ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

Transcription

1 ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING GAMSBY AND MANNEROW LIMITED CONSULTING PROFESSIONAL ENGINEERS GUELPH OWEN SOUND LISTOWEL - KITCHENER EXETER January 2012 Our File:

2 Page i TABLE OF CONTENTS 1.0 INTRODUCTION BACKGROUND METHODOLOGY DESCRIPTION OF WATERSHED FREQUENCY ANALYSIS MIDUSS MODELLING WATER SURFACE PROFILE MODELLING (HEC-RAS) MODELLING RESULTS SUMMARY AND CONCLUSIONS... 6 LIST OF TABLES Table 1 Critical Elevations at St. George WPCP Table 2 IDF Parameters Table 3 Flow Modelling Summary Table 4 Flood Elevations for Critical Cross-Sections Table 5 Pre to Post Floodplain Elevations at Cross-Section LIST OF FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Tributary of Fairchild Creek Watershed Catchment Areas 100 Year Design Storm Event Floodplain Extents Regional Storm Event Floodplain Extents Tributary of Fairchild Creek Flow Profile LIST OF APPENDICES Appendix A Appendix B Appendix C Frequency Analysis MIDUSS Modelling HEC-RAS Output ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

3 1.0 INTRODUCTION ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING Gamsby and Mannerow Ltd. (G&M) together with process specialists from Conestoga-Rovers and Associates (CRA), University of Western Ontario (UWO), and Huber Environmental Consulting (HEC) were retained by the St. George Landowners Group to complete an Optimization Study of the St. George Water Pollution Control Plant (WPCP). The primary objective of this Study was to develop a recommended alternative for wastewater treatment servicing to accommodate planned community growth in St. George. This Technical Memorandum describes the background, methodology, and results of establishing floodplain levels in the Fairchild Creek receiving stream in the vicinity of the St. George Water Pollution Control Plant (WPCP) under extreme storm events. This Memo presents the impacts due to potential flooding at the expanded plant site as a result of extreme storm events. Other Technical Memoranda were prepared by the project team to cover other aspects of the overall Optimization Study. 2.0 BACKGROUND The plant is owned by The County of Brant and operated under contract by the Ontario Clean Water Agency (OCWA). The St. George WPCP was constructed in 1981 as a package extended aeration plant with a rated hydraulic capacity of 1,063 m 3 /d. In 2005, the plant was re-rated to a capacity of 1,300 m 3 /d as a result of process upgrades. The receiving stream for final effluent from the plant is an un-named tributary of Fairchild Creek. The location of the outfall is currently (2012) to a stranded oxbow of the receiving stream. A future expanded St. George plant would require extending the footprint of the site to the west by approximately 8 metres. It is a standard requirement of Conservation Authorities to evaluate if any infilling of a floodplain will impact flood levels, and if so to mitigate any potential impact (i.e. providing an equivalent floodplain storage volume). Preliminary results of the Optimization Study were presented to Brant County, Grand River Conservation Authority (GRCA), and other interested parties at Brant County offices in Paris on June 3, At that presentation, GRCA requested the study team conduct site-specific analysis and modelling of the floodplain in the vicinity of the plant to ensure that the future plant would not impact or be impacted by flood elevations in the tributary of Fairchild Creek. Table 1 summarizes some critical elevations at the St. George WPCP.

4 Page 2 Table 1: Critical Elevations at St. George WPCP Grit Channel Top of Tank Elevation Aeration/Clarifier Top of Tank Elevation Control Building (Finished Floor) Driveway surrounding WPCP Filter Room Operating Platform (basement of control building) m m m ± m (varies) m It is noted that GRCA presents estimated regional flood levels in Fairchild Creek in the vicinity of the St. George plant on their web site. However, the GRCA does not consider this information to be accurate since it was completed as a desk-top analysis only. In addition, GRCA mapping in the area of the site was based on a 5-metre contour interval which is insufficient to establish flood elevations with confidence and/or accuracy. Consequently, the study team conducted detailed site specific topographic surveying, aerial mapping, and hydrologic and hydraulic modelling of various design storm events to establish flood elevations. The 25-year and 100-year design storm events and the Regional Storm (Hurricane Hazel 1954) were utilized for this assessment. 3.0 METHODOLOGY 3.1 DESCRIPTION OF WATERSHED Site specific topographic surveying was completed for several hydraulic structures in the vicinity of the WPCP. Selected structures represent control elements that can have a significant impact on water elevations within the stream channel during design storm events. Additional topographic site information was obtained through aerial photography and digital mapping provided by Northway Mapping Inc. Based on flown contour data obtained in 2006, at a scale of 1:20,000, detailed topographic contour mapping was provided at a 1-metre contour interval. The level of accuracy of the flown contour data is reported to be 600 mm horizontally and 700 mm vertically. Through visual interpretation of 1:50,000 scale topographic maps obtained from the Natural Resources Canada National Topographic Services, the drainage area discharging to the tributary of Fairchild Creek was determined. The total drainage area is estimated to be square kilometres (9,258 hectares). The majority of the 9,258 hectare drainage catchment area is rural (i.e. farmland and forested area) with the exception of the Town of St. George. Row crops, forage and pasture areas represent approximately 2/3 of the land use within the catchment area. From Ontario Soil Survey maps produced by the Ontario Department of Agriculture, the native soils within the catchment area are identified as mainly silt and loam. The hydrologic soil types for these soils are defined as Type B-BC soil. The average overland slope across the catchment was calculated to be 0.5%. ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

5 Page FREQUENCY ANALYSIS Data from a flow monitoring station downstream of the Town of St. George was provided by Environment Canada. The flow monitoring station, located on Fairchild Creek just upstream from the confluence with the Grand River (Identification Number 02GB007), provided 44 years of stream flow data. The flow monitoring station is approximately 12 kilometres downstream of the subject site with an estimated contributing drainage area of square kilometres (37,982 hectares). Design flows through the tributary of Fairchild Creek at the St. George WPCP were estimated by a Frequency Analysis based on flow records from the flow monitoring station and adjustments to the flow rates based on the contributing drainage area. The drainage areas are shown in Figure 1. Based on the maximum instantaneous discharge values for each of the 44 years of data from the flow monitoring station, the 25 year and 100 year design storm flows were calculated to be m 3 /s and m 3 /s respectively. Details are included in Appendix A. The design storm flows from the flow monitoring station were than transposed to represent the design storm flows at the existing bridge along German School Road, located downstream of the WPCP, using the following ratio between discharge and drainage area: Q2 = Q1 * (A2/A1) 0.75 Q2 = m 3 /s * (9,258 ha/37,982 ha) 0.75 Q2 = m 3 /s Where: Q1 = Instantaneous 1:25 year flow at the Brant Monitoring Station Q2 = Instantaneous 1:25 year flow at the German School Road Bridge A1 = Total catchment area of the Brant Monitoring Station A2 = Total catchment area upstream of the German School Road Bridge Therefore, based on the design storm flows from the flow monitoring station, the estimated design storm flows at the existing bridge at German School Road, downstream of the WPCP, were calculated to be m 3 /s and m 3 /s, for the 25 year and 100 year design storm events, respectively. 3.3 MIDUSS MODELLING The hydrologic modelling software, MIDUSS, was utilized to estimate the design storm flows. The 25 year and 100 year design storm flow rates, adjusted for the MOE Cambridge-Galt rain gauge Chicago Storm Parameters, were also utilized in the modelling analysis. Historical flow data from Hurricane Hazel (1954) was utilized for the Regional Storm. The IDF parameters were based on the MOE Cambridge-Galt rain gauge No which provided 15 years of rain data from 1978 to IDF parameters are summarized in Table 2. ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

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7 Page 4 Table 2: IDF Parameters 25 Year 100 Year a = b = c = r = t d = Rainfall depth (mm) The average hydrologic soil type, determined to be B-BC, was used in conjunction with the land use information to estimate a curve number (CN) of 67.7 for the contributing drainage catchment area. The SCS infiltration method, which adjusts the runoff coefficient to account for larger storms when the ground becomes saturated, was used for the catchment. A Lag and Route command was also utilized in the MIDUSS modelling to account for the large contributing drainage area. From the MIDUSS modelling, a design flow rate of m 3 /s was identified for the 25 year design storm event, m 3 /s for the 100 year design storm event and m 3 /s for the Regional Storm. Table 3 summarizes the results from the two methods of flow modelling. Table 3: Flow Modelling Summary Design Storm Frequency Analysis (m 3 /s) MIDUSS Modelling (m 3 /s) 25 Year Year Regional There is the large increase from the 100 year flow to the Regional Storm flow. Extensive sensitivity analysis has been completed, and the results suggest that the catchment produces flows within the range shown in Table 3. The results from the MIDUSS modelling have been used for the HEC-RAS model. The IDF storm parameters, Regional Storm data and MIDUSS flow modelling are included in Appendix B. ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

8 Page WATER SURFACE PROFILE MODELLING (HEC-RAS) Topographical information provided by Northway Mapping Inc., along with the site specific topographic survey data obtained for each hydraulic structure, was utilized to generate crosssections of the Fairchild Creek tributary. Based on these cross-sections, the HEC-RAS model for the tributary of Fairchild Creek was created, from the upstream side of Burt Road (abandoned) past the St. George WPCP to the downstream side of German School Road. Stations along the Fairchild Creek tributary were assigned, with Station representing the downstream side of German School Road. The locations of cross-sections used are represented on Figures 2 and 3. Cross-sections at Station 2+840, and intersect the existing WPCP. Two additional cross-sections were added at Station and to simulate pre- to post-development fill area associated with the WPCP expansion. As detailed topographic data for the creek bed were not available, a typical cross-section through the creek bottom was created based on surveyed cross-sections and applied throughout the modelling. Table 4 summarizes the flood elevation under all flow profiles for the critical cross-sections under pre and post-development conditions. Table 4: Flood Elevations for Critical Cross-sections Station 25 Year Storm (m) 100 Year Storm (m) Regional Storm (m) Pre Post Pre Post Pre Post The effect of the WPCP expansion is only seen under the Regional Storm event. The increase in flood elevation is negligible at 0.01 metres. A detailed summary of the HEC-RAS model and cross-sections showing the WPCP expansion have been included in Appendix C. Electronic copies of the modelling files have been included on a CD attached to the back cover of this document. 4.0 MODELLING RESULTS 1. Under pre-development or existing conditions, the water surface elevation at the outlet of the WPCP (Sta ) was calculated to be metres and meters, for the 25 year and 100 year design storm events, respectively. The water surface elevation at the outlet of the WPCP was calculated to be metres for the Regional Storm. The extent of the 100 year and regional flood events under pre-development and post-development has been shown on Figure 2 and 3. For further detail of cross-section flood elevation, refer to Appendix C. ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

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11 FLOW PROFILE - FAIRCHILD CREEK REGIONAL EVENT FLOODING ELEVATION YEAR EVENT FLOODING ELEVATION ELEVATION (m) YEAR EVENT FLOODING ELEVATION CHANNEL BOTTOM (FAIRCHILD CREEK) GERMAN SCHOOL RD. DRIVEWAY No.1 DRIVEWAY No.2 MAIN CHANNEL DISTANCE (m) ST.GEORGE WPCP LOCATION 5625 BURT RD. (ABANDONED) NTS JANUARY 2012 Plotted On: January 31, OS-FIG4.dwg

12 Page 6 2. The flood elevation under the Regional Storm event is above the elevation of the filter building platform and consequently this final treatment step would be impacted for both the existing and expanded plants. 3. Under post-development conditions, there is a 0.01 metre change in the water surface elevation during the Regional Storm event at the WPCP. Table 5 below summarizes the modelling results. Table 5: Pre to Post Flood Elevations at Cross-Section Flood Event Pre-Dev. Elev. Post-Dev. Elev. Change in Elev. 25 Year Year Regional SUMMARY AND CONCLUSIONS Hydraulic modelling of the tributary of Fairchild Creek was completed using HEC-RAS. Topographic data obtained from aerial mapping and site specific survey data of structures along the Fairchild Creek tributary was utilized to generate the model. Design flows determined in MIDUSS were used as imports in HEC-RAS for the 25 Year, 100 Year and Regional Storm events. Expansion of the St. George WPCP is predicted to have a negligible impact on the flood elevation through this section of the Fairchild Creek tributary. The flood level for the Regional Storm at the WPCP would be metres, which is below the top of the wall of the plants aeration/clarifier tankage and the Control Building finish floor elevation of metres. However, the predicted flood elevation is above the elevation of the filter building platform of metres and consequently this final treatment step including the filter itself would be impacted for both the existing and expanded plants. The design of the WPCP expansion may require the addition of an emergency effluent pumping station to create a hydraulic break and avoid backflow under the Regional Storm event. All of which is respectfully submitted. GAMSBY AND MANNEROW LIMITED Per: Per: Paul McLennan, P.Eng. Grant Parkinson, P.Eng. ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

13 Page 7 REFERENCES GRCA Mapping GRCA Produced using information under License with the Grand River Conservation Authority Grand River Conservation Authority, MNR, NRVIS, WRIP Produced using information provided by the Ministry of Natural Resources, Copyright Queen's Printer, MPAC Queen's Printer for Ontario and its licensors May Not be Reproduced Without Permission. THIS IS NOT A PLAN OF SURVEY. ONT Includes material 2011 of the Queen's Printer for Ontario. All rights reserved. Teranet Teranet Land Information Services Inc. and its licensors May not be reproduced without permission. MNDM Various Authors, , Quaternary and Pleistocene Geology, Southern Ontario, Ontario Geological Survey. Ministry of Transportation Ontario, , MTO Drainage Management Manual. Soil Mapping Various Authors, 1967, Soils of Wentworth County, Ontario, Scale 1: Various Authors, 1996, Soils of Waterloo County, Ontario, Sheet 3, Scale 1: Ontario Institute of Pedology, 1990, Soils of Brant County, Ontario. Sheet 1, Scale 1: ST. GEORGE WPCP OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING

14 ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING APPENDIX A Frequency Analysis

15 Maximum Instantaneous Discharge (m³/s) Year Rank Normal Distribution Qi = Qmean + z *Stdev F(Qi) = 1-1/i Flow Return F(Qi) Z Total St. George Period Value (m³/s) (m³/s) St. George Flow Ratio Q2 = Q1 (A2/A1)^ catchment Qst.george = Qtotal (9,258/37,982)^ Regional Frequency Analysis St. George Floodplain Modelling G&M: St.George is 9,258 hetares out of 37,982 hectare total Statistical Values count mean variance standev skew max

16 ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING APPENDIX B MIDUSS Modelling

17 Short Duration Rainfall Intensity Duration Frequency Data Données sur I intensité, la durée et la fréquence des chutes de pluie de courte durée Intensity(mm/h) / Intensité(mm/h) Caution/Sujet à caution : Average 95% Confidence Interval > ±25% Intervalle de confiance moyen 95% > ±25% 95% Confidence Interval > ±25% Intervalle de confiance de 95% > ±25% 2011/05/17 CAMBRIDGE GALT MOE ON years / ans Latitude 43 o 20 N Longitude 80 o 19 W Elevation / Altitude 268 m Return Periods/ Périodes de retour Years / ans Minutes Duration/Durée Hours/Heures

18 Regional Storm Parameters St. George Floodplain Modelling G&M: Hour (hr) Depth (mm) 96.3% (mm) The MTO Drainage Manual defines the regional storm based from the historical data of Hurricane Hazel. For larger catchments the depth of rainfall for the storm can be reduced by a factor. For drainage areas that are between 91 km² and 115 km² the depth can be reduced to 96.3% of the original depth.

19 St. George Floodplain Mapping G&M: Year Design Storm " MIDUSS Output >" " MIDUSS version Version 2.25 rev. 473" " MIDUSS created February-07-10" " 10 Units used: ie METRIC" " Job folder: C:\Miduss" " Output filename: Cambridge 025 year-final.out" " Licensee name:." " Company Gamsby and Mannerow Limited" " Date & Time last used: 19/12/2011 at 11:42:51 AM" " 31 TIME PARAMETERS" " Time Step" " Max. Storm length" " Max. Hydrograph" " 32 STORM Chicago storm" " 1 Chicago storm" " Coefficient A" " Constant B" " Exponent C" " Fraction R" " Duration" " Time step multiplier" " Maximum intensity mm/hr" " Total depth mm" " 6 025hyd Hydrograph extension used in this file" " 33 CATCHMENT 101" " 1 Triangular SCS" " 1 Equal length" " 1 SCS method" " 101 St. George Catchment" " % Impervious" " Total Area" " Flow length" " Overland Slope" " Pervious Area" " Pervious length" " Pervious slope" " Impervious Area" " Impervious length" " Impervious slope" " Pervious Manning 'n'" " Pervious SCS Curve No." " Pervious Runoff coefficient" " Pervious Ia/S coefficient" " Pervious Initial abstraction" " Impervious Manning 'n'" " Impervious SCS Curve No." " Impervious Runoff coefficient" " Impervious Ia/S coefficient" " Impervious Initial abstraction" " c.m/sec" " Catchment 101 Pervious Impervious Total Area " " Surface Area hectare" " Time of concentration minutes"

20 " Time to Centroid minutes" " Rainfall depth mm" " Rainfall volume ha-m" " Rainfall losses mm" " Runoff depth mm" " Runoff volume ha-m" " Runoff coefficient " " Maximum flow c.m/sec" " 34 LAG AND ROUTE" " 2 Conduit typechannels" " Initial Peak runoff" " Total Area" " Aspect ratio" " Flow length" " Average flow" " Average stream slope" " Manning 'n' - Pipes" " Manning 'n' - Channels" " Manning 'n' - Mixed" " Channel lag minutes" " Reservoir lag minutes" " 0 Lags set explicitly" " User defined Channel Lag" " User defined Reservoir Lag (0.0 c.m)" " 10 Reservoir lag set in minutes." " 0.0 Reservoir volume" " c.m/sec" " 40 HYDROGRAPH Add Runoff " " 4 Add Runoff " " " " 64 SHOW TABLE" " 2 Flow hydrograph" " 4 Inflow Hydrograph" " Maximum flow c.m/sec" " Hydrograph volume c.m" " 38 START/RE-START TOTALS 101" " 3 Runoff Totals on EXIT" " Total Catchment area hectare" " Total Impervious area hectare" " Total % impervious 0.600" " 19 EXIT"

21 St. George Floodplain Mapping G&M: Year Design Storm " MIDUSS Output >" " MIDUSS version Version 2.25 rev. 473" " MIDUSS created February-07-10" " 10 Units used: ie METRIC" " Job folder: C:\Miduss" " Output filename: Cambridge 100 year-final.out" " Licensee name:." " Company Gamsby and Mannerow Limited" " Date & Time last used: 19/12/2011 at 11:41:11 AM" " 31 TIME PARAMETERS" " Time Step" " Max. Storm length" " Max. Hydrograph" " 32 STORM Chicago storm" " 1 Chicago storm" " Coefficient A" " Constant B" " Exponent C" " Fraction R" " Duration" " Time step multiplier" " Maximum intensity mm/hr" " Total depth mm" " 6 100hyd Hydrograph extension used in this file" " 33 CATCHMENT 101" " 1 Triangular SCS" " 1 Equal length" " 1 SCS method" " 101 St. George Catchment" " % Impervious" " Total Area" " Flow length" " Overland Slope" " Pervious Area" " Pervious length" " Pervious slope" " Impervious Area" " Impervious length" " Impervious slope" " Pervious Manning 'n'" " Pervious SCS Curve No." " Pervious Runoff coefficient" " Pervious Ia/S coefficient" " Pervious Initial abstraction" " Impervious Manning 'n'" " Impervious SCS Curve No." " Impervious Runoff coefficient" " Impervious Ia/S coefficient" " Impervious Initial abstraction" " c.m/sec" " Catchment 101 Pervious Impervious Total Area " " Surface Area hectare" " Time of concentration minutes"

22 " Time to Centroid minutes" " Rainfall depth mm" " Rainfall volume ha-m" " Rainfall losses mm" " Runoff depth mm" " Runoff volume ha-m" " Runoff coefficient " " Maximum flow c.m/sec" " 34 LAG AND ROUTE" " 2 Conduit typechannels" " Initial Peak runoff" " Total Area" " Aspect ratio" " Flow length" " Average flow" " Average stream slope" " Manning 'n' - Pipes" " Manning 'n' - Channels" " Manning 'n' - Mixed" " Channel lag minutes" " Reservoir lag minutes" " 0 Lags set explicitly" " User defined Channel Lag" " User defined Reservoir Lag (0.0 c.m)" " 10 Reservoir lag set in minutes." " 0.0 Reservoir volume" " c.m/sec" " 40 HYDROGRAPH Add Runoff " " 4 Add Runoff " " " " 64 SHOW TABLE" " 2 Flow hydrograph" " 4 Inflow Hydrograph" " Maximum flow c.m/sec" " Hydrograph volume c.m" " 38 START/RE-START TOTALS 101" " 3 Runoff Totals on EXIT" " Total Catchment area hectare" " Total Impervious area hectare" " Total % impervious 0.600" " 19 EXIT"

23 St. George Floodplain Mapping G&M: Regional Design Storm " MIDUSS Output >" " MIDUSS version Version 2.25 rev. 473" " MIDUSS created February-07-10" " 10 Units used: ie METRIC" " Job folder: C:\Miduss" " Output filename: Cambridge 100+ year-final.out" " Licensee name:." " Company Gamsby and Mannerow Limited" " Date & Time last used: 19/12/2011 at 11:40:04 AM" " 31 TIME PARAMETERS" " Time Step" " Max. Storm length" " Max. Hydrograph" " 32 STORM Historic" " 5 Historic" " Duration" " Rainfall intensity values" " " " " " " " " " " " " " " " " " " " " " Maximum intensity mm/hr" " Total depth mm" " 6 101hyd Hydrograph extension used in this file" " 33 CATCHMENT 101" " 1 Triangular SCS" " 1 Equal length" " 1 SCS method" " 101 St. George Catchment" " % Impervious" " Total Area" " Flow length" " Overland Slope" " Pervious Area" " Pervious length" " Pervious slope" " Impervious Area" " Impervious length" " Impervious slope" " Pervious Manning 'n'" " Pervious SCS Curve No." " Pervious Runoff coefficient" " Pervious Ia/S coefficient" " Pervious Initial abstraction" " Impervious Manning 'n'" " Impervious SCS Curve No." " Impervious Runoff coefficient"

24 " Impervious Ia/S coefficient" " Impervious Initial abstraction" " c.m/sec" " Catchment 101 Pervious Impervious Total Area " " Surface Area hectare" " Time of concentration minutes" " Time to Centroid minutes" " Rainfall depth mm" " Rainfall volume ha-m" " Rainfall losses mm" " Runoff depth mm" " Runoff volume ha-m" " Runoff coefficient " " Maximum flow c.m/sec" " 34 LAG AND ROUTE" " 2 Conduit typechannels" " Initial Peak runoff" " Total Area" " Aspect ratio" " Flow length" " Average flow" " Average stream slope" " Manning 'n' - Pipes" " Manning 'n' - Channels" " Manning 'n' - Mixed" " Channel lag minutes" " Reservoir lag minutes" " 0 Lags set explicitly" " User defined Channel Lag" " User defined Reservoir Lag (0.0 c.m)" " 10 Reservoir lag set in minutes." " 0.0 Reservoir volume" " c.m/sec" " 40 HYDROGRAPH Add Runoff " " 4 Add Runoff " " " " 64 SHOW TABLE" " 2 Flow hydrograph" " 4 Inflow Hydrograph" " Maximum flow c.m/sec" " Hydrograph volume c.m" " 38 START/RE-START TOTALS 101" " 3 Runoff Totals on EXIT" " Total Catchment area hectare" " Total Impervious area hectare" " Total % impervious 0.600" " 19 EXIT"

25 ST. GEORGE WATER POLLUTION CONTROL PLANT OPTIMIZATION STUDY TECHNICAL MEMORANDUM FLOODPLAIN MODELLING APPENDIX C HEC-RAS Output

26 Cross-Section Pre-Development St GeorgePre_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional Legend WS Regional WS 100 yr WS 25 yr Ground BankSta Elevation (m) Station (m)

27 Cross-Section Post-Development St GeorgePost_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional Legend WS Regional WS 100 yr WS 25 yr Ground BankSta Elevation (m) Station (m)

28 Cross-Section Pre-Development St GeorgePre_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional 216 Legend WS Regional WS 100 yr WS 25 yr Ground Bank Sta Elevation (m) Station (m)

29 Cross-Section Post-Development St GeorgePost_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional 216 Legend WS Regional WS 100 yr WS 25 yr Ground BankSta Elevation (m) Station (m)

30 Cross-Section Pre-Development St GeorgePre_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional Legend WS Regional WS 100 yr WS 25 yr Ground BankSta Elevation (m) Station (m)

31 Cross-Section Post-Development St GeorgePost_ Plan: Plan 01 27/01/2012 Flow: 25yr, 100yr, Regional Legend WS Regional WS 100 yr WS 25 yr Ground BankSta Elevation (m) Station (m)

32 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Pre-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) yr yr Regional Bridge yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional

33 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Pre-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional Bridge 25 yr yr Regional

34 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Pre-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) yr yr Regional Bridge yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional Bridge 25 yr yr Regional

35 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Post-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) 25 yr yr Regional Bridge yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional

36 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Post-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional Bridge 25 yr yr Regional

37 St. George Water Pollution Control Plant - Floodplain Modelling Hec-Ras Summary - Post-Development G&M: River Station Profile Total Flow Minimum Channel Elevation Water Surface Elevation Critical Water Surface Energy Grade Elevevation Velocity Channel Flow Area Top Width (m³/s) (m) (m) (m) (m) (m/s) (m²) (m) 25 yr yr Regional Bridge yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional yr yr Regional Bridge yr yr Regional