Hydraulic Capacity Review Rangitaiki River and Reids Floodway

Transcription

1 Hydraulic Capacity Review Rangitaiki River and Reids Floodway February 2011

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3 Contents Executive Summary Introduction Hydrology and Sea Levels Design Hydrographs Sea Level MIKE11 Model Update Channel Geometry Update Energy Losses Due to Bridge Piers and Decks and Other Channel Features Model Calibration and Verification Design Scenarios Model Boundary Conditions Relative Timing of Tide Level and Flood Discharge Hydrographs Spillweir Geometry at Entrance to Reids Floodway Model Log Update Results of Model Simulations Definition of Simulation Scenarios Water level long section results Hydraulic Capacity Review Standard Design Combination Scenarios Channel Geometry Effects Sea Level Influence Current Scheme Capacity Climate Change Influence on Water Levels in the Rangitaiki River Flow Split in Rangitaiki River and Reids Floodway Comments on One-Dimensional Model configuration of MIKE11 Model Treatment of Reids Floodway Channel Roughness in One-Dimensional and Two-Dimensional Computational Hydraulic Models Superelevation of Flow Around Bends Comments and Recommendations on Future Flood Scheme Upgrade Comments Recommendations References Final i

4 Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G EBOP MIKE11 Model Log Updated MIKE11 Model Log MIKE11 Model Chainages and Comparison of Model Predictions with MIKE FLOOD Model of Wallace (2010a) Bridge Head Loss Calculations Tabulated Flood Levels from MIKE11 Model Simulations Log Sheet of Model Simulation Files Drawings for New State Highway 2 Bridge Final ii

5 Figures Figure 2-1: Rangitaiki River at Te Teko Design Hydrographs... 2 Figure 2-2: Rangitaiki River Mouth design storm surge scenarios for existing climate... 4 Figure 2-3: 2040 Rangitaiki River Mouth design storm surge scenarios... 4 Figure 2-4: 2090 Rangitaiki River Mouth design storm surge scenarios... 5 Figure 3-1: Effects of varying timing of flood discharge and tide level hydrograph peaks on Rangitaiki River Water Levels for 100 year flood and 20 year storm surge combination Figure 3-2: Effects of varying timing of flood discharge and tide level hydrograph peaks on Reids Floodway Water Levels for 100 year flood and 20 year storm surge combination Figure 4-1: Rangitaiki River water level long section - Comparison of 100-year and 20-year ARI flood and storm surge combinations for existing river and floodway geometry Figure 4-2: Reids Floodway water level long section - Sensitivity test for energy loss factors with existing floodway geometry for current 100-year ARI flood with 20-year ARI storm surge Figure 4-3: Reids Floodway water level long section Comparison of 100-year and 20-year ARI flood and storm surge combinations for existing floodway geometry Figure 4-4: Rangitaiki River water level long section Effect of changes in spillway geometry for 100-year ARI flood and 20-year ARI storm surge Figure 4-5: Reids Floodway water level long section Effect of changes in floodway geometry for 100-year ARI flood and 20-year ARI storm surge Figure 4-6: Comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the 100-year ARI flood and 20-year ARI storm surge Figure 4-7: Comparison between flood discharge hydrographs in Reids Floodway immediately downstream of the Reids Floodway Spillweir for the 100-year ARI flood and 20-year ARI storm surge Figure 4-8: Rangitaiki River water level long section Sensitivity to climate change increases in flood discharge for future design with 100-year ARI flood and 20-year ARI storm surge Figure 4-9: Reids Floodway water level long section Sensitivity to climate change increases in flood discharge for future design including new SH2 Bridge with 100-year flood and 20-year ARI storm surge Figure 4-10: Comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the climate change affected 100- year ARI flood and 20-year ARI storm surge Figure 4-11: Comparison between flood discharge hydrographs in Reids Floodway immediately downstream of the Reids Floodway Spillweir for the climate change affected 100-year ARI flood and 20-year ARI storm surge Figure 6-1 Typical channel cross-section on Reids Floodway (cross-section 21 at chainage 11747m) Final iii

6 Tables Table 2-1: Peak storm surge values used in the different simulations... 3 Table 3-1: Bridge locations on Reids Floodway... 6 Table 3-2: Bridge locations on Rangitaiki River... 7 Table 3-3 Bridge geometry details, flow properties and estimated head loss values... 8 Table 3-4 Description of different geometry scenarios assessed in model simulations Table 3-5 Boundary conditions applied to MIKE11 model Table 4-1 Matrix of simulations carried out for hydraulic capacity review Table 5-1: Influence of the storm surge peak on the water level in the Reids Floodway and the Rangitaiki River Table 5-2: Comparison of water level along the Rangitaiki River for different boundary condition scenarios Table 5-3: Flow split between the Rangitaiki River and the Reids Floodway for different flow scenarios Final iv

7 Executive Summary The hydraulic capacity of the Rangitaiki River Reids Floodway system was assessed using an existing MIKE11 model of the system with updated cross-section survey data for both watercourses. Different scenarios were investigated including various boundary conditions representing the effects of future climate change. Similarly different system geometries were investigated including the current floodway geometry, and a future floodway geometry. The future floodway geometry included a widened channel in the lower part or the floodway (as proposed in the Resource Consent Application) and a new State Highway 2 Bridge over the floodway. For the hydraulic capacity assessment, it was noted that: The updated 100-year flow in the Rangitaiki River for the current situation is 24 m 3 /s higher than the flow value used in previous reviews. The bulk of this additional flow is conveyed by Reids Floodway. The storm surge peak was approximately synchronized with the peak flow in the river at the mouth. The backwater effect in both the river and the floodway increased as a consequence. The updated survey data includes bridge cross-sections (2 for the Rangitaiki River, 9 for the Reids Floodway) which were not represented in the previous model. Some of these sections create major channel constrictions and the associated head losses were reflected by the incorporation of expansion loss factors. River bed levels in the lower part of the Rangitaiki River have risen in the last time causing a slight loss of hydraulic capacity. The current capacity of Rangitaiki River without freeboard is estimated to be about 622 m 3 /s based on the 2009 survey data, a reduction of 24 m 3 /s since the previous survey. The current capacity of Reids Floodway is estimated to be about 67 m 3 /s. For the current 100-year flood of 804 m 3 /s, the Rangitaiki River is estimated to convey 670 m 3 /s and Reids Floodway 134 m 3 /s. Upgrading the spillweir at the entrance to Reids Floodway to allow the spillweir to discharge 191 m 3 /s in the 100-year flood case reduces the discharge in the main river to 613 m 3 /s. Further investigations should be carried out, in particular: The optimisation of the configuration and geometry of the spillweir entrance to Reids Floodway; The influence of the sand spit at the mouth of the river on the water levels in the river and the Reids Floodway; Sensitivity testing of peak flood levels in Reids Floodway to channel friction assumptions; Adjustment of peak flood levels at the outside of bends in the Rangitaiki River for the effects of flow superelevation; Determining the best approach to increasing the Rangitaiki River channel capacity (i.e. raising stopbank levels, dredging the river bed at selected locations or a combination of both) and the critical sections that require improvements. Final 1

8 1 Introduction Opus International Consultants was commissioned by Bay of Plenty Regional Council (BOPRC) to carry out a hydraulic capacity review of the Lower Rangitaiki River and the Reids Central Floodway. This review is based on: an existing MIKE11 model provided by the Client; updated survey data (last survey in 2008 and 2009), updated values of flows and sea levels for the existing situation and the 2040 and 2090 climate change scenarios; and drawings for a new State Highway 2 Bridge over Reids Floodway 2 Hydrology and Sea Levels 2.1 Design Hydrographs The design hydrographs in the model are based on the hydrograph of the July 1998 calibration flood at Te Teko. This hydrograph was linearly scaled to the maximum peak flows determined by frequency analysis. The previous simulations were carried out with a 100-year event peak flow of 780 m3/s, and a 20-year event peak flow of 505 m3/s. The updated peak flow values for Te Teko provided by BOPRC are 539 m3/s for the 20-year event and 804 m3/s for the 100-year event. An analysis of climate change effects was carried out based on the Ministry for Environment guideline document (MfE, 2008a) and the calculated 100-year peak flow values are 862 m3/s for the 2040 and 939 m3/s for the 2090 climate change scenarios. The different design hydrographs are presented in Figure 2-1. Figure 2-1: Rangitaiki River at Te Teko Design Hydrographs Flow (m 3 /s) Time (Days) 20 Year flood - Qmax=539 m3/s Year flood - Qmax=862 m3/s 100 Year flood - Qmax=804 m3/s Year flood - Qmax=939 m3/s Final 2

9 2.2 Sea Level A dynamic storm surge hydrograph is used as a downstream boundary condition in the model. This hydrograph includes the tide and the storm surge generated by the same meteorological conditions during flood events. Based on Blackwood s (2000) report, the design peak storm surge used in the different simulations are: 1.92 m for the 20 year storm surge 1 ; 2.36 m for the 100 year storm surge. The climate change effects on the sea level were also determined based on the recommendations from the Ministry for Environment guideline document (MfE, 2008b). The minimum and maximum values of the expected sea level rise range were both used as downstream boundary conditions in the model, mainly to check the model sensitivity. A summary of the peak storm surge values and of the tide hydrographs used in the simulations are presented in Table 2-1 and in Figures 2-2, 2-3 and 2-4. Table 2-1: Peak storm surge values used in the different simulations Actual peak (RL m) 2040 climate change scenario peak (RL m) 2090 climate change scenario peak (RL m) Base value Conservative value Base value Conservative value 20 year storm surge year storm surge Note that all levels quoted within this report are referenced to the mean sea level (MSL) Moturiki vertical datum. Final 3

10 Figure 2-2: Rangitaiki River Mouth design storm surge scenarios for existing climate Sea Level (RL m) Time (Days) Actual 20 Year storm surge Actual 100 Year storm surge Figure 2-3: 2040 Rangitaiki River Mouth design storm surge scenarios Sea Level (RL m) Time (Days) 2040 Base 20 Year storm surge 2040 Conservative 20 Year storm surge Final 4

11 Figure 2-4: 2090 Rangitaiki River Mouth design storm surge scenarios Sea Level (RL m) Time (Days) 2090 Base 20 Year storm surge 2090 Conservative 20 Year storm surge Final 5

12 3 MIKE11 Model Update 3.1 Channel Geometry Update The geometry of Reids Floodway is shown in the following A3 size drawing. The location of the existing stopbanks forming the floodway are shown along with the proposed widened section of the floodway at the lower end. All the MIKE11 model simulations carried out as part of this capacity review are based on updated river cross-sections surveyed in April The downstream part of Reids Floodway (downstream of the Thornton Road Bridge (at model chainage 20197m) was surveyed in 2008 and was not updated. The cross-section which represents the sand spit at the Rangitaiki River mouth (cross-section 1A at river chainage 24550m in the model) was updated in 2004, just after the July 2004 flood event. This is a morphologically highly active area and it is most probable that the cross-section has reshaped over the recent years. The cross-section area is likely to be smaller today than represented in the model, i.e. not conservative (see the comparison between the scoured 2004 cross-section and the unscoured cross-section surveyed in 1987 (Opus, 2006). However the sand spit will probably scour out quickly in a flood event. Further sensitivity investigations should be carried out to determine the impact of the cross-section on upstream water levels. The updated survey data also includes nine new bridge cross-sections on the Reids Floodway upstream of the Thornton Road Bridge which brings the total number of bridges on the floodway to eleven. Two additional bridges have also been identified on the Rangitaiki River. A summary of the bridges on the Reids Floodway and on the Rangitaiki River is presented in Tables 3-1 and 3-2. The representation of these bridges and the hydraulic effects of them is discussed in Section 3.2 below. Table 3-1: Bridge locations on Reids Floodway Bridge Name / Identification Reids Floodway Chainage (m) Bridge between cross-section 22 and McCracken Rd McCracken Road Bridge Bridge between cross-sections 20 and Railway Bridge SH2 Bridge McLean Road Bridge Bridge between cross-sections 10 and Bridge between cross-sections 8 and Bridge between cross-sections 6 and Thornton Road Bridge Bridge C1 (just upstream of confluence with river) Final 6

13 Table 3-2: Bridge locations on Rangitaiki River Bridge name / identification Rangitaiki River Chainage (m) Railway Bridge SH2 Bridge (cross-section 27) Thornton Road Bridge Energy Losses Due to Bridge Piers and Decks and Other Channel Features All bridges will provide some degree of obstruction to flood flows and induce head losses. Analyses were therefore carried out to assess the magnitude of these losses and to ascertain whether they needed to be represented in the MIKE11 model to complement the energy losses due to channel friction. Table 3-3 summarises geometric details of each bridge (number of spans, total span length, approximate deck thickness, number of piers and pier width) and flow properties (maximum flow depth and velocity) for a representative model simulation. The State Highway 2 road bridge and the railway bridge over the Rangitaiki River, the railway bridge across Reids Floodway and the Thornton Road bridges over the Rangitaiki River and Reids Floodway were all assumed to have just enough freeboard to remain clear of the peak flood level profiles for the various flood scenarios so that head losses for these structures will be induced primarily by the piers. Two methods were used to estimate the pier-induced head losses for these structures Yarnell s method and the rational method (Montes, 1998). The estimated head loss values are summarised in Table 3-3. Appendix D provides more details of the calculations. The estimated head loss values for these bridges are small (generally < 0.03m) so that it was assumed the losses would be overshadowed by the energy losses due to channel friction. On this basis it was concluded that these bridges did not need to be represented in the MIKE11 model. The existing State Highway 2 road bridge across Reids Floodway will be partially submerged and will behave effectively as a submerged culvert. It also acts as severe channel constriction where the floodway berm switches from the right bank to the left bank (refer to the drawing on the next page). It was therefore represented in the MIKE11 model as a culvert structure. In the case of the proposed new State Highway 2 road bridge, the structure will have a much greater span (thereby reducing the degree of channel constriction) and have sufficient clearance above flood flows flowing down the floodway. The equivalent culvert in the MIKE11 model will therefore not be submerged. One of the significant advantages of describing the State Highway 2 bridge across Reids Floodway as a culvert in the MIKE11 model is that reflects the significant expansion loss experienced by flood flows passing through the structure spreading out over the left bank flood berm downstream. Final 7

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15 Table 3-3 Bridge geometry details, flow properties and estimated head loss values Bridge Bridge between C/s 22 and McCracken Bridge No. of Spans Total length (m) Deck Thickness (m) No. of Piers Pier Shape Pier Width (m) Flow Condition Effective Pier Width (m) Flow Depth (m) Flow Velocity (m/s) Head Loss (m) Yarnell / Rational submerged McCracken Bridge submerged Bridge between C/s 20 & C/s submerged Railway Bridge ? 5 circular SH2 Bridge ? 2 McLean Bridge Bridge between C/s 10 & C/s 11 Bridge between C/s 8 & C/s 9 Bridge between C/s 6 & C/s semi circular nose and tail row of 5 square piles row of 4 circular piles partly submerged Not calculated 0.4 submerged submerged submerged ?? submerged Thornton Rd Bridge? ?? 0.35 submerged Confluence bridge? 20.31???? Railway Bridge on Rangitaiki River Thornton Rd Bridge on Rangitaiki River probably submerged ? ???? ? 90.91???? Final 8

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17 Most of the farm access bridges along Reids Floodway are low single spans structures spanning the central low flow channel and will be completely submerged under the various flood scenarios being considered. The deck of each bridge will therefore behave as a horizontal rectangularshaped flow resistance element. The head loss in each case induced by this flow resistance element was estimated by translating the deck geometry to an equivalent vertical pier and applying the two pier loss methods (Yarnell s method and the rational method (Montes, 1998)) outlined previously. The calculated head loss values are again summarised in Table 3-3 with full details given in Appendix D. As was the case with the road and rail bridges, the estimated head loss values for these farm access type bridges are mostly very small (generally < 0.01m). It was again assumed that the head losses due to the flow resistance of the decks of these bridges would be overshadowed by the energy losses due to channel friction and on this basis it was concluded that most of the farm access bridges did not need to be represented in the MIKE11 model. The exceptions were the farm access bridges between cross-sections 8 and 9 and between 6 and 7 (model chainages 18066m and 18813m respectively) located on the very narrow lower part of Reids Floodway. The estimated head losses for these bridges are more significant. In the existing situation these bridges also pose a significant channel constriction so that the head losses arising from the expansion of flows onto the floodway berm downstream will mask the head losses due to their submerged decks. The effects of these expansion losses were represented in the MIKE11 model with expansion loss factors of 0.3 and 0.35 for the two bridges respectively. In the proposed modified (future) floodway design, the constricting effects of these bridges between cross-sections 8 and 9 and between 6 and 7 will be eliminated so that the expansion losses for these bridges could be safely omitted from the MIKE11 model for the design scenarios considering this case. Other geometric features on Reids Floodway could also potentially induce significant head losses: the sudden expansion downstream of the State Highway 2 bridge; and the gradual contraction of the floodway upstream of the very narrow lower section The head losses induced by the former feature are effectively represented in the model by the culvert description of the State Highway 2 bridge. The head loss factor for the gradual contraction was estimated to be less than 0.1 so that the induced head losses are small enough to ignore. It was concluded that neither feature needed to be represented in the MIKE11 model. 3.3 Model Calibration and Verification The existing MIKE11 model supplied by BOPRC had previously been calibrated against data from recent flood events. It was assumed that the same calibration factors (Manning s n channel roughness values) could be applied to the updated model with the 2009 cross-section data. It is important to recognise that the calibration factors are influenced by the choice of hydraulic radius definition for the relevant cross-section data. Final 10

18 In the case of the existing MIKE11 model based on the 2005 cross-section data, the model calibration had been established with the resistance radius formulation selected to define the hydraulic radius for the cross-section data for the Rangitaiki River branch. The same resistance radius formulation was therefore selected for the definition of the hydraulic radius for the 2009 cross-section data for the Rangitaiki River branch in the update MIKE11 model. In contrast the BOPRC model log notes (Appendix A) explicitly state that the conventional total area hydraulic radius formulation was selected for the Reids Floodway cross-section data in the original MIKE11 model. The same total area hydraulic radius formulation was maintained for the Reids Floodway branch cross-section data in the updated 2009 MIKE11 model. The Reids Floodway branch for the future design scenarios (see next section) incorporates a constant Manning s n channel roughness factor. While this is considered to be a reasonable choice of n value for a grassed channel, there still remains some uncertainty over the exact value of the channel roughness factor. It is therefore recommended that the sensitivity of the future floodway design is checked for Manning s n values in the range during the detailed design process for the floodway. To check the model configuration and setup, it was run for the previous 100-year peak flood estimate of 780 m 3 /s and a peak tide level of RL 1.806m. The peak flood level predictions from this simulation were then compared with those from a separate MIKE FLOOD model constructed for the purpose of a floodplain hazard assessment of the Rangitaiki Plains (Wallace, 2010a) and referenced in the peer review of the July 2009 draft of this report (Wallace, 2010b). The MIKE FLOOD model incorporated a number of changes: Some of the cross-sections with wide berms along the river including the tightly meandering reach downstream of Te Teko were modelled in two dimensions; The cross-section chainages were remeasured; The approaches to the Reids Floodway Spillway were modelled in two dimensions; and The reconfigured model was recalibrated against the July 2004 flood with minor changes to flow resistance values. Appendix C presents a tabulated comparison of the MIKE11 and MIKE FLOOD model predictions in the main river for the above flood case. The peak flood level predictions of the MIKE11 model are all within 0.05m of those of the MIKE FLOOD model, except at the extreme upstream end of the model where the definition of the river and floodplain is more coarse. The differences in the lower part main river are considered to be primarily attributable to the slight differences in crosssection chainages between the two models. As a consequence of this check, the MIKE11 model was considered verified for the purposes of this hydraulic capacity review. 3.4 Design Scenarios Several simulations were carried out with the updated channel geometry. Two other scenarios, including the proposed Lower Reids Floodway and SH2 bridge designs, were also assessed. The three geometry scenarios are presented in Table 3-3. Final 11

19 Table 3-4 Description of different geometry scenarios assessed in model simulations Geometry ID Geometry Name Geometry Description 0 Former scheme River and Reids Floodway cross-sections and spillway geometry based on 2004/2005 survey 1 Existing Scheme Based on 2008 / 2009 surveyed cross-sections, including 11 bridge cross-sections on Reids Floodway Existing geometry of the spillway 2 Future Design Based on 2008 / 2009 surveyed cross-sections for the Rangitaiki River and upstream of cross-section 9 on Reids Floodway, including 11 bridge cross-sections on floodway Cross-sections downstream of cross-section 10 on Reids Floodway according to design in Resource Consent Application (Opus International Consultants, 2008) Designed spillway: 163m wide fixed spillway at RL=7.15m / 70m wide fully deflated rubber dam at RL=5.9m Based on 2008 / 2009 surveyed cross-sections for the Rangitaiki River and upstream of cross-section 9 on Reids Floodway, including 11 bridge sections on floodway Cross-sections downstream of cross-section 10 on Reids 3 Future Design Floodway according to design in Resource Consent +SH2 Bridge Application (Opus International Consultants, 2008) Designed spillway: 163m wide fixed spillway at RL=7.15m / 70m wide fully deflated rubber dam at RL=5.9m New SH2 bridge section on Reids Floodway Design based on BBO drawings (2006) (see Appendix G) Final 12

20 3.5 Model Boundary Conditions BOPRC, in its Hydrological and Hydraulic Guidelines (Everitt, 2001), specifies design standard combinations for floods and sea levels. These were tested to compare the effects between: a 100 year flood with a 20 year storm surge (Q 100 : T 20 ); a 20 year flood with a 100 year storm surge (Q 20 : T 100 ). The difference between the two scenarios above was assessed only for the current flows and sea levels. The different combinations of boundary conditions used in the model are presented in Table 3-5. Table 3-5 Boundary conditions applied to MIKE11 model Scenario Scenario Description Peak Flow Value (m 3 /s) Peak Tide Level (m) A Former 100 year flood with 20 year storm surge B 20 year flood with 100 Year storm surge C 100 year flood with 20 Year storm surge D year flood with base 20 Year storm surge E year flood with conservative 20 Year storm surge F year flood with base 20 Year storm surge G year flood with conservative 20 Year storm surge Relative Timing of Tide Level and Flood Discharge Hydrographs A peer review of the July 2009 draft of this report suggested that the peaks of the flood discharge and tide level hydrographs shown in Figures 2-1 and 2-2 respectively may not be synchronised to give the maximum possible flood levels at the mouth of the Rangitaiki River. The relative timing of the flood discharge and tide level hydrographs was investigated. The first of the two largest peaks on the tide level hydrograph in Figure 2-2 lags the peak of the flood discharge hydrograph at Te Teko (25km upstream of the river mouth) by about 11.5 hours. Travel time of the flood discharge peak downriver caused the peak discharge at the river mouth to occur approximately 2.5 hours after the tide level peak. A sensitivity test was carried out to assess the effects of advancing the tide level peak relative to the flood discharge peak by about 3 hours so that low tide after the first tide level peak in Figure 2-2 was coincident with the arrival of the flood discharge peak at the river mouth. The effects of this modification of the timing of the tide level hydrograph are shown in Figure 3-1 for the Rangitaiki River and in Figure 3-2 for the Reids Floodway. The two figures compare the predicted peak water levels for the case of a 100 year flood with a 20 year storm surge. In the main river the peak water levels differ by at most 0.02m. It was concluded that lagging the tide level hydrograph by 2.5 hours to exactly match the arrival time of the flood discharge peak at the river mouth would have an insignificant effect on peak flood levels in the main river. Final 13

21 Figure 3-1: Effects of varying timing of flood discharge and tide level hydrograph peaks on Rangitaiki River Water Levels for 100 year flood and 20 year storm surge combination Thornton Rd Bridge 3.50 Level (m) 3.00 Rangitaiki River Estuary Water level - Coincident peak discharge and low tide level 1.50 Water level - Original flood discharge and tide level hydrographs Chainage (m) Figure 3-2: Effects of varying timing of flood discharge and tide level hydrograph peaks on Reids Floodway Water Levels for 100 year flood and 20 year storm surge combination 4.50 REIDS CANAL RANGITAIKI RIVER 4.00 Bridge between crosssections 6 & Level (m) 3.00 Rangitaiki River Estuary 2.50 Confluence Reids Canal / Rangitaiki River 2.00 Water level - Coincident peak discharge and low tide level 1.50 Water level - Original flood discharge and tide level hydrographs Chainage (m) Final 14

22 In the lower part of Reids Floodway, the peak flood levels for the two flood cases barely differ although, in the upper part, the differences are slightly greater due to the backwater effect upstream of the very narrow lower section of the floodway. While it was not considered necessary to change the timing of the tide level hydrographs for all the required model simulations in this investigation, we recommend for the detailed design of the floodway that the sensitivity of peak flood level is checked for coincidence of peak flood discharge at the river mouth with high and low tide levels. 3.7 Spillweir Geometry at Entrance to Reids Floodway Currently the spillweir at the entrance to Reids Floodway consists of a low point in the right bank stopbank along the Rangitaiki River. It has been configured in the MIKE11 model as a sequence of parallel broad crested overflow weirs (ten weirs in total, each being 23.3m wide). The crest levels of this sequence of weirs follows a stepped profile which approximately matches the existing stopbank profile. It was noted that the default calculation procedure within the MIKE11 software produced an effective discharge coefficient of C d 0.8 for each broad crested weir rating (where the rating is defined by an equation of the form Q = C d (2/3)( 2g/3) B H 3/2 2 ). The trapezoidal profile of the actual spillweir suggests that a discharge coefficient C d = 0.8 will significantly underestimate the spillweir discharge capacity. The discharge rating for each broad crested weir in the MIKE11 model was therefore specified by means of a user-defined rating with an effective discharge coefficient of C d = The BOPRC model log sheet in Appendix A notes a similar adjustment made to the ratings of the weirs representing the spillweir at the entrance to Reids Floodway. In the future it is proposed to modify the current spillweir at the entrance to the Reids Floodway as part of the overall floodway upgrade by incorporating an inflatable rubber weir set at a lower level than the rest of the spillweir. The rubber weir would normally be deflated but it would be inflated whenever a certain flood level trigger point upstream was reached. The inflated weir would initially prevent the spillweir from operating. However it would be deflated if a second higher flood level set approximately at the 40 year flood level was reached upstream. This would allow floodwaters to then flow down the floodway and provide relief to the flood protection stopbanks in the lower river. The resource consents granted for the future upgrade of Reids Floodway allow for a maximum spill discharge of 200m 3 /s. The inflatable rubber weir has been sized to be about 70m wide (covering three of the ten spillweir segments in the MIKE11 model). The invert level of the rubber weir section in the model was adjusted by trial and error to produce a peak spill discharge of just under 200m 3 /s. Assuming a constant level of RL 7.15m for the remaining part of the grassed spillweir and with the rubber weir section located at the downstream end of the spillweir (where 2 In this weir discharge rating equation, Q is the discharge, C d is a discharge coefficient, B is the width of the weir, H is the upstream head on the weir and g is the gravitational acceleration. The discharge coefficient C d for a round nosed or trapezoidal profile broad-crested weir where flow separation at the leading edge of the weir does not occur typically has a value of about Final 15

23 ground levels upstream are lower and would require less excavation to form an approach channel), the optimum level for the invert of the rubber weir was found to be about RL 5.9m. The MIKE11 model for the future Reids Floodway simulations (Series 2 and 3 from Table 3-4) was run in two steps. For the first step, the model was configured with all ten weir segments in the model representing the spillweir at the entrance to Reids Floodway set at a crest level of RL 7.15m. For the second step, the model was configured with the rubber weir section of the spillweir set at an invert level of RL 5.9m. The switch between the two model configurations occurred when the flood level in the main river at the upstream end of the spillweir reached RL 7.0m which coincided approximately with the peak level of the 20 year flood at that location. The weir ratings for these two model configurations for the future Reids Floodway simulations were defined in the same manner as for the current spillweir geometry (i.e. with an effective weir discharge coefficient of C d = 0.95) 3.8 Model Log Update The original log sheet maintained by BOPRC and describing modifications and improvements to the MIKE11 model over time is appended in Appendix A. An updated log sheet summarising the update of the MIKE11 model with the 2009 cross-section data has been prepared to complement the original BOPRC log sheet. This is appended in Appendix B. Final 16

24 4 Results of Model Simulations 4.1 Definition of Simulation Scenarios Different simulations including various design and boundary condition scenarios were carried out. The matrix presented in Table 4-1 describes the different simulations which were run for the capacity assessment. Table 4-1 Matrix of simulations carried out for hydraulic capacity review Geometry scenarios Geometry Geometry 2 Future Design 3 Future Design + SH2 Bridge A: Former 100 Year flow with 20 Year Storm Surge Simulation 0A Simulation 1A Boundary Conditions scenarios B: 20 Year flow with 100 Year Storm Surge C: 100 Year flow with 20 Year Storm Surge D: Year flow with base 20 Year Storm Surge E: Year flow with conservative 20 Year Storm Surge F: Year flow with base 20 Year Storm Surge G: Year flow with conservative 20 Year Storm Surge Simulation 1B Simulation 1C Simulation 2C Simulation 3C Simulation 1D Simulation 2D Simulation 3D Simulation 1E Simulation 2E Simulation 3E Simulation 3F Simulation 3G 4.2 Water level long section results The results of the different simulations are presented as water level profiles in the following figures: Figure 4-1 and 4-3 show the comparison between water level profiles from Simulations 1B and 1C in the Rangitaiki River and in the Reids Floodway; Figure 4-2 shows the results of a sensitivity test for water levels in Reids Floodway from simulation 1C with and without energy loss factors for critical bridges; Figure 4-4 shows the comparison between water level profiles in the Rangitaiki River for the 100 year flood / 20 year storm surge case for the current and future Reids Floodway geometries (Simulations 1C, 2C and 2D); Figure 4-5 shows the comparison between water levels in Reids Floodway for the 100 year flood / 20 year storm surge case for various floodway geometries (Simulations 1C, 2C and 3C); Final 17

25 Figure 4-6 shows the comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the 100 year flood / 20 year storm surge case for various floodway geometries (Simulations 1C and 2C/3C); Figure 4-7 shows the comparison between flood discharge hydrographs in the Reids Floodway immediately downstream of the Reids Floodway Spillweir for the 100 year flood / 20 year storm surge case for various floodway geometries (Simulations 1C and 2C/3C); Figure 4-8 shows the comparison between water levels in the Rangitaiki River for the climate change affected 100 year flood / 20 year storm surge cases (Simulations 3C, 3D and 3F); Figure 4-9 shows the comparison between water levels in the future Reids Floodway for the climate change affected 100 year flood / 20 year storm surge cases (Simulations 3C, 3D and 3F); Figure 4-10 shows the comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the climate change affected 100 year flood / 20 year storm surge cases (Simulations 3C, 3D and 3F); Figure 4-11 shows the comparison between flood discharge hydrographs in the Reids Floodway immediately downstream of the Reids Floodway Spillweir for the climate change affected 100 year flood / 20 year storm surge cases (Simulations 3C, 3D and 3F); The water level predictions for all model simulations are summarised in tables in Appendix E. Final 18

26 Figure 4-1: Rangitaiki River water level long section - Comparison of 100-year and 20-year ARI flood and storm surge combinations for existing river and floodway geometry Upper end of the spillway Lower end of the spillway SH2 Bridge Rangitaiki river / Reids Canal Confluence Rangitaiki river Estuary Level (m) Chainage (m) Existing bottom level Existing LB Level Existing RB Level Q20=539m3/s / T100 Water level - Scenario 1B Current scheme - Q100=804m3/s / T20 Water level - Scenario 1C Final 19

27 Figure 4-2: Reids Floodway water level long section - Sensitivity test for energy loss factors with existing floodway geometry for current 100-year ARI flood with 20-year ARI storm surge Spillway McCraken Rd Bridge SH2 Bridge McLean Rd Bridge Bridge between XS 8 & 9 Bridge between XS 6 & 7 Thornton Rd Bridge Reids Canal / Rangitaiki River Confluence Rangitaiki River Estuary 2 Level (m) Chainage (m) Existing bottom level Existing LB Level Existing RB Level Q100=804m3/s / T20 Water level without ennergy losses applied Q100=804m3/s / T20 Water level with energy losses applied Final 20

28 Figure 4-3: Reids Floodway water level long section Comparison of 100-year and 20-year ARI flood and storm surge combinations for existing floodway geometry Spillway McCraken Rd Bridge SH2 Bridge McLean Rd Bridge Bridge between XS 8 & 9 Bridge between XS 6 & 7 Thornton Rd Bridge Reids Canal / Rangitaiki River Confluence Rangitaiki River Estuary 2 Level (m) Chainage (m) Existing bottom level Existing RB Level Current scheme - Q100=804m3/s / T20 Water level - Scenario 1C Existing LB Level Current scheme - Q20=539m3/s / T100 Water level - Scenario 1B Final 21

29 Figure 4-4: Rangitaiki River water level long section Effect of changes in spillway geometry for 100-year ARI flood and 20- year ARI storm surge Upper end of the spillway Lower end of the spillway SH2 Bridge Rangitaiki river / Reids Canal Confluence Rangitaiki river Estuary Level (m) Chainage (m) Existing bottom level Existing LB Level Existing RB Level Current scheme - Q100=804m3/s / T20 Water level - Scenario 1C Future design - Q100=804m3/s / T20 Water level - Scenario 2C Future design - Q100=862m3/s / T20 Water level - Scenario 2D Final 22

30 Figure 4-5: Reids Floodway water level long section Effect of changes in floodway geometry for 100-year ARI flood and 20- year ARI storm surge Spillway McCraken Rd Bridge SH2 Bridge McLean Rd Bridge Bridge Between XS 8 & 9 Brdige between XS 6 & 7 Thornton Rd Bridge Reids Canal / Rangitaiki River Confluence Rangitaiki River Estuary 2 Level (m) Chainage (m) Existing bottom level Existing LB Level Existing RB Level Current scheme -Q100=804m3/s / T20 Water level -Scenario 1C Future design -Q100=804m3/s / T20 Water level -Scenario 2C Future design -Q100=804m3/s / T20 Water level -Scenario 3C Final 23

31 Figure 4-6: Comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the 100-year ARI flood and 20-year ARI storm surge Discharge (m 3 /s) Simulation 1C 200 Simulation 2C/3C Time Final 24

32 Figure 4-7: Comparison between flood discharge hydrographs in Reids Floodway immediately downstream of the Reids Floodway Spillweir for the 100-year ARI flood and 20-year ARI storm surge Discharge (m 3 /s) Simulation 1C Simulation 2C/3C Time Final 25

33 Figure 4-8: Rangitaiki River water level long section Sensitivity to climate change increases in flood discharge for future design with 100-year ARI flood and 20-year ARI storm surge Upper end of the spillway Lower end of the spillway SH2 Bridge Rangitaiki river / Reids Canal Confluence Rangitaiki river Estuary Level (m) Nb: The scenario "Future Design + SH2 Bridge Q100=862m3/s Conserv T20" is not represented here because the water level is exactly the same than the future design Chainage (m) Existing bottom level Existing LB Level Existing RB Level Future design - Q100=804m3/s / T20 Water level - Scenario 3C Future design Q100=862m3/s / T20 Water level - Scenario 3D Future design Q100=939m3/s / T20 Water level - Scenario 3F Final 26

34 Figure 4-9: Reids Floodway water level long section Sensitivity to climate change increases in flood discharge for future design including new SH2 Bridge with 100-year flood and 20-year ARI storm surge Spillway McCraken Rd Bridge SH2 Bridge McLean Rd Bridge Bridge Between XS 8 & 9 Brdige between XS 6 & 7 Thornton Rd Bridge Reids Canal / Rangitaiki River Confluence Rangitaiki River Estuary 2 Level (m) Chainage (m) Existing bottom level Existing LB Level Existing RB Level Future design -Q100=804m3/s / T20 Water level -Scenario 3C Future design Q100=862m3/s / T20 Water level -Scenario 3D Future design Q100=939m3/s / T20 Water level -Scenario 3F Final 27

35 Figure 4-10: Comparison between flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the climate change affected 100-year ARI flood and 20-year ARI storm surge Simulation 3C Simulation 3D Simulation 3F 500 Discharge (m 3 /s) Time Final 28

36 Figure 4-11: Comparison between flood discharge hydrographs in Reids Floodway immediately downstream of the Reids Floodway Spillweir for the climate change affected 100-year ARI flood and 20-year ARI storm surge Simulation 3C Simulation 3D Simulation 3F 200 Discharge (m 3 /s) Time Final 29

37 5 Hydraulic Capacity Review 5.1 Standard Design Combination Scenarios The water level plots presented in Figures 4-1 and 4-3 show that the water levels are higher in most parts of the river and the floodway with a combination of a 100 year flow and a 20 year storm surge than with a 20 year flow and a 100 year storm surge. The Rangitaiki River downstream of the confluence with the Reids Floodway is the only reach affected by the higher storm surge peak level. Therefore the combination of a 100 year flow and a 20 year storm surge is recommended for the capacity assessment. 5.2 Channel Geometry Effects Some of the bridges in Reids Floodway considerably reduce the floodway capacity and contribute to stopbank overflows. As discussed in Section 3.2, the pier and deck effects of most bridges are minor but the contraction and expansion effects due to some comparatively narrow bridge crosssections are significant, in particular at the SH2 bridge (chainage 12659), the bridge between cross-sections 8 and 9 (chainage 18066) and the bridge between cross-sections 6 and 7 (chainage 18813). Figure 4-2 shows the effect of representing these head losses in the model on the backwater profile along the floodway for 100-year flood / 20-year storm surge case. They increase water levels along the floodway very slightly. Figure 4-4 shows the effect on flood levels in the Rangitaiki River for the 100-year flood / 20-year storm surge case. It compares peak flood levels for a future upgrade to Reids Floodway (with a deflatable rubber component on the entrance spillweir) with those for the current floodway and spill weir geometry. The effect of the upgraded floodway is to reduce flood levels in the main river downstream of the Reids Floodway Spillweir. The left and right stopbanks are still overtopped in places. Figure 4-6 compares the flood discharge hydrographs in the main river immediately downstream of the Reids Floodway Spillweir for the current 100-year flood / 20-year storm surge case. The upgraded spillweir reduces the downstream peak discharge in the main river from about 675 m 3 /s to 615 m 3 /s. Figure 4-5 compares peak flood levels along Reids Floodway for the current and upgraded floodway for the 100-year / 20-year storm surge case. Flood levels are considerably reduced upstream of the widened section of floodway. However stopbanks along the floodway are still not high enough to contain the peak flood discharge. The upgraded State Highway 2 bridge also helps to reduce upstream flood levels slightly. Figure 4-7 compares flood discharge hydrographs for the Reids Floodway Spillweir for the 100- year flood case. The upgraded spillweir allows a peak discharge of 191 m 3 /s down the floodway compared to 134 m 3 /s for the current fixed crest spillweir. Final 30

38 The cross-section survey data for the main river upstream of the spillway appear to be incomplete (for example left stopbank crests have not been surveyed at cross-sections 43b and 43c). Therefore the water levels in this area (upstream chainage 8000) shown in Figures 4-1 and 4-4 could have been overestimated due to the glass wall assumption of the model. 5.3 Sea Level Influence As outlined in Sections 2.2 and 3.3, the climate change scenarios were run with base and conservative peak storm surge values. Table 5-1 compares the extent of the backwater effect due to a storm surge peak increase for both the Rangitaiki River and the Reids Floodway. The backwater effect is most pronounced in Reids Floodway where the effect of increased storm surge for 2090 extends right back to the downstream side of the entrance spillweir. Table 5-1: Influence of the storm surge peak on the water level in the Reids Floodway and the Rangitaiki River Storm Surge Difference (m) Chainage of significant 3 backwater effect (m) Reids Floodway Rangitaiki River CC (Q100=862 m3/s) CC (Q100=939 m3/s) CC (Q100=862 m3/s) CC (Q100=939 m3/s) Current Scheme Capacity The current capacities of the Rangitaiki River and the Reids Floodway were determined considering the bankfull maximum flows in the channel (i.e. without freeboard) for the existing channel configuration (2008/2009 survey data) and a 20 year storm surge. The current capacity of the Rangitaiki River is estimated to be 622 m 3 /s (spill over the right bank at chainage 17810m). The current capacity of the Reids Floodway is estimated to be 67 m 3 /s (spill over the left bank at chainage 17082m). The comparison of the Rangitaiki River capacity with the latest survey data and the 2005 survey data shows that the hydraulic capacity of the river has decreased by around 24 m 3 /s over this period (the river capacity with the 2005 survey data was estimated to be 646 m 3 /s). This is mainly due to a rise of the bottom level in the lower reach of the Rangitaiki River (average increase of 0.22m from the spillway (c/s 36 at chainage 10470m) to the mouth (c/s 1A at chainage 24450m) and locally up to 1.4m). The comparison of the Reids Floodway capacity between 2005 and 2009 is difficult to assess because the critical bridges identified in Section 3.2 were not included in the previous simulations and present major flow constrictions. The spill from the Rangitaiki River into the Reids Floodway over the existing spillweir commences at a flow of 594 m 3 /s in the river. The spill into the Reids Floodway with the upgraded spillway 3 A significant backwater effect is considered to be a difference between water levels greater than 0.02m. Final 31

39 commences at a flow of 591 m 3 /s (this specified to occur when the upstream river level reaches 7.0 m and the inflatable rubber weir is assumed to be deflated). 5.5 Climate Change Influence on Water Levels in the Rangitaiki River Figure 4-8 shows peak flood level profiles along the Rangitaiki River for the upgraded Reids Floodway and various climate scenarios for the 100-year flood / 20-year storm surge case. As would be expected, the flood levels gradually increase with increasing peak discharge (804 m3/s for the current climate, 862 m3/s for the 2040 climate scenario, and 932 m3/s for the 2090 climate scenario). Figure 4-10 shows flood discharge hydrographs in the Rangitaiki River immediately downstream of the Reids Floodway Spillweir for the same three climate scenarios. The peak discharge occurs after the rubber weir section of the spillweir has been deflated (which is indicated by the initial peak in the hydrograph, the sudden drop in discharge and the subsequent gradual rise to the maximum peak). Figure 4-9 shows peak flood level profiles along Reids Floodway for the upgraded floodway and the same three climate scenarios for the 100-year / 20-year storm surge case. This shows a similar pattern to the peak flood level profiles for the main river and reflects the gradually increasing peak discharge down the floodway resulting from the assumption of a fully deflated rubber weir section to RL 5.9m. If it was considered desirable to maintain the maximum discharge down Reids Floodway to the current consented limit of 200 m3/s, then the flexibility of the rubber weir means that it could be possible to only partially deflate it to a certain level to pass the allowable flow as climate change takes effect. This highlights the need to determine an operational strategy for the rubber weir during the detailed design process for the upgraded Reids Floodway. Table 5-2 summarises the water levels at four specific cross sections in the Rangitaiki River for different boundary condition scenarios and the same channel geometry configuration (upgraded lower Reids Floodway and new SH2 bridge). Final 32

40 Table 5-2: Comparison of water level along the Rangitaiki River for different boundary condition scenarios Cross section ID Chainage (m) Thornton Rd Description Just downstream Reids Floodway spillweir SH2 Bridge at Edgecumbe Around McLean Rd Thornton Rd Bridge 3C: Current 100 Year flow with 20 Year Storm Surge Water level (m) for different boundary condition scenarios 3D: Year flow with base 20 Year Storm Surge 3E: Year flow with conservative 20 Year Storm Surge 3F: Year flow with base 20 Year Storm Surge 3G: Year flow with conservative 20 Year Storm Surge Compared with the current situation, the water levels are between m higher in the 2040 climate change scenario, and m in the 2090 climate change scenario. The existing stopbank scheme is not sufficient to contain the flood flows of the 2040 and 2090 climate change scenarios. 5.6 Flow Split in Rangitaiki River and Reids Floodway Table 5-3 illustrates the flow split between the Rangitaiki River and the Reids Floodway for different spillway designs and different flows in the River. The proportion of flow into the Reids Floodway increases with an increase of total inflow, whereas the proportion of flow in the Rangitaiki River downstream the spillway, reduces. Table 5-3: Flow split between the Rangitaiki River and the Reids Floodway for different flow scenarios Spillway scheme Current spillway geometry Designed spillway geometry Total inflow Flow in Reids Floodway Flow in Rangitaiki River (m 3 /s) (m 3 /s) Q 20 = 539 m 3 /s Former Q 100 = 780 m 3 /s Q 100 = 804 m 3 /s Q 100 = 862 m 3 /s Q 100 = 804 m 3 /s Q 100 = 862 m 3 /s Q 100 = 939 m 3 /s Final 33

41 6 Comments on One-Dimensional Model configuration of MIKE11 Model 6.1 Treatment of Reids Floodway There has been some discussion of the relative merits of modelling Reids Floodway by means of one-dimensional (MIKE11) and two-dimensional hydraulic modelling software (MIKE21/MIKE FLOOD) because of the compound shape of the floodway cross-section. Figure 6-1 shows a typical cross-section of Reids Floodway (cross-section 21) with a narrow low flow main channel (in this particular part of the floodway, along the left bank) and a very wide berm. The aspect ratio between the berm width B and the low flow main channel width b in this case is B/b 16 ( 290m wide berm and 18m wide main channel). 4.5 Cross-section 21 of Reids Floodway Level (m) Distance (m) Figure 6-1 Typical channel cross-section on Reids Floodway (cross-section 21 at chainage 11747m) The peak flood level at this cross-section for Simulation 1C (100-year flood / 20 year storm surge) is RL 4.01m. Ignoring the fact that the current stopbanks confining the floodway are below this peak level (and would therefore be overtopped), the peak flood level means that there would be more than 2m depth of water flowing over the floodway berm. Final 34

42 The relative depth of floodplain flow to main channel flow (where H is the flow depth in the main channel and h is the depth of the main channel below the berm) is expressed by the ratio (H-h)/H. In this case the berm is not a constant height h above the main channel river so the relative depth ratio (H-h)/H is in the range The very wide nature of the berm relative to the main channel and the depth of the flow mean that the berm component will dominate the conveyance capacity of the floodway. It therefore seems intuitively reasonable to model such a channel using a one-dimensional modelling approach. Ackers (1993) reports on some UK experimental research in the 1990 s in the conveyance capacity of two-stage or compound channels. The aspect ratios B/b 16 and (H-h)/H = indicate the Reids Floodway cross-section is outside the range of the model channels tested experimentally to assess their conveyance properties. However for those narrower channels tested, as the depth aspect ratio (H-h)/H increases above 0.4, a compound channel starts to behave more and more like a single channel due to the depth of berm submergence. In this case the even larger value of the width aspect ratio B/b means that this trend would be even more accentuated. On the basis of this experimental evidence then, it is perfectly reasonable to model Reids Floodway using a conventional one-dimensional modelling approach with appropriate contraction and expansion loss factors applied at sharp changes in channel geometry. 6.2 Channel Roughness in One-Dimensional and Two-Dimensional Computational Hydraulic Models It is important to note that, even though one and two-dimensional hydraulic models both use Manning s n channel roughness (or Chezy C resistance factor) as an empirical flow resistance parameters to represent frictional effects, the roughness concept is entirely different for the two situations (Morven et al, 2008). For a one-dimensional model, the friction factor represents the shear stress exerted by the entire channel cross-section boundary (including the bed and banks). It is a lumped parameter required to reflect the frictional effects of skin drag (roughness due to surface texture only), form drag (roughness due to surface geometry including bed forms) and shape drag (roughness due to channel shape, meanders and bends etc.). In calibrating a one-dimensional model against observed flood levels and flows, the effects of flow turbulence are also implicity included in the derived calibration roughness factors along with the effects of skin drag, form drag and shape drag. In contrast, in a two-dimensional model, the friction factor only represents the shear stress exerted by the simulated flow on the base of a vertical column of water (within each grid cell). This is not the same situation as in a one-dimensional model. For this reason Manning s n channel roughness or Chezy C friction factor values are not transferable between one and two-dimensional computational hydraulic models. Final 35

43 6.3 Superelevation of Flow Around Bends One of the fundamental assumptions of a one-dimensional computational hydraulic model is that the water surface elevation across a cross-section is constant. In practice, this is not true around bends as the centrifugal force causes the water surface to be elevated with higher levels on the outside of the bend and lower levels on the inside. In this context then, where significant bends occur in the Rangitaiki River as seen in Drawing in Sections 3, the predicted flood levels given in Appendix E must be corrected for superelevation effects by the equation (ASCE, 1995) y = cv 2 w/gr where y = rise in water surface level from the channel centreline to the outside of the bend, C = coefficient depending on flow type and cross-section shape, V = average flow velocity, w = channel width, g = gravitational acceleration and r = bend radius. Superelevation of flow round bends is automatically accounted for by two-dimensional computational hydraulic models for which a curvilinear model grid is more appropriate than a conventional rectangular grid. 7 Comments and Recommendations on Future Flood Scheme Upgrade 7.1 Comments The geometry of the proposed spillweir at the entrance to Reids Floodway has only been designed to a very preliminary level and needs to be the subject of a further optimisation study as part of the detailed design process for the floodway. The optimisation study would enable the following weir parameters to be determined: Inflatable rubber weir length Inflatable rubber weir invert level Inflatable rubber weir crest level Number of inflatable weir segments Fixed weir length and crest level Such a study would need to take account of: Constraints on rubber weir design and performance The topography of the approach channel in front of the rubber weir Final 36

44 The design of the optimised spillweir geometry needs to be flexible enough not to preclude further upgrading of Reids Floodway in the future for flows greater than the currently consented 200 m 3 /s. 7.2 Recommendations The following recommendations arise out of this hydraulic capacity review of the Rangitaiki River and Reids Floodway: An optimisation study should be undertaken to optimise the configuration and geometry of the spillweir at the entrance to Reids Floodway. Sensitivity testing of peak flood levels in Reids Floodway to the Manning s n channel roughness assumptions should be undertaken as part of the process of determining design flood level and design crest profiles for the stopbanks confining the floodway. Flood levels around the outside of bends in the Rangitaiki River should be adjusted for the effects of flow superelevation as part of the process of determining design flood level for the river and design crest profiles for the stopbanks. Sensitivity testing of peak flood levels to the sediment bar at the river mouth should be carried out as part of the process for determining design flood levels and design crest profiles for the stopbanks in the lower part of the main river and Reids Floodway. Sensitivity testing of peak flood levels in the lower part of the main river should be checked for the coincidence of peak flood discharge at the river mouth with high and low tide levels. As part of the process for determining design flood levels and crest levels in the Rangitaiki River, the best approach to increasing Rangitaiki River channel capacity with the required freeboard (raising stopbank levels, lowering river bed levels or a combination of both) should be investigated. Final 37

45 References Ackers, P (1993). Flow formulae for straight two-stage channels. J. of Hydraulic Research, Vol. 31, No. 4. pp ASCE (1995). Hydraulic Design of Flood control Channels. Technical Engineering and Design Guides as adapted from US Army Corps of Emgineers No.10, ASCE Press, New York, POP. Blackwood, P L (2000). Review of the Flood Carrying Capacity of the Rangitaiki River Below Edgecumbe. Environment Bay of Plenty. Operations report 2000/ pages. Bloxam, Burnett and Olliver (2006). Reids Central Canal Bridge SH2. Long section sheets 1 and 2 drawings. Drawing numbers /P126 and P127. Everitt, S C (2001). Hydrological and Hydraulic Guidelines. Environment Bay of Plenty. Guidelines 2001/ pages. Morvan, H, Knight, D, Wright, N Tang X and Crossley, A (2008). The concept of roughness in fluvial hydraulics and its formulation in 1D, 2D and 3D numerical simulation models. J. of Hydraulic Research, Vol. 46, No. 2, pp Ministry for Environment (2008a). Climate Change Effects and Impacts Assessment: A Guidance Manual for Local Government in New Zealand. 2 nd Edition. Mullan B; Wratt D; Dean S; Hollis M; Allan S; Williams T; Kenny G and MfE. Ministry for Environment, Wellington. Xviii pages. Ministry for Environment (2008b). Coastal Hazards and Climate Change: A Guidance Manual for Local Government in New Zealand. 2 nd Edition. Revised by Ramsay D. and Bell R. (NIWA). Prepared for MfE. viii pages. Montes, S (1998). Hydraulics of Open Channel Flow. ASCE Press. Opus International Consultants Ltd (2006). Edgecumbe Urban and Rural Flood Hazard: Mitigation Options Study. Appendix pages. Opus International Consultants Ltd (2008). Edgecumbe Rangitaiki Plains Flood Mitigation Project. Lower Reids Floodway Widening Plan & Typical cross-sections. References: 10/1530/ Sheets 7 and 8. Wallace, P (2010a). Hydraulic Modelling of the Rangitaiki Plains. Draft report prepared by River Edge Consulting Ltd for Environment Bay of Plenty. Wallace, P (2010b). Rangitaiki River Modelling Review. Letter to Bay of Plenty Regional Council from River Edge Consulting Ltd, dated 17 December Final 38

46 This page has been left intentionally blank Final 39

47 Appendix A EBOP MIKE11 Model Log

48

49 Model Log: Recalibration PMW Purpose: To find and replicate the calibration simulation, and prepare the model for recalibration. To recalibrate the model with the channel markers on the Rangitaiki River re-located to the stopbank crests Setting up for recalibration. Collecting and checking the files from the original calibration and creating a new folder for these. Note that the original calibration HD parameters file has the wave approximation method set to Fully dynamic. I have been told that the more recent High order fully dynamic is the method of preference. I cant recall why. It may be a more recent method than the original model. Had to alter the boundary file and Network file: Boundary file referred to a tide level time series in the H drive that M11 couldn t find. There was an identically named file in the R Drive next to the calibration sim file (used that). The network file needed to be resaved to update its format. To do this without altering the original I saved a copy to the working folder: recalibrationPLB. Am getting good replication with this except for about 50mm at river distance Cant find source of this discrepancy (see Excel workbook). Following changes made to replication model: Resistance Radius changed to Total Area Hydraulic Radius on Reids Central Floodway (this Floodway was not included in original calibration). Resistance Radius retained on main river channel. Wave approximation retained at fully dynamic. Did not change to High order fully dynamic. (up to 50mm difference would have been caused by this). [discussed and decided not worth changing] Reid Central run with 1994 cross sections with channel markers un-corrected but roughness lowered to (reids not included in the original calibration) [it was found that including the Floodway, caused levels to lower by up to 29mm at that location in the river, probably though dampening of the tide and extra storage by water flowing up into the Floodway.] I considered changing the method of level selection from automatic to equidistant but found that it caused discrepancies in the order of 0.1m so left that to the discretion of the original modeller Recalibration of Rangitaiki River Model refer to the model report of October PLB had not included in-channel markers to delineate the berm-main channel boundaries. I notice that the Reid Central cross sections had differential roughness values added. Checked with PLB and he did not include these type of markers in the Rangitaiki Channel due to the small size of the berms. I will not change this

50 Altered the bed resistance at chainage 4960 to 5880 from to Some other minor alterations were made to the bed resistance as shown in the electronic workbook. Verification against 2004 floods: For the reach downstream of about Kokohinau, the peak levels in the river were caused before the stopbank breached. Therefore the event was modelled up until the time of the breach. This involved truncating the river gauge trace at Te Teko (updated NIWA rating, confirmed somewhat by the Matahina Dam outflow record). The time of truncation was taken as the time of the breach minus the river flow time lag between Te Teko and the breach site. The results give good representation of the recorded levels. Several flood levels are recorded much lower than the rest. I put this down to the second peak, experienced following the breach The recent GPS survey of the Rangitaiki Stopbank profile has shown that the model setup for the spillway is up to about 0.4m lower than surveyed. This is confirmed by the Total Station survey of March this year. This impacts on the verification simulation of the 2004 event, which had shown good matching against recorded levels. The previous verification simulation (results file Calib04) had estimated that 67 m3/s spilled on Sunday morning 18 July 2004 before the breach occurred downstream and lowered levels in that section of the river. With the alteration to the spillway, (results file Calib04a) the model now estimates that only 35 m3/s spilled at that time. This leads to a localised increase in modelled river levels of about 0.174m. This does not match nearly so well the recorded levels. However, as the difference is a result of sensitivity to a 32 m3/s peak flow difference, c.f. estimated peak flow before the breach of 690 m3/s (4.6%), and due to the uncertainty of flow measurement at Te Teko and other effects such as diffuse flows, and routing effects, it is considered that the channel bed roughness values should be retained. There is not enough certainty in the 2004 data to warrant re-calibration of the model at this stage The extents and explanations for the above discrepancy were thoroughly looked into. This is written up in a memo PMW Memo to PLB. He has approved the content of the memo and that the model can be released in its updated format. The spillway weir was modelled with 10 parallel weirs, each 23.3m wide, based on the 2005 surveyed crest level. The Broad Crested Weir module was used in the Network File, and the Free overflow factor of was applied to give a weir coefficient of 2.2 (1.703 x = 2.2). The 1% AEP river flow with spillway at 2.5% AEP operation level results for OPUS were based on the existing weir because it closely represents that design case. The 5% operation level simulation was modelled with a flat crest parallel to the river profile during a 1% Flood. This was therefore an iterative procedure (single iteration).

51 Appendix B Updated MIKE11 Model Log

52

53 (Opus International Consultants) cross-section data inserted in model cross-section database Resistance radius formulation selected for Rangitaiki River cross-sections as per previously calibrated versions of model Total area hydraulic radius formulation selected for Reids Floodway cross-section as per previous versions of model 2. Cross-section at Thornton Rd Bridge on Rangitaiki River inserted at chainage 22650m 3. Existing State Highway 2 bridge over Reids Floodway represented in model as rectangular culvert with following dimensions width 19.67m depth 5.59m invert level -1.5m RL length 8m 4. New State Highway 2 bridge over Reids Floodway represented in future floodway model as rectangular culvert with following dimensions width 39m depth 7m invert level -1.95m RL length 20m This description is based on an equivalent waterway cross-sectional area to the actual trapezoidal area shown on the new bridge drawings in Appendix G. The upstream and downstream cross-sections in the MIKE11 model network file had to be adjusted to be rectangular-shaped using the same approach to enable the culvert rating to be calculated by MIKE Head losses for most other Reids Floodway and Rangitaiki River bridges were estimated to be small enough to be ignored (refer Appendix D and Table 3-3). Exceptions were the bridges between cross-sections 8 and 9 and between 6 and 7 in the very narrow existing lower section of Reids Floodway. Only three bridges were therefore represented in the MIKE11 model for the existing floodway geometry. 6. The two farm access bridges between cross-sections 8 and 9 and between 6 and 7 were initially represented as submerged culverts with overflow in the MIKE11 model but they induced significant model instabilities. As the greatest contributing factor to the head losses resulting from these structures is the expansion of flood flows downstream of the bridge openings, the effects of these bridges were represented in the MIKE11 model by means of

54 expansion loss factors (with values of 0.3 and 0.34 for the bridges between cross-sections 8 and 9 and between 6 and 7 respectively). 7. The widened floodway in the future design removes the constrictions induced by these bridges so that the expansion loss factors were removed from the future floodway versions of the MIKE11 model. 8. The weir discharge ratings for the ten 23.3 wide weir segments making up the spillweir at the entrance to Reids Floodway were defined with an effective discharge coefficient of C d = The stepped weir profile for the existing Reids Floodway spillweir geometry reflects the current stopbank crest level profile. 10. For the future upgraded spillweir with a 70m wide rubber weir section, the rubber weir invert level was optimized at RL 5.9m to achieve a maximum spillweir discharge of less than 200 m 3 /s. The remainder of the spillweir was fixed at a constant level of RL 7.15m.

55 Appendix C MIKE11 Model Chainages and Comparison of Model Predictions with MIKE FLOOD Model of Wallace (2010a)

56

57 Rangitaiki River Cross-section Locations and Chainages Model Chainage (m) Peak Flood Level (m MSL) River Name Cross-section Location Peer Reviewer's MIKE FLOOD model MIKE11 model Peer Reviewer's MIKE FLOOD model Opus adapted MIKE11 model Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 51c Rangitaiki River 51b Rangitaiki River 51a Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 47b Rangitaiki River 47a Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 43c Rangitaiki River 43b Rangitaiki River 43a Rangitaiki River Rangitaiki River 41a Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 37updated Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 28B Rangitaiki River Rangitaiki River 28A Rangitaiki River Railway Railway Bridge Rangitaiki River 27 SH2 Bridge Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Thornton Rd Thornton Rd Bridge Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River Rangitaiki River 1a Rangitaiki River SEA

58 Reids Floodway Cross-section Locations and Chainages River Name Cross-section No. MIKE11 Model Chainage (m) Reids Floodway 24a Reids Floodway Reids Floodway Reids Floodway Reids Floodway Bridge McCrak/ Reids Floodway McCraken Bridge Reids Floodway Reids Floodway Bridge20/ Reids Floodway Reids Floodway 19A Reids Floodway Railway_Bridge Reids Floodway SH2_Bridge Reids Floodway Reids Floodway Reids Floodway Reids Floodway Reids Floodway Reids Floodway Reids Floodway Reids Floodway McLean_Bridge Reids Floodway Reids Floodway 11A Reids Floodway Reids Floodway Bridge10/ Reids Floodway Reids Floodway Reids Floodway Bridge8/ Reids Floodway Reids Floodway Reids Floodway Bridge 6/ Reids Floodway Reids Floodway Reids Floodway Reids Floodway Thornton Bridge Reids Floodway Reids Floodway 2A Reids Floodway Reids Floodway Reids Floodway BridgeC Reids Floodway xns near confluence

59 Appendix D Bridge Head Loss Calculations

60

61 Date: 16 Feb 2011 Project Name: Rangitaiki River & Reids Canal hydraulic capacity Project Number: Spreadsheet Title: BACKWATER EFFECT OF BRIDGE PIERS Calculation of head loss through a bridge due to bridge piers References: R. Croad (2001) Ava Rail Bridge. Report prepared by Opus International Consultants. Ref: 5-C Status: Final. S. Montes (1998). Hydraulics of Open Channel Flow. ASCE Press. 100 year ARI + Climate Change Bridge Option Velocity Depth Effective waterway width Effective pier thickness YARNELL'S METHOD RATIONAL METHOD B t α K Fr 0 y Cd m Fr 0 λ f(fr o,λ)=0 y y (m/s) (m) (m) (m) (-) (-) (-) (m) (-) (-) (m) (-) (-) (m) (m) Bridge between C/s 22 and McCraken B McCraken Bridge Bridge between C/s 20 & C/s Railway Bridge SH2 Bridge McLean Bridge Bridge between C/s 10 & C/s Bridge between C/s 8 & C/s Bridge between C/s 6 & C/s Thornton Bridge Confluence bridge Railway Bridge on Rangitaiki Thornton Bridge on rangitaiki Run Code Max Head Loss HEAD LOSS DUE TO BRIDGE PIERS (YARNELLS METHOD) Equations y = KFr K + Fr + y 0 ( 5 0.6)( α 15α ) Notation Fr 0 y = y 1 - y 0 K α Froude number downstream of bridge Head loss through bridge pier Pier shape parameter Ratio of pier-width to spn Pier shape K Semicircular nose and tail 0.9 Lens-shaped nose and tail 0.9 Twin-cylinder piers with connection diaphragm 0.95 Twin-cylinder piers without diaphragm degree triangular nose and tail 1.05 Square nose and tail 1.25 HEAD LOSS DUE TO BRIDGE PIERS (MONTES RATIONAL METHOD) Equations Notation 2Fr y λ = y 0 t m = 0.5C d B d 2 0 λ(1 + λ)(2 + λ) = λ + m(1 + λ) 2 ( 1 5 ) C = C + Fr d 0 0 y = y y 1 0 Fr = 0 U 0 gy 0 Fr 0 y = y 1 - y 0 λ Uo y 1 y 0 m C d C d0 t B Froude number downstream of bridge Head loss through bridge pier Non-dimensional backwater ratio Velocity downstram of bridge Water depth upstream of bridge Water depth downstream of bridge Contraction ratio Drag coefficient Basic drag coefficient (1.16 for circular piers) Thickness of bridge pier Spacing between bridge piers Drag Coefficeints Cd Square nose and tail 3.56 Square nose, semicircular tail 3.32 Semicircular nose, square tail 1.16

62 Appendix E Tabulated Flood Levels from MIKE11 Model Simulations

63

64 Rangitaiki River - Predicted Peak Flood Levels Cross-section MIKE11 Model Left bank level Right bank Peak Flood Level (m MSL) Chainage (m) (m MSL) level (m MSL) Sim 0A Sim 1A Sim 1B Sim 1C Sim 1D Sim 1E Sim 2C/3C Sim 2D/3D Sim 2E/3E Sim 3F Sim 3G c b a b a c b a a updated B A a SEA

65 Reids Floodway Predicted Peak Flood Levels Cross-section MIKE11 model Left bank level Right bank Peak Flood Level (m) Chainage (m) (m MSL) level (m MSL) Sim 0A Sim 1A Sim 1B Sim 1C Sim 1D Sim 1E Sim 2C Sim 2D Sim 2E Sim 3C Sim 3D Sim 3E Sim 3F Sim 3G 24a Bridge McCrak/ McCraken Bridge Bridge20/ A Railway_Bridge SH2_Bridge McLean_Bridge A Bridge10/ Bridge8/ Bridge 6/ Thornton Bridge A BridgeC xns near confluence

66 Appendix F Log Sheet of Model Simulation Files

67

68 Reids Floodways Flood Study Project.Sim11.NWK11.XNS11.BND11.HD11.RES11 Boundary Conditions t Description Model setup Current scheme (actual geometry) scenario 1A RB_2009update_ Q780_Old_20Ys urge_v2_2011_6. sim _v2_with loss coeff for bridge.nwk11 update2011_v2_ copied CS for bridge loss coeff.xns11 RB_Q780_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update.hd11 RB_2005_Q780_ Old_20Y_v2_20 11_6.res11 Former Q100=708 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and Reids cross-sections (except for the 8 most d/s XS of Reids, surveyed in 2008) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 No designed spillway Former 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) Current scheme (actual geometry) scenario 1B RB_2009updateF inal_q539_actu al_100ysurge_v2 _2011.sim _v2_with loss coeff for bridge.nwk11 update2011_v2_ copied CS for bridge loss coeff.xns11 RB_Q539_100Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update.hd11 RB_Update2009 Final_Q539_Act ual_100y_v2_20 11.res11 Q20=539 m3/s D/s Water level = Actual 100Y tide hydrograph (peak WL = 2.36 m) 15s Actual network with 2009 update of Rangitaiki and Reids cross-sections (except for the 8 most d/s XS of Reids, surveyed in 2008) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 No designed spillway Actual 20Y flood hydrograph (u/s BC), Actual 100Y tide hydrograph (d/s BC) 1

69 Current scheme (actual geometry) scenario 1C RB_2009updateF inal_q804_actu al_20ysurge_v10 _2011.sim _v2_with loss coeff for bridge.nwk11 update2011_v2_ copied CS for bridge loss coeff.xns11 RB_Q804_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update.hd11 RB_Update2009 _Q804_Actual_2 0Y_v10_2011.res 11 Q100=804 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and Reids cross-sections (except for the 8 most d/s XS of Reids, surveyed in 2008) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 No designed spillway Actual 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) Current scheme (actual geometry) scenario 1D RB_2009updateF inal_q862_2040_ 20Ysurge_v10_2 011.sim _v2_with loss coeff for bridge.nwk11 update2011_v2_ copied CS for bridge loss coeff.xns11 RB_Q862_20Y_2 040SeaLev.bnd1 1 HD0511_2008-7xns update.hd11 RB_Update2009 _Q862_2040_20 Y_v10_2011.res Q100=862 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.12 m) 15s Actual network with 2009 update of Rangitaiki and Reids cross-sections (except for the 8 most d/s XS of Reids, surveyed in 2008) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 No designed spillway Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) Current scheme (actual geometry) scenario 1E RB_2009updateF inal_q862_2040_ Conserv20Ysurg e_v10_2011.sim _v2_with loss coeff for bridge.nwk11 update2011_v2_ copied CS for bridge loss coeff.xns11 RB_Q862_20Y_2 040_ConservSea Lev.bnd11 HD0511_2008-7xns update.hd11 RB_Update2009 _Q862_2040_Co nserv20y_v10_2 011.res Q100=862 m3/s D/s Water level = 2040 conservative 20Y tide hydrograph (peak WL = 2.19 m) 15s Actual network with 2009 update of Rangitaiki and Reids cross-sections (except for the 8 most d/s XS of Reids, surveyed in 2008) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 No designed spillway Climate change Y flood hydrograph (u/s BC), Climate change 2040 conservative 20Y tide hydrograph (d/s BC) 2

70 Future design scenario 2C (new canal design) RB_2009update_ WideCanal_Q80 4_Actual_20Ysur ge_2011_update d_spillway_prio rtoflood.sim _v5.nwk11 update2011_v5. xns11 RB_Q804_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 04_Actual_20Ys urge_2011_upd ated_spillway_ PriorToFlood.re s11 Q100=804 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Actual 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Q80 4_Actual_20Ysur ge_2011_update d_spillway_20yr Flood.sim _v6.nwk11 update2011_v5. xns11 RB_Q804_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 04_Actual_20Ys urge_2011_upd ated_spillway_ PriorToFlood.re s11 Q100=804 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Actual 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) 3

71 Future design scenario 2D (new canal design) RB_2009update_ WideCanal_Q86 2_2040_20Ysurg e_2011_updated _spillway_prior ToFlood.sim _v5.nwk11 update2011_v5. xns11 RB_Q862_20Y_2 040SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 62_2040_20Ysur ge_2011_update d_spillway_prio rtoflood.res Q100=862 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.12 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Q86 2_2040_Conserv 20Ysurge_2011_ updated_spillwa y_20yrflood.sim _v6.nwk11 update2011_v5. xns11 RB_Q862_20Y_2 040SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 62_2040_20Ysur ge_2011_update d_spillway_prio rtoflood.res Q100=862 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.12 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) 4

72 Future design scenario 2E (new canal design) RB_2009update_ WideCanal_Q86 2_2040_Conserv 20Ysurge_2011_ updated_spillwa y_priortoflood. sim _v5.nwk11 update2011_v5. xns11 RB_Q862_20Y_2 040_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 62_2040_Conser v20ysurge_2011 _updated_spill way_priortoflo od.res Q100=862 m3/s D/s Water level = 2040 conservative 20Y tide hydrograph (peak WL = 2.19 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change 2040 conservative 20Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Q86 2_2040_Conserv 20Ysurge_2011_ updated_spillwa y_20yrflood.sim _v6.nwk11 update2011_v5. xns11 RB_Q862_20Y_2 040_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 62_2040_20Ysur ge_2011_update d_spillway_prio rtoflood.res Q100=862 m3/s D/s Water level = 2040 conservative 20Y tide hydrograph (peak WL = 2.19 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change 2040 conservative 20Y tide hydrograph (d/s BC) 5

73 Future design scenario 3C (new canal design and new SH2 bridge) RB_2009update_ WideCanal_Ne wsh2_q804_act ual_20ysurge_20 11_updated_spil lway_priortoflo od.sim _v7.nwk11 update2011_v6. xns11 RB_Q804_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q804_ Actual_20Ysurg e_2011_updated _spillway_prior ToFlood.res11 Q100=804 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Actual 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Ne wsh2_q804_act ual_20ysurge_20 11_updated_spil lway_20yrflood. sim _v8.nwk11 update2011_v6. xns11 RB_Q804_20Y_ ActualSeaLev.b nd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_Q8 04_Actual_20Ys urge_2011_upd ated_spillway_ PriorToFlood.re s11 Q100=804 m3/s D/s Water level = Actual 20Y tide hydrograph (peak WL = 1.92 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Actual 100Y flood hydrograph (u/s BC), Actual 20Y tide hydrograph (d/s BC) 6

74 Future design scenario 3D (new canal design and new SH2 bridge) RB_2009update_ WideCanal_Ne wsh2_q862_204 0_20Ysurge_201 1_updated_spill way_priortoflo od.sim _v7.nwk11 update2011_v6. xns11 RB_Q862_20Y_2 040SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=862 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.12 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Q86 2_2040_Conserv 20Ysurge_2011_ updated_spillwa y_20yrflood.sim _v8.nwk11 update2011_v6. xns11 RB_Q862_20Y_2 040SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=862 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.12 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) 7

75 Future design scenario 3E (new canal design and new SH2 bridge) RB_2009update_ WideCanal_Q86 2_2040_Conserv 20Ysurge_2011_ updated_spillwa y_priortoflood. sim _v7.nwk11 update2011_v6. xns11 RB_Q862_20Y_2 040_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=862 m3/s D/s Water level = 2040 conservative 20Y tide hydrograph (peak WL = 2.19 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change 2040 conservative 20Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Ne wsh2_q862_204 0_Conserv_20Ys urge_2011_upda ted_spillway_20 yrflood.sim _v8.nwk11 update2011_v6. xns11 RB_Q862_20Y_2 040_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=862 m3/s D/s Water level = 2040 conservative 20Y tide hydrograph (peak WL = 2.19 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change 2040 conservative 20Y tide hydrograph (d/s BC) 8

76 Future design scenario 3F (new canal design and new SH2 bridge) RB_2009update_ WideCanal_Ne wsh2_q939_209 0_20Ysurge_201 1_updated_spill way_priortoflo od.sim _v7.nwk11 update2011_v6. xns11 RB_Q939_20Y_2 090SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q939_2 090_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=939 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.42 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Ne wsh2_q939_209 0_20Ysurge_201 1_updated_spill way_20yrflood.s im _v8.nwk11 update2011_v6. xns11 RB_Q939_20Y_2 090SeaLev.bnd1 1 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=939 m3/s D/s Water level = Y tide hydrograph (peak WL = 2.42 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change Y tide hydrograph (d/s BC) 9

77 Future design scenario 3G (new canal design and new SH2 bridge) RB_2009update_ WideCanal_Ne wsh2_q939_209 0_Conserv_20Ys urge_2011_upda ted_spillway_pri ortoflood.sim _v7.nwk11 update2011_v6. xns11 RB_Q939_20Y_2 090_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q939_2 090_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=939 m3/s D/s Water level = 2090 conservative 20Y tide hydrograph (peak WL = 2.72 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : m Run simulation up to 22:00 on 1/1/1990 which will be used for hotstart condition for the simulation for deflated weir condition Climate change Y flood hydrograph (u/s BC), Climate change 2090 conservative 20Y tide hydrograph (d/s BC) RB_2009update_ WideCanal_Ne wsh2_q939_209 0_Conserv_20Ys urge_2011_upda ted_spillway_20 yrflood.sim _v8.nwk11 update2011_v6. xns11 RB_Q939_20Y_2 090_ConservSea Lev.bnd11 HD0511_2008-7xns update_scenari o2c.hd11 RB_2009update _WideCanal_N ewsh2_q862_2 040_20Ysurge_2 011_updated_sp illway_priortof lood.res Q100=939 m3/s D/s Water level = 2090 conservative 20Y tide hydrograph (peak WL = 2.72 m) 15s Actual network with 2009 update of Rangitaiki and U/s Reids cross-sections Designed cross-sections d/s in Reids Canal. Update cross-section at SH2 bridge (chainage 12659) Insert culvert for SH2 bridge (chainage 12659) Applied loss coefficients for bridges between crosssections 8&9 and 6&7 Designed spillway : 7 U/s 7.15m and 3 D/s 5.9m Start simulation from 22:00 on 1/1/1990 by use of initial condition from prior to flood result file and overwrite the result to the same result file Climate change Y flood hydrograph (u/s BC), Climate change 2090 conservative 20Y tide hydrograph (d/s BC) 10

78 Summary of the boundary conditions used in the model (including descriptions of the dfs0 files) Boundary conditions US boundary condition DS boundary condition File name File name Peak Flow value (m3/s) File name Peak water level value (m) Q20_Rangitaiki_Inflow.dfs0 / 100Y_Rangitaiki_StormSurge / RB_Q539_100Y_ActualSeaLev.bnd11 Q539_Actual 539 Actual_100Y 2.36 RB_Q804_20Y_ActualSeaLev.bnd11 Q100_Rangitaiki_Inflow.dfs0 / Q804_Actual Y_Rangitaiki_StormSurge.dfs0 / Actual_20Y 1.92 RB_Q862_20Y_2040SeaLev.bnd11 Q100_Rangitaiki_Inflow.dfs0 / Q862_ Y_Rangitaiki_StormSurge.dfs0 / 2040_20Y 2.12 RB_Q862_20Y_2040_ConservSeaLev.bnd11 Q100_Rangitaiki_Inflow.dfs0 / Q862_ Y_Rangitaiki_StormSurge.dfs0 / 2040_20Y_Conserv 2.19 RB_Q939_20Y_2090SeaLev.bnd11 Q100_Rangitaiki_Inflow.dfs0 / Q939_ Y_Rangitaiki_StormSurge.dfs0 / 2090_20Y 2.42 RB_Q939_20Y_2090_ConservSeaLev.bnd11 Q100_Rangitaiki_Inflow.dfs0 / Q939_ Y_Rangitaiki_StormSurge.dfs0 / 2090_20Y_Conserv 2.72 Boundary Condition Actual Widened Canal Widened canal + SH2 Bridge RB_Q780_20Y_ActualSeaLev.bnd11 (A) RB_Q539_100Y_ActualSeaLev.bnd11 (B) RB_Q804_20Y_ActualSeaLev.bnd11 (C) RB_Q862_20Y_2040SeaLev.bnd11 (D) RB_Q862_20Y_2040_ConservSeaLev.bnd11 (E) RB_Q939_20Y_2090SeaLev.bnd11 (F) RB_Q939_20Y_2090_ConservSeaLev.bnd11 (G) Number of simulations 13 11

79 Appendix G Drawings for New State Highway 2 Bridge

80

81 l Ca nal Ce ntra st Re i ds Ea Co as t Ma in Tr un kr ail wa y (C los ed )

82 NOT FOR CONSTRUCTION

83