, lumped modelling of all the catchments should be performed to see if this method might be satisfactory. 3. This section of the study was used to determine the impervious fraction to be used for each catchment. Table 3.1 showed that imperviousfractions can be calculated in various ways.

133 Chapter 4 - Nonlinear Split Modelling with the Loss Rate Model 4-31 The finally adopted impervious fractions may need to be modified. The high parameter C values obtained for the very small events suggest that the imperviousfraction may actually be lower for storms that produce only a small amount of runoff. 4. In this chapter, the area exponent in the WBNM pervious area and impervious area lag equations is.57. As the pervious and impervious areas have very different characteristics, the exponent used for impervious areas may need to be modified. The trend infigures4.2 suggests this may be the case. This will be examined if the methods suggested above do not produce better results. 5. The factor IMPFACT which controls the lag time of impervious surfaces could be too low, thus requiring large parameter C values to compensate. In this chapter, IMPFACT is set at.111. IMPFACT will be modified if the above modifications do not produce better results. At present seven catchments have been used in the study. A further two urban catchments will be added to the study (Jamison Park and Vine Street) and more storm events will also be modelled on each catchment to increase the sample size. Two rainfall loss models will also be used. They are: I. The initial loss-constant loss rate rainfall loss model. 2. The initial loss-runoff proportion model. This will be done to determine which of the two rainfall loss models is better for use on urban catchments. The next two chapters consider lumped modelling as an alternative to split pervious-impervious modelling.

134 Chapter 5 Lumped Modelling with the Loss Rate Model

135 Chapter 5 - Lumped Modelling with the Loss Rate Model LUMPED MODELLING with the CONSTANT LOSS RATE MODEL 5.1 Introduction In chapter 4, seven urban catchments were modelled using the split catchment option with the LR rainfall model. Ten storm events were calibrated on each catchment. The results were studied and it was found that the calibration parameter C was at least two times the value for rural catchments (Boyd 1987). It was decided to stop modelling at that stage and to determine why this was the case. It was also decided to test whether or not lumped catchment modelling was a valid alternative to split catchment modelling. When lumped catchment modelling is performed, both the pervious and impervious areas are represented by one storage. The rainfall losses and calibration parameter C apply to this single storage and represent an average of values on the pervious and impervious surfaces. Lumped modelling of urban catchments is performed by many existing methods, including Rao et al (1974), RORB (Laurenson et al, 1985, 1986, 1995), RAFTS (Goyen et al, 1976), and the original version of WBNM (Boyd etal, 1979,1987). The storm events for each catchment were calibrated the same way as for the split catchment modelling process with the initial losses and loss rates being adjusted in the input data file until the calculated runoff volume was the same as the recorded runoff volume. The parameter C was then adjusted to match the calculated peak discharge with the recorded peak discharge. Parameter C obtained from this process is effectively a weighted value representing both the pervious and impervious surfaces. If the impervious fraction is large, the parameter C required to calibrate the model will be expected to be low and vice versa. This weighted parameter C should be related to the impervious fraction and the urban fraction of th catchment. Thus the weighted calibration parameter can be converted to an equivalent rural catchment value. The procedure is discussed in section 5.2. The input data files used for the split catchment modelling were modified to perform the lumped catchment modelling by changing the imperviousfractionto zero. Thefilescan be seen in Appendix A.

136 Chapter 5 - Lumped Modelling with the Loss Rate Model Procedure for Adjusting the Calibration Parameter The value of the calibrated parameter C varies in response to the degree of urbanisation of the catchment. In order to compare values for different catchments, Boyd (1987) showed the equivalent rural parameter C could be derived from the following relationship. C = C_ (l + URB) 1 * equation 5.1 The difficulty with this relationship is that the value of URB is subjective, and an explicit m required. This has been handled in the RAFTS-XP model by deriving a value of URB from the imperviousfraction IMP, using a simple linear relationship (table 5.1 andfigure5.1). Table Relation between Impervious and Urbanisation (from RAFTS-XP, 1994) Impervious fraction (IMP) Urbanised fraction (URB) Figure Plot of URB against IMP (from RAFTS-XP, 1994) Table 5.2 shows URB and IMP for each of the catchments investigated in the present study.

137 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-4 Table 5.2 Urban Fractions using RAFTS-XP Method Catchment Curtin Mawson Long Gully Creek Giralang Maroubra Strathfield Fisher's Ghost Creek Jamison Park Vine Street Impervious fraction (IMP) Equivalent Urban fraction (URB) Results for the Canberra Catchments Curtin Calibration for fourteen storm events was carried out for the Curtin catchment. The results are summarised in table 5.3. A plot of the rural catchment calibration parameter against the peak recorded flowrate can be seen infigure5.2. The average rural catchment calibration parameter C^ for the Curtin catchment was As can be seen from the plot, there is a small amount of scatter in the results, but no trends with the range of C ra being.37 to ' 8 «o.«.4.2 ( OuiBn 1 Plot of Parameter C against Qrec 1 I" : 5 1O Qrsc(nOs) Figure Plot of C^ against Flowrate for Curtin Initial calibration was achieved by adjusting the rainfall losses so that the calculated and r runoff volumes matched. Parameter C was then adjusted to match the peak discharge. Reasonable agreement between peak discharges was achieved, however on close inspection of the hydrographs correct reproduction was not achieved. This was particularly apparent in multi burst storms. For example, for the event on the 5/2/71 a relatively low constant loss rate of 3.77 mm/hr was required to match volumes, but with this loss rate thefirstrainfall burst was removed thus producing no calculated runoff, but the recorded hydrograph showed a minor peak. This effect was also observed in events 5/11/74, 2/3/78 and 23/3/78. In other events where rainfall losses were relatively low the calculated hydrograph preserved the temporal pattern evident in the rainfall.

138 Chapter 5 - Lumped Modelling with the Loss Rate Model W D BOO 1 Ttrs(rrH) Tha(iTVi) Tln»<irfn) Hyetograph 1 1 Hyetograph 1 5* 1 1 * g 2»? - rfl [ OR*'"' ^ J 1 Curw B/ant & OjrthMMlO Evtrt rikita. JE l _R«nM Curtin Sfanl DtUMM ISO Tbnf(mrij T>r»(rt*i) Th»(l*) t Hyetograph 1 Curttn IMP-O.O Evsnt «1 1 M = J 1 «i- a 2 I RsWsl Curtin &snt Evsnt I Hydrograph Tlna(irtn) Tlna(rrin) E_i 1 71ms (n*>) I Hyetograph] Curtin Evsnt Curtin IMP-O.O (U-77 Evsnt Curtin Evsnt Hydrograph Tkm(inin) Thns(mn) Curon TVi»(rtn) CumM-o. J»l-7BE»«nt S-2-81 Fjert

139 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-6 I Hydrograph I I Hydrograph I 12 1C _ Tln»<rrin) [ Hyetograph I Tiratrrin) I ihyetograph I i* CUfQn IMP Evsnt Cur* 1S-1-33 Evsnl Figure Hydrographs for Curtin Table Summary of Results for Curtin Event Initial Loss Curb Cmr Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (nrrvs) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean.74 Std Dev Mawson The Mawson catchment was modelled using all eleven storm events with fair calibration being achieved for all events. The rural catchment calibration parameter C^ was found to be , with figure 5.4 showing the amount of scatter in the results. The range of the rural catchment calibration parameters was.23 to Table 5.4 shows the results obtained after the calibration.

140 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-7 I blot of Parameter C against Qrec I O.5 M«w«on I " * Qrsc(ntVs) Figure Plot of C M against Flowrate for Mawson Plots of the calculated and recorded hydrographs along with the rainfall hyetographs were prepar for each of the calibrated events. For events with more than one rainfall burst similar trends were found to those observed for the Curtin catchment. Seefigure5.5. Table Summary of Results for Mawson Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 13/2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean.75 Std Dev.45 Hydrograph [Hydrograph [Hydrograph _Cslcuhtod _RKoroad 1. E I»(IT*I) Hyetograph I 1 Hyetograph 1 Hyetograph -4 I 2 n Mswson IMP Evsnt UTT- -a Hms(trin} [ RmM» [ 1 1 W. - ft < 8 I -; J h towil Tkni(mn)

141 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-8 I Hydrograph I Hydrograph I. 3-2 dfcut*tsd _Rscoro>d _Cifcuott»d C Tlnsi(mti) SO 1 12 Tlms(rrtn) TVnt(n*}) [Hyetograph Hyetograph I 12 12,. = 1 c- 1. I urn. a»««i 4 " k RsinfsB I S: R»W»I ol ibnsilrfc ^ 1 him ton Mwrwi hwton B/t* W-77 Ennt Ey«n [Hydrograph I I Hydrograph I 3 ' D TlmB(n*i) Trm(nln) I Hyetograph] = S Ll L_ [ row*! 1 5 n fin nrtfilil I I Hydrograph I Tims<n*>) 1 2 A^ T»T» (rrtn) 1 Hyetograph 1 4 I 3D 5" 2 I 1 " JL... L Ksmrson S2-81 Ey*n Figure Hydrographs for Mawson Long Gully Creek The Long Gully Creek catchment was modelled using all fourteen storm events with fair calibration being generally achieved. The rural catchment calibration parameter C^was found to be , with figure 5.6 showing the amount of scatter in the results. The range of the rural catchment calibration parameters was.43 to 1.6. Table 5.5 shows the calibration results. Plots of the calculated and recorded runoff hydrographs and rainfall hyetographs can be seen infigure5.7.

142 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-9 Plot of Parameter C against Qrec J [Long Guly Ossii] Qrsc (m3/s) Figure Plot of C^,.against Flowrate for Long Gully Creek Table Summary of Results for Long Gully Creek Event initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean.87 Std Dev.38 [Hydrograph Hydrograph] Hydrograph 2. _CttuW«_RKonM 5 io s, I 4 _Csfcusrtsd _fswortsd too Tfcmfirin) Ttns(rrtn) Hyetograph [ Hyetograph 1 f- I» s QR>M>I Long Guy Cram Brant Long Guly Crssk B.snt

143 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-1 Hydrograph I 1 Ttm(mn) Tvm(rnn) Hyetograph i< ii r 1 Hydrograph 1 A / w /K /J \ \ / / ^ ;/,,, ms (rrtn) Hyetograph 1 jt OR«nf»I 4 i".: 1 * - nfl.4 IE 2 Long GkilyCMMfcIMP-. Long GJy Cr k U m 1 jnw> Jh Tms(rrtn) Lortg Gu*y Cf esk Emnt Burt Evsnt 1 Hydrograph 1 I Hydrograph I Tfrm(rrtn) «- * " i\ v I2 1, _C»fcuartsd 1 15 Tlms(nln).Rscordsd f 4 * 2 2 I, " l\ V 5 1 Ttra(mn) Tins (rrtn] Long GwsyOssfc IMP-. Long Guly Crssk Long Guly Creek Evsnt Evsrt Evsnt t Hydrograph I 1 Hydrograph 1 S Timi(rrtn)! A. _CalcuMsd _Rscorosd i< Tims (rrtn) SO Tkrs(mln) I Hyetograph? 4. D'*"^ 2. Long Guly Crssk Brsnt Long Guly Crssk IMP B Evsnt Long Guty Crssk Evsnt [Hydrograph! Hydrograph [ 1 2 I' th l\ K V. 1 ISO 2 Tkm(mn) [ Hyetograph I U l\~ 4 Tta»(n*i) [ Hyetograph (WnfH jfel. Lang Oufy Crssk ttrfp Evsnt Long Guly Crssk Evsnt Figure Hydrographs for Long Gully Creek

144 Chapter 5 - Lumped Modelling with the Loss Rate Model $.\\ Giralang The Giralang catchment was modelled using all fourteen storm events with fair calibration being achieved for all events. The rural catchment calibration parameter C mr was found to be , with figure 5.8 showing the scatter in the results. The range of the rural catchment calibration parameters was.19 to Table 5.6 shows the calibration results. Hydrographs can be seen in figures Plot of Parameter C against Qrec ' O.S GSsng Qrsc(rrOs) Figure Plot of C^against Flowrate for Giralang Table Summary of Results for Giralang Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 27/3/76 14/1/77 6/4/77 27/1/78 2/3/78 23/3/78 9/1/78 2/2/8 5/2/81 6/1/81 24/3/82 15/1/83 13/12/83 25/3/ Mean.77 StdDev.48

145 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-12 Hydrograph 1 * 4 S 2 li 7 V " TiT»<irtn) I: " r 1 2 I" 1 Hyetograph 1 Tm.(r*] QBJWH Gmtong 5-2 io B. Irnnrrn Grtfang bm" B/M EaM A -. 4 f 2 1. IHydrographl ^ \ Tlmt(rrtn) a« JLJI L GirsUng Btsnt Ttms(rrin) [Hyetograph I - A Jiuk Giralang Evsnt? 1S -I Gralsr. DMP-O.O Evsnt Tkm(irtn) I Hydrograph I I Hydrograph I Hrrnfrrtn). 4 %3 S 2 It tn A \^ TTmsfmh) 1 f. e i; - I f\ \ //^ A : l\f\ J. V, X 5 1 Th»(mh) [Hyetograph Jfl Trrs(rrtn) Gtmlsng IMP-.1 Giralang Evsnt Ewsnt Tlrrs(rrtn) 2 4 SO TWra(rrtn) I Hyetographl Hyetograph 1 Tkna(mti) i». 1. ols JUL D*** S-io S s "J Lil Urn Rattfaf Olalsng Gtratsng Giralang 6-I-BI Evsnt 24-3-B2 Bfsnt &snt

146 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-13 if 6 1 s * h 1 Hydrograph 1 :/V //,, i^r* D Tlm(rtn) Hyetograph 1 _.r ([' l Tknt(n*i] Gfrlhng »fn j: 1" D«*M ' 4 ^ I 2 " 4 n Grtfcnfl 25-3-M Event I Hydrograph I «_ Tln»(n*i) _CilcuanM QruM Figure Hydrographs for Giralang 5.4 Results for the Sydney Catchments Maroubra The rural catchment calibration parameter C ror was found to be , but one storm (28/4/88) produced a value of 6.1, which greatly affected the mean and standard deviation of the results. If this event is omitted from the study, there is considerable reduction of scatter in the results, and the value of C^reduces to See figure 5.1 a and b. Figure 5.11 shows the plots of the calculated and recorded hydrographs and the rainfall hyetograph for a number of storm events. As can be seen, the calibration of the multi-peak events was fair, but in all the cases the rainfall losses assigned to balance the calculated and recorded runoff volumes were sufficiently high to eliminate the minor bursts from the recorded hydrographs. Also calculated recessions were generally flatter than the recorded recessions. Table 5.7 shows the calibration results. 2 ( Plot of Parameter C against Qrec Qrsc(rrtVs) I! ( I Plot of Parameter C against Qrec I * rse(nfln») IMaroubm (all svsnts)j JHsraubn (28/4/88 omiasd) (a) (b) Figure Plot of C^ against Flowrate for Maroubra

147 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-14 Table Summary of Results for Maroubra Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 1/3/ /3/ /3/ /3/ /3/ /4/78 18/5/78 19/6/79 2/6/79 17/3/83 18/6/83 6/11/84 8/11/84 11/12/84 1/5/85 12/4/86 3/7/87 4/1/87 2/4/88 28/4/ Mean 1.24 Std Dev 1.27 Mean.99 Excluding 28/4/88 StdDev.6

148 Chapter 5 - Lumped Modelling with the Loss Rate Model Hmt<n# 2 4 SO 8 1 Tkm(rrtn) Tlms(rrtn) Msroubn Evsnt MaroUsa Bfsri Tirm(mn) I" 2 S. UiUffllrffh gr1nfa«tlrm(frtn) Evsnt Maroubra Evsnt TlmB(rrtn) Ewnt Mareubnt Evsnt 1 Hydrograph 1 2!l.5 i,.5 / / i i i Ttom{rrtn) Tlms(rrin) «hroi»a /ant I" Maroubra Evsnt [Hyetographl nn i. Tlm»(rrtn) nn»ml« Evsnt

149 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-16 Hydrograph I Hydrograph [ I Hydrograph I - A 1" ij 'V Hma(rrtn) _CatuUled _Rscordsd : k. 1" BO Ikn(mh) _CalcuaM _Rac<*d») "I Tma(nti) _oeuaim _Raeordad [ Hyetograph [ 1 Hyetographl 1 Hyetograph [ 1 s Mreubra 8-ll-84Ev.nl il TlmB(rrtn) 1 aralnfall 1 I: I: ii ij Mroubra Evant Hlh>. _... Tfn.(mn) 1 QRaMat [ 1 6: = 4 % X 2 J Tkm(mn) Maroubra Evsnt 1 nrawal 1 Hydrograph ' «.6.8 C : i I Hydrograph \ tv V>^\ TV=^ _CalcukM 1 Hyetograph 1? d Jin iil I DRaWal I Maroubra Evant Maroubra Evsnt Msroubrs Evsnt I Hydrograph I Hydrograph.CaJcuWad.Racordad! 4 I Tlms(rrtn) t Hyetograph I too ar»w"" Tkna(n*i) Maroubra Evsnt Maroubra Event Figure Hydrographs for Maroubra

150 Chapter 5 - Lumped Modelling with the Loss Rate Model Strathfield The rural catchment calibration parameter C^was found to be , with the values ranging from.29 to Figure 5.12 shows the plot of the rural catchment calibration parameter against the peak recorded discharges. Table 5.8 shows the calibration results. 5 4 i: - ( St»thiMd Plot of Parameter C against Qrec - Figure Plot of C mr against Flowrate for Strathfield It can clearly be seen that the larger events required high parameter C values to obtain proper calibration of the peak discharges. A similar trend was observed for Strathfield in chapter 4. The events that produced the higher calibration parameters (4/6/86, 3/4/88, 13/2/88 and 28/4/88) were all large rainfall events (total rainfall depths between 42.1mm to 139mm). These events were all multi-peak events and the plots of two hydrographs and hyetographs can be seen infigure5.13. As the rainfall losses were all quite low, the calculated hydrographs closely follow the temporal pattern of the rainfall hyetograph. The reason these events may have required slightly higher parameter C values is that the calculated peak discharge was overestimated by WBNM requiring higher parameter C values. The reason the recorded peak discharges may be lower is that the channel section where the stream gauge is located at the catchment outlet may have overtopped causing flows to be diverted. Manning's calculations performed by the author on the channel section indicate the capacity of the channel to be about 2 m 3 /s. This suggests the channel has capacity for larger events (for example, 6 year ARI event on the 4/6/86, peak flow of m 3 /s). But diverted flows upstream of the gauge could have occurred. The single burst events again seem to have performed better than the multi-peak events, but the overall performance is still not good when compared to the split catchment option. Events on the 3/9/77, 4/4/81, 4/4/81B, 3/12/82, 3/8/83, 16/3/83, 3/4/85, 1/5/85 and 4/7/88 all calibrated very well with very good timing between the calculated and recorded peaks. The only thing in common with these events is that the rainfall hyetograph climbs very quickly to its peak intensity and the rainfall stops, with little or no rainfall after the peak. See figure 5.13 for the hydrographs.

151 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-18 Table Summary of Results for Strathfield Event Initial Loss Loss Rate (mm/h) Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate 3/9/77 4/9/78 2/3/81 2/4/81 4/4/81B 4/4/81 3/12/82 25/3/82 3/9/83 16/3/ (m 3 /s) (m 3 /s) /5/ /4/ /11/ /5/ /4/ /8/ /2/ /4/ /7/ /4/ Mean 1.3 Std Dev 1.11 Hydrograph Li [nrahfaa.cafcuwad [ r h 2 25 i: I Hydrograph I t/v _Calcuatsd» 4 6 Tlrrs(rrtn) - 1 Hyetograph 1 m 1 1 ;' Jj _Racordsd I Hydrograph] Sbathbsld IMP-. _CifcuarbM Abcordsd Cvsnt

152 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-19 I Hydrograph I I Hydrograph I Hydrograph I 1 2 TKra(rrtn) _CalcinatBd _RscordBd Tlma(mn) V a A / \ l \ -,/S km (n*i) _Caleiaatad _Racorasd f 15 to!c s & J lllnlhnittiinrm Ralntafl StrathfWd r«rt StnthnsW Evsnt Sbathnskl B Evsnt I Hydrograph 1 Hydrograph SO - /\ t m 1 -// /TV\ // \ * 1,, >=T= / V^ Tm(rrtn) _ Cat mated _Rscwded 1 Hyetograph 1 F L * 1 I«1 Rainfall StrathfMd SiramitoU Evsnt Evsnt Evanrt Tlma(rrtn) Tkna(n*.> 1 2 Tkna{mh) Tkna(nin) StrartnfWd Evsnl Strathflatd Evsnt StmthfisM IMP Evant SiraOTflsU Evsnt

153 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-2 I Hydrograph I I Hydrograph I I Hydrograph I _Catu!»tad S.8.Caleutatsd ^L^ SO Tmsfrrtn) TkTB(rrtn) i Hma(nai).rSjcordsd [Hyetograph Ttrrs(rrin) St rath/isid S'iratWatH Strath H»M Evsnl Brant Evsnt c I Hydrograph I r A _R»cofd«J t 1 nrrs(rrtn) 1 Hyetograph 1 I 1 I- s \.Ak Tlma(lnh) SbathfJab Brant a»r"> Figure Hydrographs for Strathfield Fisher's Ghost Creek The rural catchment calibration parameter C^was found to be , with the values ranging from.62 to Figure 5.14 shows the plot of the rural catchment calibration parameter against the peak recorded discharges. As can be seen, this catchment has a low amount of scatter, and the average calibration parameter obtained was very close to 1.5. Table 5.9 shows the calibration results. I Plot of Parameter C against Qnecl /I 1 15 Drac(rrfl/») ifkhsfachosloisikl Figure Plot of C mr against Flowrate for Fisher's Ghost Creek Figure 5.15 shows the hydrograph and hyetograph plots from the calibration results. The calibration obtained from most of the events is fair (4/5/81, 19/1/81, 2/3/83, 24/1/87 and 28/4/88). As in previous catchments, the major burst seems to have calibrated well, but the minor bursts lack the accuracy of the major ones. This indicates that lumped modelling with the initial loss constant loss

154 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-21 rate rainfall loss model may not be appropriate for multi-peak events. Poor calibration was obtained for the other events (2/11/81, 17/3/83, 15/1/86, 24/5/88) mainly because the rainfall losses used to balance the calculated and recorded runoff volumes were too high, thus cutting off the minor rainfall bursts. The results for single burst storm events seem to be better than the multi-peak events with good calibration being achieved for the event on 25/12/81, 26/1/84 and 8/11/84. The hydrograph for the event on the 5/3/83 shows there may be data errors. The rest of the events do not calibrate as well, the main reason being the high rainfall losses applied for volume balancing. The majority of the rainfall hyetograph is removed by WBNM, leaving only the top part of the rainfall to be used to calculate the hydrograph. Note possible errors in the gauging equipment for event 5/6/88. Table Summary of Results for Fisher's Ghost Creek Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate 2/11/81 4/5/81 19/1/81 25/12/81 17/3/83 2/3/83 5/3/83 27/11/83 13/12/83 26/1/84 7/2/84 8/11/84 9/11/84 8/12/85 15/1/86 6/8/86 18/11/86 24/1/87 5/6/88 24/5/ Mean 1.47 StdDev.6 (m 3 /s) (m 3 /s)

155 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-22 I Hydrograph I & 2 ti^d ni(rrtn) - A 1 2!< * \\\ 1 V 1 Hydrograph 1 / JVA.. 7~3 r*» Tfcns(irtn) Calculi tad _fskrdad I Hydrograph ] k -s 4 I! i A r^=t..^=* Vr»(rrtn).Cafcuartsd. Hyetograph l Hi. Jl OfeMaa Frahefe Ghost Crssk Evsnt Flansfa Ghost Ossk 4441 Evsnt F*h»C* GhoB **k Evsnt V h 4 i M ^ 2 " A 1 Hydrograph 1 *Sl\ 1 > 1 1 i Tlma(rrfn) 1 Hyetograph 1 - J i_no IDhiJU Favhsra Gheat Crssk Evsnt i 2 I Hydrograph I A fl r hi \ _CalcuWsd _Racortsd In \\ ' V Tlma(nin) Flshsfa Ghost Qssk Evsnt 6 «o 2 Hyetographl JlLiUu^ Ftohar's Ghost Crssk Evsnt RaM* r 2 2 b ^ 1 Hydrograph e 3 Tfna(rrtn) _CateulatBd _Record*d V " 2 * I Hydrograph I I Hydrograph I k. _Cak=uortsd V _Rsconisd 5 2 I' fl Tkne(rrtn) Ttaa (nsi) _Cateiaatad _ I-!«s nanata Ghost Craak S*«3E»anl 1 Hyetograph 1 Tl K ma (min) jnr»* rf * 1 1" I Event *AML Tbna((rfn) ^K- 1 arattfad I J- 4 i" ij L Th»(nti) Ftohsfs Ghost Ossk Evsnt RaWal I I Hydrograph I _G»fcut»t»d _Recordsd Tl-n»(rrtn> TVrafmn)! Hyetograph I H. Ji Tima(rrtn) HshsfaGhoatCissk Fisbsi's Ghost Ossk Evsnt Evsnt

156 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-23 Hydrograph I Tkms(mr) Hydrograph] X M _.Calcut«tsd Turn <n#>) _Rseofdsd!. Hydrograph soa Tme(mn) [Hyetograph I Fbhsrs Ghost Crssk RalWa Ghost Crssk Fsihsrs Ghost Crssk Evsnt Evsnt Evsnt I Hydrograph I [Hydrograph I. AAJl rr<j " > _Cateus*sd _Rscoraed i < I 2 ~AA _ Calculated Ttne(frin) Tena(rrin) Tem(mh) Hyetograph 7 X 2 Fshsfa Ghost Crssk Fshefa Ghost Crssk Fs hsr a Ghost Crssk Evsnt Evsnt Evsnl i.- «"i 2 - il- Hydrograph Trne(rrtn).Calculated.Rseordsd Hydrograph I p LA Time (mn] nahsr*a Ghost Crssk Evsnt Flshsr-s Ghost Crssk S-S-88 Event Figure Hydrographs for Fisher's Ghost Creek

157 Chapter 5 - Lumped Modelling with the Loss Rate Model Jamison Park The rural catchment calibration parameter C,^ was found to be , for all the events, with values ranging from.39 to Figure 5.16 shows the plot of the rural catchment calibration parameter against the peak recorded discharges. As can be seen, this catchment has a low amount of scatter. Table 5.1 shows the calibration results. [Plot of Parameter C against Qrec I 3?2 1 t ; < Jamison Park] Qrsc(rr8/a) Figure Plot of C^ against Flowrate for Jamison Park Figure 5.17 shows the hydrograph and hyetograph plots for the events in Jamison Park. The results seem fair, but the high rainfall losses assigned to balance volumes have removed some of the minor bursts of rainfall, producing a smooth calculated hydrograph which does not represent all the minor fluctuations in discharge which are apparent in the recorded hydrographs. Very good calibration results were obtained for the events single burst events 4/1/86, 3/6/86, 8/2/8 4/4/88B and 6/4/88B. The events with the B are events that occurred later in that day. The similarities between these events is that some initial catchment wetting occurred earlier in the day, and the catchment soil had been semi-saturated. Lower loss rate values were then required to balance calculated and recorded runoff volumes. The other events were not as good, with the recorded hydrographs being very 'blocky' or square looking. This indicated the time step at which the data was collected may have been to large, although the calculated hydrographs were smooth.

158 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-25 Table 5.1- Summary of Results for Jamison Park Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12/ /9/ /1/ /4/ /1/ /1/ /1/ /4/88B /4/88B /2/88B /2/ /5/ /4/ Mean 1.32 Std Dev.65 I Hydrograph I Hydrograph Hydrograph 1. I.8 - _C*JCUBASC' Calculated _? Tana (nil) nrnb(irin) i' "T 1 " 1 * 1 ' Par* 3-83 Event

159 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-26 o.s " i o.i [Hydrograph ^.4 _ Hydrograph I 7bna(mh) rryetographl 2 I R»^al Tkna(frin) 1 Oc Jamison Parte Evsnt [Hydrograph Tme (rm] j..8 1 ooe * E.4.2 1? i v 112, SO, 4 SO. TTmB(mh) Hyetograph I SO 7*i»(n*i) I 1! 3. io * 8. Trmlrtn) Rahlal a J - nmr m Tlma(rrtn) Park Erai JarrtsonPar* Evsnt Jamtaon Psrk Evsnt I Hydrograph I flms(mfn) a 2 \A. 1 o.u S.1 E.5 p : L Park Event Hyetograph I ihn ORarMI? Hyetograph I - 2 I" n n Jamison Peru 2L1-88 Event Tima(mti) T)ms(mh) I: *!c 2 _ Hyetograph] ORsMaa JarrmonPark Evsnt Js melon Park Event Jembon Park B Evsnt

160 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-27 I Hydrograph 1 Hydrograph I Hydrograph I -..8 _CaJeuWsd 1,.6 _Calciitatsd TTrre(rrtn) _ s^ 5 1 TkTw(n*i) 1! Tlrrs(mn) RamiaO m LJL Jsmann Paik Evsnt.Psik -2-MB Evsnt atneen Park Evsnt 1 Hydrograph 1 I Hydrograph I O8? Th»<mh) _Racordsd f ra ;/V -2.1 u -/,,,, ^ TTrrslrrtn] 1 Hyetograph 1 ~ E 8 z 8 s * 2 r i n O Ramiall _ 2- n Jamieon Park Evsnt Jamison Park S Event Figure Hydrographs for Jamison Park

161 Chapter 5 - Lumped Modelling with the Loss Rate Model Results for the Melbourne Catchment Vine Street There was a total of eleven storm events available for use in calibration of the Vine Street catchment. The rural catchment calibration parameter C^ was found to be very high at , with the values ranging from 12 to Figure 5.18 shows the plot of the calibration parameter against the peak recorded discharge. The main reason for the high calibration parameter values is that Vine Street has a very high imperviousfraction (.31), in fact, the highest of all the catchments. As there is a lot of impervious area on the catchment, more runoff is being produced from the catchment due to lower infiltration. As can be seen from the hydrograph plots, the overall calibration is fair. I Plot of Parameter C against Qrec I S f Qr*c(m3/») Figure Plot of C w against Flowrate for Vine Street Figure 5.19 shows the hydrographs. In all the cases, the hydrographs follow the temporal pattern of the rainfall hyetographs, with very good calibration being obtained for events 15/2/72, 4/2/73 and 15/5/74. The event on the 8/11/87 was a three burst event with the final burst being cut off by the high rainfall loss applied to balance the runoff volumes. The events on the 7/4/77 and 15/1/83 calibrated poorly for the initial rainfall burst mainly because the events were calibrated for the peak discharge which occurred after thefirstrainfall burst. I Hydrograph I O Tkra <i*] JL^L. LL 1U. Ta»(i*t) Ottawa! Tln»(i*i) a (1*1) QRJKU VhaSnjat Vina S»«t tmp- VhaSrast Brant Evsnt Brant

162 Chapter 5 - Lumped Modelling with the Loss Rate Model Hydrograph 1 [Hydrograph 1 Hydrograph 1 'K a" 1.5 /,,,, Tbna(rnh) 1 _Cafculetsd j _Rscordsd Tlme(mh) t ^ - / f\ \ / V i ^^ ji "nrm(rm) _Caiciaatad _Rseordsd I Hyetograph Tena(irth) VlnsStrsst VlnsSCrsst V ma Strew Evsnt 2» Event Event Ttna(rrtn) RantaB VlnsStrsst Evsnt We Street Evsnt VlnsStrsst 1-9-8S Event I Hydrograph I Hydrograph! 2 Js- _Calciiata<J _n»c<mlsd SO 1 15» 1 Tna(rrtn) V :/V _ Calculated _ 1 2 3t W TbnB(trtn) 1 * s jii bb, TkmlfWi) VlnsStrsst EVsnt arawu J- 1(X 1 B w 61 3 «1» jj. ^ Time (nan) VLnsStrssI Evsnt lafwnfalj Figure Hydrographs for Vine Street

163 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-3 Table Summary of Results for Vine Street Event Initial Loss Curb Crur Calculated Rainfall Total Calculated Loss Rate Excess Rainfall Peak Peak (mm/h) Flowrate Flowrate (m 3 /s) (m 3 /s) 15/2/72 4/2/ /5/ /1/ /12/ /11/ /4/ /1/ /9/ /12/ /11/ Mean 4.25 Std Dev Discussion of Results This section of the study looked at the possibility of using lumped modelling with the LR rainfall l model for urban catchments. The findings from the study are discussed below. Events which required high rainfall losses to balance the calculated and recorded runoff volumes consist almost entirely of runoff from the impervious parts of the catchment, with very little runoff from pervious areas. This indicates that runoff from pervious surfaces is low, thus the high losses used to calibrate the model to be justified. These events did not reproduce the temporal pattern of the rainfall hyetograph in the calculated hydrograph because the high losses cut off the minor rainfall bursts. Multi-peak events which require low rainfall losses to calibrate, contain runoff from both pervious and impervious surfaces. In most of these cases, the lower rainfall losses did not cut off the minor rainfall bursts, thus the rainfall hyetograph temporal pattern was retained and WBNM was able to calculate a hydrograph showing all the bursts. The calibration for these events was generally better than for the events with high loss rates, but the minor peaks were not always as correctly reproduced, indicating problems in the modelling. It is possible that a loss model based on runoff proportions will give better results for these events. This model will be tested in chapter 6.

164 Chapter 5 - Lumped Modelling with the Loss Rate Model 5-31 Single rainfall burst events performed well for both totally impervious events (events that calibrated with high rainfall losses) and combined pervious and impervious events (low rainfall loss events). Another feature observed in most events was that the recorded hydrograph fell very quickly compared to the calculated hydrograph. This suggests that the impervious part of the catchment may be discharging faster than the model predicts because the impervious area lag times are less than the weighted pervious-impervious values used in lumped modelling. Figure 5.2 shows the rural catchment calibration parameter against the peak recorded discharge for all events. The mean rural parameter C was found to be 1.35 with a standard deviation of The problem of high parameter C values for small events has not been rectified, although most of these are associated with Vine Street. Figure 5.21 shows there is little variation between parameter C and the catchment area. The high value in the figure (C=4.25) is associated with Vine Street. A plot of C against the ratio of runoff volume ratio (Vper/Vtot = ratio of pervious area runoff volume and total runoff volume) can be seen infigure5.2b. If the high values associated with Vine Street are ignored, then there are slight trends between the type of storm event and parameter C. But figure 5.2a indicates that small events require high parameter C values. 1 8 o 6 1 < 2, ' c I Plot of Parameter C against Qrec P&fetee* ete Qrec (rrtvs) Lumped Catchments Initial Loss-Loss Rate] 8 Plot of Parameter C against Vper/Vtot 6 r 2-25C ) ( I Vper/Vtot Lumped Modelling, Loss Rate, All Catchmentsj 1 (a) (b) Figure Plot of C mr against Flowrate for all Catchments Plot of Parameter C against Area 2 4 ti 3 to a 2 o 3 1 C 1 2 Area (km2) Lumped Catchments Initial Loss-Loss Ratej 3 Figure Plot of Average C mr against Catchment Area for all catchments

165 Chapter 5 - Lumped Modelling with the Loss Rate Model Conclusions Lumped catchment modelling with LR rainfall loss model for urban catchment modelling is not a good method compared to the results obtained in chapter 4. The main reason is that the pervious and impervious areas of the catchment are not being represented properly. Pervious and impervious areas are very different in that the pervious areas absorb rainfall and impervious areas do not. They differ in roughness so the time taken for water to run off the catchment is very different and must be treated with different lag times. Rainfall losses on impervious areas are small and this means that essentially all the rain falling on an impervious area is contributing to runoff. The shape of the impervious area hydrograph is also different to the pervious area hydrograph because the response time (ie. the time taken for the hydrograph to rise and then fall) is much faster than the hydrograph for the pervious area. This is mainly due to the roughness of the catchment; impervious areas tend to be smoother than pervious areas. The following conclusions can be drawn from the study: 1. Lumped catchment modelling produced fair results, but is generally not as good as split catchment modelling. 2. Lumped modelling with the LR model for multi-peak events with high loss rates is poor because the high loss rates cut off small rainfall bursts. The rainfall hyetograph temporal pattern is not retained and the calculated hydrograph loses its accuracy. The use of runoff proportion rainfall loss model may be better for all types of storms because it does not cut off all the rainfall and preserves the shape of the rainfall hyetograph. This method will be tested in chapter On average, the rural catchment parameter C values were lower than those for split modelling. The most likely reason for this is the soil loss model. LR (as opposed to a soil moisture accounting model) assumes a constant continuing loss for the duration of the event. In the real world, soil wetting and losses decrease over the duration of the storm, and more runoff is produced. But at the start of the event, the losses into the soil are higher than assumed in the LR model. This is probably why in some events, the rising limb of the calculated hydrograph is faster than the recorded, and the calculated hydrograph recession is slower than the recorded. Most of the events used in this study we very large in magnitude. Only the most intense bursts within the rainfall hyetographs were used in calibration. The catchment was initially wet, thus initial losses low to compensate for this. If the entire storm event was used, the initial losses would have been higher, and continuing losses lower. 4. The recorded hydrograph recessions were steeper than the calculated hydrograph recessions which indicates that the weighted pervious-impervious lag parameter in lumped modelling is too high, so that split catchment modelling may be better because different lag times can be applied to the different catchment surfaces.

166 Chapter 5 - Lumped Modelling with the Loss Rate Model A feature common to all the catchments is the flatter recession in the calculated hydrograph. Lumped modelling uses a weighted average pervious-impervious value of lag time which is greater than the impervious lag time. The result is that the calculated recession falls less rapidly than the recorded recession when the impervious area runoff is draining from the catchment. This indicates that split modelling may again be better than lumped modelling.

167 Chapter 6 Lumped Modelling with the Proportion Model

168 Chapter 6 - Lumped Modelling with the Proportion Model r>-2 6. LUMPED MODELLING with the RUNOFF PROPORTION MODEL 6.1 Introduction This chapter investigates the effectiveness of lumped modelling with an initial loss-runoff proportion (RP) rainfall loss model. The objective was to achieve a more representative rainfall excess hyetograph than that which was obtained using an initial loss-continuous loss rate (LR) rainfall loss model. New WBNM input data files were set up to perform this modelling. A CD in appendix A contains all the input datafilesfor the lumped catchment initial loss-runoff proportion modelling. The results obtained from the modelling are assessed in the following sections on a catchment by catchment basis, and an overall review is given at the end of the chapter.

169 Chapter 6 - Lumped Modelling with the Proportion Model Results for the Canberra Catchments Curtin The results for all calibrated events for Curtin are summarised in table 6.1. A plot of the calibra parameter against the peak recorded flowrate can be seen in figure 6.1. The average calibration parameter C^ for the Curtin catchment was when modelled with the initial loss-constant loss rate rainfall model, and has now dropped to for modelling with the initial loss-runoff proportion rainfall loss model. As can be seen from the plot, there is a small amount of scatter in the results, but no apparent trends. i o.e -J.8 O 4.2 Cuion I Plot of Parameter C against Qrec I Qrec(mafe) Figure Plot of C mr against Flowrate for Curtin Figure 6.2 shows the hydrographs for lumped runoff proportion modelling. These plots show the improvements obtained with the runoff proportion model compared with those obtained using an initial loss-constant loss model (chapter 5). Generally the shape of the calculated hydrograph fits better with recorded hydrograph modelling, particularly for the smaller fluctuations in discharge.

170 Chapter 6 - Lumped Modelling with the Proportion Model 6-4 Table Summary of Results for Curtin Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Calculated Rainfall Peak Flowrate Peak Flowrate (m 3 /s) (m 3 /s) 26/1/71 5/2771 1/2/71 13/2/72 21/3/ /11/74 14/1/77 6/4/77 2/3/78 23/3/ /1/ /2/81 6/1/ /1/ Mean Std Dev I Hydrograph I I Hydrograph I Hydrograph 25 ~ ? 1 i 5^ M S i Time (mir) Thnt(n*i) Hyetograph 2 4 BOO 8 1 Tmne(rrin) - " An -anifiiji. Q LaWBkA^Hltll - Curtki IMP Event Curtin IMP Event Cuitln IMP Even! i- S 2 1 I Hydrograph I A /\ - / \ \ / y \ >*= ^, Tlrra(rrin) Tlma(n*i) 1 Hyetograph s» J 1 J k ] arew.a I Curtin IMP Ewnl Curtin IMP Event Curtin IMP Event

171 Chapter 6 - Lumped Modelling with the Proportion Model 6-5 I Hydrograph] I Hydrograph] SO Tlrr»(mY.) Tkm<n*i) Hyetograph 4? 4 3 \\ 2. " h_nthtlm_ Curtin IMP Event Curtin IMP-O o Event Tire (rnln) nme(rrtn) Trre(rrtn) Event Curtta IMP-O.O Event Curttrt IMP-.] S Event i - C 2! Hydrograph! L/V. D Tkm(irtn] _CelcuWod _ " 4» S 2 & 1 r Hydrograph! 1 A.. I ) JO Tmt(mn) _CalcuM*d I 2 Curtin IMPHD.O e-i-ot Event Hyetograph 1 I i Trm(nai) I'M jotemtf 1 J. 2 I" Curtin IMP Event Hyetograph I. I Tlma(irfB) lar-wab I Figure Hydrographs for Curtin

172 Chapter 6 - Lumped Modelling with the Proportion Model Mawson The calibration parameter C mr was found to be for the initial loss-constant loss rate mo and for the initial loss-runoff proportion model. Again, the adjusted calibration parame has reduced significantly. Figure 6.3 shows the amount of scatter in the results. The range of the calibration parameters was.12 to 1.8. Table 6.2 shows the results obtained after the calibration. u Plot of Parameter C against Qrec 1 _ - a a o-6 O Qrec(ffl3/t) [Mew eon Figure Plot of C,^ against Flowrate for Mawson Plots of the calculated and recorded hydrographs along with the rainfall hyetographs are shown in figure 6.4. Again, the results are a significant improvement over those obtained using a constant l model. The temporal pattern of the rainfall hyetograph has been retained by using the initial lossrunoff proportion model, and events with multi-peaks all calibrate well, except for events 5/2/82 a 5/11/74.

173 Chapter 6 - Lumped Modelling with the Proportion Model 6-7 Table Summary of Results for Mawson Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Peak Flowrate Flowrate 13/2/72 21/3/74 5/11/74 14/1/77 6/4/77 2/3/78 23/3/78 9/1/78 6/1/81 5/2/81 15/1/ (m 3 /s) (m 3 /s) Mean.46 StdDev.28 I Hydrograph^ I Hydrograph 1 Hydrograph X 15 L Th»(n*i) i Tlme(mr),2 I"? 1 I 5 _ 1 15 ^M-_Cifcjiated Time (mil) I Hyetograph I 2 I Irvn DR«W«i nteinfea : Meweon IMP Event Maw eon IMP Even! levwon tmp Event Ttm(rrtn) Tfri»(frin) [Hyetographl Hyetograph j I Hyetographl 12 = 1 a _ k. J = 1 2 Mavevn IMP Event i IMP Event IMP Event

174 Chapter 6 - Lumped Modelling with the Proportion Model 6-8 I Hydrograph I?2 _C*tu*t»d Trre(rrtn; 1 Hyetograph I f 1 1» s L m.,.~. Trme(rrtn) Timt(n*) lemwn MP-..VI-78 Event IMP Event Hydrograph I Hydrograph Tcne(rrtn) r -WVi I QRaMal I Mavwnn IMP Even! Figure Hydrographs for Mawson Long Gully Creek The calibration parameter C^ was found to be for the constant loss model compared to for the runoff proportion model. Figure 6.5 shows the amount of scatter in the results for the runoff proportion model. The range of the calibration parameters was.2 to.81. Table 6.3 shows the calibration results. I Plot of Parameter C against Qrec] X ILona Qu* CKaak Qraerntta) Figure Plot of C^ against Flowrate for Long Gully Creek Plots of the calculated and recorded runoff hydrographs and rainfall hyetographs can be seen in figures 6.6. The runoff proportion model produces improvements in most of the events.

175 Chapter 6 - Lumped Modelling with the Proportion Model 6-9 Table Summary of Results for Long Gully Creek Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate (m 3 /s) (m 3 /s) 26/1/71 5/2/71 1/2/71 13/2/72 21/3/74 5/11/74 14/1/77 6/4/77 2/3/78 23/3/78 9/1/78 5/2/81 6/1/ /1/ Mean.49 StdDev.22 Hydrograph I Hydrograph I 1 Hydrograph 1 2 r Thn(mii) 12 I: i a jd. \ Tk»(n*)) _Cafcutated _ 2 t m 1 m 1 i\ h 1 l\ i ' sj\ D 2 4 Tra (mh) Hyetograph limh.jlb TWn»(rrin) TVne(rrwi) Long- Gutty C*efc Una Gofy Creek f long Gully Creek Event IMP-O Event IMP Event IUP* nn(irin) r t/v _Caicut«teti 4 b 1 Hydrograph km (mri) 2 3 Tln»(n* Tbm(iTt.) Lena Gully Creek Long Guly Creek Long Guly Creek Event IMP-O * Evertl M:P Event MP-O.

176 Chapter 6 - Lumped Modelling with the Proportion Model 6-1 i e 4 -a 1 Hydrograph 1 l\ /\ /\ -,/V 5 1 ISO 2 25 Tkm(nin)?ioo IQMM 1 a M Long Gully Creek 1 *-1-77 Event IMP-. 1 Hyetograph 1 a 4 is 1. Hydrograph 1 " /TV v UradTh) "rrf. Long Gully Creek Event IMP-. 1. I»- * 6. I:: 1 Long Gully Creek Event IMP-.C I Hydrograph I 2 3 Tlm>(m*i] Tkre(mn) Long Gully Creek 23^-78 Event IMP-. Long Gully Creek B-1-7B Event IMP-. Long Gully Creek Event IMP-. I Hydrograph I Hydrograph] _Celcueried _ f" e Time (fit.) F Long Gully Creek Event IMP-. I Hyetograph f L Reinfri Long Gully Creek Event IMP-. Figure Hydrographs for Long Gully Creek

177 Chapter 6 - Lumped Modelling with the Proportion Model Giralang The calibration parameter C m was found to be using the constant loss rate model and using the runoff proportion model. Figure 6.7 shows the amount of scatter in the results for the runoff proportion model. The range of the calibration parameters was.2 to 1.4. Table 6.4 shows the calibration results. Figure Plot of C against Flowrate for Giralang The single burst events produced only fair calibration, with the calculated and recorded hydrographs being very 'blocky'. The main reason for this is that the events are quite small (short in duration) which indicates that most of the runoff is being produced by the impervious parts of the catchment and in most of the events, the runoff volume ratio (Vper/Vtot) is less than.5. This is supported by the results in chapter 4 for Giralang. The 'blocky' hydrographs suggest that runoff from the catchment occurs quickly. The results indicate that lumped modelling may not be adequate for events in which impervious runoff is the dominant component. Figure 6.8 shows some of the hydrographs.

178 Chapter 6 - Lumped Modelling with the Proportion Model 6-12 Table Summary of Results for Giralang Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Peak Flowrate Flowrate (m 3 /s) (m 3 /s) 27/3/76 14/1/77 6/4/77 27/1/78 2/3/78 23/3/78 9/1/78 2/2/8 5/2/81 6/1/81 24/3/ /1/83 13/12/ /3/ Mean.41 Std Dev.33 I Hydrograph I I Hydrograph] [Hydrograph m * Pv i I- T\, ^p^r - Hyetograph Tbn>(rrin).Cefcuerted. 1 3 S» - [ I" Glmleng IMP Event 1 rrinrrrrnvv. Trr»(rrin} RaWal Glmleng IMP Event -xti J lllrrrrm Tlrm(rtin) GtaLeng IMP Event 1 Hydrograph 1 : k ^ IV m.2 - // \>Qv //,.V^* Tfma(mtij 1 Hyetograph 1 _CeteuMted _ S 2 i, 1 Hydrograph 1 LA 5 1 Tina (n*i) 1 Hyetograph 1 15 s to : «I J 5 Gkeleng MP-OO Event IllLfrin»(n*>) y 4 i 3 2 fi1 _ : ii Ik. ronn GfeftLeng IMP Event 1S S 1!c 5 tfl 1 1 Jll 1 Tkm(mn) Glmleng IMP Event

179 Chapter 6 - Lumped Modelling with the Proportion Model 6-13 I Hydrograph I Hydrograph] Hydrograph I.O4.3 J.O2 f Tina (n*i) I, 2 ii Cetoartea 6 1; 1 ISO 2 25 Tlm<mh) Glmlang IMP Event Glmleng IMP Event Giralang IMP Event «1 12 TTmefrrtni Urn* (min) Time (rm) Hyetograph] * to jfaflj ar>int«ii Glmleng IMP-. Glmleng IMP-. Glmleng IMP Event Event 1S-1-83 Event I Hydrograph I 1 Hydrograph 1.Celcutfted.fiecofded e? * tfv : /^V Glmleng IMP Event Glmleng IMP Event Figure Hydrographs for Giralang

180 Chapter 6 - Lumped Modelling with the Proportion Model Results for the Sydney Catchments Maroubra The mean calibration parameter for the runoff proportion model was , compared to with the constant loss rate model. Figure 6.9a and b shows the plot of the calibration parameter against the recorded peak discharge. Table 6.5 shows the calibration results. (a) (b) Figure Plot of C^,. against Flowrate for Maroubra Figure 6.1 show the plots of the calculated and recorded hydrographs and the rainfall hyetographs. The runoff proportion model retained the temporal pattern of the rainfall hyetograph, and in most cases the calculated runoff hydrograph agrees with the recorded hydrograph. As the runoff proportion model retains the temporal pattern of the rainfall hyetograph, all ordinates in the hyetograph are retained and the hydrograph calculated retains the temporal pattern of the rainfall. On the other hand, if a high constant loss rate is required to match the calculated volume with the recorded volume, the ordinates in the hyetograph which are smaller than the constant loss rate assigned are removed and do not contribute calculated runoff. This is clearly seen in events 5/3/77, 8/11/84 and 2/4/88. The event on the 18/6/83 is a good example of runoff proportion's ability to retain the rainfall temporal pattern. In loss rate modelling (chapter 5), the higher losses removed all the rainfall from the start of the event and runoff was not calculated. The use of runoff proportion rectified this problem.

181 Chapter 6 - Lumped Modelling with the Proportion Model 6-15 Table Summary of Results for Maroubra Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate 1/3/77 5/3/77 3/3/78 17/3/78 27/3/78 13/4/78 18/5/78 19/6/79 2/6/79 17/3/ (m 3 /s) (m 3 /s) /6/83 6/11/ /11/ /12/ /5/ /4/ /7/ /1/ /4/ /4/ Mean.35 StdDev.19 I Hydrograph! I Hydrograph I.4» Tkm(rrtn) I" " f^ 3 '.5 V -. >S nme(mri).calculated.reworded nfetf** i Time (IT*.) Meraubn IMP-O Event Meraubm IMP Event i IMP Event

182 Chapter 6 - Lumped Modelling with the Proportion Model T>re(rrin) [Hyetographl Tlme(rrtn) Tim (IT*.) tehfao Maroubra emp-o.o Event IMP Event Merwtx* IMP»Q.Q Event I Hydrograph to TkT»(rrfn) I Hyetograph] Tkra(mtr>) jddh Da. Maroubra IMP-. 1fr6-79 Event Maroubra 1MP-O Event I Hydrograph I ; i5o. '' 1. \ Mnraubm IMP Event Meroubre IMP Event < IMP Event Tkra(rmi) nrre(mn) Event Tto»<irin) Maroubra IMP Event i IMP-. 1*85 Event

183 Chapter 6 - Lumped Modelling with the Proportion Model 6-17 I Hydrograph Trm(irin) Hyetographl ' -.8 e> «.6 I - 4 C.2 2 ; 15 1 Hydrograph 1 :Jk _Ctk.uU*d Time I Hyetograph] _ i M L ML ' ' l-il Time (min) Maroubra MP-. Meroubm IMP-. Meroubm IUP Event Event Event too Tkm (fl*)) I Hydrograph I A _Olcufcted Tlme(rrin) _ Figure Hydrographs for Maroubra Strathfield The calibration parameter for the runoff proportion model was found to be , compared to for the constant loss rate model. Figure 6.11 shows the plot of the calibration parameter against the peak recorded discharges for the runoff proportion model. Table 6.6 shows the calibration results. I Plot of Parameter C against Qrec I «* Qrac(nfl/ft) Figure Plot of C wr against Flowrate for Strathfield Figure 6.12 shows the calibration results using the runoff proportion model. Improvements in the shape and fit of the calculated hydrographs (compared to the constant loss model) were noticed in events 21/5/83, 3/4/88, 3/9/77 and 16/3/83, but the event on the 2/3/81 calibrated poorly compared to constant loss modelling. In this event the recorded hydrograph has a very blocky shape which

184 Chapter 6 - Lumped Modelling with the Proportion Model 6_lg emulates the rainfall pattern. The rainfall is relatively small and most of the runoff is thought to be produced from the impervious areas where the storage volume is low and response is quick. Given that the catchment is small it is reasonable to expect that the runoff hydrograph will closely resemble the shape of the rainfall pattern. The lumped model gives a poor result because the whole catchment is assumed to contribute runoff and the catchment storage is overestimated causing smoothing of the hydrograph shape. Table Summary of Results for Strathfield Event Initial Curb Crur Calculated Rainfall Total Calculated Loss Prop. Excess Rainfall Peak Peak Flowrate Flowrate 3/9/77 4/9/78 2/3/81 2/4/81 4/4/81B 4/4/81 3/12/82 25/3/82 3/9/83 16/3/83 21/5/83 7/4/84 8/11/84 1/5/85 3/4/85 4/8/86 13/2/88 3/4/88 4/7/88 28/4/ (m 3 /s) (m 3 /s) Mean.87 StdDev.94

185 Chapter 6 - Lumped Modelling with the Proportion Model 6-19 I Hydrograph I Hydrograph I I Hydrograph I f - * 2. _rmcoroed _CeJcua»ted _ TlrTe>(rrtn) I Hyetograph 1 IMP-. Event SoeihfleM IMP Even 1 StmthfMd IMP Event lllimu Tkn(n*)) TVnt(rrin) fhyetograph I RiW-J! StmthfeM IMP Event Stmthfleld IMP Event Stmthfleld IM P Event Hydrograph] 1 Hyetograph 1 ' LJL _ Calculated Krrin) _ i - r Strath tuldii E Tkm(rrin) I Hyetograph StrethlWd imp-,o Event Stathfteld IMP Event Tkm(rrin) Stmthfleld IMP-. T-4-64 Event

186 Chapter 6 - Lumped Modelling with the Proportion Model 6-2 I Hydrograph I I Hydrograph I 1 Hydrograph 1 1 s 1 I 8-4 i- :-A _C6teuW»d ) C Tkna(mVt) StrethfleldlMP-O.O JL Event rkna(rrtn) I Rtftfafl I 1 * 4 1* : i: c " 1 1 = Strathfield LMP Event - / \ nma(rrin) riw(mh) _CslcuMed _ I CRilnfel I «4 1» 'K?2 il G 2 4 SO Tkmlnti) 1 Hyetograph 1?2 i,s Z 1«I i i i i Strathfield IMP Event Ilk Tkra(rrai) _CtlCUlelad _ or>w»l 1 I Hydrograph I i 1 r y Wi Tim (min) Strethfleld IMP Event I Hydrograph I Hydrograph 1 J? - _ Calculated Calculated _ Tfrefrrtn) TVnt(rrin) Tk (rnh) Strethfleld MP-O.O Event Strath Held IMP Event Figure Hydrographs for Strathfield

187 Chapter 6 - Lumped Modelling with the Proportion Model Fisher's Ghost Creek The mean calibration parameter C^ was found to be for runoff proportion modelling, compared to for constant loss modelling. Figure 6.13 shows the plot of the calibration parameter against the peak recorded discharges. Table 6.7 shows the calibration results. 1 Plot of Parameter C against Qrec ' ifwiers Cheat Creek j Qrec (rrfl/t) Figure Plot of C^ against Flowrate for Fisher's Ghost Creek Figure 6.14 shows the hydrograph and hyetograph plots from the calibration results. Better calibratio was obtained for the event on the 5/3/83, 7/2/84 when modelled with the runoff proportion model than with the constant loss rate model. The high rainfall losses used to balance the calculated and recorded runoff volumes removed most of the minor rainfall and the calculated hydrograph shape lost accuracy. The runoff proportion retained the rainfall temporal pattern and the fit between the calculated and recorded hydrographs was better. But on the other hand, poorer fit was obtained for events 19/1/81, 6/8/86, 24/1/87, 15/1/86, 2/3/83 and 24/5/88 with runoff proportion modelling than loss rate modelling. The multi-peaks in these events were retained by the runoff proportion model, which was reflected in the calculated hydrograph. The reason for this is that the loss model (constant loss rate and runoff proportion) are not representing the real losses occurring for this event. In reality, the losses are high at the start of the event and decrease over the duration of the event. A reducing losses rate (exponential decay) may be required to correctly model these events and others like them.

188 Chapter 6 - Lumped Modelling with the Proportion Model 6-22 Table Summary of Results for Fisher's Ghost Creek Event Initial Loss Prop. Curb Crur Calculated Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate (m 3 /s) (m 3 /s) 2/11/81 4/5/81 19/1/81 25/12/81 17/3/83 2/3/ /3/ /11/ /12/ /1/ /2/ /11/ /11/ /12/ /1/ /8/ /11/ /1/ /6/ /5/ Mean.82 Std Dev.47 I Hydrograph I Hydrograph 1 I Hydrograph I nma(irtn) I b : JSrV Tbm(mtr) Tlmt(rre-t) _dlcumed _ [Hyetograph] JLI Dm (rrin) Tlmt(min) TVnj(rrti) Flahert Cheat Oeeks Event IMP-. Flattere Che al Creek 4-S-61 Event IMP-. Rehere Cheat Creek Event WP-J3

189 Chapter 6 - Lumped Modelling with the Proportion Model 6-23 I Hydrograph I SO TOO t2c 14 Taia(rrfn) t m 2 * I Hydrograph I A \ td\ ln\ rv 5 1 ISO 2 Tlrna(rrin) _CaLcuim1ed _RKorded I' 1 Hydrograph 1 i 1 - A a 2 / / J \ V JJ, L^- / Hyetograph 4 n 3 ^2 4" si - Jlwuu Tlma(rtln) Trma (rrtn) ReWa Gnoe Creek Event IMP-. FMtefe Gho at Creek Event tmp-. Rshere Ghost Creek Event IMP TOO 15 TTrreCm*) Tlrm(rrtn) TVna(rrin) Fhttor'sGltoat Creek Event IMP-. I Hydrograph I L R*iei*aCho«Creek Event IMP , 1 Hyetograph jjil^ Rahera Gho* Creek Event IMP-. 1 Hydrograph 1 i: S 2 I,! /v nrre(rrin) 5! /v -. 4 e y/, Hyetograph Tire (min) I Hyetograph] A Ttrrefrri/i) JllPltato, Fenefa Ghost Cieek Event tmp-o.c FleWeGho* Cieek Event IMP-. Flewa Gho* Creek Ev-ntlMP-O.O Tkm(irin) I- Th»{mn) RiWifl R ew» Gno* Creek Event MP-. Ratter's Ghoat Creek Event IMP-.

190 Chapter 6 - Lumped Modelling with the Proportion Model 6-24 I Hydrograph I I Hydrograph 1 Hydrograph Tfrm>(rrin) i: iil Jk l 2 4( 7Vre(rr(n) _Cefcuerteti _ ~ 8 -L A 1 «lid 4 r ^ i ^ WUvV Th»(rnh) 2 2 _CelculBted. Hyetograph \ * S 4 " li III ill nramaa 1 I 2 Rahfn ReSera Ghost Creek Event tmp-. Rshere Ghost Creek Event MP-O.O FlaiaTaGhaa Craak Evant IMP- 1 2' I Hydrograph I S Th>(n*i) s i: 1 Hydrograph 1 a> 2 2 2, /*J r* i i 1 2 TVm n*n) 1? * 1 i" *o i - : Rahefs Ghost Creek Event IMP-. jtjn RsWaGho* Creek Event IMP-. Figure Hydrographs for Fisher's Ghost Creek Jamison Park The calibration parameter C^ was found to be for runoff proportion modelling, compared to for the constant loss rate model. Figure 6.15 shows the plot of the calibration parameter against the peak recorded discharges. Table 6.8 shows the calibration results. I Plot of Parameter C against Qrec I V\ Park! Figure Plot of C mr against Flowrate for Jamison Park Figure 6.16 shows the hydrographs calibrated on Jamison Park. The results are better than those using the constant loss rate model as the rainfall temporal pattern is retained. Some adjustments were made to the initial losses though out the study (eg. event 21/3/83 was calibrated with initial loss of mm in chapter 5 and in this chapter with 9 mm). The reason for this is that at that time in the study, a computer virus destroyed the data files (on hard drive and backups). Clean datafiles were created

191 Chapter 6 - Lumped Modelling with the Proportion Model 6-25 from the raw rainfall data, and the exact rainfall temporal patterns were not extracted. Note in the event on the 21/3/83 the hyetographs in figure 5.17 and There is an initial rainfall burst in figure 6.16 with a peak of about 3 mm/hr which is missing from figure But, the results do not vary significantly, and the event is still valid. Table Summary of Results for Jamison Park Event Initial Curb Crur Calculated Rainfall Total Calculated Loss Prop. Excess Rainfall Peak Peak Flowrate Flowrate (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12/ /9/ /1/ /4/ /1/ /1/ /1/ /4/88B /4/88B /2/88B /2/ /5/ /4/ Mean.86 Std Dev 1.12 [Hydrograph [Hydrograph I Hydrograph SOO SO 1 15 Ttaa(nai) Tim (n*l) Tlme(rrtn) 1 Hyetograph WAUsit L_ Ja*»a>itPa*latP-O Evaiit ar«"a» 6 <!- 6 4 I * l 1 Hyetograph 1 j»me*np»rsrlmp-o Event 1 I. _. Re*ifef 1 - J.r *>nperklmp* Event " Unnn n OMM

192 Chapter 6 - Lumped Modelling with the Proportion Model 6-26 I Hydrograph I Hydrograph I 5 c _ Cilc u* ted Tim (min) 4. I 3_ o»««t 6 4 r Hyetograph 1 ^,.L ol DD nni-it-i D«iWU Jamison IMP-. Perk IMP-. Jamison Pmrk IMP Event Event Event [Hydrograph] Tkni(nin) r\ Hydrograph! \ A \ ^ _CafcuMted. I I Hydrograph I fu _Cs.fcuk.ted 5 1 Tai»(mJn) I Hyetograph n- rm m mm Jamison Perk IMP-. Park IMP Event Even, Hydrograph I Hydrograph I ThTBifrrtr.) 1 Hyetograph I Hyetographl 1 * 4 - nn C 2 r-ir-i erk IMP-. i Event Jamison Per* IMP Event Jamison Park MP Event I Hydrograph I I Hydrograph] S" _CtfcuMad TTrm(rrri) (rran) Hyetograph I 15 _ ark IMP-. 6 Event a HmB(rrtn) Jamlean Park IMP Event Rain fell Jemta>n Park IMP B Event

193 Chapter 6 - Lumped Modelling with the Proportion Model 6-27 I Hydrograph I Hydrograph 1 1 Hydrograph 1.Calcuaaad _Fax:ortBd _Cafcufcrted. I " iv. _Ca1CUtet*d 1..6 S Trrsi(rre-i) Trns(rTtrt) \> lyetograph 1 [Hyetograph I i i Hyetographl rl I * 11 nr»wn 2 - [ n n n Q«i««1 Janeson Park IMP B Event Jemiean Park IMP B Event Jamison Park IMP Event [Hydrograph r\ Tbm(nin) nrr*(rrtn) Trni(rrtn) Jemlson Peri.IMP Event Jamison Park IMP Event Figure Hydrographs for Jamison Park 6.4 Results for the Melbourne Catchment Vine Street The calibration parameter C^ was found to be for the runoff proportion model, compared to for the constant loss rate model. Figure 6.17 shows the plot of the calibration parameter against the peak recorded discharges. As can be seen, parameter C increases slightly for larger discharges, which indicates lumped modelling to be inaccurate. Figure 6.18 shows the hydrographs. Thefit between the calculated and recorded hydrographs is fairly good. Table 6.9 shows the calibration results obtained. Figure 6.18 shows the hydrographs. Events on the 15/5/74, 15/1/83 and 7/4/77 showed a similar trend to that described in section for Fisher's Ghost Creek.

194 Chapter 6 - Lumped Modelling with the Proportion Model 6-28 I Plot of Parameter C against Qrec I : , ,6 Qrec(rraa) Figure Plot of C wr against Flowrate for Vine Street Table Summary of Results for Vine Street Event Initial Curb Crur Calculated Rainfall Total Calculated Loss Prop. Excess Rainfall Peak Peak Flowrate Flowrate (m 3 /s) (m 3 /s) 15/2/ /2/ /5/ /1/ /12/ /11/ /4/ /1/ /9/ /12/ /11/ Mean Std Dev I Hydrograph I I Hydrograph I Hydrograph _ Calculated _ Catenated I OS Time (IT*)) TTrra(mri) Tlma(rrtn) 1 Hyetograph Trr»(mr» Vine Sbeet imp Event Raln.«i : Vine Sheet IMP Event ^25 fe*> S- 15 1'" s! Vine Street IMP Event

195 Chapter 6 - Lumped Modelling with the Proportion Model 6-29 I Hydrograph I Hydrograph I Hydrograph I V* " /\ 2 1 -/Y o.s r / ^~ J,,,,, TVrafrrin) _ Calculated. o.s _ Calculated. « TBTHfrrtn) 1 ^ 4 [ Hyetographl ar»wab! 2 & rt Trns(mn) Vine Street MP Event vine Street imp-o.i Event Vine Street IMP-.C Event TrnMrrtn) ne Street IMP Event Vine Street IMP Event Vine Street IMP Event 1 Hydrograph 1 b i/v. r e Tsni(mri) Vine Street IMP Event Vine Street IMP Event Figure Hydrographs for Vine Street

196 Chapter 6 - Lumped Modelling with the Proportion Model Discussion of Results and Conclusions The mean parameter C for all the catchments using lumped catchment modelling and a runoff proportion rainfall loss model was.84 with a standard deviation of.91, compared to using a constant loss rate rainfall model. The calibration parameter value has reduced and the relative scatter has reduced indicating the runoff proportion method is less susceptible to variation for different catchments. The reason the runoff proportion model produces lower parameter C values is that with a constant loss rate, the excess rainfall depth is concentrated in the intense burst, whereas with the runoff proportion all ordinates are factored down in the same proportion. Consequently the excess rainfall in the most intense period is smaller in the runoff proportion model, and a smaller lag parameter C is required to match the calculated and recorded peak discharges. Figure 6.19b shows a plot of C against the runoff volume ratio for all the catchment and all storms. similar figure (figure 5.2b) for constant loss rate modelling can be seen in chapter 5. There is a smaller amount of scatter in the results for runoff proportion modelling than in those for constant loss modelling and the reason for this is probably due to the loss model. Figure 6.2 shows parameter C does not vary significantly with catchment area (as in chapter 5). The high outlier value is again associated with Vine Street. Plot of Parameter C against Qrec Plot of Parameter C against Vper/Vtot 4 o 3 -! 1 15 Qrsc (rrols) ILumped Catchments Initial Loss- Proportion I (a) **** :y>s*eve,^emky~ Vper/Vtot Lumped ModePing, Proportion. AP Catchments] (b) Figure Plot of C w against Flowrate for all catchments Plot of Parameter C against Area S3 6 o Area(km2) Split Catchments Proportion Figure Plot of C mr against Catchment Area for all catchments

197 Chapter 6 - Lumped Modelling with the Proportion Model 6-31 The following conclusions can be drawn from the study: 1. The slower recession after the peak discharge seen in the chapter 5 results has been reduced in this chapter. For example, this was noticed in some of the Curtin events (13/2/72, 26/1/71, 9/1/78). 2. Lumped modelling with the runoff proportion rainfall loss model performed better than lumped modelling with the constant loss rate model. In general, the results obtained in this chapter were quite good and the calculated recession curves in most of the storm events on all the catchments were matched to the recorded. 3. In lumped modelling, parameter C tended to be very sensitive to the loss model used. On average, C was lower for runoff proportion. But in events where the peak recorded discharges were low (less than 25 m 3 /s), both runoff proportion and constant loss rate required high parameter C values to calibrate (see figures 5.2 and 6.19). This indicates lumped modelling may not be a good procedure for urban catchments. The reason for this is that lumping the pervious and impervious areas together averages the rainfall losses and parameter C. This then combines the runoff from both pervious and impervious areas. 4. Lumped modelling does not predict the relative amounts of runoff from the impervious and pervious surfaces. 5. The LR and RP loss models may not be representing the real losses occurring on a catchment for a particular storm event. In reality, the losses over the period of a storm may reduce (exponentially) and the rainfall models used do not reflect this. 6. It would be more accurate to model multi-peak events as a number of single burst storm events with individual rainfall losses. It has been shown that runoff from impervious and pervious areas behave differently, and by trying to lump the two together to accurately predict runoff is very difficult. The results in chapter 4, showed that split modelling is potentially better than lumped modelling, but problems arose in the way WBNM modelled the impervious parts of the catchment. These problems will be addressed in the following chapters.

198 Chapter 7 Split Modelling with the Loss Rate and Proportion Models

199 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models SPLIT MODELLING with the LOSS RATE and RUNOFF PROPORTION MODELS 7.1 Introduction In this chapter, the nine urban catchments will be modelled as split catchments with the LR and RP rainfall loss models, and with WBNM running nonlinear on pervious surfaces and linear on impervious surfaces. The impervious fractions used are those calculated from rainfall data (IMPDC^J,). Split catchment modelling was performed with WBNM in chapter 4 on seven urban catchments. At that time, the model was written to run with a nonlinearity of negative.23 for both the pervious and impervious areas. The final results showed that the mean calibration parameter was 2.27, larger than that for rural catchments (typically 1.29 to 1.7). A problem in the way WBNM calculated the lag times for the impervious part of the catchment was identified. For events which consisted mainly of impervious runoff, larger parameter C values were required to calibrate the model. The reason for this was that for these events, WBNM was calculating a larger peak discharge, and high C values were needed to reduce it to the recorded value. This could be caused by the nonlinear impervious runoff component of the model reducing the lag effect for the larger impervious discharges. Researchers such as Nash (196), Schaake et al (1967), Viessman (1968), NERC (1975), Espey et. al (1977) and Cordery (1981) have modelled catchments linearly with success in the past, and to try to correct this problem, it was decided to model the impervious areas as linear. The discharge exponent in equation 2.31 was therefore changed to. The results of the calibration runs are presented below.

200 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models initial Loss-Constant Loss Rate Results (LR) Results for the Canberra Catchments Curtin The results for Curtin catchment are summarised in table 7.1. Plots of the calibration parameter against the peak recordedflowrate and the runoff volume ratio can be seen infigure7.1. As can be seen, there are no strong trends, but the results scatter quite a lot. Event 21/3/74 was omitted because the calculated and recorded runoff volumes did not balance. Note in particular that no trend is apparent for parameter C against the runoff volume ratio (figure 7.1b), in contrast to the results of chapter 4 (figure 4.2b), indicating that the use of linear modelling for impervious runoff is warranted. In general, the C values have decreased by more than half compared to those when WBNM was running nonlinear for both the pervious and impervious areas (chapter 4). Parameter C for Curtin is now All the multi-peak events performed very well when compared to the those in chapter 4. Hydrographs can be seen infigure7.2. (a) (b) Figure Plot of C against Flowrate and Ratio for Curtin (LR)

201 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-4 Table Summary of Results for Curtin (LR) (IMP=.17) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) {m*/s) (m 3 /s) 26/1/ /2/ / /2/ /3/ /11/ /1/ /4/ / /3/ /1/ /2/ / /1/ Mean.85 Std Dev.3 Hydrograph] Hydrograph Hydrograph].-.2 S iso.calculated Calculated. ' 1 TS 2 Tins O Tlmi(min) o 2 ^OO BOO aoo 1 TVre(rrtn) CurUn IMP-O.17 Curtin IMP- 17 Curtin IMP Event Event Event I Hydrograph I 1 Hydrograph! I Hydrograph l f 4 i/\. _CafcuMad * 2 _» 2 4 CO SO 1 12 TlrT»(rrin) 1 1 J 6 </k c Tln» (fieri) _ calculated 1 a * J a 1 i i } TiTB(rrin) _Cateua*ad _Racortad f" : Hyetographl JIL Th»<rtn> j- ioo i M a "aw* 1 * 2 2 Hyetographl ; L i Tkmfn*.) IcjRalnfaJ I 1" 1" Hi Hyetograph 1.1 TKa(iiti) QHM Curt*, IMP-O 17 Curtin IMP-.17 Qirtm IMP-O Event Event Event

202 7 - Split Modelling with the Loss Rate and Proportion Models I Hydrograph I I Hydrograph I I Hydrograph I 2. Tkia(irin) eo 1 12 TVnt(lrtn) T*T»(mn) Event Thm(n*i) S 2 I" CurUr. IMP-, Event I k-nrwirim- CuttM IMP-O Event RaWaB TamflTaT.) Tina(rnJn) Tim(frin) Cur*. IMP-O Event CurtJn IMP Event Curun IMP-O Event I Hydrograph I Hydrograph I Time.Calculated. A 4 I- e K TTrre(rr*n) Curt* IMP-O.l Event CUftLn IMP Event Figure Single Peak Events for Curtin (LR)

203 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Mawson The mean calibration parameter C was calculated to be A slight trend can be seen in figure 7.3a and b, although there is some scatter in the results. An overall reduction in parameter C occurred over the value obtained in chapter 4. For events where impervious area runoff was greater than from the pervious areas, parameter C is slightly larger (Vpe/^tot <.5). Table 7.2 shows a summary of the results obtained after the calibration. Figure 7.4 shows the hydrographs. I Ploi of Parameter C against Qrec 1 1 Plot of P arameter C against Vper/Vtot 1 O 1.5 > I ' - S Orac(n<Va) MaweanlMP-.2l o 1.5 * I ' _ Mawson IMP-.21 Vpef/Vtot (a) Figure Plot of C against Flowrate Ratio for Mawson (LR) (b) Table Summary of Results for Mawson (LR) (IMP=.21) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (m 3 /s) (m 3 /s) 13/2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /1/ /1/ Mean.69 Std Dev.45

204 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Hydrograph 1 f i\ v^ - i / V ^w 5 l,. >s= too I Hydrograph I r 25 & 15 a : 1 I 5 I Hydrograph I Trre(rrln) me (rrtri) I Hyetograph Hyetograph l - i RatiraJ & i- 4 J«WJI. in RaMaa Mawson im P-.21 Mawson LVP-.21 fvewsonmx) Event Event event I Hydrograph I T)me(mri} Tbni(rnri] rryetographl. 1= im ^!n*wa«k»waonw.21 ka»aonmm)j1 MwaonM* byari B-4-77E»art &ant 1 Hydrograph 1 t % 1 A n \ i \ ^ \ Th»(nai) 1 Hyetograph 1 I IX f 5 n fin. m TJma(rm) a*w*i Mawson IM P Event Mawson LWP Brers rvar* son WP-O Ev art [Hydrograph A TTme(rrtn) 1 Hyetograph Mi L *wsonrvpo^i Brant Maw son irtmjil Event Figure Hydrographs for Mawson (LR)

205 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Long Gully Creek The mean calibration parameter C was found to be A large amount of scatter was evident for the smaller events as can be seen in figure 7.5a. These events produced runoff from both pervious and impervious areas. There also seems to be a slight trend between parameter C and the runoff volume ratio. The more impervious events tend to require larger parameter C values to calibrate. Table 7.3 shows the calibration results. Plot of Parameter C against Qrec 1 I Plot of Parameter C against Vpef/Vtotl o k r "?.v.... Lone Guly Creek IMP-.5J Qrec (Ira's) O 6 * r Long Guly Creek IMP-.5 Vper/Vtot (a) (b) Figure Plot of C against Flowrate and Ratio for Long Gully Creek (LR) Plots of calculated and recorded runoff hydrographs can be seen in figure 7.6. Overall performance of WBNM was satisfactory for all the multi-peak events. On the other hand, some of the single peak events (26/1/71, 13/2/72, 6/4/77, 9/1/78) performed poorly. The high rainfall losses have cut off the rainfall at the end of the event, and pervious area runoff contribution has been removed.

206 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-9 Table Summary of Results for Long Gully Creek (LR) (IMP=.5) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (imm/ti) (m 3 /s) (m 3 /s) 2671/ / / /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ / / Mean 2.21 StdDev 1.7 Hydrograph I Hydrograph I Hydrograph f 2-1 IM (frirt) nms(rrwi) ThTB.(TTtn) I Hyetograph long Guly f>ee* lone GuCy Creek Evert MM>.S Event MM) 5 LU ow*» Ttm{rTB*>) Long Guty Creak Brent fcex Tkna(mln) I Hyetograph X Tire>(nin) IX Tkm(rrtn) T.TT»(rnn) UngGutyCree* /ent W<i.5

207 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-1 I Hydrograph I I Hydrograph I A_ Tkne(nai) _CaleuMed _ i Tkna(rrtn) _CsCu*ta<j _f«jeoraed 1 Hyetograph 1 i «>- 5 «- k Time(rrwi) ftewel Raws* Long Gulp Creek Event WP-.5 Long Guly Creel Event MM). OS Long Guly Creek Event MM) 5 I Hydrograph I Tkm(rnh) trne(rrin) Tirre(rm) Long Guly Cieek ( Event IMP-.5 Long Gutty Creek Event MM). 5 Long GuBy Creek Event MM) 5 I Hydrograph I v : -K. _Catcuerted.. T2 b c » Trna(Mn) 1 Hyetograph 1 if 3 b c I Hydrograph I _CdcuWad Tim (nan) /\ 1 1 Hyetograph 1 1 * J-4 - I 2 \ Tlma(mr) Long Only Greek Event IMP-.5 1 QRamfaB a 2 "JL I 1. 7sie»<rnh) Long Guly Craak Evert MM) 5 1 QRaWH 1 Figure Hydrographs for Long Gully Creek (LR)

208 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Giralang The mean calibration parameter calculated for Giralang was A reduction in the scatte and magnitude of parameter C was obtained, compared to the value in chapter 4 (figure 4.8), but the trend between parameter C and the runoff volume ratio (figure 7.7b) has not been eliminated. Table 7.4 shows the calibration results. Figure 7.8 shows the hydrographs. I Plot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtot].5 L i i t igsetane IMP-L22] G»alanglMP-.22 (a) Figure Plot of C against Flowrate Ratio for Giralang (LR) (b) Table Summary of Results for Giralang (LR) (IMP=.22) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 27/3/ /1/ /4/ /1/ /3/ /3/ /1/ /2/ /2/ /1/ /3/ /1/ /12/ /3/ Mean.83 StdDev.57

209 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-12 I Hydrograph ] [Hydrograph I Hydrograph ] _Cafc>uHad _RacorcM r TVre(rrin) Ttrm(rrtn) Guano MMJJZ Evaft Thna(Rto) Gfrakng MM B»nt Tkrsi(rnh) 3D t -2 I,. ' n nnnmn & Ostsng MMD Sranl ThsifrTin) Tb-ra>(rr*i) 2 4 SO TlrrB(mn) Tkm(rrin) Hyetograph nrrflln ii RaWan ^^IMIIIPUB, Geahna IMP-.22 GfeakngMM).22 GaaJang ftf-^ Event Evart Evart 1 2O Trna trin) a(r*] s *>}- JO GrtBtng IMP Event Gfraiang MMX B/ert [Hydrograph I TTrre(rrtn) ^ 1 E B I" e".8 C.2 l -ta Tam(mn) I Hyetographl gbawal Grt-no IMP4J Evant ol llllfc 1 GrtBng IM Bram Tim (nti)

210 er7' - Split Modelling with the Loss Rate and Proportion Models Hydrograph 1* \K _ S h Ttaa(irai) I Hyetographl CMuMBd _r*coroad 1 Hydrograph 1 = M 1 «l;v i BO _caeuatad _Raeortad GHIang W E»««RahraH i 4 2 S ' n l_ prawal G*»»ro MM>.22 2S-3-S4Ev.nl Figure Hydrographs for Giralang (LR) Results for the Sydney Catchments Maroubra The mean calibration parameter for Maroubra was found to be The calculated and recorded runoff volumes for a number of events did not balance and these were omittedfromthe study (table 7.5). Figure 7.9a and b shows the plot of the parameter C against the recorded peak discharge and runoff volume ratio, respectively. contribution was mainly from the impervious parts of the catchment due to the very pervious nature of the soil in the catchment (sand). Table 7.5 shows the calibration results. I Plot ot Parameter C against Qrec I Plot of Parameter C against Vper/Vtot] [Maroufeia IMP-.18 (a) (b) Figure Plot of C against Flowrate and Ratio for Maroubra (LR) Figures 7.1 show the plots of the calculated and recorded hydrographs and the rainfall hyetograp for all storm events. As can be seen, the calibration of the multi-peak events was good. An improvement in thefit of the hydrographs is evident compared to the hydrographs obtained when WBNM used a nonlinear routing for impervious runoff (chapter 4). All the single peak events performed reasonably well except for 3/7/87 where WBNM picked up the two small bursts of rainfall which were nine minutes apart and calculated two peaks. The recorded event on the 3/3/78 shows the recorded hydrograph to bulge out after the peak. This is because of the

211 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-14 continuation of rainfall after the main burst. The calculated hydrograph shows this to some extent, but not completely because the loss rate assigned to balance the volume was higher than the rainfall. This also occurred on 2/6/79 and 11/12/84. Another feature in some of the hydrographs was the quick dissipation of the calculated runoff after the peak. This is evident on the 18/6/83. This can be attributed to the high rainfall losses assigned to balance runoff volumes. The calculated hydrograph before the peak closely follows the recorded. dissipation then occurs quickly after the peak. Due to the high losses, there is no pervious area runoff contribution after the peak. The impervious area contributes, but the dissipation of the runoff is now faster. Thus, the calculated hydrograph does notfitthe recorded after the peak. This was also noticed in some of the Canberra catchments. The runoff proportion rainfall losses model may account for these types of events because it allows a proportion of all the rainfall on the pervious surfaces to contribute to runoff. This shows that the rainfall loss model being used may be too simplistic, as discussed in chapter 6. Table Summary of Results for Maroubra (LR) (IMP =.16) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m'/s) (m 3 /s) 1/3/ /3/ /3/ /3/ /3/ /4/ / /6/79 B /6/ /3/ / /11/ /11/ /12/ / /4/ /7/ /1/ /4/ /4/ Mean 3.36 Std Dev 1.9

212 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-15 I Hydrograph I I Hydrograph.4. I TVna(ntn) 2 4 SO 8 1 Tlma(n*i) 4- I» 12 RaUM Tna(frin) EVart Maroubra (MP Event 1" I Hydrograph I U ^ I 1 15 Tkm(rrin) _Calcuinad. 1 Hyetograph 1 Hyetograph] -4 -C 2 r Mareubra IMP-.1S Event Mareubra imp Event Mareubra IMP-O.I Event nme(rrtn) Hareubn MP Event t l _ Meroubre IMP-.1B Event 1 M fe JO 1 Hyetograph 1 Jill j orattfan Meroubre IMP Event I Hydrograph I ^ L f\ 11. /, v ^ 2 4 Una (irin) 1 Hydrograph 1?.9 1 f /I.4.2 ik Hyetograph 1 M -2 ' rl i jqralnral 1 1S 1 I 5 rj Mareubra tmp Event Maroubra IMP Event

213 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-16 r-! g 1 o.s 15 I Hydrograph I [ A A too 2m Ttme(mn) I Hydrograph I 1 2W Tlmelrrtr) I Hydrograph I I 1 armmtt Mroubra MM E» art toroixa MM) Ey art MVMtva M> S-teEvart Hydrograph Tan(irto) I Hyetographl 1.2 i ' «.8-1 OJ _/ I * V\ 1 15 v^i- - Tlme(rrtn).Calculated? 15 _ S 1 IE 5! L Event Maroubra IMP Event Maroubra IMP Event [Hydrograph] Hydrograph Tma(mJn) Trme(rrtn) Maroubra fcwie Event Maroubra MMJ Event Hrra(rrtn) Figure Hydrogra iphs for Maroubra (LR)

214 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Strathfield Parameter C for Strathfield was found to be Figure 7.1 la shows the plot of parameter C against the peak recorded discharges, with a slight trend in the results, but a large amount of scatter. Figure 7.11b shows a large amount of scatter, but there is an overall reduction in the magnitude of parameter C compared to the results in chapter 4. Table 7.6 shows the calibration results. I Plot of Parameter C against Qrec I I Plot of Parameter C against VperA/tot 1 O 3 k r e 1 < StraSMtotd IMP-.281 «*,, f r Qfe*(m3/») (a) O 3 - ( Vper/Vtot jstrrttfield IMP-.291 (b) ^ Figure Plot of Parameter C against Flowrate and Ratio for Strathfield (LR) Plots of all hydrographs can be seen in figures The fit of the calculated and recorded hydrographs has improved, indicating the modifications to WBNM to be satisfactory. The single peak events also performed well with very good calibration being achieved for most of the events. For 3/9/77, 4/9/78, 4/4/81 and 8/11/84, the calculated discharges after the peak seem to have been underestimated by WBNM. These events have high rainfall losses, and the problem of the rainfall hyetograph being cut off and pervious area runoff contribution being eliminated has occurred. In these cases, the runoff proportion model may be better and will be discussed later.

215 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-18 Table Summary of Results for Strathfield (LR) (IMP =.29) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 3/9/ /9/ /3/ /4/ /4/81B /4/ /12/ / /9/ / /5/ /4/ /1/ B/11/ /5/ /4/ /8/ /2/ /4/ /4/ Mean 1.33 StdDev 1.4

216 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-19 Hydrograph I I Hydrograph I I Hydrograph I _Cata*Bad _Racortad i " n 5tmtnfMd IMP-29! 3-»-77 Event Hyetographl 2 4 SO 8 1 Iha(irin) Tlrr»(rnh) StnthfteH IMP-O B Event SttathSeM tmpeq2» Event Tl»T»(nai) IJlrJIlTlW, DR»W*I rrtfll liininiiirniii-i Strathneld IMP-O 29 Strathneld IMP-Q.2B Strathneld imp-o Event 4-4-8t Event *-4-«f B Event Tlrra(rr«n) Tlrr»(rr*i) i Hyetograph I. M.A i - ara*rai I i n m=n. Strathneld IMP-^9 Straw Md MKL2S SttathneM IMP-Q.2S Event Evert Event Hydrograph Tlrra(rrwi) 5 1 ISO 2 Tkmfrrtn) 1 * h J VJAT- SO 1 15 TH»(r*i) StraHM MM) J» 1RJ-«3E»a«StnmrialO MMU S3&M

217 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-2 I Hydrograph I I Hydrograph] *nt<rrin) Strathneld IMP-.2B Event Strathneld IMP Event I Hydrograph !/V = i 2 ii Strathfield MP-.2S Event StrattrfWd MMI29 4*86 Evert IStratM.eldlVP Brent Hydrograph 1 1 _ Calculated i 5 J \JWvv Tkm(rtti) TkT»(mh) SrratWwld WP Brant StnJWIeWlVP Brant Figure Hydrographs for Strathfield (LR)

218 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Fisher's Ghost Creek The mean parameter C for Fisher's Ghost Creek was found to be , with the values ranging from.84 to Figure 7.13a shows parameter C has a low amount of scatter for larger sized events and for small events, parameter C tended to be higher. Figure 7.13b shows that the change to WBNM from nonlinear to linear impervious area modelling have reduced the trends between parameter C and the type of event. Table 7.7 shows the calibration results. s 1! c Plot of Parameter C against Qrec 1 -. * * Hehere Gheat Creek IMP- J r>ee(m s) I Plot of Parameter C against Vper/Vtot 5-3. # 22 1 " * ( o.a Vpef/VtOt Rehefe Gho* Geek IM P-Q 251 (a) (b) Figure Plot of Parameter C against Flowrate Ratio for Fisher's Ghost Creek (LR) The calibration obtained from most of the events is fair (4/5/81, 19/1/81, 2/11/81, 2/3/83 and 24/1/87). As in previous catchments, the major burst seems to have calibrated well, but the minor bursts lack the accuracy of the major ones. This may indicate that using the initial loss-constant loss rate rainfall loss model may not be appropriate for multi-peak events. The calibration for the other events (17/3.3, 15/1/86, 24/5/88) was not as good as above because the high rainfall losses used to balance the calculated and recorded runoff volumes, caused some of the minor rainfall bursts to be removed. The calculated hydrographs lacked the detail of the recorded ones. Figure 7.14 shows the hydrographs and hyetographs for all rainfall events on the Fisher's Ghost Creek catchment. The overall results are much better than the results obtained in chapter 4.

219 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-22 Table Summary of Results for Fisher's Ghost Creek (LR) (IMP =.25) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 2/11/ /5/ /1/ /12/ /3/ /3/ /3/ /11/ /12/ /1/ /2/ /11/ /11/ /12/ /1/ / /11/86 B /1/ /6/ /5/ Mean 2.23 Std Dev 1.16 [Hydrograph] 1 15 Tin* (into) 1 Hydrograph 1 ~ 4 j, \A _CaJeuMed « Trre(mr) _ I. * 5 * i, fefce. I Hydrograph ITmeOrin) _ Calculated I- s 1 Hyetograph 1 : ij- TJrmffrin) Flehefe Cheat Creek Event tmp-.23 Fnhefa Cheat Creek " Event IMP-25 Ffchefe Ghost Creek Bient l*m).2s

220 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-23 Hydrograph] 1 Hydrograph I j Hydrograph J _ Calculated Ctlcuttted. _Ca(citff*d _ha%ofded -J I I L TtT»(rr*l) 5 1 Tlmi(rrln) 5 2 1fT»(fT*l) Reher*» Cheat Creek Event IMP-.2S Fisher's Ghost Qeek Event JMP-o tkm(mh) Fisher's Ghost Creek Fisher's Ghost Creek 1 4 = 2 Fisher's Ghost Crssk uillljii Rainfall Event IMP Event IMP Biert.MP-C ~nrn»((rtr>) t/v _Cabutitsd c ; 2 Tkrafrm) Hyetograph 1 1 i; I, i 1 i» s Hydrograph 1 -J- Im*- _ ffrcorded V I' 2 1 Hydrograph 1 *^T. i TTmafmtt) Reher's Cheat ChMk Event IMP-.2S Fanefs Chest Creek Event IMP-.25 Fisher's Ghost Creek ft Event (MP TTn»(rrtn) [Hyetograph] D Tkm(rrin) Event IMP-.25 'tim Fishers Ghost Creek Evsnt IMP- 2! F»hefi Ghost Creek 1S-1-86 Event LMPeQJS

221 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Hydrograph I I Hydrograph I I Hydrograph]? - k *V\ TVne'rrin) TVna(rrsi)!. s S 4 I: Tta*(rnh) Father's Ghost Crssk Bv«nt IVP-.25 TVna(n*i) ftsrtef* Ghost Creek Tlma(mjn) Evsnt IMP-.23 Rshsf*» Ghost Crssk Evert MM),2S 1 Hydrograph 1 I Hydrograph 4 I. [.A AH fi. W\ JWVK J. yw> Tsiw(n*l] TVm(rrtn] _Caln*Hsd _ F«h«rs Ghost Crssk Br snt IVPeO. 25 Fisrw-s Ghost Creek < Evsnt MM>.25 llrm(rrin) Figure Hydrographs for Fisher's Ghost Creek (LR) Jamison Park The mean calibration parameter C for Jamison Park was found to be Figure 7.15a show parameter C against the peak recorded discharges. The plot shows a trend in which parameter C is larger for smaller discharges. Table 7.8 shows the calibration results. I Plot of Parameter C against Qrec I [ Plot of Parameter C against Vper/Vtotl» 'I 1 ' 9» +, * JS Qrec (no/s) (Jemtson Pa*IMP-.2T parreeon Park IMP-.21 ] (a) (b) Figure Plot of C against Flowrate and Ratio of Ratio for Jamison Park (LR) Figure 7.16 shows the hydrographs. Fair hydrograph fit was obtained for the events on the 3/6/86, 1/1/87, 1/1/88, 21/1/88, 4/4/88B and 9/4/88. The other events were not as good, with the recorded

222 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-25 hydrographs being very 'blocky' or square looking. This occurs because the time step at which the data was collected was too large. Note that all these storm events are small (less than 1 year ART). Table Summary of Results for Jamison Park (LR) (IMP =.21) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12/ S/9/ /1/ /4/ /1/ /1/ /1/ /4/ /4/ /2/88B /2/ /5/ /4/ Mean 3.58 StdDev 2.8 I Hydrograph I I Hydrograph] I Hydrograph I 1.8. b.4.2 i N j i 1 Jt; Tm{rm).Cateiialad.Racordad?.15 - I I Hma(iriri) \a«*<* jamaonpw»** LVart Tana(rrfn) Jarooi Fart M* &ranl ikon PafkMP-.21

223 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-26 I Hydrograph a(irai) Tlm(irin) Hyetograph I I nma(rrtn) Pa* IM P Event RaWsl so lao I- r. - 1 Hyetograph 1 TlmB(n*i) Jamison PsrklMP Event DRaMaJ 1, S. 1 Jearteon Park MP-21 T-l-87&ert [Hyetograph] ^ I Hydrograph I L - 1 Aft. J iml 7kna(irai) f, 1 2,V,VL phyetograph I Hydrograph.8,6 w n J rv-v. V-r> SO nms(rrin) Hyetograph I CateuMsd. I Hydrograph I.2S L fl.2.15 K \k /W.1.5 NJ 7 VV , I. A _ Calculated _ RaWsB I I T T *! m : nrhrrfell Jamison Parte lwp-21 1-SJ37 Brant ijarrmon Par* MM12I t-f 2-87 Brant Jamison Perk IM P Event tme(mt.) 1 Ttia(nti) ParttlMP.-21 T-T-M Evatn pramal IS. It flu ORHnfad On JsrrfconPirHMMD.21 i-*-aa event Jsmeon Psht IMP Event Hydrograph I K1214 Tima{n*)) VI I In Jamxm Park M" Evarl RaWal 8-4 f 2 & "nil nil I Ctalr Jon Pert IMP Event i Hyetograph prawal In n n n M i w s Jamison Park IM P MB Event 1 Hyetograph 1 h rtm n RaMtf

224 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-27 Hydrograph I I Hydrograph I I Hydrograph I.4 ~ J SO 1 Tsm(rrin) Tl-ne(rrln) Tim(mn) i ED LL Rirrfsl Jamison Perk Ml P B Event Jamison Park M P Event Jamison Park IMP-2\ Event 1 Hydrograph 1 I Hydrograph 1?.8 ~Z.4 %.2 If* _Racordad?.3 1 V Tlrna(frtn) Hyetograph 1 1 Hyetographl 2- - S. s - r 4-2. n ORamfal 2.5 f 2 > 1 s 1 '.5 - Perh IM P-.21 Jamison Park IM P-.21 8*88 Event Event Figure Single Peak Events for Jamison Park (LR)

225 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Results for the Melbourne Catchment Vine Street The mean parameter C for Vine Street was found to be with the values ranging from 2.57 to Again, this catchment produced the highest parameter C values of all the catchments. Figure 7.17 shows the plot of parameter C against the peak recorded discharges. There is a fair amount of scatter in the results, but no trends to indicate that parameter C varies with the size of the storm. But, a trend was obvious between C and the runoff volume ratio. For impervious events, a higher parameter C was needed to balance calculated and recorded runoff volumes. Table 7.9 shows the calibration results obtained. The reason for this is possibly that the directly connected impervious fraction is too high, causing WBNM to overestimate the discharges and high parameter C values are needed to reduce the peak discharges. 12 o 1 i: S 4 Plot of Parameter C against Qrec 1 e 14 1«l.S S 2.6 JvTne Street IMP-.311 Qrac(irtya) (a) o'.r be. I 6 " Plot of Parameter C against Vper/Vtot O.S O.B * 4 - VperJVtot s^* 7... Vme Street IMP-.311 (b) Figure Plot of Parameter C against Flowrate and Ratio for Vine Street (LR) Figure 7.18 shows the hydrographs and hyetographs. In all the cases, the hydrographs follow the temporal pattern of the rainfall hyetographs, with very good hydrograph fit being obtained for events 15/2/72, 4/2/73, 15/5/74 and 7/4/77. The event on the 8/11/87 was a three burst event with the final calculated runoff burst being smaller than the recorded. In the constant loss rate modelling, this burst was totally cut off by the high rainfall loss applied to balance the runoff volumes. proportion will be tested to see if there is an improvement in hydrograph fit for such events.

226 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-29 Table Summary of Results for Vine Street (LR) (IMP =.31) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 15/2/ /2/ / B /1/ /12/ /11/ /4/ /1/ /9/ B /12/ /11/ Mean 5.19 StdDev 2.39 Hydrograph Hydrograph Hydrograph _ calculated _ B _ Calculated. s 1.5 _ Calculated _ Tfre(rrin) 2 4 rnb(rrin) Time (rrinj Hyetograph Hyetograph Ra'irfaB 3 c 25 - f 2-1S I 1 Q Rainfal T«r»(rrin) Vine area l*>= Brent Tare(mn) Vile Street M>= Event TiiB(mh) Vine Street MF>= Brent Time (rrin) TirrB(rrin) Tirre(rrin) Hyetograph Hyetograph Hyetograph ; 4. I 2. TnB(mh) Viie Street avf= Brent U -J Rairt at = 4 % 2 Time (mil) Vine Street M*= Brent Rainfal 12 C- 1. f 8-6. <. g 2. ol T«rB(rrin) Vine Street IVP= Brent Rainfal

227 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-3 Hydrograph Hydrograph Hydrograph L Trre(rrin) _ Calculated _? C.5 JSm TaiB(mn).Calculated. i Time (rrin) _ Calculated _ Hyetograph 6 Vine Street rjp= Brenl 4. Rainfal 2 1 l_i^ Tire (rrin) TUB (rrin) Tare (rrin) Vine Street IMP= Event Viie Street M»= Brent Hydrograph Hydrograph Tins (rrin).calculated. I 2 2 m V 1 2 Tvre(rrin) _ Calculated. Hyetograph "ill Tki Trre(rriri) Vine Street l^p=.3i Brent Tine (rrin) Viie Street Mfeo Brent Rainfall Figure Single Peak Events for Vine Street (LR)

228 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Initial Loss- Proportion Results (RP) Results for the Canberra Catchments Curtin The mean calibration parameter C for Curtin was found to be The value has slightly decreased over the loss rate model which had a mean parameter C of (section ). As can be seen in figure 7.19, there is a small amount of scatter in the results, but no strong trends. Parameter C is slightly higher for more impervious events (figure 7.19b), but the trend is not as strong as it was in chapter 4 when the impervious areas were nonlinear. Table 7.1 summarises the results. (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Curtin (RP) One noticeable improvement in the hydrographs was seen on 15/1/83 (see figure 7.2). This event produced two distinct rainfall bursts some time apart. The runoff proportion model compensated for the differing rainfall bursts and both the hydrograph peaks calibrated well. In chapter 4, WBNM averaged the loss rate over the whole event, which produced a smaller calculated peak discharge for the minor burst.

229 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-32 Table Summary of Results for Curtin (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 26/1/ /2/ /2/71..8S /2( /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1 /B1..18 D /1/ Mean.75 StdDev.32 Hydrograph [.Hydrograph] _Cifcutatod 12 1 _atuttw _RpcordM 3 1 _C*tutat9d _ 1 ~ so 1 - l! Evwrt 1 ISO 2 25 TlrT»(rrin) 1 Hye tograph I II arfflwil. (rrtn) T-rm(rrtn) Curtin IMP-O EvMt Tirm(rrtn) 2 Curtin IMP Ev*nt Tkm(rrtn) too 15 2 Th»(rrtn) nrr»(rrtn) Curtin IMP 1«-72E ICurtlr. IMP-O Event Tim* (rrin) Curtin IMP Evtnt Tim (rrtn)

230 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-33 I Hydrograph I I Hydrograph I I Hydrograph] f" J. eo 1. Tam(rrin) I Hyetograph BO 1 12 Tm(frin} Tlrm(rrin) Curtin IMP Emnl Thm(nin) : [ I h-j-innnrwttlmi(mjn) Curtin IMP-O.17 6-*~77Ev*rrt Curtin IMP Evant TW(rrtn) 5 1 ISO 2 25 Tlrm<rrin) Tina {rrtn) jyblm. CurWit IMP Ewnt icurtfnimp Evwit Curtin IMP-O.17 I Ewnt Figure Hydrographs for Curtin (RP)

231 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Mawson The mean parameter C for Mawson was found to be which is a slight reduction over LR modelling. Figure 7.21 shows there is some scatter in the results. There is a slight trend between parameter C and the peak discharge. The more impervious events required higher parameter C values. Table 7.11 shows the calibration results. [Plot >r Parameter C against Qrec I [Plot of Parameter C against Vper/Vtot I 1.2 O S i - e.2 a» *.8 luawaonii Mawaon IM P-.21 (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Mawson (RP) Plots of the calculated and recorded hydrographs along with the rainfall hyetographs were prepared for each of the calibrated events to determine the performance of WBNM. An improvement was seen for the event on 6/1/81 (figure 7.22) because runoff proportion allowed some pervious runoff after the peak. The high loss rate removed this rainfall in section , and the shape of the hydrograph suffered. Table Summary of Results for Mawson (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 13/2/ /3/ B /11/ /1/ /4/ / /3/ /1/ /2/ /1/ /1/ Mean.53 StdDev.38

232 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-35 I Hydrograph I I Hydrograph I I Hydrograph 25 - f\ rg 2 _ Calculated 15 u 1 V^ _Racorde<3 i: \\ V, i,. >=fc 2 4 BO 9 too 12?" 2 1 L *T\ A / >** -1\ 5 1 ISO 2 flmtcirtn) _ Calculated _Raeortted!.. a 5 1 i > TVra(irin) Hyetographl 1 w.4» 2 & (1 [ 1 jfhjv.111 ;"awai HMIMM> brant l*waonm* E»ar«I Hydrograph I 1 Hydrograph 1 Tkna(nvi? 4 a 1 2 o 1 =/^, 1 2 V, 3 4 Tlrr.(rrin) t Hyetograph I QRiWifl WtawiwntVPO Br fit Mwraon MM) Bran. I Hydrograph I I 5 IJV _ T2 1 Cat listed.ftecanted 1 Hyetograph 1 lantann MP Evwrt Trmfrrwt) 1 5 n MaWanMM> yam IK FteWal ; *WtonlWP" Evart [Hydrograph IHydrograptil BO 1 12 Tkm(rrtn) A Tim (rrin) Mlm aon W.21 S-2-SIBranl nrdnn»jl Th»(Frfn) RaMaJ Maw»on MMI Brart Figure Hydrographs for Mawson (RP)

233 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Long Gully Creek The mean parameter C for Long Gully Creek was found to be There is a large of amount of scatter in parameter C between 3 and 5 m 3 /s, and it can be seen that there is a trend between parameter C and the peak discharges (figure 7.23a). This trend occurs for events which contribute more impervious area runoff (Vpe/V,,,, <.5) (figure 7.23b). This also occurs in the LR results. Table 7.12 shows the calibration results. 1 I 2 1 Plot of Parameter C against Qrec 1 * * Qrac(m3/a) jlong Guly Craak IMP-.5J V I 2 8. Plot of Parameter C against Vper/Vtotl *.2.4 o.e.b 1 Vpar/Vtot Long GulV Craak IMP-.5J (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Long Gully Creek (RP) A slight improvement in the hydrograph was noted for the event on the 5/2/71 (figure 7.24). The small rainfall burst at the start of the event was retained by the runoff proportion, producing a better calculated hydrograph. The rest of the hydrographs were very similar to the LR results.

234 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 1-31 Table Summary of Results for Long Gully Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 26/1/ /2/ B /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ X 5/2/ /1/ /1/ Mean 1.59 StdDev Hydrograph a 1 1 >. \ 4 V TVr*(rrtn) 1 Hyetograph ^J V- _Cateut»t«J _ 5- s Long QJ* Craak Brent MMJ.5 I lobamal i. r f\ I Hydrograph I iv km(rrtn] Tlmt(rrin) Long Gully Cmafc EvwrtWPH> Tint (rrin) Hyetograph % 4- Jl n**** Trm(nin) Long *y Craak brant M*O.S Tjm(irtn) Tkm'nti) Long Guajr Craak Brant KP4.5

235 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-38 I Hydrograph I _Csfcula1ad.ftocorctod 5 1M ISO 2 25 Tkm(irin) _ 4 I! 1 Hydrograph -ftv k, Hyetograph 1 _CslcuWad Hydrograph 1 \.K «4» S 2 I, Tltm(rrtn) 1 * l 4» 'rrr \ QRaWaa Long Cully Craak ErantlMP-O.OS Long Gu»y Craak 6*77 tvanl IMOi Long G*iry Craak Btant MM).S Hydrograph _C»icut«tad _Racwdad _Catu*tad _Recoroad Tina (mo] 1 Hyetograph 1 "S - QRaWal Long Guly Craak & art **P«. OS T1ra{rrtn) [Hyetograph Long Gully Craak Evant IMP- OS Tkm(rrtn) Long GuDy Craak Event MP-.5 I Hydrograph I I Hydrograph] Km Tlrna(rrtn) 1 Hyetograph i" F 1 i. Tirmfrrtr.) O Rainfall 1 2- I" prawal Long Gully Craak Evant IMP-.5 Long Guly Craak Brant MMKB Figure Hydrographs for Long Gully Creek (RP) Giralang The mean parameter C for Giralang was found to be Figure 7.25 shows there is some scatter in the results, but no strong trends. The values have again reduced over those for loss rate modelling (chapter 7). Table 7.13 shows the calibration results. No obvious improvements in the hydrographs for Giralang were noticed over those modelled with the LR model. Figure 7.26 shows the hydrographs.

236 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Plot of Parameter C against Qrec 1 1P lot of P arameter C against Vper/Vtot 1 o * * * Orac(lrO/a) G«an IMP-^2 o 2 i I 1.5 I 1 -m OS GtT*rang IMP-.22] Vpaf/VW (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Giralang (RP) Table Summary of Results for Giralang (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 27/3/ /1/ /4/ /1/ /3/ /3/ /1/ /2/ /2/ /1/ /3/ /1/ /12/ /3/ B Mean.72 Std Dev.66

237 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-4 Hydrograph] 2 4 SO 8 Tma(n*>) l K 1 1 Hydrograph 1 Hydrograph [Hydrograph].4 5" SO nma(rrtn) TLma(rrin) Tkra(rrtn) Gating MM Brant 15 S 1 I' L^jJl bk _ Giralang IVP Evant Glmlang IMP Evant I Hydrograph J Hydrograph I _ Calculated _Racordad 2 4 CO IVm(inn) 2 4 SO Tbna(rrtn) Hyetograph SO nrra(mn) 5" s» i" - m Giralang IMP Evant QraLwo IW-O Ev art I Hydrograph I I HydrograpM I Hydrograph] r.1 _ Cat u Wed _Racarda<l > o.i SO 8 1 DO 12 lira (rrin) TVnjflT*) r Hyetographl so 2 i» -. i n Giralang lmp-_ Evant tlmt(irtn) Glra»nglVP Ev art,5 4-1 S 5 ;J,Mm G*ralmngMM) Evanl RanfaB

238 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-41 ^8 t 4 o *' _ 1 Hydrograph 1 /A fl \A ij \f\ ft * \ "// >*. // Tbna(rrin) 1 IA 2 4 Tkna(mh) Hydrograph! I, J,,^-r> _CalcukaKl _Raeartad QroMal RaWal l-^-nnn Graar-3 IMP Evant Gaalang MMI ^4 Evtrt Figure Hydrographs for Giralang (RP) Results for the Sydney Catchments Maroubra The mean parameter C for Maroubra was found to be Figure 7.27 shows the plot of the parameter C against the recorded peak discharge and ratio of pervious and total runoff volume. Table 7.14 shows the calibration results and figure 7.28 the hydrographs. 1 Plot of Parameter C against Qrec 1 I Plot of Parameter C against VperA/totI o «a 1< L 2 ( * * MaR>i*MalMP-.16 *. i, i OS Qrac(m3/a (a) o» * & 2 ( (Maroubra IMP..18 * Vpar/Vtot (b) Figure Plot of Parameter C against Flowrate and Ratio for Maroubra (RP)

239 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-42 Table Summary of Results for Maroubra (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 1/3/ /3/ /3/ /3/ /3/ /4/ /5/ /6/ /6/ /3/ /6/ /11/ /11/ /12/ /5/ /4/ (7/ /1/ /4/ /4/ Mean 3.23 Std Dev 2.1 A slight improvement was noticed in only the event on 17/3/78 (figure 7.28). The rest of the hydrographs were similar to the LR results. Hydrograph Hydrograph _CafcuMad _RKordad Tarn (rrin) 2 4 Tkm(rrai) [Hyetograph Tlrm(mn) Hyetograph 1 S 1 RaWan,.rf yiltri Tim (rrtrt) ar***! MBrsxijra UP- W ferart Event \tar<xi*- hf>-q Evart

240 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models ISO 2 TVna(rTB-i) Tara(rrtn) I Hyetograph [Hyetograph I 4 _ Tlma(rrtn) v TTma(rrtn) 2. L -jfhvjl. Tin* (rrin) Uaroubra IMP-, Evant Mareubra IMP Evant Manoubm IMP- 1 e S-3-77 Evant Hydrograph Tirra{rrtni Hydrograph s «& Maroubra (MP-.1BI Evant th- TJrnj(rrtn) 1 Hydrograph QRsHaft L [ RaWal j Trra(rrtn] 1 Hydrograph 1 Maroubra MP-.16] Evant Tiff, (rnri) A?.6 o.4 1 ' " f\ 2 - A J S^>> V Tin*.* _Cafcutta _Racofad I Hyetographl IHyetographl t IM P-.1 C 2 X 15 too vant Bra*. \ * ' Ralrtfafl &2 I" nn n Maroubra IM P *83 Eva* lorrtifrt 1 Hydrograph 1 1 Hydrograph 1 1 Hydrograph 1 f" 7 2 "3».1 : A. 2 4 e 71mt(rt*i) D _ CafcuWad _RKordad I" 2 1 I OS ( h 1 2 3C Tkm (rrtn) 1 _CllcuMad «I" JKA 1 2 3C TrmB(rrai) ro _CalcuaTta<l I _RBcordad 1 Hyetograph 1 mjif r»(rrtn) Mamubn IMP Evant TV f 1 or*** I s : il Maroubra MM) En or* TJma (irtft) JQRaMtf I 5 ** 1 * 3 3- MroKira MM MBiart nm»(n*>) a*&«*

241 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-44 I Hydrograph I Tln»<nlr.) I Hydrograph I _CaleUkt«<l _Racordad 1.2 1'..8 * «.6 i" C :J.2 1 Hydrograph 1 L _Cafcuktad _Raeonted Tar»(rrtn) Maroubra IMP-.16 Mareubra NP W8 Evant Evant Evant Hydrograph Hydrograph I '- _C«fcu*at«i _Racordad Tkna(rrtn) TlrnB(rrtn) fhyetograph I 12.. y too.. ] 1 ' : niyhljlaaji RaWH I Maroubra MMJ aeEvart Maroiira r*- is 2W-88 Ev.nl Figure Hydrograph for Maroubra (RP) Strathfield The mean parameter C for Strathfield was found to be Figure 7.29 shows the plot of the calibration parameter against the peak recorded discharges and runoff volume ratio. It can clearly be seen that parameter C tends to be higher for higher discharges, as occurred in the LR results. The events that produced these high values (4/6/86, 3/4/88, 13/2/88 and 28/4/88) were all large (total rainfall depths between 42 to 139mm). But these trends are not very strong. The hydrographs obtained for runoff proportion modelling were very similar to those in chapter 7. Table 7.15 shows the calibration results and figure 7.3 the hydrographs. O 3 * m ( 1 Plot of Parameter C against Qrec 1 * 5 1 IS 2 Orac(mVa) a r ( 1 Plot of Parameter C against VperA/tot 1 -,»,» Vpar/VM jstrathnam IMP-O_29J Sttath(laid IMP-C28 (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Strathfield (RP)

242 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-45 I Hydrograph I 1 Hydrograph 1 i 7; P ' A * : /k _ Calculated _Racoroad _CaCuat»d _Racordad lrra<rrai) [HyelDgraph I Th»(irin) Trna mm] Tmi(r*>) StralrrlaM IMP-29 SoatftlUM IMP-2v Sfiatftflald IM P-.29 3*^7 Evant Evant Evant Tkna(irtn] Tlma(frin) Time (mh) 1 Hyetograph 1 1 Hyetograph 1 Strain (laid IMP Evant -= = 6 r 4 '"..I Strathflald IMP Evant n!, 1 15 io c 5 Strathflald IMP Evant i jf m- fjrhnlall Trra(mri) Tlma(rrtn) Hyetograph I 1 Hyetograph Jk.i ^^ Rahfal

243 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-46 I Hydrograph I I Hydrograph] I Hydrograph I 1 a - / «- 4 2 b. - \[ ]/ \v N^ i>,,>«sor _C»fcutatod Racordad.CalcutaM.Ftecordtd Tfene(r*i) Tbm<rrtn) StrathfMdM^^ Evart Strathflald IMP-.29 1*85 Evant I Hydrograph I Hydrograph I I Hydrograph I IV _RKxrd*d _CMeuM«d _RacordM I" k (rrin) Tkn(rrtn) Thna(rrin) I Hyetographl 1 Hyetograph 1 a*"* -j. 12 f 1 I 8 r 6 S «A 2 _ - 1 StntnflaM IMP Evant StrattifWd IUP>^ Evant Strsmflald IVP» Evant Figure Hydrographs for Strathfield (RP)

244 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 1-41 Table Summary of Results for Strathfield (RP) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m'/s) 3/9/ /9/ /3/ /4/ /4/ /4/ / /3/ /9/ /3/ /5/ /4/84 O.OO /1/ B/11/ /5/ /4/ /8/ / /4/ /4/ Mean 1.22 StdDev 1.

245 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Fisher's Ghost Creek The mean parameter C for Fisher's Ghost Creek was found to be Figure 7.31 shows the plot of the calibration parameters against the peak recorded discharges. As can be seen, this catchment has a low amount of scatter and parameter C has reduced. There was no noticeable improvement in thefit of the calculated and recorded hydrographs for runoff proportion modelling. The event on the 13/12/83 produced a poorer fit than for the same event when modelling with LR. This was a totally impervious event, with a calculated runoff volume more than twice the recorded. With LR, the volumes for the same event balanced. Table 7.16 shows the calibration results andfigure7.32 the hydrographs. I Plot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtotl 1 [fiartaraghoat Craak IMP-.251 I Rahara Ghoat Craak IMP-251 (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Fisher's Ghost Creek (RP) _ I, I Hydrograph I w JV/V Tkm(irtn) i 2 I Hydrograph I I ft 1 _C-lcuMad \\ 1 /il K M^ *Tm(i*i) I Hyetograph I"- I 9 - J ClaiM S 1. S 1 _ TwTmt (fflbj F*rw» Ghost Craafc Brant I FlaWaGho*: Craak 4-W1 Evant IMP-.25 Planar Gho* Craak Evant IMP-.25 i Hydrograph I Hydrograph Tm(rrtn) Raw*Gho* Craak 25*12-81 Evant IMP- 29 Rfhar*sGno* Craak Evant IMP-.25 il: i : :BiiLiiiJu JU Fiahsf'a Ghost Craak Brant M * 25 i Rwrfall

246 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-49 I Hydrograph I I Hydrograph I V nmtflrt.) Hyetograph Rater's Ghost Crssk Bfsnt WFHD.2S FlfiW* Ghost Craak 27*11-83 Evant IMP-2$ %9 4 - «LJ L- Rahara Ghoat Craak Evant IMP-.2S 1 Hydrograph 1 SO Ttow(rnln) -. 4 #Vv Ax I. S 2 X I, - / \ V V^: _//,, T T*m(nai) LML^. Ft-harsChott Craak Evant IMP-.2S R-hafaGhoat Craak Evant IMP-.25 Tmafrrtn) RaWsGho ft Craak Evant IMP-.25 Hydrograph I i: ^v 5 2 i, SO Tlms(irtn) I Hyetographl _Racordad >re (rrai) RfhartGho* Craak Evant IMP-.25 R-hoT* Gho* Craak Evant IMP-.25 Rater's Ghost Crssk Evsnt MMX25 i 'Mk 1 L Ofatifaa t Ghoat Craak &anlmm).25 Hyetographl 2 4 < Ttm(rrai) FwatC^MOMk 1 a.114 Evant M P-^S i E 2 8 jlii Hyetographj DHan'a" Tir»(mn) flahara Ghoat Craak E»ant MMJ2S

247 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-5 [Hydrograph] Tkna(nai) Fahara Ghoat Craak M4etVantM*al25 IJhlLiu. RahaTa Ghoat Craak 24-5J8 r»ant MMJ.25 nnamm Figure Hydrograph for Fisher's Ghost Creek (RP) Table Summary of Results for Fisher's Ghost Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 2/11/ /5/ /1/ / /3/ /3/ /3/ /11/ /12/ B /1/ /2/ /11/ /11/ /12/ /1/ /8/ /11/ /1/ /6/ /5/ Mean 2.11 StdDev 1.24

248 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Jamison Park The mean parameter C for Jamison Park was found to be Figure 7.33 shows the plot of the parameter C against the peak recorded discharges. There is large amount of scatter in the C values for the small events, which was also found in Maroubra. This may indicate that the model may be sensitive on small catchments, and the results from Vine Street may support this. Table 7.17 shows the calibration results. Plot of Parameter C against Qrec j 1 Plot of Parameter C against Vper/Vtotl to 1 -*. *; ;* v f. ( fjamawn PsricMP-.211 OS Qrac(mya) (a) 1 - *.2 * Vpsr/Vtot (Jamaon Park IM P-.21 (b) Figure Plot of Parameter C against Flowrate and Ratio for Jamison Park (RP) Figure 7.34 shows the hydrographs. Poorer calibration was achieved for the event on 7/11/84 compared to the LR model, where as better results were obtained for 9/4/88 compared to the LR results. As the runoff proportion model retains the pervious area rainfall temporal pattern, the second peak discharge was retained in the calculated hydrograph, where there is only one peak in the recorded. For the LR model, the second burst was calculated, but was not as predominant. Note however that two distinct rainfall bursts like this would be expected to produce two hydrograph peaks. This indicates that the recorded data may be in error for this event.

249 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Hydrograph I [Hydrograph I H>drograph! 4 _CaJculatsd.Rseordsti I "«-i _Calcutslsd _Racordsd Tkna(mh) 71ms (rrtn) TYnafrm) I-- Tai»(i*) Jairtaon Park W MJ Brant [Hyetograph I i njl. Jsmaon Park WP & art "15 _ =- 1 IE 5 n E irrasan Park IMP- J1 3-6-M Evant Hyetographl QRiirrfal Tlm»(rrir,) Time (rrin) rhyetographl 1 4 _ 3 3. Q Rainfal = 2. 2_ 1 _ 2 1. Jamlasn Park tu P-.21 Jami.cn Park IMP- 21 Jtrmon P»rh IVP Evan) Evant Evsnt I Hydrograph I I Hydrograph I I Hydrograph I JO.!!? 7 o.i o.5 ( Tims (rrin) r^aflla-wt _Rscordsd ~.6 % ^ ( Ttoa(irai) _Cati4>tad _Rscordsd vh - 2 %.15 S oot ISO 2( 1 Ttm(i*) _Catulatad [ M t Hyetograph I 1 Hyetograph j Hyetograph J I:: \JL-L Tkra Jamaon PsrK MH *S7 Evsnt (rrtn) I^I j. 12 if a < mm m 2 Tamil*) JantaonParkMMl er &ant nr*wsb S & 2 Time (rm) Jamlaan Park IMP Evsnt n n jaratnal Hydrograph I Hydrograph I [Hydrograph].2$ f ",.15 a o.i.5 _Catuatacl ^Rscontod?o.oe _ f Tims (rrtn) 1" Siol. I! frllll On Tlma{rrtn) Jamttvon Park IVS^O.M \ai*mii 6 Hyetographl J] I II lli Tina (rrin) Jamaon Part M>a.21 Ftamroi Brant Evant

250 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-53 I Hydrograph I I Hydrograph] _Cafcuialad _Ffccordsd 1 ' r < Tin* (rrin) Tbni(irin) lima (rrin) 1 Hyetograph 1 1 Hyetograph 1 ru TV* (rrin) janamal I 1 s 4 I 2 \u\ IflflRfl >" J 4 fl» h limn,n RUrfal Jamison Park MP Evant Jamson Park IM P Evant Jamison Pan. IM p Evanl TkntCirin) I Hyetograph I Hyetographl 1 Hyetograph 1 I:.C 2 & 1 5 S 6 nn r m n n R*W JarraBnPsrkMP BEvanl Jamltvn PartlMP B Evan) Jamison Pan. IM P Evant 1 Hydrograph 1 Hydrograph ffx? Hyetograph SO Tkm<[rtn) _ 6 - F 4 - S 22-. n Rahlal Jamiaon ParkMP-^1 S-3-M Evant Jamiaon Park IM P Evanl Figure Hydrographs for Jamison Park (RP)

251 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 1-54 Table Summary of Results for Jamison Park (RP) Event Pervious Initial Pervious c Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12rB /9/ /1/ /4/ /1/ /1/ /1/ /4/88B /4/88B /2/88B /2/ /5/ /4/ Mean 3.19 Std Dev The Melbourne Catchment Vine Street The mean parameter C for Vine Street was found to be , which is lower than the value obtained from LR modelling. The event on the 29/12/75 was a totally impervious event with the calculated and recorded volumes not balancing, and was omitted from the study. Figure 7.35 shows the plot of parameter C against the peak recorded discharges and the runoff volume ratio. As can be seen, there is a large amount of scatter in the results but no trends between C and discharge (figure 7.35a). On the other hand, there is quite a strong trend between C and the runoff volume ratio (figure 7.35b), similar to that observed in the results for LR.

252 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-55 Vine Street, Maroubra and Jamison Park catchments all had large values of parameter C, and all are small catchments. This may indicate that the size of the catchment may be causing parameter C still to be high, especially on smaller catchments. This will be investigated in chapter 9. The hydrographs obtained from the runoff proportion modelling were all very similar to those in the LR modelling. No major improvements were noticed. Table 7.18 shows the calibration results obtained. I Plot of Parameter C against Qrec I Plot ot Parameter C against Vper/Vtot o» I S IVInaStiaat IMP-.311 Qrac(iiOfa) o» * I ' \flna Straat IMP-.31 I (a) (b) Figure Plot of Parameter C against Flowrate and Ratio for Vine Street (RP) [Hydrograph Tims (rrtn) K^ _CafculBtsd 4 8 _ TlrTa(mh) RUnTa! Tfcm(rrtn) VhsStrsstlvP-a Brsnt VhsStrsetMMli Brsrt Vna Straat MP Brsrt?" 1 2 I OS I Hydrograph I Ai r i. ^ / \ hr»<rrtn) I Hyetograph l I HyetographJ 1" T 1 o.s Hydrograph h~ Hyetograph vha Straat MM) »art LJ1 I \a KMI - : -M 1 Trra(irai) Vrw Straat MMJ SeVar< * 1 - F nil ITn s *> VM Straat MM)J Bart QRahfal

253 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-56 Hydrograph I [Hydrograph I I Hydrograph I Tana (rrin) 1.5. i. _ Calciilatad _Racerdad Ttaa(mh) K\ s* f\ II \\ i' r \\ 7 J ^-. r- too 15 2 Tlma(rrtn) DtaWrii ORtanisfl QRsMsi Tkns(rrin) Vina Strsat rvp-o evant Ina Straat IM P Evant Vna Straat MP Evant Hydrograph 1 I Hydrograph I A. i 1 \(.. 7~*= SO Tina (rrin).cslcutatsd 1 2 TfeT«(n*i) _ Cafculstad Vlns Straat ivp Evsnt Vlns Straat MM Evsnt Figure Hydrographs for Vine Street Table Sumn iary of f Results for Vine i Stre< *t (RP) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (thoum 3 ) (thoum 3 ) (mvs) (m 3 /s) 15/2/ «2/ /5/ /1/ /12/ /11/ /4/ /1/ B /9/ /12/ B/11/ B Mean 4.84 StdDev 2.33

254 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Discussion of Fully Nonlinear Modelling against Nonlinear Pervious and Linear Impervious Modelling using Loss Rate Model In chapter 4, the folly nonlinear runoff routing version of WBNM was used to calibrate ten events on each of the seven catchments. A comparison between those results and the results obtained in this chapter will now be made. As explained previously, WBNM originally ran at a nonlinearity of.23 for both the pervious and impervious areas. After studying the results in chapter 4, it was concluded that WBNM was not performing very well, particularly because the calibrated parameter C values appeared to be too high. It was decided to investigate the changes required to reduce the parameter C values. As the pervious part of the catchment has been extensively tested in the past, it was assumed that i performance was satisfactory, and the new impervious module was causing problems. This fact was also confirmed in the plots of parameter C against the runoff volume ratio. In most of the plots in chapter 4, there was a tendency for parameter C to be lower for events where the majority of the runoff was being contributed from the pervious areas. It was decided to run the impervious portion of the catchment linearly and retain the nonlinearity of the pervious part. By doing this, the lag time calculated by equation 2.31 was not as small as previously calculated and therefore the multiplying factor, parameter C, did not have to be as large as it was in chapter 4. Table 7.19 shows the mean parameter C values obtained before and after WBNM was rewritten. In all the catchments, the mean parameter C value was found to decrease. Long Gully Creek has the lowest imperviousfraction and modelling with the modified WBNM code produced a smaller change in the overall results compared to the other catchments. Curtin is the largest of all the catchments at 27 km 2 in area. In chapter 4, modelling with the nonl version of WBNM produced a mean calibration parameter C of In this chapter, the mean calibration parameter C obtained was.85, a reduction of more than half. Note that the large discharges in Curtin act to reduce the nonlinear lag time from equation 2.31 quite considerably. Therefore the parameter C in chapter 4 had to be quite large to compensate. The fit of the calculated and recorded hydrographs for the nonlinear pervious and linear impervious model was generally better than the old model, indicating the changes to the model to be satisfactory. The most dramatic change was seen in the Strathfield catchment with parameter C reducing from 3.16 to The main reason for this is the high impervious fraction of Strathfield (.29). The majority of the events produce more impervious than pervious runoff, and these discharges act to reduce the calculated nonlinear lag time, again requiring large values of parameter C in chapter 4. The changes in WBNM have helped reduce C by a large amount. Overall, the mean parameter C value has reduced from 2.27 to 1.63.

255 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-58 Table Parameter C values for Differing WBNM Models Catchment LR (ch4) LR (ch7) RP (ch7) Curtin Mawson Long Gully Creek Giralang Maroubra Strathfield Fisher's Ghost Creek Jamison Park NA Vine Street NA Mean 2.27* 1.63' 1.49' Mean NA 2.18* 1.99* ' excludes Jamison Park and Vine Street parameter C values * includes all catchments Figure 7.37a shows the plot of parameter C against the peak recorded discharge for all the catchments. There is quite a large scatter in the results, but it must be noted that the higher C values are for the small Maroubra, Jamison Park and Vine Street catchments, with considerably small discharges. Events producing more than 25 m 3 /s peak discharge all calibrated with a parameter C below 2.. Again, the smaller events, with discharges less than 2 m 3 /s tended to produce some scatter (figure 7.37b). Plot of Parameter C against Qrec Plot of Parameter C against Qrec o - ' T»f *%, a, 1 15 Qrec (nro/s) Qrec (nrg/s) 2 I Split Modelling, Al Catchments Spirt Modelling. All Catchments] (a) (b) Figure Plot of Parameter C against Flowrate for all Catchments with Loss Rate Model In figure 7.38, parameter C is plotted against the runoff volume ratio. When WBNM was running fully nonlinear (chapter 4 figure 4.21), the impervious events (Vper/Vtot=) consistently required very high parameter C values. From the figure, it can be seen that this trend has largely been eliminated, although there is still a slight tendency for events with more impervious runoff to require large C values.

256 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-59 Figure Plot of Parameter C against Ratio for all Catchments with Loss Rate Model 7.5 Discussion of Proportion Modelling with Nonlinear Pervious and Linear impervious using RP This section of the study investigated the ability of split pervious/impervious modelling with the runoff proportion rainfall loss model to be used for urban catchment modelling. The conclusions drawn from the findings are detailed below. In general, split modelling with the runoff proportion rainfall loss model did not dramatically impr the fit of the calculated and recorded hydrographs but it did help to preserve small peaks on the hydrograph caused by very small rainfall bursts. The reason for this is with the loss rate model, the small rainfall bursts are cut from the pervious area hyetograph, but there is always runoff from the impervious surfaces. A slightly betterfit was noted in some events with a decrease in parameter C for all the catchments. This indicates that using the runoff proportion model may be better in urban catchments because minor bursts in the hyetograph are retained. This helps the shape of the calculated hydrograph because in urban catchments, the recorded hydrograph closely follows the rainfall temporal pattern. Figures 7.39 and 7.4 show that the problem of high parameter C values for small catchments is still present. From the results in this chapter, the catchments responsible for high parameter C values are Maroubra, Jamison Park and Vine Street. These are the smallest three catchments studied. Most of their events produce more impervious area runoff than pervious area runoff because these catchments have fairly high impervious fractions.

257 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models Plot of Parameter C against Qrec og^kkivy «* i Qrec <m3/s) I Split Catchments Proportion I (a) 2 25 o I - «> Plot of Parameter C against Qrec :% *4, %e.atz$* » 1 Qrec (rrfl/s) I Split Catchments Proportion I (b) 15 2 Figure Plot of Parameter C against Flowrate for all Catchments for Runof Proportion Model 1 Plot of Parameter C against VperA/tot o 8 L 2 6 I 4 ' Vper/Vtot Split Catchments Proportion].8 Figure Plot of Parameter C against Ratio for all Catchments for Proportion Model The problem of high parameter C values for small catchments has not been alleviated. A definite trend can be seen in figure As the catchment area increases, parameter C reduces, which indicates there is a problem with the impervious area lag equation (equation 2.31). 1 Plot of Cav against Total Area Total Catchment Area (km2) 1 Figure Trend between Parameter C and Catchment Area Another problem may be the impervious fraction used on small catchments with small storm events. When there is a larger storm event, all of the directly connected impervious area contributes runoff as

258 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-61 well as some part of the pervious area. But when the event is small, some impervious areas which are directly connected but flow over a pervious area before reaching the watercourse, may not be directly contributing runoff because the runoff is absorbed into the pervious area before it reaches the watercourse. Thus using the same imperviousfractionfor both small and large storm events may not be correct. Before one can explain why this is so, one must understand what the impervious areas are made up of. The majority of directly connected impervious areas are roads. Next, some house roofs may be directly connected to the road drainage. For small events, the house roof may not contribute runoff. Depending on the location of the catchment, the house roofs may be connected to absorption trenches located in pervious areas. This runoff may be totally absorbed into the soil and the only runoff contribution is from the impervious areas. But if the storm is large enough and the pervious areas are saturated, then the house roof will contribute impervious area runoff, rather than pervious area runoff, even though the house roof is connected to a pervious area. If this was the case, the higher impervious fraction will have caused WBNM to calculate more runoff, thus higher parameter C values would be required to reduce the calculated peak discharge. This could explain the results for Maroubra, Jamison Park and Vine Street. To determine if this occurs, the rainfall and runoff data for those events identified with larger C values in Maroubra, Jamison Park and Vine Street need to be studied more closely. The method by Boyd et al (1993) used to determine the effective imperviousfraction may be used to calculated a modified imperviousfractionfor small storm events. If the trend for smaller catchments to have higher C values is not resolved by the above methods, it may be necessary to modify the impervious area lag equation. These factors will be considered in chapters 8 and Conclusions The reformulation of WBNM to run nonlinear for the pervious areas and linear for the impervious areas has improved its performance. When WBNM was a fully nonlinear runoff routing model (chapter 4), there were noticeable trends in the results, especially for events where the impervious area runoff contribution was more significant than the pervious. The parameter C values were generally higher than for events that produced both pervious and impervious runoff. The events where the pervious area contributed more runoff generally produced parameter C values closer to those for natural catchments, {Boyd (1987) C = 1.7}.

259 Chapter 7 - Split Modelling with the Loss Rate and Proportion Models 7-62 At this stage of the study, the following conclusions can be drawn: 1. Split modelling with nonlinear pervious and linear impervious has improved the results by reducing the parameter C values (table 7.19), and by reducing the trend for high parameter C values for impervious events (figure 7.37 and 7.39). 2. There is still a trend for high parameter C values for small events. These high values occur on the smallest three catchments (namely Maroubra, Jamison Park and Vine Street). Figure 7.37b and figure 7.39b shows this clearly. 3. There are still some problems for events with high loss rates. As discussed earlier in the chapter, when a high loss rate is required to balance calculated and recorded runoff volumes (ie. the runoff is predominantly from the impervious surfaces) the LR model allows no pervious area runoff contribution. All runoff is therefore from the impervious surfaces with very small lag times. Dissipation of runoff is faster than recorded and the fit between the calculated and recorded hydrographs is poor. When using the runoff proportion model, better fit was obtained for Curtin (15/1/83), Mawson (6/1/81), Long Gully Creek (5/2/71), Maroubra (17/3/78) and Jamison Park (9/4/88), which indicates that for urban catchments, the runoff proportion could be a better loss model. In chapter 8, an investigation will be made into the modified directly connected impervious fraction for small storm events on the three smallest catchments. If this method is unsatisfactory, then the area exponent in the impervious area lag equation will be modified to see if a reduction in parameter C can be achieved so as to eliminate the trend in figure 7.41.

260 Chapter 8 Modifying the Impervious Fraction

261 Chapter 8 - Modifying the Impervious Fraction.^ MODIFYING the IMPERVIOUS FRACTION 8.1 Introduction In chapter 4 of the study, three impervious fractions were tested to determine the correct IMP to be used in modelling. The IMP's were derived by different methods (as described in chapters 3 and 4). At that stage, WBNM was a fully nonlinear runoff routing model with both the pervious and impervious areas having a nonlinearity of negative.23. From the plots of parameter C against recorded discharges, and also against the runoff volume ratio, it was found that for small discharges and more impervious events a higher parameter C value was required for calibration. One reason for this was because WBNM was running nonlinear for the impervious areas, it was using lag times that were too small when near the larger discharges in the hydrograph peak. Consequently it was calculating runoff peaks for the impervious areas that were larger than recorded, and high parameter C values were needed to calibrate. A number of strategies were given in chapter 4 to reduce the trend between parameter C and the discharges. Thefirst was to run the impervious parts of the catchment linearly (chapter 7) and by doing this it was found that the trend was reduced on most of the catchments. But the trend still existed for small discharges on small catchments (figures 7.37, 7.39). Parameter C was still too high for the smallest three catchments, namely Maroubra, Jamison Park and Vine Street. Two other possibilities suggested earlier were: 1. Modelling with a modified impervious fraction (as discussed in chapter 7). 2. Modification of WBNM code for the impervious areas. The results so far have shown that the size of the catchment is a problem (smaller catchments have larger C values and larger catchments have smaller C values). This indicates that the.57 area exponent may be too high. The above two possibilities will be studied in next two chapters. Modelling in this chapter was performed with the initial loss - loss rate (LR) rainfall loss model. T loss rate model was used in an attempt to improve the performance of this model.

262 Chapter 8 - Modifying the Impervious Fraction Modified Impervious Fraction Introduction The three urban catchments which produced high parameter C values were Maroubra, Jamison Park and Vine Street. These are the smallest catchments, ranging in size from.21 to.64 km 2. After calibration of events on these catchments in chapter 7 (using LR rainfall loss model) the mean parameter C values obtained were 3.36, 3.58 and 5.19, respectively. One possible reason for the high parameter C values is that the IMP is too high. If so, this would make the runoff volumes too large and consequently would require a large value of parameter C to reduce the calculated flood peaks to the recorded values. Plots of runoff depths against rainfall depth for all events on the catchments (figures 8.1a, 8.4a and 8.7a) indicate that the values determined by Boyd et al (1993) for these three catchments to be satisfactory. However, the possibility that a smaller value of IMP might apply to the smaller events was investigated (figures 8.1b, 8.4b and 8.7b). This could represent, for example, a directly connected area consisting possibly of roads only for small events. For larger events, a larger directly connected imperviousfractioncould apply. Rainfall and runoff data for the three catchments was obtained from Bufill (1989). From the data, the smallest rainfall events were identified and a modified imperviousfraction was calculated using the method by Boyd et al (1993). Modelling in the previous chapters was done using up to a maximum of 2 storm events. In this section, all the available storm data was implemented. A total of 38 storm events were available for Maroubra (figure 8.1a), of which 13 small events (figure 8.1b) were used. For Jamison Park, a total of 85 events were available (figure 8.2a) and 28 events were used to calculated the modified imperviousfraction. For Vine Street, there was a total of 11 events available from which the 6 smallest events were chosen for the calculation of the modified IMP. The results obtained and conclusions are discussed below.

263 Chapter 8 - Modifying the Impervious Fraction Maroubra The modified effective impervious fraction for Maroubra was calculated to be.12 (figure 8.1a). The effective impervious fraction for all available storms calculated by Boyd (1993) was.16 (figure 8.1b). The roadways make up 3 % of the Maroubra catchment, but the modified impervious fraction is very low. The reason for this is that Maroubra is located on very highly pervious sandy soil. The soil quickly absorbs any water. Because of the age of the minor drainage system within Maroubra, underground pipes may be broken allowing water to be absorbed into the ground, removing what enters the watercourse section. 35 I & 2 fc 1 5 o Plot of against Rainfal ~ /+}+ i i i t ) Rainfal Maroubra IMP=.12 (a) f 4 3 Q. ts * Rot of against Rainfall Rainfall imaroubra, 38 events, IMP=.161 (b) 2! > Figure Plots of against Rainfall for Maroubra The 13 events were then calibrated using the modified impervious fraction and the results can be see in table 8.1. Figure 8.2 shows parameter C against the recorded discharge and runoff volume ratio. As can be seen, parameter C has reduced from a mean of 3.36 in chapter 7 to o 8 5> 6 i 4 to * Maroubra IMP=.12 Plot of Parameter C against Qrec I I i I Qrec (rr6/s) Plot of Parameter C against VperA/tot Maroubra IMP= Vper/Vtot (a) (b) Figure Plot of Parameter C against Peak Flowrate and Ratio for Maroubra The plots show there are slight trends, with a large amount of scatter. The fit of the hydrographs obtained from this modelling is very similar to that in chapter 7. Due to the smaller impervious fraction, parameter C has reduced, but high C values are still required by the impervious events to fit

264 Chapter 8 - Modifying the Impervious Fraction 8-5 the peak discharges. Two hydrographs can be seen in figure 8.3 (events 5/3/77 and 2/6/79). The hydrographfitis similar to that obtained in chapter 7 with IMP =.16. This shows that a modified imperviousfraction may be a satisfactory way of modelling small events on small, urban catchments, but this method has not solved the problem of high parameter C values for the impervious events. It is more likely that the problem is with the impervious area lag equation and the area exponent.57 being too high. I Hydrograph I I Hydrograph I 1 Hydrograph " 1, =J K Trmirrtn)?o.e 1 2,4 o M 1aia(n*i) 1 Hyetographl f 4 s - U _rfflihjl_«* Mawoubra MP-.12 5*3-77 Ewnt woubra MP Ewnt

265 Chapter 8 - Modifying the Impervious Fraction 8-6 I Hydrograph I Hydrograph [Hydrograph] T.2 I" I 2!c 5 ^JULL Tm<rrai) Maraubn (MP MB Evwit J" 2 15 Si 1 1 K Maroubra MP Evar* 2 44 Tarn (rrin) Hyetograph 1 Figure Hydrographs for Maroubra with Modified IMP Table Summary of Results for Maroubra Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (m 3 /s) (m 3 /s) 5/3/ /3/ /3( /3/ /5( /5/78B /5( / /6/ /11/84B /11/ /5/ /11/ Mean 2.95 Std Dev 2.53

266 Chapter 8 - Modifying the Impervious Fraction Jamison Park s The modified effective imperviousfractionfor Jamison Park was calculated to be.12 (figure 8.4a). The effective imperviousfractionfor all available storms calculated by Boyd (1993) was.21 (figure 8.4b). It is interesting to note that the modified effective impervious fraction for Jamison Park corresponds to thefraction of roadways within the catchment (9% of the Jamison Park catchment comprises of roadways). This may show that for small storm events, only the roadway is contributing runoff. Water from house roofs and other impervious surfaces is probably being absorbed into pervious areas. (a) Figure Plots of against Rainfall for Jamison Park (b) Calibration of all 28 events was performed with the modified impervious fraction and table 8.2 summarises the results. The average parameter C for Jamison Park in chapter 7 was This value has reduced to 1.94 with the modified imperviousfraction. Even though the average parameter C value has reduced, a trend between parameter C and the recorded discharge still seems to exist (figure 8.5a). This again indicates problems with the impervious area lag.

267 Chapter 8 - Modifying the Impervious Fraction o e * 8 4 r 2 Plot of Parameter C against Qrec Jamison ParklMP= Qrec (trfl/s) Plot of Parameter C against VperA/tot O 6 % 4 ro ff 2 a. *^**a> -*J * * I Vper/Vtot Jamison ParklMP=.l2 (a) (b) Figure Plot of Parameter C against Peak Flowrate and Ratio for Jamison Park The hydrograph fit for most of the events was good and can be seen in figure 8.6. Most of the ot hydrographs produced good fit and were similar to those in chapter 7. 1 Hydrograph 1 [Hydrograph i -2 ftw _CUBI*M _Racontod 1 2 Tim (rrin) 1>n»(rrtr,)? 2 TTIO i Tirm{n+.) I r Hyetograph n n (n+i) I" 1-1,.15 a o.i C Jaml»n ParkiMP Evarn Evant 2 4 SO 1 Tlrna(rrin) Tkm(n*.) I" 1! s 1 Hyetograph 1 n -i Jami*>n Par*iMP» Evant..._ Jamiaon Park MP Evant J? 5 i * S ' Hyetograph In 111 Jamiaon Park MP Evant

268 Chapter 8 - Modifying the Impervious Fraction 8-9 I Hydrograph I I Hydrograph I o.oe.4 " -Ik i H \ / j. \^-^-j SO _Ca euwad _Raeordad >.6, Vr»(rrtn) Tlma(rrin) I Hyetographl in f i 1 Tto» (rrtn) iqfulfafl : Tlrr»(rrth} Tkrajfrrfn) Park IMP Evant Jamiaan Park IMP B Evant Jamlasn ParklMP Evant Hydrograph Tbra(irin) TVra(rrtn) 1 Hyetograph 1 TlmB(rrtn) T«TB (mn) = 1 I s 6 4 i 1 ranlm Jamiaon Park I Jamiaon Parte IMP-.12 Jmmtmn ParfclMP E 6447 Evant Evant [H^lrograph I V n_ IA i i i - IIAS-V B SO TV (rrtn) Tfi»(n*i) Tlma(rrtn) 'Lin D Tlma(inn) Jamiasn Park IMP- 12 Jarrtaon park MMX12 Jamaon Pirk IMP Evant Ev art Evanl.2 1" 1 Hydrograph Jlrnafmh) _Catua«aa _Racordad n 2.4 o.2 % ( 1 Hydrograph 1 n VA% 5 1 1! 4 7>m(rT*T) _CtiCUtMad _Racord*d... J, ^ low I Hydrograph I fw TVmfmh) _CatuBi«<) _Racordad 1" &2 : L. in i i-rii-i n-in TVra (rtn) Jamison Park IMP an Evant 1 Rarfan 1 i: k L i i 4 s * 1h»(irin) Jamiaon ParkMP B Evant 1 mill 1 DRiWaJI t i: 1: Hyetograph I n n ii TVm(rrtn) Jamiaon Park MP Evant 1 H»Ha»

269 Chapter 8 - Modifying the Impervious Fraction 8-1 I Hydrograph I Hydrograph Hydrograph.1..O6.4. I/V A.CaieuWad _Racordad ~.8 J L 2.4. _ Calculate.Racordad.2 I I I! ^ ^ = *».2 [ X1214 D TLm»(frfn) Tkr»<irtn) JamJaon Park IMP Evant Trna(rrtn) Jamiaon Park IM P Evart I: i 2 1 Hyetograph 1 fllli 1 Jamiaon Park IMP Evan.?s,, [Hydrograph I Tlma(mjn] J 2 1 1s S 1 I > n n Ttn»(min) I Hydrograph I A «.4 1" \K H. >>"== ' n n Jamiaon Park IMP Evant Jamlaan Park IMP Evant Jamlaan Park IMP Evant I Hydrograph I.12.!-: Jf Tim (rrtn) 1 Hyetograph B Evant S " Jamiaon ParkMP *48Eva*l 6 nn Jamison ParkiMP Evant nn n 3.6 *.6 * C.2.4 I Hydrograph I /V '/V :j - /,, X* \ _RacoRlad ~ s s * & 2 n n Jamiaon Park IMP Evant Hyetographl Figure Hydrograph fit for Jamison Park with Modified IMP

270 Chapter 8 - Modifying the Impervious Fraction 8-11 Table Summary of Results for Jamison Park Event 3/1/86 17/12/86 1/2/87 21/2/87 22/6/87 1/8/87 13/8/87B 13/8/87 17/8/87 19/8/87 6/9/87 23/1/87 24/1/87 1/12/87 4/1/88 24/1/88 7/2/88B 8/2/88 28/2/88 2/3/88 21/3/88 22/3/88 23/3/88 25/3/88 6/4/88B 9/4/88 19/4/88 8/5/88 Pervious Initial Loss Pervious Loss Rate (mm/h) c Mean Std Dev Cused Z Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (m 3 /s)

271 Chapter 8 - Modifying the Impervious Fraction Vine Street The modified impervious fraction calculated for Vine Street was calculated to be.24 (figure 8.7a), compared to IMP =.31 calculated by Boyd (figure 8.7b). As can be seen, quite a bit of scatter was present, but only a total of 11 storm events were available to choose from, and six of these were small enough for use in the modified imperviousfractionstudy. The roadways comprise of approximately 13 % of the Vine Street catchment which is half of the modified imperviousfractionvalue. This shows that other impervious areas within this catchment are connected to the watercourse, such as house roofs. 15 Q. a Plot of against Rainfall ^ ^^~ ;- 1 o c *, 1, > Rainfal Vine Street IMP=.24 (a) 5 1 [Vine Street 1MP=.311 Hot of against Rainfall Rainfall (b) Figure Plots of against Rainfall for Vine Street All the events were calibrated and table 8.3 shows the summary of the results. The mean parameter C value calculated for the modified impervious fraction was 4.84 compared to 5.19 in chapter 7. Parameter C for the modified imperviousfraction still seems to be quite high. Figure 8.8 shows plots of parameter C and the peak recorded discharges and ratio of pervious to total runoff volumes. As can be seen, parameter C is again high and a trend between C and the runoff volume ratio occurs. There is also quite a large amount of scatter. Again, the results show that there is a problem with the impervious lag equation and this must be looked at.

272 Chapter 8 - Modifying the Impervious Fraction 8-13 Plot of Parameter C against Qrec Plot of Parameter C against Vper/Vtot 8? i r i i 1 i Qrec (rrfl/s) > i l i l VperA/tot 8 (Vine Street IMP=.241 Vine Street IMP=.24 (a) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (b) The fit of the hydrographs calculated using the modified impervious fraction are good, (figure 8.9). The rest of the hydrographs were similar to those in chapter 7. This method works well, giving good hydrograph shape and fit. I Hydrograph I Hydrograph I Hydrograph _CMcutata<l _Racordac 1 a! o 2 ao ao ao 1 12 Tana (rrin) 2 ao eo so nmo(trtn) [Hyetograph is J rai OR*" Vha Straat ap> Bran vrw Straal MM) Eaart vna Straat MM & M I Hydrograph I I Hydrograph I 5 too Tana(mh) Tlma(nai) Vara Straat MM).2«1-S-8S Brant vna Straat MX) Evart Figure Some Hydrographs for Vine Street with Modified IMP

273 Chapter 8 - Modifying the Impervious Fraction 8-14 Table Summary of Results for Vine Street Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 11/1/ /12/ /11/ /9/ /11/ /12/ Mean 4.84 StdDev Discussion of Results A comparison between parameter C for the impervious fraction used in chapter 7 and the modified imperviousfractions was conducted. As can be seen in table 8.4, parameter C has decreased slightly, compared to the values in chapter 7. The reason for the reduction is that as the impervious fraction has reduced, WBNM is calculating a lower peak discharge, so a smaller parameter C value is required to fit the peak calculated and recorded discharges. Table 8.4 -Comparison of C ave for IMP DC events and for IMF ' MD events Catchment Maroubra Jamison Park Vine Street C ave for IMP DC C^ for IMP MD IMP DC - directly connected impervious fraction calculated in chapter 7 But using a smaller imperviousfractionfor the smaller storm events has not solved the problem of high parameter C values for events that produce more impervious area runoff. Figure 8.1 shows plots of parameter C against peak recorded discharges and runoff volume ratio for all three catchments. Parameter C has reduced slightly for the very small discharges, but is still high. Figure 8.1b shows that the trend between parameter C and the events producing more impervious runoff has not been eliminated. This clearly shows the problem is not one of changing the impervious fraction with the event size, but rather the problem is with modelling catchment size. The area exponent in the impervious area lag equation is not correct and needs to be modified.

274 Chapter 8 - Modifying the Impervious Fraction 8-15 Plot of Parameter C against Qrec Maroubra, Jamison Park. Vine Street Modified IMP Plot of Parameter C against Vper/Vtot * *l»^> 4> «> I S Vper/Vtot Maroubra, Jamison Park, Vine Street Modified IMP 1.2 (a) (b) Figure Plot of Parameter C against Qrec and Ratio 8.4 Conclusions Modelling with a modified impervious fraction may not be the solution to the problem of high parameter C values on small catchments. By using a lower impervious fraction, parameter C does decrease as one would expect it to. This is because there is a smaller impervious area contribution to runoff. Smaller runoff volumes are produced, thus a lower parameter C is required to calibrate the model. But a smaller impervious fraction for small storm events may be a valid assumption. In minor storm events, not all impervious areas contribute runoff (as discussed in chapter 7). The results above indicate that the problem may be with the lag equation WBNM uses on the impervious areas. Figure 7.41 shows a definite trend between parameter C and the size of the catchment. This indicates that the lag equation for the impervious areas will need to be modified. This will be studied in chapter 9.

275 Chapter 9 Modifying the Catchment Lag on Impervious Areas

276 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9^2 9. MODIFYING the CATCHMENT LAG on IMPERVIOUS AREAS 9.1 Introduction Modelling with WBNM up to this point has been done on the nine urban catchments. In chapter 4, it was found that modelling the impervious areas nonlinearly was not satisfactory. Chapter 5 and 6 showed lumped modelling to lack the required accuracy needed on urban catchments. Chapter 7 showed split modelling was better than lumped modelling, and by running the impervious areas linear, the problems encountered with high parameter C values were reduced. But this did not help reduce the parameter C values on small catchments. Figures 7.37 and 7.39 clearly show that for small discharges, parameter C is high. But, most of these high parameter C values belong to Maroubra, Jamison Park and Vine Street; the three smallest catchments. Also, figure 7.41 showed that parameter C was smaller for large catchments. This indicates there is a trend between the size of the catchment and parameter C. The cause of this is probably the lag equation is calculating the incorrect lag times (equation 2.31) This section of the study will see if this is the case. Modelling in this section was done using split catchments, nonlinear pervious area and linear impervious area. The effective impervious fractions from chapter 7 were used (not the modified imperviousfractionfromchapter 8), and both the LR and RP rainfall loss models were used. 9.2 The Impervious Area Lag Equation WBNM uses the following general lag equation for routing runoff through the pervious catchment (equation 9.1). jc = c.a 57 Q" 23 equation 9.1 On the impervious areas, this equation has been modified to represent the differences between pervious and impervious surfaces (equation 9.2). K imp = IMPFACT.C.A 57 equation 9.2 As discussed previously, problems still occur on small catchments which require high parameter C values for calibration. This indicates the exponent.57 currently being used for the pervious areas

277 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9j3 may not be applicable to impervious surfaces. Testing of equation 9.1 by Boyd has indicated it to be satisfactory for a wide range of rural catchments. This suggests that it may be satisfactory for the nonlinear pervious areas, but not for the linear impervious areas. The results obtained in chapter 7 (split catchments with loss rate rainfall loss model) were used to determine a better exponent of area A. Plots of the mean parameter C values against the catchment areas were prepared. See figure 9.1. Figure Plot of Mean Parameter C against Catchment Area As can be seen, parameter C is higher for the smaller catchments. This indicates that the area exponent.57 is too high and requires modification. In equation 9.2, the catchment lag time K is proportional to the catchment area A raised to the powe of.57 (equation 9.3). K a C A 57 equation 9.3 From figure 9.1, it can be seen that the mean calibration parameter C is also proportional to the catchment area A raised to the power of x, where x is negative (equation 9.4). Q a Ax equation 9.4 Thus for impervious areas, the lag time is proportional to the catchment area A to the power of.57 (equation 9.5). K a A equation 9.5

278 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-4 This should eliminate the trend that can be seen in figure 9.1. To determine x, the least squares regression method was used, and x was found to be Thus, the new exponent for the impervious area now becomes =.25. The new impervious area lag equation is now (equation 9.6). K^ = IMPFACT.CA 25 equation 9.6 The modelling results will be discussed below. 9.3 Initial loss-continuing Loss Modelling (LR) Results for the Canberra Catchments Curtin The mean parameter C obtained for Curtin after modelling with the modified lag was I chapter 7, the mean parameter C was.85. Due to the large size of Curtin, the.25 area exponent has helped increase the mean C value. This is better as it is closer to the mean for natural catchments (approximately 1.7). Figure 9.2 shows the plot of parameter C against the recorded peak discharge and runoff volume ratio. As can be seen, there is quite an amount of scatter in the results, but no strong trends. Comparisons betweenfigure9.2 and figure 7.1 show that the changes have not totally eliminated the trends. Table 9.1 shows the calibration results. The hydrographs can be seen in figure 9.3 and are similar to those in chapter 7 for Curtin. 23 1" 4.5 ( j Plot of Parameter C against Qrec 1 - CurOn IMP-O i One (no/») I" o 2 - K OS ( I Conn IMP- 17J IPIot of Parameter C against Vper/Vtot B 1 Vpar/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Curtin (LR)

279 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-5 Table Summary of Results for Curtin (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ /4/ ^ /3/ /1/ /2/ /1/ /1/ Mean 1.16 Std Dev.54 I Hydrograph Hydrograph] j Hydrograph _C*fcutM»d _RKord*d _C*leuM*l _fecon*d Th»(irtn) O nrm(rttn) S 1 Thm (nto) TtrT*(rrt.) Curtin IMP Ev«n, Curtin IMP Evwnl Curtin IMP"* Ewnt I Hydrograph I Trm(nin) 1 ISO TYr»(n*>) 1 Hyetograph im»(rrtn) Hyetograph 1 = 1 I * - - so 1 -E J V TVT»(mn> S ". Curtin IMP- 17 QRaMal S-ao h I Curtin IMP-.17 JIL- A [gjjyw Ev«nt Evw«

280 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-6 I Hydrograph! I Hydrograph I HyrJrograph r Calculated _RKord*d. 6 I- l>m(rrin) Ikm (irin) I Hyetograph G Tkm(rrtn) Curtn IMP E»ot Turn (rrin) : I IrUnTlnrTWv. Curtin IMP-O Evtnt I nramal I Curtin IMP Evsnt S Tltni(n*i) 1 Hyetograph Curtin IMP Evwri Tin* (rrtn) ORslntBl 1 Curtin IMP Evnnt Tfcni(it*i) 12 1 [Hydrograph C«teuM»d _RKord*d Tim (rrtn) ~. 4 I- 5 2 I 1 '&. IHydrograph] I Tiro (rrin) TVnr»(rm) Curtin IMP EVMII Curtin IMP Ev» nt Figure Hydrographs for Curtin (LR) Mawson The mean parameter C value for Mawson was found to be , which is similar to that in chapter 7. This is because Mawson is 4.45 km 2, and the new exponent has little effect on parameter C for this area. Figure 9.4 shows the plot of parameter C against the recorded peak discharge and runoff volume ratio. Again, when these figure are compared tofigure7.4, it can be seen that the trends have not been totally eliminated. There is a small amount of scatter in the results, but no strong trends. Table 9.2 shows the calibration results. The hydrographs for Mawson are similar to those in chapter 7.

281 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-7 I Plot ol Parameter c against Qrec I I Plot of Parameter C against Vper/Vtot] Qrac(ntV«) imtwwn IM P-.21 I M.mM«>r,IM P-.211 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Mawson (LR) Table Summary of Results for Mawson (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 13/2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ , /2/ /1/ /1/ Mean.68 Std Dev.45 I Hydrograph I IHydrograph] I Hydrograph I ^23 t 2 15 v: i- l\ I w t I,?-*?= ' V, Tbm(rrin) I Hyetograph] L -d Tbiwfnt.) 1 J 2 IA y, >*== Tlrm(mn) Time (rrtn) 1 Hyetograph 1 ; I 2 JIVJL 111 linn _C*lcut*ted _R»car*d rawu IMMMI IMP-.21 kanvaonmto Ewnt S rei«

282 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-8 I Hydrograph I I Hydrograph I Tiro (rrin) 12 O 1 LJDL MwaonM* evanl orwrai c-1 f 8 6. I - fl» r*wwll«w Br «_ii-l 2 4 Tina (rrtn) Hyetograph I it. i 1 T1rr»(irin) Tiro (rrin) Tiro (rrin) 1 Hyetograph 1 1 w I 2 iu.mil = 4 Tiro (rrin) MaMwen IM P Ev-nt I rjrdnftf f s UwKnMM):i &«nt p firu. ^ Riinfall MM ton MM) Evftrt -rfjill Jllhrr^ RiWarf Figure Hydrographs for Mawson (LR) Long Gully Creek The mean parameter C value obtained for Long Gully Creek was Figure 9.6 shows a slight trend between C and the discharge, but for small discharge events, the amount of scatter is quite large. Parameter C is still fairly high for more impervious events, but an overall plot of parameter C against the discharges for all the catchments is required to see if trends still exist. There is a definite reduction in the average parameter C values after modification of the area exponent in the lag equation. Table 9.3 shows the calibration results and section 9.5 will discuss the results. The hydrograph plots (figure 9.7) are again similar to those in chapter 7.

283 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-9 I Plot of Parameter C against Qrec I I Plot of Parameter C against Vper/Vtotl.. * I Long -u»y CfMlt IMP-.SI Qr«e (m3/t) [Long Guty Cr*+k IMP Vpar/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (LR) Table Summary of Results for Long Gully Creek (LR) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (thoum 3 ) (m 3 /s) (m*/s) 26/1/ /2/ /2/ /2/ S /3/ / /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean 1.67 StdDev.98

284 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-1 I Hydrograph I Hydrograph Tam<Mn) TH»(irai) Lang Gully Oaak Evant lup- OS o 2 ao eo go Tim (rrin) Long Guly OMIC Brwrt M»«.QS Hyetograph JWL (Wnfal Tirm(rrin) ao» I J [Hyetographl l : il Long Guly Crwk Brant MMJ.S TVr»(rrin) 1 15 Tkm(rrin) Tim (rrin) 1 Hyetograph 1 Long Gully Ovak Evt>M IMP- 5 Long Gdty CrMk Br«nt MM) a Tina (rrin) 6 \A I - Long Ggfly CrMlr Br«nt MM) 5 RUnfM I Hydrograph I 1 Hydrograph 1 I Hydrograph I f i 4 ^ CalcuW>d.RacortM «4 1 = - 2 l i ft h Mi i\\, 1^ Thrm(rrin} _OICUktKJ.RtcoroM ahw(mln) Figure Hydrographs for Long Gully Creek (LR)

285 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Giralang The mean parameter C value found for Giralang was As Giralang is a small catchment and a low mean parameter C was required for calibration in chapter 7, parameter C has further reduced due to the modification of the area exponent. Figure 9.8 shows there are slight trends in the results and a smaller amount of scatter than the results in chapter 7 (figure 7.7). This shows the modifications performed to WBNM have helped to lessen the variation in parameter C. Table 9.4 shows a summary of the results. Ploto Parameter C against Qrec J 1 Plot of Parameter 6 against Vper/Vtot j 1.2 O 1 i GtaknglMP-.22 * > Or*: (rrfl*) \2 O i 1" E.6.4 i i, Giralang IMP-.22 Vper/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Giralang (LR) Table Summary of Results for Giralang (LR) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 27/3/ /1/ /4/ /1/ S /3/ /3/ ,3 9/1/ /2/ /2/ /1/ /3/ /1/ /12/ /3/ Mean.62 StdDev.35

286 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-12 I Hydrograph I I Hydrograph I I Hydrograph I I _cacuat»>a _fibcordad Trna(irtn) Tt-nt fin*.) Hn»{n*i) 1 Hyetograph 1 4-T _- IL_ : JL -= 2 QfteMai!c io Gaiang M*-} &art Grmng MMJ EV.VD Giralang MMU2 S-«-77&mt 1 Hydrograph ?1J 1 * I OS 1, \ w\ ±J fla _ Calcutta*. _ 1 2 3O 4 5 Tkm(nln) Time (mn) Tirm(rrin) j Hyetograph I : 3 2 I ii L Tm(rnjn) 1 f 1s i.1 j ^jjlj. MM3.22 Gtakng MM3.22 Giralang IMP-.22 TBBrtrnt Ewnt Evant 1 Hydrograph 1 1 Hydrograph ~ - A \ -, J I 1,Ws_ \ Hrnafntt) 1 1 ' * 6 i; \ fi\ \ / I _C*cuatacl viv _ t y >=> Time (rm) 1 Hyetograph 1 I" * _ t" - m T1rm(irin) That (rrin) Glral.nrj IMP-.22 Glr»lang IM P-.22 Graivig MP Evwrt Evant Evan I Hydrograph I 1" I Tn»(rrin) 1., n l, J V* Tm(irin) Pl aii i rain ouanfai W 1 12 Tim (rrin) Jifc QRahfaf Slialang MP Ewnt Giralang MHL22 24.M2 6M Gr»«ng MM) 22 1S-1 «J3 Brant

287 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-13 I Hydrograph I I Hydrograph I.CalctiWad.RacorOad I. 4 I Tlma(irai) RaWaJ Oraianj MMJ E» art Ora.t«r>a 4VP Brtjnl Figure Hydrographs for Giralang (LR) Results for the Sydney Catchments Maroubra The mean parameter C value for Maroubra has reduced significantly from in chapter This is very good, indicating the modifications to the impervious lag equation to be working for small catchments. Figure 9.1 shows there is some scatter in the results, but no trends. A summary of the results can be seen in table 9.5, and hydrographs can be seen in figure I Plot ot Parameter C against Qrec I [Plot of Parameter C against VperA/tot i 2! is.. > MamubialMP*).18 [Maroubra IMP-.16 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (LR)

288 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-14 Table Summary of Results for Maroubra (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 1/3/ / /3/ /3/ /3/ /4/ /5/78 B /6/ /6/ /3/ /6/ /11/ /11/84 B /12/ /5/ /4/ S1 3/7/ /1/ /4/ /4/ Mean 1.64 Std Dev.81 Hydrograph [Hydrograph 1 Jo.: 2 4 SO 8 roo Tana(rrai) rhyetograph SO 1 Tam(nti) Hyetographl f 1 n e _* imldiw-- Mvoiiya W Event

289 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-15 Tim. (rrin) M 1 Time (rrin) s x n Tkna(irin) Tin* (rrin) I IMP-.16 Maroubra IMP-.16 Maroubra imp-o.ie Eve* Event Evant Tin* (rrin] l Hyetograph I i' " jjllllttw^ Tlme(ri*,) i IMP Evant Maroubra IMP Event Maroubr* LVP Event I Hyetograph] i RaWal I 5 r f l l 15 Z 1 Al Manubra IMP-.16 Mamubn EvaM Evant 8-11-S5 Evant MP-. Hyetograph ISO i 1 orawn a QRaWaa Mraubra M=-.i Evant *vata*a l* Ev art Namibia 1MP Evant

290 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-16 Hydrograph 1 I Hydrograph I 1.2 " It to.: A e o.6 cis" i- il-v.2 D J,^-, T1n*(n*i) i ' Trna(iTBi) _CaKJaiad _RKordad rhyetograph I Maroubra IMP Event Meroubm IMP Event Mr«lvaa«M> Evant Figure Hydrographs for Maroubra (LR) Strathfield The mean parameter C for Strathfield was found to be , very similar to that in chapter 7. There still seems to be a trend between parameter C and the peak recorded discharge for Strathfield which has been apparent throughout the study. None of the modifications have helped alleviate the problem, but the large amount of scatter in the results between 14 and 18 m 3 /s in figure 9.12a indicates that the trend may not be significant. In figure 9.12b, no trends are present. Table 9.6 summaries the calibration results, and the hydrographs can be seen in figure I Plot of Parameter C against Qrec I 1 Plot of Parameter C against Vper/Vtot 1 O 3 > I 2 m S. 1 S Qrac(mVa) StajthlWd < IMP*.29 (a) 4> O 3 * I 2 " «s. i < Vper/Vtot l&atliimd (MP-.29) (b) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (LR)

291 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-17 Table Summary of Results for Strathfield (LR) Event 'ervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 3/9/ /9/ /3/ /4/ /4/81B /4/ /12/ / /9/ /3/ /5/ /4/ /1/ /11/ /5/ /4/ /8/ /2/ /4/ /4/ Mean 1.22 Std Dev.95 IHydrograph! [Hydrograph I Hydrograph _ Calculated Time (11*1) Hyetograph 1 Hyetograph 1 'HlJ 1 DfaWal Strattifleld MP-.2S Event Sir.mfi.1 IMP S-76 Evant Tam(rrai) Trna(rr» Hyetograph] i IIIILllTTru- Sua thfieldimp« Event

292 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-18 Hydrograph I Hydrograph I I Hydrograph I Tn*(rrfn) Tlrnefrrin) Hyetograph 2 1 S - 1 IS 1 «5 [fl rrff lllhlltihtm>iii>, TV *(IT*.) QRiWal StrathfleW IMP-29 Strathfield IMP-.29 St re th field IMP E**nt Event B Event SO Trne(rrri) Tlrre (rrin) I Hyetograph StathHetd (Mp-o 29 Stnthf laid IW--29 I Strath field IMP-.2* Event 2S-3-82 Evert Event I Hydrograph nmblrrtn) T»ne(mh) :A/^ _Ctte.jM.hsd 5 1 Time mn] 1 Hyetograph 1 Hyetograph? 2 1 J5 * 1 5 il Ralnf_ = 4-3!E 2 i QRaMall Strathfield MP Evert Strathfield MP-Q *«Evert Strathfield M Evert Th*(rrfn] Tin* (rrin. 'Straw*ktKP* Event ( StntMleM IMP- J Event - : : JI Hyetograph i i li Strathfield IM P Event

293 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Hydrograph 1 I Hydrograph [Hydrograph] 4 " /ff\ 1.3 i 2 it - /A\ : V TVi*(n*,) //,, s^=* _Cic«_ted _RMordM] V 1 JU\M 2 4 Tlmi(n1n) Trrm (rrin).calculated.. I.Hyetograph I QJMAI Suethfieid IMP-29 Strathfield MM1.29 Strathfle-LUP-_» Event Evant Evert I Hydrograph I Hydrograph _Cafcutti*d _Racon*sd ~Z Tbna(mh) TVr»(rrtn) [Hyetograph StrathfaUd M=-J Q8 &/ert StraW Wd MMI Evert Figure Hydrographs for Strathfield (LR) Fisher's Ghost Creek The mean parameter C value for Fisher's Ghost Creek was found to be , a slight reducti over the value determined in chapter 7. The trend between C and the peak recorded discharge is still evident, but not strong. Figure 9.14b shows that the trend between parameter C and the runoff volume ratio has been alleviated. Table 9.7 shows a summary of the calibration results, the hydrographs can be seen infigure9.15. I Plot of Parameter C against Qrec] I plot of Parameter C against Vper/Vtot I it. Vpar/VW ikehe/agfte* Creek JMP--251 F1aharaGhaa.Cl»aaiMP-o55 (a) (b) Figure Plot of Parameter C against Qrec Ratio for Fisher's Ghost Creek (LR)

294 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-2 Table Summary of Results for Fisher's Ghost Creek (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 4/5/ /1/ /11/ /12/ /3/ /3/ , /3/ /11/ /12/83 D /1/ /2/ /11/ /11/ /12/ /1/ /8/ /11/ /1/ /5/ /6/ Mean 1.95 Std Dev.95

295 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-21 I Hydrograph I IHydrographl IHydrographl _Cttl«M _RKoroad I 2 o 2 4 eo ao ioo 12 no Trm(ntl) Tkna(trai) 2 4 Tin* (rrin) Fun < Ghoat Oe*k Time (rrin) Event!Mf*-o 25 Fltfiefa Ghoat Creak Event IMPNJJS 1" = 4 9!c 2 iil_ii_l Flaher'a Ghost Creak 2D-3-83 Evert UP-2S pralnfafl Hydrograph t 2 I' - Av //\\ - / W. 7 Kl Tin* (rrin) Tin* (rrin) Raher"* GhoaJ Creak FiatieTa Ghoat Greek Rahefa Ghoat Greek & em MP Event MP Event imo Hydrograph l> S 2 I, ; / ^ TVT*(n*>) Time (rrri) Time (rrin) UU ReiafiGnee Cra** Event MP-O^S Rainfall ReWe Ghoat Greek vartt IMP-.25 I Hydrograph TVre(rrtn) I Hyetograph Tlmi(rrin) ft 1 * \J V Tarafnai) 1 < Th»(r* HawraGhaa Craak 9-11-w EvaM IMP-.25 FbJiaraGhe«Craak Ev.nl IM P-.2S

296 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-22 Hydrograph I IHydrographl IHydrographl _ Calculated. I Time (rrir) Trre(mn) Time (rrin) 1 Hyetograph 1 LL low S 2 Father's Grwst Creek Evert MP- 25. J- 1 I 6 i_ B. 6 - t 2 * RaheCeGhaat Creek JI_. JL_ Event IMP-.29 * 2 S a. _ Rafter's Ghoet Creek Event MM) ) RanfaU IHydrograph Hydrograph _ Calculated _ Tkne(rrin) TVre(rra-i) i:l prawall Fisher's Ghost Creek Event I M _ Fisher's Ghost Creek Event MPO.25 Figure Hydrographs for Fisher's Ghost Creek (LR) Jamison Park The mean parameter C found for Jamison park was , which is a significant reduction ove that in chapter 7 of The large reduction is directly associated with the modification to the area exponent in the impervious area lag equation. The trend in figure 9.16a has almost been removed, compared to that present in figure 7.15a in chapter 7. Table 9.8 shows a summary of the calibration results, and figure 9.17 the hydrographs. (a) (b) Figure Plot of Parameter C against Qrec Ratio for Jamison Park (LR)

297 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-23 Table 9.8 -Summary of Results for Jamison Park (LR) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12/ /9/ /1/ /4/ /1/ /1/ /1/ /4/88B /4/88B /2/88B /2/ /5/ O.OO /4/ Mean 1.73 Std Dev 1.1 IHydrograph rfrydrograph IHydrograph Urna.rrin) Jvnaon Park MM Brara CRaWal 12 = 1 5. u 5 4 Ttola(ir*i) 1 " n Jsrrison Park MMJ &4 Event J IV Ramf_ r $.3 a S 2 i.1 2 S. Jamlasn Parti IM P Evant RaWas

298 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-24 I Hydrograph I Hydrograph Hydrograph y o.is i.1 o.os I -IA l\ -N*«i,^?=\ I 1 ISO 2 Tbn»((rin) _Caic_ied Tlrf*(rrin) Tbm(rrai) Hyetograph I Hyetographl Tims (rrin) RaMal S io D_ Jsmlean Park IMP- J Event Park IMP Evant Jsrrison Psrk LWPa Brent Hydrograph [Hydrograph I Tta*(rt*i) o.oe J=. luv n.4 _.2 J i^=_ 1 2, 3 r~r* 4 5 Time (rrin) fci_tsd _Rec<wod 1 Hyetograph 1 Tkne(irin) > 12 - PI, E e _ * E " fntt m RaWal f 8 = e 5 4,c s 2 n n _meon Perk IVP-.21 Jsrrison Psrk MMJ 21 Je ml ear. Perk IM P Event Evert Event -IK\ rhydi^raph) 1 a o.e n V o.s * - 4 L -1 H I o^ i \ ff ^w. r> J i 7 >- T r Tens (rrin) _CalcuBrted. Hyetograph I m 111 i * *sl Tkne(rrin) Jem.»n Par* IMP-J1J Jirreoo Par* WP-.71 PkrkhP-, Event Evsnt Evert TV* (rrin) Tkr*<rrin) _ - ntsen PsrklMP-2t Evarrt n n Tkr*(rrin) T*T*(mn) JsmdonPeiklMP Event _ L Jamte3nPerklMP B Event 1 h rimn, n RsWtf

299 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-25 IHydrographl 1 Hydrograph 1 I Hydrograph I M T>ra(iTfn) _CHci_rted. J 6 1 _ 4.2 f \\A U JWf 5 1 Tims (rrin) _ Calculated _ I iv* % 8 _Catu«ad S Th*(rrtn) _l»)eoraad Tine (rrtn) JemlaonPsrklMP B Event Jemle9nPerklMP MB Event Jemlssn PsrklMP Event.8 IHydrographl r^k S".8 r / \ m.4.2.//.. \ / / \ _ Calculated. I Hydrograph I.4 rv 5.3 _Cstuisted I Time (rrin) Jamiaon Pah. IMP-.21 nlaenpsrklmp Event Event Figure Hydrographs for Fisher's Ghost Creek (LR) Results for the Melbourne Catchment Vine Street The mean parameter C value for Vine Street was found to be This value has reduced quite a lot over the value in chapter 7 (C = ), but it is still high compared to the other catchments. There are no trends between C and the peak recorded discharge, but a trend still exist between parameter C and the runoff volume ratio (figure 9.18b) where the more impervious events tend to require higher parameter C values to calibrate. This trend was also seen in chapter 7 for Vine Street. Table 9.9 shows the calibration results. i Plot of Parameter C against Qrec J I Plot of Parameter C against Vper/Vtot M 1.«1JJ f_sc(m1/s) MM Street IMP-.311 (a) [Vine Street IMP-.31 (b) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (LR)

300 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-26 Table Summary of Results for Vine Street (LR) Event Pervious Initial Pervious Loss c Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 1572/ / /5/ / /12/ /11/ /4/ /1/ / /12/ /11/ Mean 3.78 Std Dev O Tarn (rrtn) Tbni(mh) rhyetographj OftsWsl RsnfeB I - Jl - I* " Vlns Street HF-.31 IS-2-72 Evert Vine Street MP Event Vlns Street M= *74 Evsnt IHydrograph f5 "/\ /v.. / i. r. Tims (rrtn) Hyetograph 1 r 2 t IHydrographl t/v 7 ^ Time (rrin) Tin* (rrin) 1 * 1 2 _ n j Jl ~ 1al»(mto) larahfal Trm(r*» Vina Straat MML bant Vina Straat KT Brant

301 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-27 IHydrographl Hydrograph I I Hydrograph I, 1.5 _ Calculated Cslc_rted 2 4t Tina (rrin) 2 4 eoo aoo 1 Tin* (rrin) Hyetograph I Tim (rrin) QRStlfsl!,.. orsinfsll Vine Street MM) Even! Vine Street IMP Event Vlns Street WP Evsnt I Hydrograph] Hydrograph Tkns(rrin) I 2 Tlms(rrin) VhS Street MM) Event Vra Street MM) Event Figure Hydrographs for Vine Street (LR)

302 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Initial loss- Proportion Modelling (RP) The Canberra Catchments Curtin The mean parameter C obtained for Curtin after modelling with the modified lag was chapter 1, the mean parameter C was.84. Figure 9.2 shows the plot of parameter C against the recorded peak discharge and runoff volume ratio. As can be seen, there is quite an amount of scatter in the results, but no obvious trends. Table 9.1 shows the calibration results, and figure 9.21 the hydrographs jcurttn 1 uprtj.tt] 1 Plot of Parameter C against Qrec j SO ( Orse(rrtVs) (a) [Plot of Parameter C against Vper/Vtot 1 2 o - ' r: OS 1 \S &.5 Vper/Vtot fourttn IMP-.17] (b) Figure 9.2- Plot of Parameter C against Qrec and Ratio for Curtin (RP) Table Summary of Results for Curtin (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 26/1/ / /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ / Mean 1.4 Std Dev.55

303 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-29 y 1. I M -» 6_ fi 2. Curtin IMP Event Tkm(iriri) Tkm(rrin}? Cuitht fmp-o.f Event Hydrographl // A \ // \ ^LJ. H. >t V Tims (min) Tins (rrin) 1 5 I Hydrograph I r 1 iv _v, Vv Hrrsj(rrirtJ OQ I-- "Trie (rrtn) Ctirtin IMP-O Event _Cslculstsd _Recordsd This (rrin) rhyetograph] JL Tlmi(rrin) Curtin IMP ! Event 12 j too f B. eo 1 Hyetograph n - J 1 * J i _ 2 Curtin IMP Event Time (rrin) Curtin IMP Event 1 1 so - nl _ 6 e» fl Cuitin IMP Event Hyetograph 1 : I I Tims (rrin) Tims (rrin) Curtin IMP Event Curtin IMP Event Tims (rrin) 1 Hyetographl Tlmi(rrin) Tims (rrin) I Hyetographl i «I Curtta IMP Event n 1 i Curtin IMP Event Curtin IMP Event j_ui aftwif«

304 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-3 I Hydrograph I I Hydrograph I -» 1 f * 7 8 a, 1-2 /, Tte?-, Ow Time (rrtn) _Cstulsled _. 4 U S 2 I 1 :/V.l _Cstu»tsd ) Tims (rrin) _Rseordsd Hjetograph Thns(rrin) I orslnfsl I 1 M 1-2 i 1 ^ i, Tha(mh) I RilnrM I Curtin IMP Evsnt Event Figure Hydrographs for Curtin (RP)

305 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Mawson The mean parameter C value for Mawson was found to be , which is similar to that in chapter 7. Figure 9.22 shows the plot of parameter C against the recorded peak discharge and runoff volume ratio. There is a small amount of scatter in the results, but no obvious trends. Table 9.11 shows the calibration results. I Plot of Parameter C against Qrec I IPIot of Parameter C against VperA/tot I IMawaon IMP-O-211 ± _ M ao Qrac(m34) [Meweon IMP-.21 -_. (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Mawson (RP) Hydrograph Hydrograph [Hydrograph 25 _Cstuerted _ i "a 2 _C»Jciaatafl _Rac«da<l -. 2 tutated _ Time (rrtn) Hyetograph SO 1 ISO 2 Hyetograph I Jl L h J Jl Ih.. M -, Jill QRuntsO

306 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-32 IHydrographl Hydrograph IHydrographl! M «2 1 " A ~A _(_cusrtsd _RecorOed Tim. (rrin) _Cafc(_ted.. 1. i Tims (rrin) _CslcuMsd _ Mswsan IMp»o.2i Event MswsonMM)_ Brent Mmr son MM)_t Event I Hydrograph I 1 Hyetograph 1 1 _CBJCUMS<I. _ Tent (rrin) 1 * 4.C 2 & ill Jll 11 nil n - a_vsonm>-2i snt MwsonM>aO_ Evsnt Figure Hydrographs for Mawson (RP) Table Summary of Results for Mawson (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m'/s) (m 3 /s) 13/2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean.52 Std Dev.38

307 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Long Gully Creek The mean parameter C value obtained for Long Gully Creek was Figure 9.24 shows a slight trend between C and the discharge, but for small discharge events, the amount of scatter is quite large. Parameter C is still fairly high for more impervious events, but an overall plot of C against the discharges for all the catchments is required to see if trends still exist. Table 9.12 shows the calibration results, and figure 9.25 the hydrographs. I Plot of Parameter C against Qrec] [Plot of Parameter C against Vper/Vtotl [Linfl Gii* Cieek IMP Grec(rr_») I Lens Guly Creek IMP Vper/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (RP) Table Summary of Results for Long Gully Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 26/1/ /2/ B /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Mean 1.36 Std Dev 1.11

308 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-34 IHydrographl 5 "? * 1 aj.. 1»\ «4 V 2 4 BOO J&J V- ITrm(rrfn) 1 Hyetograph 1.Csfcubtse, Ftocoroed SO «Tira(rnn) Hyetograph I I * 3 2 * ID**" Ranlaa s «QRahfal LM^ Guar Craak B/anlMH).5 Long Giilly Craak Evant IMP-.3 Umg OJry Craak 2l-3-74E»antM»<).5 Hydrograph I 1 Hydrograph ISO 2 1 I I; _««s^.^-^ _ Calculated _ Tanaprin) Tana (rrin) Time (rrtn) f Hyetographl 12 = llins(frin) D»W-* l Time (rrtn) QRsrrfstl n^w*" Long Gully Creek UngGidy Crssk Long Got, Creed Event IW PHI Event MM).5 2D-3-78 Ewer* WPaQ.5 IHydrographl Tire, <rre.) I Hyetograph i; * I, - K 1 2 3, 1 S^ Tkna.lrin) rhvetographl.calculatad.raconjao Ttra.rrin) Long Cully Creak S s 1 Long Guly Crssk Long G_y Crssk 23*3-78 EvertflUP-.5»1-7SiEvsntMP-ca5 S-2-81 Ever* M^O.CS

309 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-35 I Hydrograph I I Hydrograph I Long Cutty Creek Evant IMP-.5 Long Guly Crssk Br em IVP-O OS Figure Hydrographs for Long Gully Creek (RP) Giralang The mean parameter C value found for Giralang was Figure 9.26 shows there are no trends in the results, but there is a fair amount of scatter. Table 9.13 shows a summary of the results. I Plot oi Parameter C against Qrec I I Plot of Parameter C against Vper/Vtot I o i «e o.e -».» _ [GlraB.nglMP-.22 igtakng IMP-.22J (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Giralang (RP) 1 Hydrograph 1 I! a\. 2 4 Tha(mri) JLJ ORaWal lana(nln) Giraaing MMI BraM

310 9 - Modifying the Catchment Lag on Impervious Areas Hydrograph I I Hydrograph I Hydrograph I _CsleuMsd 2 4 « Tims (min) m»(n*,).2 J.1 fcfc Tims (rrtn) _CsksuMsd _ I Hyetograph 1 i_jk_ DBaWaa GWsng MWL Evert GrtlangMMD22 2M-7S Brant GlrslenglMP-^ Event I Hydrograph I Hydrograph ^ 1 i *.6 : fa : f\ C 2 _ Cst meted. -1 W Tlmt(irtn) 1 Hyetograph t> 6 I: «B?»xJ 1 /fl \ //ll vn TImBfrnn) V V a? * _ 3 Qlrslsng IUN.2I TlmB(n*i) f 2 L Simians IMP-o 22 m Qrssing MMX Event Event Event I Hydrograph I ms(mki) :M 1 rg.8 I",6 C Tana'iral) -I _/,, V^<r- T,N» _Cai;i»jtad _ Records [Hyetograph I a*"* GimlanalVP-.22 S-r-81 Evant OraaBiB MM) lffiEr««Giralang MM).22 1S-KM3 Erant Hydrograph [Hydrograph Tmlmti) rhyetograph Ratrrari GaalsngM* Bfart Figure Hydrographs for Giralang (RP)

311 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-37 Table Summary of Results for Giralang (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thou m J ) (m 3 /s) (m 3 /s) 27/3/ /1/ /4/ /1/ /3/ /3/ /1/ /2/ /2/ /1/ /3/ /1/ /12/ /3/ Mean.57 Std Dev.39

312 Chapter 9 - Modifying the Catchment Lag on Impervious Areas The Sydney Catchments Maroubra The mean parameter C value for Maroubra has reduced significantly from 3.36 to Th shows the modifications to the impervious lag equation to work for small catchments. Figure 9.28 shows there is some scatter in the results, but no strong trends. A summary of the results can be seen in table 9.14, and hydrographs in figure U 3 > V imarouora IMP-.16) I Plot of Parameter C against Qrec I S Orac(iKU U 3 S I 2 i < < 1 Plot of Parameter C against Vper/Vtotl " * * * luaroubra IMP Vper/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (RP)

313 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-39 Hydrograph] Hydrograph] Hydrograph.3 f o.«. et 3 o.a io.2 Tims (min) _Cslci_ted _ftecocded, 1 15 Time (mh).4 1,.3 e 2.2 _.1 SO O TVns(nln) _Cslculsted _Rec^ed fins (rrtn) Maroubra MP Event Meroubm IMP Event Maroubra IMP Event Urns (rrtn) i Hyetograph] I Hyetograpri I I 15 1 _ so ftsmfefl 3 2!c 1 nn i n ftynfsb h-usxs MP-.16 Maroubra IMP-.16 Meroubm IMP St en* Event S Event 1 2 Tkns(mtn) I Hyetograph] DR" 1 ""! rff Trno(rrtn) 1 iar»ws«meroiixi MM) Event Mero rs MM) Br snt MsroiS)rs MM). 16 t-s-65 Brent Hydrograph Maroubra IMP Event B 1 71ms (ITSI) Hyetograph ] ill LL Tims {rrtn) TJms (irtn) Thru (rrtn) Maroubra IMP Event

314 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-4 I Hydrograph I 12 V Tlme(mn] I Hyetograph 1X Time (rrtn) Mwo_ra MMD BBrsrt A ' ** ** il Figure Hydrographs for Maroubra (RP) Table Summary of Results for Maroubra (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 1/3/ /3/ /3/ /3/ /3/ /4/ /5/ /6/ /6/ /3/ /6/ /11/84 D /11/ /12/ /5/ /4/86 A /7/ /1/ /4/88.6 Z /4/ Mean 1.56 StdDev.91

315 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Strathfield The mean parameter C for Strathfield was found to be , very similar to that in chapter 7. There still seems to be a trend between parameter C and the recorded discharge which has been apparent throughout the study. No modifications have helped alleviate the problem, thus they can be said to be trivial. In figure 9.3b, no trends are apparent, but the large amount of scatter in the results between 14 and 18 m 3 /s in figure 9.3a indicates that the trend may not be-significant. Table 9.15 summarises the calibration results. 1 Plot of Parameter C against Qrec 1 I Plot of Parameter C against VperA/tot I O 3 k V Qnac(m t) o i I V _ 1? * «,», a* Vper/Vtot Strainrwk* 1UP-.2& StmthfteMIMP-a.29 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (RP) [Hydrograph Tlmt(rrtn) IHydrograph TVns(rrtn) _Ceti_ted. 5 «^w I Hydrograph _ 4 SO SO 1 Tim. (rrtn) Calculated _Rscorded fioi- Strathfleld IMP-29 3*-77 Event Strathfleld IMP Evsnt SJ.ramn.ld IMP Event Hydrograph] IHydrographl StlSthfsM IMP-.2* Evsnt Tins (rrtn) I Hyetograph li Stnth«eld IMP Event SO 1 Tlms(rrtn) StrsthtisM IMP B Evsnt

316 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-42 e> 2 X -/A IHydrographl \ rf / \ V S "I- 1 Hydrograph I Hydrograph I V Tamfifln) Tkra<rrln) Trnafrrai) _ lllm. Time (rrtn) Rahlal A-ll. r_rshfs» Thai (rrtn) StrsthtlsldlMP-.2» Event StratMMd MP-2S 25^82 Brent SUethfleld IMP-.2B 3*53 Event I Hydrograph I Tiro {rrtn) [Hyetographl fhyetograph Time (rrtn) Tims (rrtn) * 4.c r_r»wsfl StrathfMd M>*_) Evert Strotnfkeld IVP Event Strsthf Wd M-_) 7-4-S4 Event )1* (rrtn) Tims (rrtn) StratWMd efmu Event Strath field <M P Event Stistnfleld IMP Event to. n.. ilk SuaffiB.la IMP-CUB M4EM Tim (rrin) IQMM? 12. I too. iikjkjll b"«slrathr-u W-.23 Slramla*) rvp Brant

317 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-43 Hydrograph 1 Hydrograph I 1 1 * r "e/j >JW 1 2 Time (rrtn) _Cslc_rtad _Rscordsd Time (rrtn) StrathflsM N M _ Evsnt Figure Hydrographs for Strathfield (RP) Table Summary of Results for Strathfield (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 3/9/ /9/ /3/ /4/ /4/81B /4/ /12/ /3/ /9/ /3/ / /4/84 D /1/ /11/ /5/ /4/ /8/ /2/ /4/ /4/ Mean 1.11 StdDev.92

318 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Fisher's Ghost Creek The mean parameter C value for Fisher's Ghost Creek was found to be The trend between C and the peak recorded discharges is still evident, but not strong and the trend between C and the runoff volume ratio has been alleviated (figure 9.32). Table 9.16 shows a summary of the calibration results. o 4 r. 4i I Plot of Parameter C against Qrec I - +4 _ * ) Qrec(rrtVa) Hatter's Ghost Creek IMP-.251 (a) o 4 -» 3. Plot of Parameter C against Vper/Vtot *t *«2.4 O.S. Vpar/Vtot Fbh.r. Gaoat Claak IM p- 2S (b) Figure Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Creek (RP)

319 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-45 Hydrograph I Hydrograph Pahar* Ghoat Craak 5*63 Brant MMI2S Tbm{n*i) S 3 S. Time (rrtn) FlahsrsGheat Oeek Event MP-.25 J. 4 I 2 Tim (rrtn) I "J Fisher's Ghost Creak Event IMP T i/v m 2 b c 3 J- 2 1" 1 Hydrograph Tfei»(irtn) :Lb ' i l k Tfersj (n*i) RahsfsGhoat Creek 26-i -M Event iu p-o 25 LJ Cal»_tsd _ 1 DR>M*> 1 4 I it I" : J 1 * Tln*<irin) s ^ Hydrograph SO 5 Tsns(nm) H Si a r» Ghost Creak Event 1 MP Hyetograph 1 _Csiei_tsd _Rscordsd Rsnfsl 1 V 3 : c 3 J-2 i 1 _ I Hydrograph I Tim (rrtn) 1 Hyetograph 1 ' JL Tkm rrin) Flayers Ghost Creek Event IMP-.25 _Cafc_rted _Rscordsd affrwsb 1 IHydrographl IHydrograph] 4!r\. _&la_isd _ 1. % i s Trre(mn) _C_c_ted. GR>Msl I FleWaGhoc Creek 9-11-A4 Evsnt MP-.2S Fa her' Ghost Crssk IS-1-66 Event ftf-.2s I Hydrograph I [Hydrograph IHydrographl I«e 4 i: SO Tki»(rrtn) Tlrnsfn*.) I Hyetographl 12 c- 1 2 J«_ 1 olj Ji»1 O**"" Far haf» Ghost Crssk Evsnt AP-.2S Flshe/s Ghost Crssk Evant IMP-J5 Rahara Ghwt Craak Eaara I M 2

320 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-46 IHydrograph] Hydrograph 1 4» i S 2 It rjjr i i ^ * t ^" Calculated.bearded Time (rrtn) TVre(rm) _J_J! n*""" Fisher'* Ghost Creek Event IVP-.25 flatiafa Ghoat Craak , art M*Z, Figure Hydrographs for Fisher's Ghost Creek (RP) Table Summary of Results for Fisher's Ghost Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 2/11/ /5/ /1/ /12/ /3/ /3/ /3/ /11/ /12/ /1/ /11/ /11/ /12/ /1/ /8/ B /11/ /1/ / /5/ Mean 1.83 StdDev 1.3

321 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Jamison Park The mean parameter C found for Jamison park was , which is a significant reducti that in chapter 7 of The large reduction is directly associated with the modification to the area exponent in the impervious area lag equation. The trend in figure 9.34a has almost been removed, compared to the values determined in chapter 7. A sharp reduction on parameter C has occurred for the smaller discharges (between and.5m 3 /s). Table 9.17 shows a summary of the calibration results. [Hot of Parameter C sgsnst Qrse 1 IPtot Of Psnnwtef C*S(T»t VperA/tot 1 I 2 It - ( ; pemoon Pan.IMP Qrsc(rr_s) (a) 5 f' * ( i- (Jamiaon Pan. IMP-21 2 * Vpsf/Vtot (b) Figure Plot of Parameter C against Qrec and Ratio for Jamison Park (RP)

322 Chapter 9 - Modifying the Catchment Lag on Impervious Areas IHydrographl I Hydrograph I 1 2 -' o.« Tana (rrtn) O2 r\ w K>-/ 1,1 2, 3 v^ 4 5 Tkra(n*i) 5 1 ISO 2 Tkna(irln) ' - s BaaHH TTI I 1 1 m Tlrni{rTsi) nrehfh Jatmon Pair «" Evart _rnaonp«rl<m*-q2l Evsnt Jsmton Psrk IMP Evert I Hydrograph I 25 ". A fw A V A.5 r/" W Trw(nti) f.,^s- fhyetographl 1 pemteen Psrk WP Evsnt D'*' nf : M\\ n n b"** Jamaor Fark MMJ Ev art I Hydrograph] I Hydrograph I S" J tun / t t CO SO TVnt(n*i) Hyetograph 1 Hyetograph 1 - ru iqrawal I* IpXamial B 1 «af «I - 1 h n-nn n FWnfsl S- Jo ril (i*) T-Trs(mm] I,RsWal I _ Q_ gi-nfst [Jam.aon P.rf.lMP MB Evert PwkMP MB Event JenSaon Psrfc IMP- _i 5-2-M Evert

323 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Hydrograph 1 I Hydrograph I 3".6 I.4 TS.2 ^ 2 4 _CeC_rt»d _ ! _Cstt_1e _RecwOed Tlrm(rtln) lira (rrin] : r-i a 2_ n TVnstmjn) 1 Qn_nf_, Jemiaao ParklMP* Evert Jamieon Park IM P-.21 fl-*-m Event Figure Hydrographs for Jamison Park (RP) Table Summary of Results for Jamison Park (RP) Event Pervious Initial Pervious c Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 21/3/ /11/ /6/ /1/ /1/ /1/ /3/ /12/ /9/ /1/ /4/ /1/ /1/ /1/ O4.4 4/4/88B /4/ /2/88B /2/ /5/ /4/ Mean 1.51 StdDev.98

324 Chapter 9 - Modifying the Catchment Lag on Impervious Areas The Melbourne Catchment Vine Street The mean parameter C value for Vine Street was found to be This value has reduced quite a lot over the value in chapter 7 (C=4.84), but it is still high compared to the other catchments. There are no trends between C and the peak recorded discharge, but a trend still exists between C and the runoff volume ratio (figure 9.36b) where the more impervious events tend to require higher parameter C values to calibrate. Table 9.18 shows the calibration results. O 5 V _ 3 iplot of Parameter C against Qrec j -+ % Qrsc(n_s) [Vers Street IMP*.31 ] o s IS V _ 3 ( Plot of Parameter C against Vper/Vtotj (Vine. beet IMP-.311 ' ' * i i, Vper/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (RP) Hydrograph I I Hydrograph I IHydrographl 2 i..s i 1 u i f-*&j i i i _,.5 1 I _Cat_rt«Kj _CsfcUstsd _ Tims (rrtn) TkTB(rrtn) Time (rrin) I Hyetographl JL_i L_i l D M " Tims (rrtn) I".: Tims (rrin) _R»lnf_ Whs StreetII E virei street WF-aJi Event Vw Street W Evsnt IHydrographl fcT»{rrin) I Hyetographl 1 A 3 ' f.5 Jf.. i T T Tbra(nwi) _Cafcul»tad _Racorded R» W ", lri»(irai) Tarn (rrin) Vina straat MMI Brant VM Straat MM Evant Vha Straat MMJ Eaant

325 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-51 IHydrographl I Hydrograph I IHydrographl 1 _ o.s Tims (rrin) Trrre (mm] _Cetu*ted _ h 3 i' AA. l II f\ V\ V \\ / v_ Tkns(rrin) ) r- ISO 1 2 I- nram/al VM Street MM) Evsrt lfl Vine Sheet IMP-O Evsnt Vine Street MM).31 I.8-S5 Brsnt Figure Hydrographs for Vine Street (RP) Table Sumr nary of Results for Vim sstre et (RP) Event Pervious Initial Pervious c Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 1572/ /2/ / /1/ /12/ /11/ /4/ /1/ /9/ /12/ B/11/ Mean 3.42 StdDev 1.17

326 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Discussion of Results Loss Rate Modelling This chapter of the study dealt with final adjustments to the model to correct the trends that were occurring with parameter C and catchment areas. The mean parameter C values from chapter 7 were plotted against the catchment areas on a log-log scale and a trend between C and area was found (figure 9.1). Using regression, the trend was eliminated for the impervious areas by changing the area exponent in the lag equation from.57 to.25. The mean parameter C value using the modified lag equation was found to be for all the catchments. This value has reduced from in chapter 7. Although, the reduction is not large on an overall basis, the reduction in the three smallest catchments was very pronounced. Parameter C for Maroubra fell from 3.36 to 1.64 and on Jamison Park from 3.58 to Vine Street still caused problems, reducing from 5.19 to the still relatively large value of For the larger catchments, the opposite occurred. Curtin's parameter C value increased from.85 to The overall results from the modification of the impervious area lag equation was successful and thi can be seen in figure 9.38 and This plot shows parameter C against the catchment areas after modelling with the modified lag equation. The same plot in figure 9.1 showed a very pronounced trend between parameter C and the catchment area. Figures 9.38 and 9.41 shows this trend has reduced quite distinctly for both LR and RP modelling. As can be seen in figure 9.38 and 9.41, the.25 area exponent could have been reduced a little more to totally eliminate the slight trend still present. Before doing this, a test of significance at the 5 % level was performed on the regression analysis results to see if the slope was significantly different from zero. Using an average parameter C value of 1.61, standard deviation of.94 and sample size of 9 catchments, is the value of the random variable having the t-distribution with v = 9-1 = 8 degrees of freedom. From Miller, Freund and Johnson (199), for 8 degrees of freedom the probability that t will exceed is 5 % and that t will exceed is 1 %. Since t = is greater than -1.86, it can be said that slope of the line was not significantly different from zero at both the 5 % and 1 % levels. Thus, the trend between parameter C and the catchment area is not significant, and therefore the exponent of.25 was adopted.

327 Chapter 9 - Modifying the Catchment Lag on Impervious Areas o o> 1 3 Plot of Parameter C against Area * e»_.1 t i Area (km2) AH Catchments, Split Loss Rate 1 Figure Plot of Mean Parameter C against Catchment Area after modelling with modified lag equation (LR) Figure 9.39 shows plots of parameter C against the peak recorded discharge and the runoff volume ratio for loss rate modelling. As can be seen in figure 9.39a, the high parameter C values observed in figure 7.37, 7.38, 7.39 and 7.4 in the previous studies have been reduced, but parameter C is still high for small discharges. This is mainly due to the high parameter C values in Vine Street. Figure 9.39b shows that the type of event does not influence parameter C as much asit did before. High parameter C values were very common for the more impervious events in chapter 7 (both LR and RP modelling), and the changes to WBNM have helped to reduce the trend between parameter C and events which produce more impervious area runoff. rj 6? Plot of Parameter C against Qrec 1 15 Qrec (nrg/s) I Split Modeling Loss Ratel (a) O 6 4 DO r 2 Plot of Parameter C against Vper/Vtot ' / i_j»! ' J 1 ' > _ 4T Vper/Vtot Split Modelling Loss Rate (b) f _**%**.8 Figure Plots of Parameter C against Peak Discharge and Ratio (LR)

328 Chapter 9 - Modifying the Catchment Lag on Impervious Areas Proportion Modelling The parameter C values were very similar to those for loss rate modelling, but the values were s lower (see figure 9.4 and table 9.19). As discussed in section 7.5, the RP rainfall loss model will always produce lower parameter C values than the loss rate model because of the way in whichit removes the rainfall loss. Plot of Parameter C against Qrec * o j%i* «_ t Qrec (nfl/s) Split Modelling Proportion (a) 2 25 O _ r_ 2 Plot of Parameter C against Vper/Vtot»» ) Vper/Vtot [Split Modelling Proportion (b) Figure Plots of Parameter C against Peak Discharge and Ratio (RP) Plot of Parameter C against Area IU 1" * - o Area (km2) AII Catchments, Split Proportion] Figure Plot of Mean Parameter C against Catchment Area after modelling with modified lag equation (RP)

329 Chapter 9 - Modifying the Catchment Lag on Impervious Areas 9-55 Table Parameter C values for Different Loss Models Catchment Curtin Mawson Long Gully Creek Giralang Maroubra Strathfield Fisher's Ghost Creek Jamison Park Vine Street Mean Mean Chapter 4 LR NA NA 2.27* NA Chapter 7 LR * 2.18* Chapter 7 RP * 1.99* * mean parameter C excluding Jamison Park and Vine Street parameter C values * mean parameter C for all catchments Chapter 9 LR * 1.61* Chapter 9 RP * 1.43* 9.6 Conclusions In chapter 4, high parameter C values and trends between parameter C and the peak recorded discharges were observed. WBNM was then rewritten to run linearly on the impervious areas. This helped reduce the high parameter C values, but trends between the type and size of the event remained. Running the impervious areas linear was proven to be generally successful, but high parameter C values were noticed on the smallest catchments. This indicated that parameter C was now sensitive to the size of the catchment. A number of reasons for this were suggested. The first was the possibility that the impervious fract was too high. A modified impervious fraction based on the method by Boyd et al. (1993) was calculated using only the small events which produced high parameter C values. This modified impervious fraction was lower than the directly connected impervious fraction used previously. However, since the trend between catchment area and parameter C still remained (figure 8.1b) it was decided that further development of the impervious area module of WBNM was required, although for small storm events it was found that the directly connected imperviousfraction is probably smaller (chapter 8). Plots of parameter C against the catchment areas showed that C was higher for the smaller catchments and lower for larger catchments. This indicated that the exponent in the impervious area lag equation of.57 was too high, and this was modified. Using regression analysis, a new value of.25 was trialled successfully, and the trend between parameter C and the catchment area was essentially

330 Chapter 9 - Modifying the Catchment Lag on Impervious Areas eliminated. This improvement is best described in figure 9.1 (before modification of the impervious area lag equation) and figure 9.38 after modification. The average parameter C value calculated for LR modelling was 1.61 and for RP modelling was Using these values, the factor IMPFACT which is used to reduce the impervious area lag time will be adjusted in chapter 1 so the average parameter C values are about 1.7, which is approximately the value calculated by Boyd (1985) for rural catchments.

331 Chapter 1 Final Modifications to WBNM Version 2.1

332 Chapter 1- Final Modifications to WBNM Version FINAL MODIFICATIONS to WBNM Version Introduction WBNM Version 2.1 has undergone numerous modifications up to this point in the study. The following is a summary of the modifications. 1. After comparing the results of modelling using lumped pervious and impervious, with the results for split pervious and impervious area runoff, the latter produced better results andit was decided to model the urban catchments with split pervious and impervious runoff. 2. The non-linearity in the impervious area lag equation (-.23) was changed to zero. Thus the lag parameter for impervious areas was made linear and independent of the discharges. 3. The area exponent (.57) in the impervious area lag equation was found to be too high and was changed to.25. This eliminated the trend for larger parameter C values on small catchments (up to 1 km 2 ) and smaller parameter C on large catchments. The mean parameter C values calculated for the nine catchments were 1.61 for the LR model and 1.43 for the RP model. 4. Finally, the factor IMPFACT will be adjusted to increase the parameter C values determined in chapter 9 to a value close to 1.7. This is the parameter C value determined by Boyd et al (1985) for rural catchments. The following section will discuss the adjustment procedure, and WBNM will be calibrated on all events again. 1.2 Adjustment of the Factor IMPFACT As mentioned in section 1.1 above, the mean parameter C value calculated for the nine urban catchments was 1.61 and 1.43, and IMPFACT will be adjusted using these two values. The impervious area lag equation is presently as follows: K^p = IMPFACT.C.A imp 25 equation 1.1 where IMPFACT =.111 (old value) The preferred parameter C value is 1.7 as this is the value used for rural catchments. When calibrating a recorded event with WBNM, only the pervious area parameter C value needs to be assigned. The factor IMPFACT then converts the pervious area C value into the impervious area C value. From equation 1.1, it can clearly be seen that if IMPFACT is set at.111, and the calibration

333 Chapter 1- Final Modifications to WBNM Version of recorded events results in a parameter C value lower than 1.7 This suggests the IMPFACT value is too high, and needs to be reduced. The factor IMPFACT is to be adjusted as follows: IMPFACT new = C urb.impfact old / C m equation 1.2 Curb ^rur IMPFACT new IMPFACT old = 1.61 (loss rate modelling) = 1.43 (runoff proportion modelling) = 1.7 (Boyd et al for rural catchments) = the new factor =.111 Note that for events with both pervious and impervious runoff, this adjustment will exactly compensate for the impervious area runoff, but the slightly larger C value (approximately 1.7) will give a slight reduction in peak discharge from the pervious areas. However, this effect should be small to insignificant because flows near the hydrograph peak are dominated by the impervious area runoff component. As there are two values for C^, the mean of these will be used. Thus C^ is:,* =1.52 IMPFACT,^ = 1.52x.111/1.7 =.99 =>.1 Thus the new factor IMPFACT is.1. The new impervious area lag equation is now as follows: K^O.l.CA^25 equation 1.3 WBNM was rewritten to use this IMPFACT and all events on all catchments were calibrated again to see how the adjustments have performed.

334 Chapter 1- Final Modifications to WBNM Version Initial Loss-Continuing Loss Model The Canberra Catchments After adjusting IMPFACT to.1 and calibrating on recorded storms, the mean parameter C obtained for Curtin, Mawson, Long Gully Creek and Giralang can be seen in table 1.1. A slight increase in parameter C has occurred due to the adjustment of IMPFACT. The median loss rate used to balance calculated and recorded runoff volumes can also be seen in table 1.1. The loss rates in these catchments is somewhat higher than is typically found in rural catchments. The reason for this is that in events with significant amounts of impervious area runoff and little pervious area runoff, the loss rate must be high to prevent runoff from the pervious surfaces. It is possible that in rural catchments, these events would cause very low (possibly negligible) runoff and would not be included in the data set. Figures 1.1 to 1.4 show the plots of parameter C against the recorded peak discharge and runoff volume ratio for Curtin, Mawson, Long Gully and Giralang, respectively. As can be seen, slight trends are apparent in some cases but not in others. Overall, the modifications have reduced the trends apparent in chapters 4, and 7. Tables 1.2 to 1.5 summarise the calibration results for the Canberra catchments. The hydrographs for all the Canberra catchments are similar to those in chapter 7, and have not been reproduced. Table Summary of mean Parameter C and Median Loss Rates for Canberra Catchments Catchment Curtin Mawson Long Gully Creek Mean Parameter C Median Loss Rate (mm/hr) Giralang

335 Chapter 1 - Final Modifications to WBNM Version I Plot of Parameter C against Qrecj Plot of Parameter C against Vper/Vtot 1 I Cum, IMP-.17] Qrac(rrOrs) (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Curtin (LR) I Plot of Parameter C against Qrec I I Plot of Parameter c against Vper/Vtot] ot.s - «a I ' 4.3 to o i-s I t.. S * * e.5.4 OJ.6.7.» Qrac(ntta) IMawaonMP-O^tl IMawaon IMP-OJ1 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Mawson (LR) Plot of Parameter C against Qrec I I Plot of Parameter c against vper/vtotl Orae (irtva) LaiuOu»/Ci»a>IMP-.5 (a) Lang Quay OaaK M rm).5] Vparrvtd (b) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (LR) Plot ol Parameter c against Qrec IPIot ol Parameter C against Vper/Vtot Qrac(ntVa) Gia»nglMf.22 (a).2.4.b Vpar/Vtot IGtakno IMP- 22] (b) Figure Plot of Parameter C against Qrec and Ratio for Giralang (LR)

336 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Curtin (LR) Event Pervious Pervious c Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ B /4/ /3/ /3/ /1/ /2/ /1/ B /1/ Median LR 3.36 Mean 1.23 StdDev.6 Table Summary of Results for Mawson (LR) Event Pervious Initial Loss Pervious Loss Rate c Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate (mm/h) (m 3 /s) (m 3 /s) 13/2/72 21/3/74 5/11/74 14/1/77 614m 2/3/78 23/3/78 9/1/78 5/2/81 6/1/81 15/1/ Median LR 3.97 Mean.71 StdDev.47

337 Chapter 1 - Final Modifications to WBNM Version Table Summary of Results for Long Gully Creek (LR) Event Pervious Initial Loss Pervious Loss Rate C Cused Calculated Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Flowrate Peak Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 572/71 5/2/81 5/11/74 671/81 6/4/ /1/ /2/ /2/ /1/77 15/1/ /3/ /3/ /3/ B.24 26/1/ Median LR Mean 1.79 Std Dev 1.13 Table Summary of Results for Giralang (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (thoum 3 ) (m 3 /s) (m 3 /s) 27/3/ ,12 14/1/ /4/ D /1/ /3/ /3/ /1/ /2/ , 5/2/ /1/ ,36 24/3/ ,3 15/1/ /12/ /3/ Median LR Mean.64 Std Dev.39

338 Chapter 1- Final Modifications to WBNM Version Results for the Sydney Catchments The mean parameter C and median loss rates obtained for Maroubra, Strathfield, Fisher's Ghost Cr and Jamison Park can be seen in table 1.6. As in the Canberra catchments, a slight increase in parameter C has occurred due to the adjustment of the factor IMPFACT. Figures 1.5 to 1.8 show the plots of parameter C against the recorded peak discharge and ratio of pervious to total runoff volumes for Maroubra, Strathfield, Fisher's Ghost Creek and Jamison Park, respectively. As can be seen, there is quite an amount of scatter in the results, but no obvious trends. Tables 1.7 to 1.1 summarises the calibration results for the Sydney catchments. The hydrographs for all the Sydney catchments are similar to those in chapter 7, and have not been reproduced. Table Summary of mean Parameter C and Median Loss Rates for Sydney Catchments Catchment Maroubra Strathfield Fisher's Ghost Creek Mean Parameter C Median Loss Rate (mm/hr) Jamison Park

339 Chapter 1- Final Modifications to WBNM Version Plot of Parameter C against Qrec 1 1 Plot of Parameter C against VperA/tot 1 O 3 V - t OS ! Orac(naia) M«roubr» IMP- 16 O 3 I I 2 4 i -. - *> " a * ) 2.4.«.5 Vp«r/Vtot [iiureubn MP".ie (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (LR) I Plot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtotj [StmthftaW HMP-.2P (a) [ShrthlWId aip-q.2b (b) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (LR) Plot of Parameter C against Qrec I I Plot of Parameter C against Vper/Vtot Qrec (no's) \FMWGtiowtCiwkMf>-Q25\ (a) ~~~j Gho* O k IMP-.251 (b) Figure Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Creek (LR) Plot o) Parameter C against Qrec I,'».- OJS Orac(mVa) l.maon P.rtUMP-.2ll (a) 4 O «3!> PW of PararmtcrC agonal Vp«r/Vtot» * «i i i tamtaon Pwk IMP-.211 Vptr/Vtot (b) Figure Plot of Parameter C against Qrec and Ratio for Jamison Park (LR)

340 Chapter 1 - Final Modifications to WBNM Version Table Summary of Results for Maroubra (LR) Event 1/3/77 5/3/77 3/3/78 17/3/78 27/3/78 13/4/78 18/5/78 19/6/79 2/6/79 17/3/83 18/6/83 6/11/84 8/11/84 11/12/84 1/5/85 12/4/86 3/7/87 4/1/87 2/4/88 28/4/88 Pervious Initial Loss 8.6 Median LR Pervious Loss Rate (mm/h) C Mean StdDev Cused Calculated Pervious Area (thoum 5 ) Impervious Area (thoum 3 ) Rainfall Excess Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (nrvs)

341 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Strathfield (LR) Event 3/9/77 4/9/78 2/3/81 2/4/81 4/4/81B 4/4/81 3/12/82 25/3/82 3/9/83 16/3/83 21/5/83 7/4/84 8/1/84 8/11/84 1/5/85 3/4/85 4/8/86 13/2/88 3/4/88 28/4/88 Pervious Initial Loss zo Median LR Pervious Loss Rate (mm/h) C Mean StdDev Cused (thoum 3 ) Calculated Pervious Area Q Impervious Area (thou m 5 ) Rainfall Excess Total Rainfall B Calculated Peak Flowrate (m'/s) Peak Flowrate (m 3 /s)

342 Chapter 1 - Final Modifications to WRNM Version Table Summary of Results for Fisher's Ghost Creek (LR) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Loss Area Area Excess Rainfall Peak Peak Loss Rate Flowrate Flowrate (mm/h) (m 3 /s) (m 3 /s) 2/11/ /5/ /1/ /12/ /3/ /3/ /3/ /11/ /12/ /1/ /2/ /11/ /11/ /12/ /1/ /8/ /11/ /1/ /6( /5/ Median LR Mean 2.12 StdDev 1.7

343 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Jamison Park (LR) Event 21/3/83 7/11/84 3/6/86 3/1/86 4/1/86 1/1/87 1/3/87 1/12/87 6/9/87 1/1/88 1/4/88 21/1/88 2/1/88 4/1/88 4/4/88B 6/4/88 7/2/88B 8/2/88 8/5/88 9/4/88 Pervious Initial Loss Median LR Pervious Loss Rate (mm/h) C Mean Std Dev Cused (thoum 3 ) Calculated Pervious Area (thoum 3 ) Impervious Area Rainfall Excess Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (m 3 /s)

344 Chapter 1- Final Modifications to WBNM Version Results for the Melbourne Catchment The mean parameter C value for Vine Street was found to be 4.4, which is still very high comp to the other catchments. The median loss rate value was calculated to be 8.12 mm/hr. Figure 1.9 shows plots of parameter C against peak recorded discharge and parameter C against the runoff volume ratio. As can be seen, there is still a trend between parameter C and the runoff volume ratio which has not been eliminated by any modification to the model. Table 1.11 summarises the calibration results. I Plot of Parameter C against Qrec ] Plot of Parameter C against VperrVtet] 1.4 u 1J «2«Qrec(nfl/a) MSaMttMP-ojll (a) IVlnaStiaat IMP-.31 (b) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (LR) Table Sumi nary of Result s for Vin estre set (LK I Event Pervious Initial Loss Pervious Loss Rate (mm/h) C Cused Calculated (thoum 3 ) Pervious Area Impervious Area Rainfall Excess Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (m 3 /s) 15/2/72 4/2/73 15/5/74 11/1/75 29/12/75 2/11/76 714m 15/1/83 1/9*5 1/12/ / , Median LR 8.12 Mean 4.4 Std Dev 1.48

345 Chapter 1- Final Modifications to WBNM Version Results using the Proportion Model The Canberra Catchments The mean parameter C and median runoff proportion obtained for Curtin, Mawson, Long Gully Creek and Giralang can be seen in table Figures 1.1 to 1.13 show the plots of parameter C against the recorded peak discharge and ratio of pervious to total runoff volumes for Curtin, Mawson, Long Gully and Giralang, respectively. As can be seen, there is quite an amount of scatter in the results, but no strong trends. Tables 1.13 to 1.16 summaries the calibration results for the Canberra catchments. Table Summary of mean Parameter C and Median Proportion for Canberra Catchments Catchment Curtin Mawson Long Gully Creek Mean Parameter C Median Proportion Giralang.6.38

346 Chapter 1- Final Modifications to WBNM Version I Plot of Parameter C against Qrec I I Plot of Parameter C against Vper/Vtot I *.5 _t I L_ Qrec<fr_») Curt* IMP-O 17 lcuran.mp-.t7l (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Curtin (RP) I" Plot of Parameter C against Qrec I " * «. i * SO Qiae(rra/a) M«w»DniUP-Jl (a) 1" 1 Plot of Parameter C against Vper/Vtot j "* Vpw/Vtat M«w_n IM P-.211 (b) Figure Plot of Parameter C against Qrec and Ratio for Mawson (RP) 1 Plot of Parameter C against Qrec j ) Plot of Parameter C against Vper/Vtotj 5 I 3!> S 1 - * Qr«e <rrfl/i) LonD Guly CfNk IMP- 51» 3 *.... *». ** Vpw/Vtot Long Guly Cf k IMP- 5 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Long Gully Creek (RP) (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Giralang (RP)

347 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Curtin (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ /4/ /3/ /3/ /1/ /2/ /1/ /1/ Median RP.18 Mean 1.12 Std Dev.62 Table Summary of Results for Mawson (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate (m 3 /s) Flowrate (m 3 /s) 13/2/72 21/3/74 5/11/74 14/1/77 614m 2/3/78 23/3/78 9/1/78 5/2/81 6/1/81 15/1/ Median RP.36 Mean.61 Std Dev.36

348 Chapter 1 - Final Modifications to WBNM Version Table Summary of Results for Long Gully Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 26/1/ /2/ /2/ /2/ /3/ /11/ /1/ m /3/ /3/ /1/ /2/ /1/ /1/ Median RP.12 Mean 1.46 Std Dev 1.25 Table Summary of Results for Giralang (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (thoum 3 ) (m 3 /s) (m 3 /s) 27/3/76 14/1/77 674/77 27/1/78 2/3/78 23/3/78 9/1/78 2/2/8 5/2/81 6/1/81 24/3/82 15/1/83 13/12/83 25/3/ Median RP.38 Mean.6 Std Dev.43

349 Chapter 1- Final Modifications to WBNM Version 2.1 1Q The Sydney Catchments The mean parameter C and median loss rates obtained for Maroubra, Strathfield, Fisher's Ghost Cre and Jamison Park can be seen in table As in the Canberra catchments, a slight increase in parameter C has occurred due to the adjustment of the factor IMPFACT. Figures 1.14 to 1.17 show the plots of parameter C against the recorded peak discharge and ratio of pervious to total runoff volumes for Maroubra, Strathfield, Fisher's Ghost Creek and Jamison Park, respectively. As can be seen, there is quite an amount of scatter in the results, but no strong trends. Tables 1.18 to 1.21 summaries the calibration results for the Sydney catchments. Table Summary of mean Parameter C and Median Proportion for Sydney Catchments Catchment Maroubra Strathfield Fisher's Ghost Creek Mean Parameter C Median Proportion Jamison Park

350 Chapter 1- Final Modifications to WBNM Version P lot ol Parameter C agajrut Qrec I Plot o! Parameter C against Vper/Vtot I Orac(nQJa) [M.rauBf. IMP- ie [Manmbta IMP^.1B 2.4 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Maroubra (RP) Plot of Parameter C against Qrec I 1 Plot of Parameter C against VperA/tot j o s a I 2. * *. * it [StntHtoid IMP-.29j S Qr*c(n-») O 3 k r _ 1. [Stnthfeid IMP-29\ Vptr/Vtot (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Strathfield (RP) I Plot of Parameter C against Oreo I I Plot of Parameter C against VperA/tot I» ' I 3 - S 2 S RthW» Ghoat Cr*«kLMP-.25 (a) I FWiars Gho«t Craak WP-.2S1 (b) Figure Plot of Parameter C against Qrec and Ratio for Fisher's Ghost Creek (RP) I PJot of Parameter C against Qrec I Plot of Parameter C against Vper/Vtot] u 3 a i*» v - OS Qrac(tT/a] [imnten PwklMP-oiT] (a) O 3 a! 2 i 1 - iarrwottpbrklmp--1 * Vpar/Vtot (b) Figure Plot of Parameter C against Qrec and Ratio for Jamison Park (RP)

351 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Maroubra (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 1/3/ /3/ /3/ /3/ /3/ /4/ / / /6/ /3/ /6/ /11/ /11/ /12/ / /4/ /7/ /1/ /4/ /4/ Median RP.6 Mean 1.72 Std Dev 1.2

352 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Strathfield (RP) Event 3/9/77 4/9/78 2/3/ /4/81B 4/4/81 3/12/82 25/3/82 3/9/83 16/3/83 21/5/83 7/4/84 8/1/84 8/11/84 1/5/85 3/4/85 4/8/86 13/2/88 3/4/38 28/4/88 Pervious Initial Loss Median RP Pervious Proportion C Mean StdDev Cused Calculated S Pervious Area Impervious Area (thoum 3 ) Rainfall Excess Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (m 3 /s)

353 Chapter 1- Final Modifications to WBNM Version Table Summary of Results for Fisher's Ghost Creek (RP) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 2/11/ /5/ /1/ /12/ /3/ /3/ /3/ /11/83 13/12/83 26/1/ /11/84 9/11/84 B/12/85 15/1/86 6/8/86 18/11/86 24/1/87 5/6/88 24/5/ B Median RP.19 Mean 2. StdDev 1.15

354 Chapter 1- Final Modifications to WBNM Version Event 21/3/83 7/11/ /1/86 4/1/86 1/1/87 1/3/87 1/12/87 6/9/87 1/1/88 1/4/88 21/1/88 2/1/88 4/1/88 4/4/88B 6/4/88B 7/2/88B 8/2/88 8/5/88 9/4/88 Pervious Initial Loss Median RP Table Pervious Proportion C Mean StdDev Cused Summary of Results for Jamison Park (RP) Calculated (thoum 3 ) Pervious Area O.OE Impervious Area (thoum 3 ) Rainfall Excess D Total Rainfall Calculated Peak Flowrate (m 3 /s) Peak Flowrate (m 3 /s)

355 Chapter 1- Final Modifications to WBNM Version The Melbourne Catchment The mean parameter C value for Vine Street was found to be 3.64 and the median runoff propo was.6. Figure 1.18 shows plots of parameter C against peak recorded discharge and parameter C against the runoff volume ratio. As can be seen, there is still a trend between parameter C and Vper/Vtot which has not been eliminated by any modification to the model. Table 1.22 summaries the calibration results for Vine Street. 1 Plot of Parameter C against Qrec 1 I Plot of Parameter C against VperA/tot j o" * 1 s- fij o«- 2» Qrec(nrOr«) < IMP-.311 (a) (b) Figure Plot of Parameter C against Qrec and Ratio for Vine Street (RP) Table Summary of Result; > for Vin estre et(rp ) Event Pervious Pervious C Cused Calculated Pervious Impervious Rainfall Total Calculated Initial Area Area Excess Rainfall Peak Peak Loss Proportion Flowrate Flowrate (m 3 /s) (m 3 /s) 15/2/ /2/ /5/ /1/ /12/ /11/ m /1/ /9/ /12/87 8/11/ Median RP.6 Mean 3.64 StdDev 1.42

356 Chapter 1- Final Modifications to WBNM Version Discussion of Results Final Analysis of Results The final modifications to the latest version of the Watershed Bounded Network Model, WBNM Version 2.1 have been made. Calibration of a total of 144 storm events on nine urban catchments has been done, using the initial loss-constant loss rate rainfall loss model and the initial loss-runoff proportion rainfall loss model. From the results, plots of parameter C against the peak recorded discharge and parameter C against the runoff volume ratio were plotted on an individual catchment basis (sections 1.3 to 1.4) and combined for all the catchments. Figure 1.19 and 1.2 show the plots for loss rate and runoff proportion modelling. Note the high parameter C values for small discharges. Most of these high parameter C values are for the Vine Street catchment. Although there has been a general reduction of parameter C throughout the study, Vine Street still produced parameter C values that were higher than the other catchments, and Giralang and Mawson have produced lower parameter C values. See figure One cause of the high parameter C values on Vine Street would be an overestimate of the impervious fraction or catchment area, but careful checks of these by the author has shown the values used in the study to be correct. An overestimate in these values would cause the model to overestimate runoff and would require high parameter C values (with corresponding high model lag time K) to reduce the calculated discharges. The opposite effect could explain the low parameter C values on Giralang and Mawson. It is worth noting that similar results for the above three catchments have been reported in other studies (NCDC, 1989). Although there are minor trends between parameter C and the peak recorded discharges and runoff volume ratio for each individual catchment (figures 1.1 to 1.18), overall the trends are not significant (figures 1.19 to 1.2). The amount of scatter in parameter C reduces significantly between chapter 4 and chapter 1 (except for Fisher's Ghost Creek) indicating the changes performed to WBNM has improved its performance on urban catchments (table 1.23).

357 Chapter 1 - Final Modifications to WBNM Version Table Comparison between Parameter C in Chapter 4 and 1 (LR) Catchment Curtin Mawson Long Gully Creek Giralang Maroubra Strathfield Fisher's Ghost Creek Jamison Park Vine Street Chapter 4 Parameter C Values (LR) Mean Standard Deviation Chapter 1 Parameter C Values (LR) Mean Standard Deviation Plot of Parameter C against Qrec Plot of Parameter C against Vper/Vtot *_** Qrec (rrfl/s) Split Modelling Loss Rate All Catchments 2 25 Split Modelling Loss Rate All Catchments «* * :.8 (a) Plot of Parameter C against Qrec (b) Plot of Parameter C against Vper/Vtot I o &i» i 1 15 Qrec (rrfl/s) Split Modelling Loss Rate Vine Street Results Omitted Vper/Vtot Split Modelling Loss Rate Vine Street Results Omitted (c) (d) Figure Plots of C against Qrec for Loss Rate Modelling

358 Chapter 1- Final Modifications to WBNM Version Plot of Parameter C against Vper/Vtot Qrec (Ira's) Split Modelling Proportion AD Catchments (a) 15 Plot of Parameter C against Qrec 1 Split Modelling Proportion All Catchments (b) Plot of Parameter C against Vper/Vtot X «> Qrec (m3/s) Split Modelling Proportion Vine Street Results Omitted I Vper/Vtot Split Modelling Proportion Vin Street Results Omitted *. (c) (d) Figure Plots of C against Qrec for Proportion Modelling Figure 1.21 and 1.22 show plots of the mean parameter C value for each catchment against the size of the catchment for loss rate and runoff proportion modelling. As can be seen, with the modifications to the area exponent in the impervious area lag equation from.57 to.25 in chapter 1, the trend that was present in chapter 7 has been dramatically reduced, if not, eliminated. The average parameter C for loss rate modelling is 1.7 and for runoff proportion modelling is 1.5. Plot of Parameter C against Area * 1 C ave = " Area (km2) All Catchments. Split Loss Rate] 1 Figure Plot of C ave against Catchment Area for Loss Rate modelling

359 Chapter 1- Final Modifications to WBNM Version Plot of Parameter C against Area * * C = v -'ave A 1.5 « Area (km2) [All Catchments, Split Proportion 1 Figure Plot of C ave against Catchment Area for Proportion modelling In figure 1.23, the average parameter C values determined in this chapter for each catchm plotted with values of parameter C for rural catchments (Boyd, 1976). As can be seen, the values for urban catchments do not deviate significantly from those determined by Boyd (1976) for rural catchments. 1 o I a "»o Hot of Parameter C against Catchment Size Urban Catchments Rural Catchments C=1.7 -* n Catchment Area (km2) Figure Comparison C urt> and C^ against Catchment Area

360 Chapter 1- Final Modifications to WBNM Version Statistical Analysis of Results Figure 1.24 and figure 1.25 show the statistical analysis of all the pervious loss rates and perv runoff proportions used to balance the calculated runoff volumes with the recorded. A total of 122 storms where the volumes balanced were used in the analysis. The median pervious area loss rate was calculated to be 23.1 mm/hr and the median pervious area runoff proportion was.2. The median loss rate and median runoff proportion calculated in this study are very high compared t values suggested for use in design purposes in Australian Rainfall and (ARR 1987). A median loss rate of 2.5mm/hr is recommended for use on catchments in eastern New South Wales and Victoria. The reason the loss rates in the study are high is mainly because of the way WBNM calculates the runoff volume. Events consisting mainly of impervious area runoff, rainfall losses on the pervious areas must be high as most of the runoff is generated by impervious surfaces. But, on rural catchments, these events would produce lower runoff, due to higher losses on pervious surfaces. Frequency Distribution of Loss Rates «15 a> 1 1 * 5 5 JIII du lallil[alljlltliltli»«> a iliiifili a II i imi I Loss Rate Values (mnrvhr) Figure Frequency Distribution of Individual Loss Rate values Frequency Distribution of Proportion I OrtlmM r^mlti i ftoportionvalues Figure Frequency Distribution of Individual Proportion values WBNM Version 2.1 was rerun for all catchments with parameter C set to 1.7 for the loss rate model and 1.5 for the runoff proportion model. Values of LR and RP were selected to give correct volumes. The impervious area initial loss was also varied between and 1 mm. This was done to determine the performance of WBNM for thefinallyadopted parameter C values. The mean error between the

361 Chapter 1- Final Modifications to WBNM Version calculated and recorded discharges was calculated and the results analysed. The aim of this analysis was to determine the likely accuracy of the model when applied to ungauged catchments. The results can be seen in table Table Mean of Errors between the Two Loss Models Catchment Curtin Mawson Long Gully Creek Giralang Maroubra Strathfield Fisher's Ghost Ck Jamison Park Vine Street Mean Error with LR(%) H-imp=mm ILH =1mm Error with RP (%) IL^Omm 1^=1 mm Note: Error = ABS((Qcalc - Qrec)/Qrec x 1 (%) where Qcalc - calculated peak discharge Qrec - recorded peak discharge As can be seen, the overall average error between the calculated and recorded discharges for both the loss rate and runoff proportion rainfall loss models is 31 %. On an individual catchment basis, there was very little difference between the error for the loss rate model and the runoff proportion model. Again, due to the fact that Vine Street produced the highest mean parameter C value (4.4 for loss rate and 3.64 for runoff proportion), the error calculated was also very high. WBNM was found to estimate the calculated discharge within + 15% of the recorded value, in 6% of the events. Calculated discharges were overestimated by more than 15% for 3% of the events. This was for both the loss rate and runoff proportion rainfall loss models. For Vine Street, in all the events, the calculated discharge was overestimated. For the Canberra catchments (except in Curtin), WBNM underestimated the calculated discharges morefrequently. For the Curtin catchment, WBNM overestimated the calculated discharges for events where runoff was predominantly from the impervious areas. The calculated discharges were underestimated for the events in which pervious area runoff was predominant. In the Sydney catchments, there were more events where the discharges were overestimated. In all the catchments, when the pervious and impervious area contribution was similar (ie. Vper/Vtot =.5), the calculated and recorded discharges were similar when parameter C was 1.7 for loss rate

362 Chapter 1- Final Modifications to WBNM Version and 1.5 for runoff proportion. When the size of the storm was considered, it was found that for large events, WBNM underestimated the calculated discharges and overestimated them for the smaller events. A similar result occurred for Mawson, Giralang, Fisher's Ghost Creek, and Jamison Park. These results follow from the variation of parameter C with event size as discussed in section Due to Long Gully Creek having such a low directly connected impervious fraction (IMP=.5), these trends did not occur. In most of the events, pervious area runoff was greater than impervious area runoff as it can be said the catchment is essentially rural. The Maroubra catchment is situated on highly pervious sandy soil and no matter what size storm occurs, pervious area runoff contribution will be less than impervious. This is clearly evident from the results, so the analysis above does not apply to Maroubra. For Strathfield, the calculated discharges were underestimated for events where the impervious area contribution was greater than the pervious. There were two large events (5 and 6 years ARI on the 28/4/88 and 4/8/86, respectively) where more pervious area runoff occurred. In both events, the calculated discharges were overestimated by WBNM.

363 Chapter 1- Final Modifications tn WBNM Version Recommendations for using WBNM Version 2.1 WBNM Version 2.1 has been developed to calculate runoff hydrographs from rainfall hyetographs on both rural and urbanised catchments. This study concentrated on the development of WBNM for use on urbanised catchments. From the study, the following recommendations can be made on using WBNM to calculate runoff hydrographs. 1. Split catchment modelling is a better method of representing the complexities associated with urban catchments. Split modelling allows pervious and impervious areas on a catchment to be modelled separately. By doing this, the runoff hydrographs from the pervious areas can be calculated separately from the impervious area hydrographs. The total contributionfromthe subcatchment is then calculated by adding the two hydrographs at the outlet. At the start of the study, WBNM calculated lag times from the pervious and impervious areas using the same lag equation (equation 2.31). It was found that by using this general equation for both areas, parameter C was very high for small storm events and small catchment sizes. The cause of this was found to be the way WBNM was modelling the impervious areas. The pervious area lag equation has been used for a number of years, and it would be unlikely that it was causing the problems. The impervious area lag equation was modified tofinallyrun linearly, with an area exponent of.25 and an impervious area lag reduction factor IMPFACT of Lumped modelling of urban catchments, using a single storage to represent both the pervious and impervious areas, was also found to be satisfactory, but the results for split modelling were better. Lumped modelling was particularly successful for single burst storm events. 3. It was found that both the initial loss-constant loss rate rainfall loss model and initial lossrunoff proportion rainfall loss model were appropriate for use on urban catchments. The loss rate model is mostly used in design offices today, but this study showed that the runoff proportion model was as good, if not better than the loss rate model for urban catchments. But for multi burst storm events (chapter 6) it was found that the losses in reality decay exponentially. Multi burst events should therefore be modelled as a number of single burst events with individual rainfall losses. The runoff proportion model performed better for events where more impervious area runoff contribution occurred. In these events, it was found that the loss rates required to balance the calculated and recorded runoff volumes were very high and in some cases, all impervious area runoff occurred with little pervious area contribution. In these cases, the high loss rates cut off the small

364 Chapter 1- Final Modifications to WBNM Version rainfall from either side of the main burst in the rainfall hyetograph. This allowed no pervious area runoff, and thefit between the calculated and recorded hydrograph suffered. On the other hand, when the runoff proportion model was used, a small proportion of the pervious area rainfall was retained, and the minor ordinates on the hyetograph contributed some rainfall excess, giving a better calculated hydrograph. 4. The mean parameter C value calculated for the loss rate model was found to be slightly higher than for the runoff proportion model. The runoff proportion rainfall loss model will always produce lower parameter C values than the loss rate model because of the way in which it removes the rainfall loss. For the runoff proportion model, the rainfall excess hyetograph is calculated by removing a proportion of the rainfall. The loss rate model removes an average amount of rainfall over the entire duration of the event. Thus the runoff proportion model will always remove less rainfall than the loss rate model for the minor rainfall ordinates at the beginning and end of a storm. At the peak rainfall intensity, the runoff proportion model will always remove more rainfall than the loss rate model. Thus the rainfall excess at this point in the hydrograph will always be lower for runoff proportion modelling than loss rate modelling. WBNM then requires a lower parameter C. 5. When using WBNM to calculate design discharges, parameter C can be set at 1.7 when using the initial loss-constant loss rate rainfall loss model. If using the initial loss-runoff proportion rainfall loss model for calculation of design discharges, parameter C should be set at about 1.5.

365 Chapter 11 Application of WBNM to a Subdivided Catchment

366 Chapter 11 - Application of WBNM to a Subdivided Catchment APPLICATION of WBNM to a SUBDIVIDED CATCHMENT 11.1 Introduction Up to this stage of the study, the nine urban catchments were modelled as one subcatchment effects of the watercourses sections on modelling results were not specifically considered. The results have been presented in chapters 4 to 1 and show that modelling with one subcatchment is quite satisfactory. The results from this study are consistent with those of Bufill (1989) who also modelled a number of urban catchments as one subcatchment, and obtained good results. Many hydrologic computer models, including WBNM, divide the catchment into subcatchments a watercourse sections. The aim of this chapter is to model one of the nine urban catchments whenit is subdivided into a number of subcatchments. It was decided to subdivide the Curtin catchment into 4, 5, 11 and 19 subcatchments. The reason for selecting Curtin was due to its large size (27 km 2 ) and because the Mawson and Long Gully Creek catchments make up subcatchments within the Curtin catchment. This allowed separate rainfall gauges and recorded hydrographs to be used for these subcatchments. Due to the size of the catchment, three rainfall gauges give a better description of the rainfall pattern. One may ask why all the urban catchments were not subdivided from the start of the study. determine the ability of WBNM to model urban catchments in its initial form,it was decided to model the urban catchments with one subcatchment. This avoided the need to model watercourse sections, as they were lumped together with the overland flow surfaces. In other models (such as RORB), the lag is factored down using a relation of type (1+U) X without specifically considering watercourse sections. It was discovered at an early stage of the study that WBNM did have problems with the way it modelled impervious surfaces and it was decided to concentrate on these problems by modelling catchments with one subcatchment before extending the study to subdivided catchments. For this part of the study, a site visit to the Curtin, Mawson and Long Gully Creek catchm undertaken to survey the watercourse sections. Field data on the watercourse sections was collected to help calculate the stage-discharge relationships for the watercourses. From this, average lag times through a watercourse section can be calculated and these values can be used as a guide for modelling the watercourse sections Watercourse Section - Data Collection and Analysis A site visit was conducted in late December, The aim of the visit was to determine t condition of all watercourse sections within the Curtin catchment. This data was required to estimate

367 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-3 Manning's roughness coefficients which are needed to determine the watercourse factors WCFACT for use in WBNM. WBNM has three methods which allow routing of upstream hydrographs through watercourse sections. They are: 1. Muskingum Cunge routing, which allows for both attenuation and translation of the runoff hydrograph. 2. A time delay, by which the hydrograph is delayed by a user specified time (in minutes). 3. Nonlinear channel routing. Nonlinear routing uses a reduced watercourse factor WCFACT whose default is.6 for channels in natural condition (ie. the lag time for flow through the watercourse of a WC type subcatchment is 6% of the lag time for transformation of rainfall excess to runoff on the same subcatchment). This is based on studies of the lag properties of real catchments (Boyd, Bates, Pilgrim and Cordery, 1987; Kemp and Daniell, 1995) and has been found to give good results for a wide range of catchments. This should be used for all natural catchments. If the channel is modified (eg. concrete lined), this value of.6 should be factored according to the ratio of travel times through the watercourse for modified/natural channel conditions. Suggested values of watercourse factors can be seen in table Table Recommended Watercourse Factors (Boyd et al., 1994) Watercourse Type Natural channel Gravel bed with rip-rap Excavated earth Concrete lined Watercourse Factor WCFACT For example, the travel time through a concrete lined channel is approximately one third of the travel time in the channel in natural condition. Muskingum Cunge routing requires values of K (minutes) and x. K is approximately equal to the travel time of the hydrograph peak through the watercourse reach. A large value of K causes the peak of the outflow hydrograph from the reach to occur some considerable time after the peak of the inflow hydrograph at the top of the reach. Parameter x (in the range. to.5) defines the translation effect of the flood wave. If x=., the peak of the outflow hydrograph intersects the falling limb of the inflow hydrograph. If x=.5, the outflow peak occurs at nearly the same time as for x=., but the peak discharge is close to the inflow peak discharge (ie. the flood hydrograph is translated with little attenuation). As x increases from. to.5, the time of the outflow peak varies only slightly, but the peak discharge increases in value up to the peak discharge of the inflow hydrograph.

368 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-4 Delay of the hydrograph requires a delay time (in minutes) to be specified. The outflow hydrograph is then simply delayed by this time. Nonlinear routing uses a concentrated storage element to represent the stream channel. This will be quite satisfactory in most cases. If the channel reach is long and distributed routing is required, you can either use two or more nonlinear elements in series, or Muskingum routing, or delay the hydrograph. A strong point of WBNM is this separate routing of runoff from upstream subcatchments through the stream channel (with shorter travel time reflecting the faster flow velocities), and routing of rainfall excess to the stream as overland flow. This becomes important when changes to a subcatchment are made. For example, if the watercourse is modified by concrete lining but the subcatchment land surfaces remain in natural condition, WBNM can model this. Alternatively, if the subcatchment is urbanised but the watercourse remains in natural condition, WBNM models this. In some other models, where upstream runoff and rainfall excess are lumped together and routed through the same storage, these separate effects cannot be easily modelled. The nonlinear channel routing method was used in this study. To determine the appropriate watercourse factors for the channels in the Curtin catchment, channel dimensions and channel bed slopes were surveyed. The constructed channel sections were found to be symmetrical, and to simplify discharge calculations and data presentation, dimensions of half of the channel are given. See figure Long section information was also collected to determine the average channel bed slope at each location. Figure 11.2 shows the data collected. Table 11.2 shows the dimensions of the channel cross sections and channel bed levels. RL middle RL bottom Channel Bed Type Figure Typical Channel cross section Detail

369 Chapter 11 -Application of WBNMto a SubdividedCatchment 11-5 U/S of where crosssection was measured ~~ 1 Location of cross-section D/S of where cross- RL U/S section was measured RL bottom RLD/S / c A / D Figure Typical Channel Long Section Detail A Table Cross Section and Long-Section Data Dimensions Dimension Cross Section Location on Map (metres) A B c D RLtop RLmiddle RLbottom RLU/S RLD/S Channel Bed Type C C G/M G/M G/M G/M G/M G/M G/M Channel Side Type G/M G/M G/M G/M G/M G/M G/M G/M G/M Key : C - concrete, G/M - granite in mortar The Manning's roughness coefficient was also determined for each channel cross section. Photographs of the channelised sections were taken, in all cases are looking in the upstream direction. The photographs correspond to the sections where the cross sectional data for the channels was collected. All channels are trapezoidal in cross section and have a triangular low flow section which is trowelfinishedconcrete. The rest of the channel is made from granite stacked to form the channel section and then mortared in place. This increases the effective channel roughness, to slow water travelling in the channel. From the site inspection, the photographs, Australian Rainfall and (ARR1987), and reference books including Vennard and Street, (1982) and French (1985), the Manning's Roughness Coefficient was estimated: 1. The natural creeks located in Curtin catchment at present do not have a surface width at bankfiill stage of more than 3 metres. They are fairly clean and winding, with some pools and shoals. The references suggest a Manning's Roughness of between.33 and.45.

370 Chapter 11 - Application of WBNM to a Subdivided Catchment For the lined channels located within the catchment, the references suggest values of.12 to.15 for trowelfinishedconcrete sections and.15 to.17 for dressed stone in mortar. As can be seen, Manning's Roughness for lined channels is approximately two to three times smaller than for a creek in natural conditions. The channel section between where Yarralumla Creek and Long Gully Creek intersect (locations 3 and 7) and the outlet at location 1, is different to the channels elsewhere in the catchment. In this section, the bed is constructed from trowelfinishedconcrete, and the sides of granite in mortar. The channel section between locations 3 and 6, and 7 and 1 all are of granite in mortar construction. From these observations, it was concluded that two Manning's roughness coefficients would be used for the lined channel section and another for the natural. These are: for trowelled concrete bed and granite in mortar sides channels (see photographs 11.1, and 11.4) for granite in mortar sides channels (see photographs 11.5, 11.6, 11.7, 11.1, 11.11, and 11.13) for natural creeks that are fairly clean and winding with some pools (see photograph 11.9). Therefore, for modelling purposes, the watercourse factor in channelised sections will initially be to.2, and for natural sections to.6 because the Manning's roughness ratio of approximately 3 to 1 between natural and lined channels. The slopes and Manning's roughness at each location are summarised in table Note that location 6 has no cross section. Stormwater at this point discharges from the Mawson catchment via three circular and two rectangular culverts. See photographs 11.7 and Table Channel Bed Slopes at Various Locations Location Slope (%) Manning's n

371 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-7 Photograph Channel at Curtin Gauging Station, Outlet Curtin Catchment (Location 1) Photograph Channel Section Yarralumla Creek, U/S of Curtin Gauging Station (Location 2)

372 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-8 Photograph Drop in Channel Section Yarralumla Creek, U/S of Curtin Gauging Station (Location 2) Photograph Merging of Yarralumla Creek and Long Gully Creek (Location 3 and 7)

373 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-9 Photograph Yarralumla Creek, Mawson Reach (Location 4) Photograph Yarralumla Creek, Mawson Gauging Station (Location 5)

374 Chapter 11 - Application of WBNM to a Subdivided Catchment 11-1 i*-**v. P^ i^r* Photograph Pipes Draining Mawson Catchment into Yarralumla Creek, Just U/S of Photograph Pipe and Culvert Draining Mawson Catchment into Yarralumla Creek, Just U/S of Mawson Gauging Station (Location 6)

375 Chapter 11 - Application of WBNM to a Subdivided Catchment Photograph Yarralumla Creek in Natural State, U/S of Mawson Gauging Station (Location 6) Photograph Long Gully Creek, Just D/S of Long Gully Gauging Station (Location 8)

376 Chapter 11- Application of WBNM to a Subdivided Catchment Wk Photograph Long Gully Creek, Start of Newly Channelised Section (Location 9) Photograph Upper Reaches of Long Gully Creek, in the new Isaacs Residential Subdivision (Location 1)

377 Chapter 11 - Application of WBNM to a Subdivided Catchment Photograph Start of Piped Section, Draining Upper Reaches of Long Gully Creek, Isaacs Residential Subdivision (Location 1) From this data, the discharges for different stages and at different locations along the watercourse were calculated using Manning's equation: Q = A.R 2/3.S 1/2 /n equation 11.1 A simple computer program was written to calculate the discharges at the different locations. The maps in section 11.3 show the locations at which discharge data were calculated. Stage - discharges can be seen in tables 11.4 to Figure 11.3 shows plots of flowrate against channel cross sectional area. From these plots, the flow velocity for a particular flow depth can be determined (slope of the line through the origin). The celerity of the flood wave is the slope of the tangent to the plotted curve and will always be higher than the flow velocity. From these plots, the flood travel time in the channel can be determined as well as the flow lag time between subcatchments, knowing the length of the channel section.