Appendix J. Horse Creek Northern MLA Hydraulic Study. Document Name i Insert Month/Year

Transcription

1 Appendix J Horse Creek Northern MLA Hydraulic Study Document Name i Insert Month/Year

2 New Hope Coal Horse Creek Northern MLA Hydraulic Study 31 March 2014

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4 Contents Page number 1. Introduction Background Scope of study 1 2. Hydrology Adopted peak flows Inflow hydrographs Local inflows Calibration 7 3. Hydraulic modelling West Surat Rail Link Revised model Boundary conditions Model scenarios Validation Results Global mapping Conclusion References 13 Parsons Brinckerhoff B-UGE-RPT-004 RevB i

5 List of tables Page number Table 2.1 Peak flows adopted for the northern MLA hydraulic model revision 3 List of figures Page number Figure 1.1 Elimatta Mine MLA and Horse Creek hydraulic model extents 2 Figure 2.1 Inflow hydrographs for existing conditions and Stage 3 creek diversion 4 Figure 2.2 Hydrological model (RAFTS) showing sub-catchments and node locations 5 Figure 2.3 Local inflow hydrographs 6 Figure 3.1 Upstream inflow hydrograph comparison for the existing conditions scenario 9 Figure 3.2 Downstream boundary relationship between discharge and water level based on 0.1 % slope 9 List of appendices Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Existing conditions flood mapping Northern rail spur flood mapping Southern rail spur flood mapping Afflux mapping Global mapping West Surat Rail Link Hydraulic Model Report Parsons Brinckerhoff B-UGE-RPT-004 RevB ii

6 1. Introduction This report documents the revision of the hydraulic study for the West Surat Rail Link. This hydraulic study focuses on MLA (the northern MLA) and is an extension of the Elimatta Mine flood study undertaken for MLA (the southern MLA), which includes the creek diversions for Stages 1, 2 and 3. The purpose of this hydraulic study was to update the existing conditions hydraulic study for MLA with the revised hydrology and boundary conditions arising from the flood study undertaken for MLA (the southern MLA). Two proposed scenarios were undertaken based on the Stage 3 Horse Creek diversion works from the southern MLA combined with two rail options (northern and southern rail spurs) within MLA Background Two previous reports are available that provide background information for Horse Creek and Elimatta Mine. These are: Horse Creek Base Case (Natural Conditions) and Diversion Flood Study for Elimatta Mine (reference: G-TPT-RPT-003 RevA, March 2014). This report includes the description of the revised hydrology for Horse Creek undertaken as part of the peer review process, and describes the proposed Stage 3 creek diversion. This is referred to as the March 2014 report. West Surat Rail Link Hydraulic study (reference: B-RPT-001 RevA_Hydraulic-final-ae, 19 September 2012). This report describes the work undertaken in developing the hydraulic model to assess the impacts of the rail spurs within the northern MLA (MLA 50270). The hydraulic model developed for this report was adopted and updated as part of this report. This is referred to as the West Surat report. 1.2 Scope of study The scope of this hydraulic study is to: Revise the existing conditions hydraulic model to reflect the changes in upstream inflows as determined by the March 2014 flood study. This included the revised hydrology as a result of the peer review process. Revise the hydraulic model to reflect the Stage 3 creek diversion within the southern MLA in combination with the northern rail spur alignment and (separately) with the southern rail spur alignment. Undertake the hydraulic modelling for the above for the 100 year ARI event only. Generate maps depicting the flood extents (water levels), depths and velocity for the 100 year ARI flood event, and to provide a global map of flood extent (water elevations) covering both MLAs. Document the changes to the West Surat hydraulic model. Figure 1.1 presents the extent of the Horse Creek hydraulic modelling. In particular it shows the two MLAs and the hydraulic model coverage of Horse Creek. This figure also shows where the hydrograph was extracted from the southern MLA model as input to the northern MLA model. Parsons Brinckerhoff B-UGE-RPT-004 RevB 1

7 Figure 1.1 Elimatta Mine MLA and Horse Creek hydraulic model extents Parsons Brinckerhoff B-UGE-RPT-004 RevB 2

8 2. Hydrology Details of the revised hydrology adopted for this report are contained in the March 2014 report. The sections below detail the specific inflows (boundary conditions and local flows) adopted as part of this study. 2.1 Adopted peak flows Table 2.1 presents the peak flows adopted as part of this revision. Details of these inflows are provided in the following sections and the locations of the sub-catchment are shown in Figure 2.3. Table 2.1 Peak flows adopted for the northern MLA hydraulic model revision Location Scenario 100 year ARI peak flow (m 3 /s) 1000 year ARI peak flow (m 3 /s) Inflow Existing Inflow Stage 3 diversion A05 subcatchment Existing & Stage 3 diversion A06 subcatchment Existing & Stage 3 diversion A06a subcatchment Existing & Stage 3 diversion A05a subcatchment Existing & Stage 3 diversion A04 subcatchment Existing & Stage 3 diversion A03 subcatchment Existing & Stage 3 diversion Inflow hydrographs The downstream hydrographs for the 100 year ARI and 1000 year ARI existing conditions (referred to as base case (natural conditions) in the March 2014 report) and the 100 year ARI and 1000 year ARI Stage 3 creek diversion were extracted from the March 2014 hydraulic model. The location of the hydrograph extraction is shown in Figure 1.1. Figure 2.1 presents the 100 year ARI existing conditions hydrograph and the Stage 3 creek diversion hydrograph. Figure 2.2 presents the 1000 year ARI hydrographs. These hydrographs are the upstream boundary conditions for the northern MLA hydraulic model. The differences in the hydrographs are a result of the Stage 3 creek diversion in the southern MLA (MLA50254). Minor smoothing of the hydrographs (up to 2 hour time step) was undertaken to maintain hydraulic model stability. The influence of the smoothing is minimal on the overall flood extents for the northern MLA hydraulic study. Parsons Brinckerhoff B-UGE-RPT-004 RevB 3

9 Figure yr ARI inflow hydrographs for existing conditions and Stage 3 creek diversion Figure yr ARI inflow hydrographs for existing conditions and Stage 3 creek diversion Parsons Brinckerhoff B-UGE-RPT-004 RevB 4

10 2.3 Local inflows The local inflows were extracted from the hydrological model (XP-RAFTS) that was revised as part of the March 2014 study. The catchment and node locations are presented in Figure 2.3 and the local inflows are shown in Figure 2.4 for the 100 year ARI event and Figure 2.5 for the 1000 year ARI event. The local inflows remain the same for all scenarios. Figure 2.3 Hydrological model (RAFTS) showing sub-catchments and node locations Parsons Brinckerhoff B-UGE-RPT-004 RevB 5

11 Figure yr ARI local inflow hydrographs Figure yr ARI local inflow hydrographs Parsons Brinckerhoff B-UGE-RPT-004 RevB 6

12 2.4 Calibration The XP-RAFTS model developed by Parsons Brinckerhoff for the West Surat Rail Link project was undertaken to establish baseline hydrological characteristics for Horse Creek. This original hydrological model adopted the ARBM loss model and storage coefficients. Following the Horse Creek Flood Study Peer Review (WRM, 2013), the XP-RAFTS model was revised to use the Initial Loss / Continuing Loss method and removed the storage coefficients. The flood frequency analysis (FFA) was used for the calibration of the revised XP-RAFTS model. Calibration to the FFA and not the historical events allowed improved calibration across all flood events (small to medium to large floods). The WRM Peer Review indicated that the previous model calibration was poor for the small to medium magnitude events. The FFA adopted for calibration purposes (as noted in the WRM Peer Review) gave reasonable estimates of design discharges at the Windamere gauge and is therefore suitable for calibration purposes. Various initial loss and continuing loss values were tested to calibrate the XP-RAFTS models to the flood frequency analysis results for each ARI event at the Windamere gauge. Parsons Brinckerhoff B-UGE-RPT-004 RevB 7

13 3. Hydraulic modelling 3.1 West Surat Rail Link A two-dimensional hydrodynamic TUFLOW model of Horse Creek was developed by Parsons Brinckerhoff as part of the West Surat Rail Link Hydraulic Study (September 2012). This was used to estimate design flood levels under existing conditions. Hydraulic model parameters were adopted from the West Surat Rail Link Hydraulic Study model for consistency with this flood model. 3.2 Revised model Other than upstream boundary conditions and local inflows, no further changes were made to the TUFLOW model developed and adopted as part of the West Surat Rail Link. 3.3 Boundary conditions Inflows The inflows to the hydraulic model are presented in Section 2 of this report. The inflow hydrograph to the existing conditions hydraulic model was checked against the XP-RAFTS hydrograph as well as the hydraulic output files for the 1D domain (creek channel) and the 2D domain (floodplain) at the same location (A07). Figure 3.1 shows good correlation between the 100 year ARI hydrological model flow (XP-RAFTS total hydrograph at A07) and the extracted hydrograph from the March 2014 report hydraulic model (added as TUFLOW model inflow at A07). The difference between these hydrographs is attributed to the extracted hydrograph from the Horse Creek diversion model (March 2014 report) taking into account flow attenuation, floodplain dynamics and losses. The 2D flow only hydrograph represents the discharge within the floodplain only, while the 1D flow only represents the flow in the creek channel only. These are split due to the model representing the creek channel as a 1D network rather than a 2D gridded domain. The combination of the 2D and 1D hydrographs match the inflow hydrograph (TUFLOW model inflow at A07). This is expected and shows that the model is processing the inflow hydrographs correctly. Parsons Brinckerhoff B-UGE-RPT-004 RevB 8

14 Figure 3.1 Upstream inflow hydrograph comparison for the 100 year ARI existing conditions scenario Downstream boundary The downstream boundary of the revised hydraulic model remains the same as the West Surat Horse Creek model. This is a height-discharge type with channel gradient of 0.1%. Figure 3.2 shows the computed relationship. Figure 3.2 Downstream boundary relationship between discharge and water level based on 0.1 % slope Parsons Brinckerhoff B-UGE-RPT-004 RevB 9

15 3.4 Model scenarios The TUFLOW models were used to simulate the 100 year ARI event and the 1000 year ARI event. The following model scenarios were undertaken: 1. MLA existing conditions + MLA existing conditions 2. MLA Stage 3 diversion + MLA northern rail spur alignment 3. MLA Stage 3 diversion + MLA southern rail spur alignment. 3.5 Validation We are unaware of any surveyed flood level information available in the MLA; therefore it has not been possible to calibrate the hydraulic model by comparing water levels predicted by the model with recorded water levels for a known flood event. This was also the case for the southern MLA hydraulic model and the West Surat Rail Link Hydraulic Study year ARI results Results for the revised hydraulic modelling are presented in the following appendices for flood extents (maximum water levels), maximum depths and maximum velocities. Appendix A: existing conditions hydraulic model Appendix B: Stage 3 creek diversion and northern rail spur alignment Appendix C: Stage 3 creek diversion and southern rail spur alignment. The change in maximum water levels (afflux) was calculated based on the following and is contained in Appendix D: Northern rail spur and existing conditions (Northern MLA extents only) Southern rail spur and existing conditions (Northern MLA extents only) Water levels Water levels in all three cases for MLA range between 235 m AHD and 220 m AHD. The water surface gradient is approximately 0.1 % from upstream to downstream over the 10.1 km length of Horse Creek. All model scenarios show that MLA is partially inundated for the 100 year ARI flood scenario. This is approximately 7% of the total MLA extent. The northern rail spur alignment slightly increases the flood extent upstream of the rail crossing, however, downstream of the rail crossing there is no significant changes to the flood extent. The afflux map (Appendix D) for the northern rail spur alignment shows the change in water levels (in metres). Peak water levels increase up to 0.30 m immediately upstream of the rail crossing. This increase dissipates approximately 1.5 km upstream. The water levels are similar to the existing conditions (+/ m) beyond the 1.5 km distance. Downstream, there is a small area of reduced peak water levels, however overall there is minimal change (+/ m) in peak water levels due to the rail crossing. Parsons Brinckerhoff B-UGE-RPT-004 RevB 10

16 For the southern rail spur alignment there is a noticeable decrease in flood extent immediately downstream of the rail crossing. Overall, downstream there is minimal change in peak water levels. Upstream of the southern rail crossing option, afflux is shown in the western part of the rail alignment near the MLA boundary. This is part of the main Horse Creek channel and the afflux propagates for approximately 800 m upstream. On the eastern section of the rail alignment, afflux is shown within the tributary of Horse Creek. This afflux propagates upstream for approximately 2.2 km. The majority of afflux shown in Appendix D is outside the MLA area. The cause of the afflux is directly related to the rail alignments Depths For the majority of the floodplain the flood depths across all scenarios do not exceed 2 m. The impact of the rail alignments on the flood depths is visible in the maps provided (specifically, Figures 2, 5 and 8). For both rail alignments, the increase in depths is located mainly upstream of each alignment (as expected) Velocities The maximum velocities presented in Figures 3, 6 and 9 show that the higher velocities occur within the Horse Creek channel itself. For the rail options, there are increased velocities shown where hydraulic structures for the rail crossing are located. This is expected as the contraction of flows through a bridge or culvert will increase velocities. 3.7 Global mapping The maximum flood extent for the 100 year ARI flood and the 1000 year ARI flood for the following scenarios is presented in Appendix E. These maps provide the overall flood extent across the two hydraulic models and two MLAs: MLA existing conditions with MLA existing conditions MLA Stage 3 creek diversion with MLA northern rail spur MLA Stage 3 creek diversion with MLA southern rail spur. Parsons Brinckerhoff B-UGE-RPT-004 RevB 11

17 4. Conclusion This study documents the changes to the West Surat Rail Link hydraulic model. This revised hydraulic model was adopted as the existing conditions hydraulic flood model for Horse Creek in relation to MLA The following changes were adopted: The inflow hydrograph was changed to reflect the existing conditions hydrograph and the Stage 3 Horse Creek diversion hydrograph from the previously completed hydraulic modelling for MLA (March 2014). The local inflow hydrographs were extracted from the revised hydrological model (XP-RAFTS) and reflects the changes made as part of the peer review process of the hydrological model. No other changes were made to the hydraulic model. The three scenarios undertaken for this report reflect the 100 year ARI design flood event and the 1000 year Ari flood event, as follows: 1. MLA existing conditions + MLA existing conditions 2. MLA Stage 3 diversion + MLA northern rail spur alignment 3. MLA Stage 3 diversion + MLA southern rail spur alignment. The maximum flood extents from each of the scenarios above were merged with the maximum flood extents of MLA to provide the overall flood extent of the two MLAs for the 100 year and the 1000 year ARI flood events. The northern and southern rail crossing alignments impact the flood characteristics on the floodplain in terms of increased depths, velocities and afflux, however these changes are relatively confined and the flood extent remains relatively unchanged. No optimisation of the hydraulic structures for the rail alignments was undertaken. It may be possible to further reduce the floodplain impacts through further detailed design of these structures. Parsons Brinckerhoff B-UGE-RPT-004 RevB 12

18 5. References Parsons Brinckerhoff (2012) West Surat Rail Link Hydraulic Study. Report B-RPT-001 RevA_FINAL. 19 September Northern Energy Corporation Ltd. Parsons Brinckerhoff (2014) Horse Creek Base Case (Natural Conditions) and Diversion Flood Study for Elimatta MIne. Report G-TPT-RPT-003 RevA. 13 SMarch New Hope Coal. Parsons Brinckerhoff B-UGE-RPT-004 RevB 13