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Document Name i Insert Month/Year Appendix J Horse Creek Northern MLA Hydraulic Study
Document Name i Insert Month/Year
Appendix J Horse Creek Northern MLA Hydraulic Study
New Hope Coal
Horse Creek Northern MLA Hydraulic Study31 March 2014
Parsons Brinckerhoff | 2172847B-UGE-RPT-004 RevB i
New Hope Coal Horse Creek Northern MLA Hydraulic Study
ContentsPage number
1. Introduction 1
1.1 Background 1
1.2 Scope of study 1
2. Hydrology 3
2.1 Adopted peak flows 3
2.2 Inflow hydrographs 3
2.3 Local inflows 5
2.4 Calibration 7
3. Hydraulic modelling 8
3.1 West Surat Rail Link 8
3.2 Revised model 8
3.3 Boundary conditions 8
3.4 Model scenarios 10
3.5 Validation 10
3.6 Results 10
3.7 Global mapping 11
4. Conclusion 12
5. References 13
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List of tablesPage number
Table 2.1 Peak flows adopted for the northern MLA hydraulic model revision 3
List of figuresPage number
Figure 1.1 Elimatta Mine MLA and Horse Creek hydraulic model extents 2Figure 2.1 Inflow hydrographs for existing conditions and Stage 3 creek diversion 4Figure 2.2 Hydrological model (RAFTS) showing sub-catchments and node locations 5Figure 2.3 Local inflow hydrographs 6Figure 3.1 Upstream inflow hydrograph comparison for the existing conditions scenario 9Figure 3.2 Downstream boundary relationship between discharge and water level based on
0.1 % slope 9
List of appendices
Appendix A Existing conditions flood mappingAppendix B Northern rail spur flood mappingAppendix C Southern rail spur flood mappingAppendix D Afflux mappingAppendix E Global mappingAppendix F West Surat Rail Link Hydraulic Model Report
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1. IntroductionThis report documents the revision of the hydraulic study for the West Surat Rail Link. This hydraulic studyfocuses on MLA 50270 (the northern MLA) and is an extension of the Elimatta Mine flood study undertakenfor MLA 50254 (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 50270 withthe revised hydrology and boundary conditions arising from the flood study undertaken for MLA 50254 (thesouthern MLA). Two proposed scenarios were undertaken based on the Stage 3 Horse Creek diversionworks from the southern MLA combined with two rail options (northern and southern rail spurs) within MLA50270.
1.1 BackgroundTwo 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:2172847G-TPT-RPT-003 RevA, March 2014). This report includes the description of the revisedhydrology for Horse Creek undertaken as part of the peer review process, and describes the proposedStage 3 creek diversion. This is referred to as the “March 2014” report.
West Surat Rail Link – Hydraulic study (reference: 2178003B-RPT-001 RevA_Hydraulic-final-ae, 19September 2012). This report describes the work undertaken in developing the hydraulic model toassess the impacts of the rail spurs within the northern MLA (MLA 50270). The hydraulic modeldeveloped for this report was adopted and updated as part of this report. This is referred to as the “WestSurat” report.
1.2 Scope of studyThe scope of this hydraulic study is to:
Revise the existing conditions hydraulic model to reflect the changes in upstream inflows as determinedby the March 2014 flood study. This included the revised hydrology as a result of the peer reviewprocess.
Revise the hydraulic model to reflect the Stage 3 creek diversion within the southern MLA incombination 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 floodevent, 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 MLAsand the hydraulic model coverage of Horse Creek. This figure also shows where the hydrograph wasextracted from the southern MLA model as input to the northern MLA model.
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Figure 1.1 Elimatta Mine MLA and Horse Creek hydraulic model extents
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2. HydrologyDetails of the revised hydrology adopted for this report are contained in the March 2014 report. The sectionsbelow detail the specific inflows (boundary conditions and local flows) adopted as part of this study.
2.1 Adopted peak flowsTable 2.1 presents the peak flows adopted as part of this revision. Details of these inflows are provided in thefollowing 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 ARIpeak flow(m3/s)
1000 year ARIpeak flow(m3/s)
Inflow Existing 792.06 1937.43
Inflow Stage 3 diversion 848.99 2049.70
A05 subcatchment Existing & Stage 3 diversion 38.60 91.69
A06 subcatchment Existing & Stage 3 diversion 27.54 63.05
A06a subcatchment Existing & Stage 3 diversion 18.54 39.80
A05a subcatchment Existing & Stage 3 diversion 21.25 45.85
A04 subcatchment Existing & Stage 3 diversion 22.35 50.91
A03 subcatchment Existing & Stage 3 diversion 52.99 128.66
2.2 Inflow hydrographsThe 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 3creek diversion were extracted from the March 2014 hydraulic model. The location of the hydrographextraction is shown in Figure 1.1.
Figure 2.1 presents the 100 year ARI existing conditions hydrograph and the Stage 3 creek diversionhydrograph. Figure 2.2 presents the 1000 year ARI hydrographs. These hydrographs are the upstreamboundary conditions for the northern MLA hydraulic model. The differences in the hydrographs are a result ofthe 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 modelstability. The influence of the smoothing is minimal on the overall flood extents for the northern MLAhydraulic study.
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Figure 2.1 100 yr ARI inflow hydrographs for existing conditions and Stage 3 creek diversion
Figure 2.2 1000 yr ARI inflow hydrographs for existing conditions and Stage 3 creek diversion
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2.3 Local inflowsThe local inflows were extracted from the hydrological model (XP-RAFTS) that was revised as part of theMarch 2014 study. The catchment and node locations are presented in Figure 2.3 and the local inflows areshown in Figure 2.4 for the 100 year ARI event and Figure 2.5 for the 1000 year ARI event. The local inflowsremain the same for all scenarios.
Figure 2.3 Hydrological model (RAFTS) showing sub-catchments and node locations
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Figure 2.4 100 yr ARI local inflow hydrographs
Figure 2.5 1000 yr ARI local inflow hydrographs
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2.4 CalibrationThe XP-RAFTS model developed by Parsons Brinckerhoff for the West Surat Rail Link project wasundertaken to establish baseline hydrological characteristics for Horse Creek. This original hydrologicalmodel adopted the ARBM loss model and storage coefficients. Following the Horse Creek Flood Study PeerReview (WRM, 2013), the XP-RAFTS model was revised to use the Initial Loss / Continuing Loss methodand removed the storage coefficients. The flood frequency analysis (FFA) was used for the calibration of therevised XP-RAFTS model. Calibration to the FFA and not the historical events allowed improved calibrationacross all flood events (small to medium to large floods). The WRM Peer Review indicated that the previousmodel calibration was poor for the small to medium magnitude events. The FFA adopted for calibrationpurposes (as noted in the WRM Peer Review) gave reasonable estimates of design discharges at theWindamere 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 floodfrequency analysis results for each ARI event at the Windamere gauge.
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3. Hydraulic modelling3.1 West Surat Rail LinkA two-dimensional hydrodynamic TUFLOW model of Horse Creek was developed by Parsons Brinckerhoffas part of the West Surat Rail Link – Hydraulic Study (September 2012). This was used to estimate designflood levels under existing conditions.
Hydraulic model parameters were adopted from the West Surat Rail Link – Hydraulic Study model forconsistency with this flood model.
3.2 Revised modelOther than upstream boundary conditions and local inflows, no further changes were made to the TUFLOWmodel developed and adopted as part of the West Surat Rail Link.
3.3 Boundary conditions3.3.1 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-RAFTShydrograph 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 ARIhydrological model flow (XP-RAFTS total hydrograph at A07) and the extracted hydrograph from the March2014 report hydraulic model (added as TUFLOW model inflow at A07). The difference between thesehydrographs is attributed to the extracted hydrograph from the Horse Creek diversion model (March 2014report) 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 creekchannel as a 1D network rather than a 2D gridded domain. The combination of the 2D and 1D hydrographsmatch the inflow hydrograph (TUFLOW model inflow at A07). This is expected and shows that the model isprocessing the inflow hydrographs correctly.
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Figure 3.1 Upstream inflow hydrograph comparison for the 100 year ARI existing conditions scenario
3.3.2 Downstream boundary
The downstream boundary of the revised hydraulic model remains the same as the West Surat Horse Creekmodel. This is a height-discharge type with channel gradient of 0.1%. Figure 3.2 shows the computedrelationship.
Figure 3.2 Downstream boundary relationship between discharge and water level based on 0.1 % slope
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3.4 Model scenariosThe 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 50254 existing conditions + MLA 50270 existing conditions
2. MLA 50254 Stage 3 diversion + MLA 50270 northern rail spur alignment
3. MLA 50254 Stage 3 diversion + MLA 50270 southern rail spur alignment.
3.5 ValidationWe are unaware of any surveyed flood level information available in the MLA; therefore it has not beenpossible to calibrate the hydraulic model by comparing water levels predicted by the model with recordedwater levels for a known flood event. This was also the case for the southern MLA hydraulic model and theWest Surat Rail Link – Hydraulic Study.
3.6 100 year ARI resultsResults 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 inAppendix D:
Northern rail spur and existing conditions (Northern MLA extents only)
Southern rail spur and existing conditions (Northern MLA extents only).
3.6.1 Water levels
Water levels in all three cases for MLA 50270 range between 235 m AHD and 220 m AHD. The watersurface gradient is approximately 0.1 % from upstream to downstream over the 10.1 km length of HorseCreek.
All model scenarios show that MLA 50270 is partially inundated for the 100 year ARI flood scenario. This isapproximately 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 (inmetres). 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 (+/- 0.15 m)beyond the 1.5 km distance.
Downstream, there is a small area of reduced peak water levels, however overall there is minimal change(+/- 0.15 m) in peak water levels due to the rail crossing.
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For the southern rail spur alignment there is a noticeable decrease in flood extent immediately downstreamof 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 nearthe MLA boundary. This is part of the main Horse Creek channel and the afflux propagates for approximately800 m upstream.
On the eastern section of the rail alignment, afflux is shown within the tributary of Horse Creek. This affluxpropagates 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 relatedto the rail alignments.
3.6.2 Depths
For the majority of the floodplain the flood depths across all scenarios do not exceed 2 m. The impact of therail 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).
3.6.3 Velocities
The maximum velocities presented in Figures 3, 6 and 9 show that the higher velocities occur within theHorse Creek channel itself. For the rail options, there are increased velocities shown where hydraulicstructures for the rail crossing are located. This is expected as the contraction of flows through a bridge orculvert will increase velocities.
3.7 Global mappingThe maximum flood extent for the 100 year ARI flood and the 1000 year ARI flood for the following scenariosis presented in Appendix E. These maps provide the overall flood extent across the two hydraulic modelsand two MLAs:
MLA 50254 existing conditions with MLA 50270 existing conditions
MLA 50254 Stage 3 creek diversion with MLA 50270 northern rail spur
MLA 50254 Stage 3 creek diversion with MLA 50270 southern rail spur.
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4. ConclusionThis study documents the changes to the West Surat Rail Link hydraulic model. This revised hydraulic modelwas adopted as the existing conditions hydraulic flood model for Horse Creek in relation to MLA 50270. Thefollowing changes were adopted:
The inflow hydrograph was changed to reflect the existing conditions hydrograph and the Stage 3 HorseCreek diversion hydrograph from the previously completed hydraulic modelling for MLA 50254 (March2014).
The local inflow hydrographs were extracted from the revised hydrological model (XP-RAFTS) andreflects 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 yearAri flood event, as follows:
1. MLA 50254 existing conditions + MLA 50270 existing conditions
2. MLA 50254 Stage 3 diversion + MLA 50270 northern rail spur alignment
3. MLA 50254 Stage 3 diversion + MLA 50270 southern rail spur alignment.
The maximum flood extents from each of the scenarios above were merged with the maximum flood extentsof MLA 50254 to provide the overall flood extent of the two MLAs for the 100 year and the 1000 year ARIflood events.
The northern and southern rail crossing alignments impact the flood characteristics on the floodplain in termsof increased depths, velocities and afflux, however these changes are relatively confined and the floodextent remains relatively unchanged.
No optimisation of the hydraulic structures for the rail alignments was undertaken. It may be possible tofurther reduce the floodplain impacts through further detailed design of these structures.
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5. ReferencesParsons Brinckerhoff (2012) West Surat Rail Link – Hydraulic Study. Report 2178003B-RPT-001RevA_FINAL. 19 September 2012. Northern Energy Corporation Ltd.
Parsons Brinckerhoff (2014) Horse Creek Base Case (Natural Conditions) and Diversion Flood Studyfor Elimatta MIne. Report 2172847G-TPT-RPT-003 RevA. 13 SMarch 2014. New Hope Coal.
