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Shepparton East Overland Flow Urban Flood Study – Final Report Reference: R.M8415.003.01.FinalReport.docx Date: March 2017

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Shepparton East Overland Flow Urban Flood Study – Final Report

Shepparton East Overland Flow Urban Flood Study - Hydrology Report Shepparton East Overland Flow Urban Flood Study - Hydrology Report

Prepared for: Goulburn Broken Catchment Management Authority

Prepared by: BMT WBM Pty Ltd (Member of the BMT group of companies)

Offices Brisbane Denver London Mackay Melbourne Newcastle Perth Sydney Vancouver


Document Control Sheet

BMT WBM Pty Ltd Level 5, 99 King Street Melbourne Vic 3000 Australia PO Box 604 Collins Street West Vic 8007 Tel: +61 3 8620 6100 Fax: +61 3 8620 6105 ABN 54 010 830 421 www.bmtwbm.com.au

Document: R.M8415.003.01.FinalReport.docx

Title: Shepparton East Overland Flow Urban Flood Study – Final Report

Project Manager: Philip Pedruco

Author: Philip Pedruco, Dexter Reynolds and Michael South

Client: Goulburn Broken Catchment Management Authority

Client Contact: Guy Tierney

Client Reference: 575

Synopsis: This report provides the methodology and results from the flood modelling and mapping for the Shepparton East Overland Urban Flood Study project.

REVISION/CHECKING HISTORY

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1 03/03/2017 MS

JL

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Shepparton East Overland Flow Urban Flood Study – Final Report i Executive Summary


Executive Summary This Executive Summary outlines the objectives, methodology and key outcomes of the Shepparton East Overland Flow Urban Flood Study.

Introduction BMT WBM Pty Ltd (BMT WBM) was commissioned by the Goulburn Broken Catchment Management Authority (GBCMA) to undertake the Shepparton East Overland Urban Flood Study. The study area is located on the eastern fringe of the city of Shepparton. Figure 1-1 shows the general location of the area in relation to its catchment and surrounding features.

The purpose of this report is to document the methodology and results of the hydrological and hydraulic modelling together with the flood mapping and risk outputs.

The study area drains both rural and urban land through a series of man-made drains rather than a natural drainage system. As such the study area’s drainage system is similar to an urban system. For this reason the flood modelling, both hydrologic and hydraulic, has been undertaken in accordance with the Melbourne Water (MW) Corporation Flood Mapping Projects Guidelines and Technical Specification.

Study Approach The study involved the following five key stages:

data collection;

hydrological modelling;

hydraulic modelling;

flood mapping and deliverables; and

reporting.

Flood Modelling This study requires the development of both hydrological and hydraulic models to undertake flood mapping of the study area. Rainfall-runoff (hydrological) modelling of the study area was undertaken with the RORB hydrological modelling package.

The RORB model underwent a joint verification in conjunction with the hydraulic model (TUFLOW) development. Following this verification the design flow outputs from RORB provided inputs into the TUFLOW hydraulic model.

The results from the hydraulic modelling were used to develop flood mapping products, undertake a flood damages assessment, and inform potential flood mitigation strategies.

The flood model provided base case or existing conditions flood information (including flood maps) for the catchment for the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% Annual Exceedance Probability (AEP) flood events. The 1% AEP flood extent and depth is shown in Figure 1. In addition to the existing conditions modelling, sensitivity testing of increased urbanisation, climate change and a combination of the two was undertaken.

Shepparton East Overland Flow Urban Flood Study – Final Report ii Executive Summary


The modelling showed that the catchment is susceptible to widespread and generally shallow slow moving flooding in even frequent (20% AEP) flood events. Whilst flooding is extensive in many of the developed areas of the catchment, it is generally confined to the road reserves, and where flows pass through residential or commercial properties the peak depths are shallow and with low velocity.

With the exception of the many retarding basins throughout the catchment and at small number of roadways, the flood hazard, as defined by the ARR revision project, shows almost the entire catchment as presenting a low risk to children.

Flood Damages Assessment A flood damages assessment was completed for the 20%, 10%, 5%, 2%, 1%, 0.5% and 0.2% AEP flood events to ascertain the economic damage from flooding to Shepparton East annually. The damages included damage to residential, commercial, agricultural and road infrastructure as well as indirect damages. A loss probability curve was produced to enable the calculation of annual flood damages. Large damages from low probability events are combined with lower damages from more frequent flood events and annual average damage (AAD) is calculated. A summary of the damages is provided in Table 1.

Table 1 Summary of Flood Damages for Shepparton East

Event (ARI)

ANUFLOOD Building Damages

RAM Agricultural

Damages

RAM Road Infrastructure

Damages

Indirect Damages

Total Damages

Contribution to AAD

PMP - - - - $126,006,700

0.2% $66,723,800 $12,437,300 $2,449,092 $29,014,400 $110,624,600 $236,631

0.5% $54,052,600 $10,971,700 $2,322,905 $20,204,200 $87,551,400 $297,264

1% $45,426,800 $9,788,900 $2,204,335 $17,226,000 $74,646,000 $405,494

2% $34,676,500 $8,804,400 $2,101,450 $13,674,700 $59,257,000 $669,515

5% $25,249,700 $7,302,300 $1,905,514 $10,337,300 $44,794,800 $1,560,777

10% $19,491,500 $6,023,600 $1,721,972 $8,171,100 $35,408,200 $2,005,075

20% $12,878,600 $5,014,300 $1,535,233 $5,828,400 $25,256,500 $3,033,235

50% - - - - - $3,788,475

Average Annual Damages $11,996,500

The existing condition AAD for the catchment is $11,996,500.

The damages within the catchment are largely driven by the damage to buildings, particularly commercial and industrial property. This is in part due to the conservative assumption of using the planning scheme rather than individual property assessments but also due to the widespread shallow flooding throughout the catchment which is a limitation of the Rapid Appraisal Method (RAM).

Shepparton East Overland Flow Urban Flood Study – Final Report iv Contents


Contents Executive Summary i 1 Introduction 1

1.1 Catchment Description 1 1.2 Study Objectives 2

1.2.1 Study Scenarios and Events 3 1.3 Study Approach 3

2 Data Collation 6

2.1 Topographic Data 6 2.2 Aerial Photography 6 2.3 Planning Scheme 6 2.4 Drainage Infrastructure 8 2.5 Historic Flooding 8 2.6 Streamflow Data 8 2.7 Rainfall Data 8

3 Hydrologic Modelling 11

3.1 Fraction Impervious 12 3.2 Rational Method 14

3.2.1 Description 14 3.2.2 Time of Concentration 14 3.2.3 Runoff Coefficient 15 3.2.4 Rainfall 15 3.2.5 Results 16

3.3 RORB Modelling 16 3.3.1 Model Schematisation 16 3.3.1.1 Catchment Delineation 17 3.3.1.2 Sub-Catchment Definition 17 3.3.1.3 Reach Types 18 3.3.1.4 Retarding Basins and Storages 19 3.3.1.5 Diversions 24 3.3.1.6 Intensity Frequency Duration (IFD) Parameters 24 3.3.1.7 Loss Model 24 3.3.1.8 Model Calibration 25 3.3.1.9 RORB Parameter Summary 27 3.3.1.10 Probable Maximum Precipitation 27

Shepparton East Overland Flow Urban Flood Study – Final Report v Contents


3.3.2 RORB Results Summary 27 3.3.2.1 Base Case Scenario 27 3.3.2.2 Developed Case Scenario 28 3.3.2.3 Climate Change Scenarios 29 3.3.3 Existing Condition Scenarios: Base Case and Developed Case Peak

Hydrographs 30 3.3.4 Climate Change Scenarios: Base Case and Developed Case Peak

Hydrographs 38 3.3.5 Comparison to Previous Models 45

3.4 Joint Verification with the Hydraulic Model 45 3.4.1 Joint Verification Process 46 3.4.2 Rainfall Analysis 46 3.4.3 Joint Verification Results 47

4 Hydraulic Modelling 50

4.1 Model Description 50 4.1.1 Model Schematisation 50

4.2 Hydraulic Modelling 51 4.2.1 TUFLOW Model Version 51 4.2.2 Model Extent 51

4.3 2D Domain 51 4.3.1 Topography 51 4.3.2 Breaklines 51 4.3.3 Retarding basins 52 4.3.4 Grid Resolution 52 4.3.5 Surface Roughness 52

4.4 1D Network 53 4.4.1 Underground Drainage Network 53 4.4.2 Drainage Network Losses 54 4.4.3 Open Drainage Network 54

4.5 Boundary Conditions 54 4.5.1 External Boundaries 54 4.5.2 Internal Boundaries 55 4.5.3 1D / 2D Linking 55

4.6 Hydraulic Model Verification 59 4.6.1 Verification of the February 2013 Flood Event 59

4.7 Design Event Modelling 61 4.7.1 Design Event Modelling 61

Shepparton East Overland Flow Urban Flood Study – Final Report vi Contents


4.7.2 Storm Duration Selection 61

5 Modelling Quality Assurance 62

5.1 Hydrologic (RORB) Model Review 62 5.2 Hydraulic (TUFLOW) Model Review 62

5.2.1 General Quality Assurance 62 5.2.2 1D Domain 62 5.2.3 2D Domain 63 5.2.4 Volume Checks and Mass Conservation 63

6 Flood Mapping and Results 65

6.1 Existing Case 65 6.1.1 Flood Depth Mapping and Description 65 6.1.2 Flood Velocity Mapping 65

6.2 Developed Case 70 6.2.1 Flood Depth Mapping and Description 70 6.2.2 Flood Velocity Mapping 70

6.3 Existing Case - Climate Change Sensitivity 75 6.4 Developed Case - Climate Change Sensitivity 78 6.5 Flood Hazard Mapping 81 6.6 Property Risk Mapping 86

7 Flood Damages Assessment 91

7.1 Methodology 93 7.2 Key Assumptions 93 7.3 Rapid Appraisal Method (RAM) Damages Assessment 94

7.3.1 RAM Building Damages 94 7.3.2 RAM Agricultural Damages 95 7.3.3 RAM Road Infrastructure Damages 96

7.4 Average Annual Damages 97

8 Flood Management 99

8.1 Background 99 8.2 Key Issues 99 8.3 Structural 99 8.4 Non-Structural 99

8.4.1 Overlays 100 8.4.1.1 Building Controls 100 8.4.1.2 Development Controls 100 8.4.2 Declared Flood Levels 100

Shepparton East Overland Flow Urban Flood Study – Final Report vii Contents


8.4.3 Planning For Climate Change 101

9 Summary and Recommendations 103

10 References 104

Appendix A Shepparton Retarding Basins – Locality Plan A-1

Appendix B Time of Concentration Calculations B-1

Appendix C IFD Table C-1

Appendix D PMF Summary Worksheet D-1

Appendix E Peak Flood Depth Maps E-1

Appendix F Peak Flood Velocity F-1

Appendix G ARR Hazardous to Children G-1

Shepparton East Overland Flow Urban Flood Study – Final Report viii Contents


List of Figures Figure 1 1% AEP Flood Depth iii Figure 1-1 Shepparton East - Locality Plan 4 Figure 1-2 Shepparton East – Catchment Plan 5 Figure 2-1 Digital Elevation Model Extent 7 Figure 2-2 Rainfall Gauges 10 Figure 3-1 RORB Model Schematisation 20 Figure 3-2 RORB Model Schematisation Main Drain 2 21 Figure 3-3 RORB Model Schematisation Main Drain 3 22 Figure 3-4 RORB Model Schematisation Urban Sub-Catchments 23 Figure 3-5 RORB Critical Hydrographs at Beckham Road 30 Figure 3-6 RORB Critical Hydrographs at Central Avenue 31 Figure 3-7 RORB Critical Hydrographs at Doyles Road 32 Figure 3-8 RORB Critical Hydrographs at Main Drain 2 Outlet 33 Figure 3-9 RORB Critical Hydrographs at 314 Old Dookie Road 34 Figure 3-10 RORB Critical Hydrographs at Railway 35 Figure 3-11 RORB Critical Hydrographs at Main Drain 3 Outlet 36 Figure 3-12 Peak Discharge Hydrographs for PMF at Key Locations 37 Figure 3-13 RORB Critical Climate Change Hydrographs at Beckham Road 38 Figure 3-14 RORB Critical Climate Change Hydrographs at Central Avenue 39 Figure 3-15 RORB Critical Climate Change Hydrographs at Doyles Road 40 Figure 3-16 RORB Critical Climate Change Hydrographs at Main Drain 2 Outlet 41 Figure 3-17 RORB Critical Climate Change Hydrographs at 314 Old Dookie Road 42 Figure 3-18 RORB Critical Climate Change Hydrographs at Railway 43 Figure 3-19 RORB Critical Climate Change Hydrographs at Main Drain 3 Outlet 44 Figure 3-20 February 2013 Rainfall Grid 48 Figure 3-21 February 2013 Thiessian Polygons 49 Figure 4-1 TUFLOW Model Layout 56 Figure 4-2 Manning’s ‘n’ Roughness Coefficient Distribution – Existing Conditions 57 Figure 4-3 Manning’s ‘n’ Roughness Coefficient Distribution – Ultimate Conditions 58 Figure 4-4 February 2013 Verification Event Peak Flood Depths 60 Figure 6-1 Existing Conditions 20% AEP Peak Flood Depth 67 Figure 6-2 Existing Conditions 1% AEP Peak Flood Depth 68 Figure 6-3 Existing Conditions 1% AEP Peak Flood Velocity 69

Shepparton East Overland Flow Urban Flood Study – Final Report ix Contents


Figure 6-4 Developed Conditions 20% AEP Peak Flood Depth 71 Figure 6-5 Developed Conditions 1% AEP Peak Flood Depth 72 Figure 6-6 Developed Conditions 1% AEP Peak Flood Velocity 73 Figure 6-7 Increase in Developed Conditions 1% AEP Peak Flood Level 74 Figure 6-8 1% AEP Peak Flood Depth – Climate Change 76 Figure 6-9 Increase in 1% AEP Peak Flood Level – Climate Change 77 Figure 6-10 1% AEP Peak Flood Depth – Developed Climate Change 79 Figure 6-11 Increase in 1% AEP Peak Flood Level – Developed Climate Change 80 Figure 6-12 Existing Conditions Flood Hazard 82 Figure 6-13 Developed Conditions Flood Hazard 83 Figure 6-14 Climate Change Flood Hazard 84 Figure 6-15 Developed Climate Change Flood Hazard 85 Figure 6-16 Existing Conditions Flood Risk to Property 87 Figure 6-17 Developed Conditions Flood Risk to Property 88 Figure 6-18 Climate Change Flood Risk to Property 89 Figure 6-19 Developed Climate Change Flood Risk to Property 90 Figure 7-1 Types and Categorisation of Flood Damage Costs - Reproduced from Rapid

Appraisal Method (RAM) For Floodplain Management (NRE 2000). 92 Figure 7-2 Existing Condition Probability-Damages Curve 98 Figure 8-1 Proposed Planning Scheme 102 Figure E-1 Existing Conditions 20% AEP Peak Flood Depth E-2 Figure E-2 Existing Conditions 10% AEP Peak Flood Depth E-3 Figure E-3 Existing Conditions 5% AEP Peak Flood Depth E-4 Figure E-4 Existing Conditions 2% AEP Peak Flood Depth E-5 Figure E-5 Existing Conditions 1% AEP Peak Flood Depth E-6 Figure E-6 Existing Conditions 0.5% AEP Peak Flood Depth E-7 Figure E-7 Existing Conditions 0.2% AEP Peak Flood Depth E-8 Figure E-8 Developed Conditions 20% AEP Peak Flood Depth E-9 Figure E-9 Developed Conditions 10% AEP Peak Flood Depth E-10 Figure E-10 Developed Conditions 5% AEP Peak Flood Depth E-11 Figure E-11 Developed Conditions 2% AEP Peak Flood Depth E-12 Figure E-12 Developed Conditions 1% AEP Peak Flood Depth E-13 Figure E-13 Developed Conditions 0.5% AEP Peak Flood Depth E-14 Figure E-14 Developed Conditions 0.2% AEP Peak Flood Depth E-15 Figure E-15 Climate Change 20% AEP Peak Flood Depth E-16

Shepparton East Overland Flow Urban Flood Study – Final Report x Contents


Figure E-16 Climate Change 10% AEP Peak Flood Depth E-17 Figure E-17 Climate Change 5% AEP Peak Flood Depth E-18 Figure E-18 Climate Change 2% AEP Peak Flood Depth E-19 Figure E-19 Climate Change 1% AEP Peak Flood Depth E-20 Figure E-20 Climate Change 0.5% AEP Peak Flood Depth E-21 Figure E-21 Climate Change 0.2% AEP Peak Flood Depth E-22 Figure E-22 Developed Climate Change 20% AEP Peak Flood Depth E-23 Figure E-23 Developed Climate Change 10% AEP Peak Flood Depth E-24 Figure E-24 Developed Climate Change 5% AEP Peak Flood Depth E-25 Figure E-25 Developed Climate Change 2% AEP Peak Flood Depth E-26 Figure E-26 Developed Climate Change 1% AEP Peak Flood Depth E-27 Figure E-27 Developed Climate Change 0.5% AEP Peak Flood Depth E-28 Figure E-28 Developed Climate Change 0.2% AEP Peak Flood Depth E-29 Figure F-1 Existing Conditions 20% AEP Peak Flood Velocity F-2 Figure F-2 Existing Conditions 10% AEP Peak Flood Velocity F-3 Figure F-3 Existing Conditions 5% AEP Peak Flood Velocity F-4 Figure F-4 Existing Conditions 2% AEP Peak Flood Velocity F-5 Figure F-5 Existing Conditions 1% AEP Peak Flood Velocity F-6 Figure F-6 Existing Conditions 0.5% AEP Peak Flood Velocity F-7 Figure F-7 Existing Conditions 0.2% AEP Peak Flood Velocity F-8 Figure F-8 Developed Conditions 20% AEP Peak Flood Velocity F-9 Figure F-9 Developed Conditions 10% AEP Peak Flood Velocity F-10 Figure F-10 Developed Conditions 5% AEP Peak Flood Velocity F-11 Figure F-11 Developed Conditions 2% AEP Peak Flood Velocity F-12 Figure F-12 Developed Conditions 1% AEP Peak Flood Velocity F-13 Figure F-13 Developed Conditions 0.5% AEP Peak Flood Velocity F-14 Figure F-14 Developed Conditions 0.2% AEP Peak Flood Velocity F-15 Figure F-15 Climate Change 20% AEP Peak Flood Velocity F-16 Figure F-16 Climate Change 10% AEP Peak Flood Velocity F-17 Figure F-17 Climate Change 5% AEP Peak Flood Velocity F-18 Figure F-18 Climate Change 2% AEP Peak Flood Velocity F-19 Figure F-19 Climate Change 1% AEP Peak Flood Velocity F-20 Figure F-20 Climate Change 0.5% AEP Peak Flood Velocity F-21 Figure F-21 Climate Change 0.2% AEP Peak Flood Velocity F-22 Figure F-22 Developed Climate Change 20% AEP Peak Flood Velocity F-23

Shepparton East Overland Flow Urban Flood Study – Final Report xi Contents


Figure F-23 Developed Climate Change 10% AEP Peak Flood Velocity F-24 Figure F-24 Developed Climate Change 5% AEP Peak Flood Velocity F-25 Figure F-25 Developed Climate Change 2% AEP Peak Flood Velocity F-26 Figure F-26 Developed Climate Change 1% AEP Peak Flood Velocity F-27 Figure F-27 Developed Climate Change 0.5% AEP Peak Flood Velocity F-28 Figure F-28 Developed Climate Change 0.2% AEP Peak Flood Velocity F-29 Figure G-1 Existing Conditions 20% AEP Peak Flood Hazard - ARR Hazardous to

Children G-2 Figure G-2 Existing Conditions 10% AEP Peak Flood Hazard - ARR Hazardous to

Children G-3 Figure G-3 Existing Conditions 5% AEP Peak Flood Hazard - ARR Hazardous to Children G-4 Figure G-4 Existing Conditions 2% AEP Peak Flood Hazard - ARR Hazardous to Children G-5 Figure G-5 Existing Conditions 1% AEP Peak Flood Hazard - ARR Hazardous to Children G-6 Figure G-6 Existing Conditions 0.5% AEP Peak Flood Hazard - ARR Hazardous to

Children G-7 Figure G-7 Existing Conditions 0.2% AEP Peak Flood Hazard - ARR Hazardous to

Children G-8 Figure G-8 Developed Conditions 20% AEP Peak Flood Hazard - ARR Hazardous to





Children G-13 Figure G-13 Developed Conditions 0.5% AEP Peak Flood Hazard - ARR Hazardous to

Children G-14 Figure G-14 Developed Conditions 0.2% AEP Peak Flood Hazard - ARR Hazardous to

Children G-15 Figure G-15 Climate Change 20% AEP Peak Flood Hazard - ARR Hazardous to Children G-16 Figure G-16 Climate Change 10% AEP Peak Flood Hazard - ARR Hazardous to Children G-17 Figure G-17 Climate Change 5% AEP Peak Flood Hazard - ARR Hazardous to Children G-18 Figure G-18 Climate Change 2% AEP Peak Flood Hazard - ARR Hazardous to Children G-19 Figure G-19 Climate Change 1% AEP Peak Flood Hazard - ARR Hazardous to Children G-20 Figure G-20 Climate Change 0.5% AEP Peak Flood Hazard - ARR Hazardous to Children G-21 Figure G-21 Climate Change 0.2% AEP Peak Flood Hazard - ARR Hazardous to Children G-22

Shepparton East Overland Flow Urban Flood Study – Final Report xii Contents


Figure G-22 Developed Climate Change 20% AEP Peak Flood Hazard - ARR Hazardous to Children G-23





Figure G-27 Developed Climate Change 0.5% AEP Peak Flood Hazard - ARR Hazardous to Children G-28

Figure G-28 Developed Climate Change 0.2% AEP Peak Flood Hazard - ARR Hazardous to Children G-29

Shepparton East Overland Flow Urban Flood Study – Final Report xiii Contents


List of Tables Table 1 Summary of Flood Damages for Shepparton East ii Table 1-1 Required Modelling Scenarios 3 Table 2-1 Rainfall Data Collected 9 Table 3-1 Planning Scheme Zone Fraction Impervious 13 Table 3-2 Calculated tc Values 15 Table 3-3 Shepparton East Runoff Coefficient Values 15 Table 3-4 Rational Method Parameters and Results for the 1% AEP event 16 Table 3-5 Retarding Basins Located with Study Area 19 Table 3-6 IFD Parameters 24 Table 3-7 kc and dav Parameters for Shepparton East outlets 26 Table 3-8 Rational Method and RORB comparisons for Shepparton East 26 Table 3-9 RORB Parameters 27 Table 3-10 Base Case Predicted Peak Discharges 28 Table 3-11 Ultimate Developed Case Predicted Peak Discharges 28 Table 3-12 Climate Change A – Increased Rainfall Intensity Predicted Peak Discharge 29 Table 3-13 Climate Change B – Increased Rainfall Intensity Predicted Peak Discharge 29 Table 3-14 February 2013 Peak Discharges 47 Table 4-1 2D Domain Manning’s ‘n’ Coefficients 53 Table 4-2 Comparison of Floodmarks to Modelled Flood Level 59 Table 4-3 Storm Durations Modelled for Final Model 61 Table 5-1 Volume Check 64 Table 6-1 Properties at Risk 86 Table 7-1 RAM Building Potential Damage Values 95 Table 7-2 Existing Conditions RAM Building Damages Summary 95 Table 7-3 RAM Agricultural Damage Values 95 Table 7-4 Existing Conditions RAM Agricultural Damages Summary 96 Table 7-5 RAM Road Infrastructure Damage Values 96 Table 7-6 Existing Conditions RAM Road Infrastructure Damages Summary 96 Table 7-7 Existing Conditions Damages Summary 97

Shepparton East Overland Flow Urban Flood Study – Final Report 1 Introduction


1 Introduction BMT WBM Pty Ltd (BMT WBM) was commissioned by Goulburn Broken Catchment Management Authority (GBCMA) to undertake the Shepparton East Overland Urban Flood Study. The study area is located on the eastern fringe of the city of Shepparton. Figure 1-1 shows the general location of the area in relation to its catchment and surrounding features.

This study requires the development of both hydrological and hydraulic models to undertake flood mapping of the study area. Rainfall-runoff (hydrological) modelling of the study area was undertaken with the RORB hydrological modelling package.

The RORB model underwent a joint verification in conjunction with the hydraulic model (TUFLOW) development. Following this verification the design flow outputs from RORB provided inputs into the TUFLOW hydraulic model.

The results from the hydraulic modelling were used to develop flood mapping products, undertake a flood damages assessment, and inform potential flood mitigation strategies.

The purpose of this report is to document the development and results of the hydrological and hydraulic modelling together with the flood mapping and risk products.

The study area drains both rural and urban land through a series of man-made drains rather than a natural drainage system. As such the study area’s drainage system is similar to an urban system. For this reason the flood modelling, both hydrologic and hydraulic, has been undertaken in accordance with the Melbourne Water (MW) Corporation Flood Mapping Projects Guidelines and Technical Specification (MW Technical Specification, MW 2011).

1.1 Catchment Description The Shepparton East Overland Urban Flood Study area, together with key drainage features, is shown in Figure 1-2. The study area is located in north-central Victoria approximately 180 km north of Melbourne and covers an area of 49 km2 to the east of Shepparton township (as shown in Figure 1-1).

There are no significant natural waterways in the study area; however, it is drained by an extensive network of manmade open drains. Goulburn Murray Water Main Drain 2 flows west from the East Goulburn Main Channel, draining agricultural land between the Midland Highway and the Broken River. Its 12.5 km length drains almost 16 km2 of predominantly agricultural land with some urban areas. The drain discharges to the Broken River between Archer Street and McPhees Road. Goulburn Murray Water Main Drain 3 flows for 20 km north-west from the East Goulburn Main Channel, crossing Central Avenue, Doyles Road and the Goulburn Valley Highway before discharging into Goulburn River at Reedy Swamp. It drains an area of around 20 km2 to the Goulburn Valley Highway, which forms the downstream extent of the study area. Open drains from agricultural properties combine with Main Drain 2 and Main Drain 3 to form a dense drainage network.

In addition to the Main Drain catchment’s there are a number of small urban catchment which drain directly to the Broken and Goulburn Rivers by the urban drainage system. These catchments only partially fall into the area to be flood mapped as discussed in Section 3.3.1.1. The Midland



Highway forms a significant ridge, largely preventing cross-catchment flows between the areas contributing to flow in Main Drain 2 and Main Drain 3. Throughout this study, the hydrological approach has considered the contributing catchments to Main Drain 2 and Main Drain 3 independently of one another as discussed in Section 3.3.1.1. Parameters and results for each of the Main Drain catchments have been reported accordingly. It is of note that any cross-catchment flow will be explicitly modelled in the hydraulic model.

The catchment area is, in general, flat with raised irrigation channels forming barriers to overland flow. For this reason the raised irrigation channels often form the catchment boundaries.

The area to be hydraulically modelled, or the study area, is limited to the extent of the LiDAR data which covers the majority of the catchment. The study area is bordered to the west by Archer Street, Hawdon Street and the Goulburn Valley Highway within Shepparton township. The irrigation channel along Channel Road forms the southern boundary of the study area. The north and east boundary of the flood mapping is limited to the available LiDAR. The flood mapping boundary together with the catchment boundary is shown in Figure 1-2.

Land use within the catchment is mixed. The majority of land use is residential and agricultural (in particular orchards). The orchards have water supplied by an extensive network of irrigation channels which, as noted above, are raised above the surrounding ground levels. Other land use types within the catchment include industrial and commercial.

1.2 Study Objectives The objective of the study was to create a hydrologic model of the catchment to model the rainfall-runoff process, as well as a 1D/2D dynamically linked TUFLOW hydraulic model to undertake flood mapping of the catchment. The results from the coupled hydrologic and hydraulic model (the flood model) were used to create flood mapping and flood risk products required as well as informing potential flood mitigation strategies. This suite of products was used to improve the understanding of flooding and flood risk in East Shepparton, now and for the future conditions.

The flood model was run for the Scenarios and Events listed under the appropriate heading below.

Specifically, the study aimed to deliver:

Flood mapping products for the four scenarios and AEP events listed below for the following variables:

○ Peak flood levels

○ Peak flood depths

○ Peak flood velocities; and

○ Flood Hazard.

The following flood risk products

○ Flood mapping products that are suitable to define planning scheme flood overlays.

○ Recommendations for flood related planning conditions.

○ Tabulated property flood likelihood.



○ Flood damages assessment using the Rapid Appraisal Method (RAM).

○ Recommendations for structural flood mitigation measures.

1.2.1 Study Scenarios and Events A number of design events and different scenarios as listed in Table 1-1 and described in more detail below.

Base:

○ Existing rainfall conditions; with

○ Current levels of development.

Developed:

○ Existing rainfall conditions; with

○ Ultimate development conditions – in line with future rezoning and development anticipated around Shepparton East.

Climate Change A:

○ Existing rainfall conditions intensified by 32%; with

○ Current (Base) levels of development.

Climate Change B:

○ Existing rainfall conditions intensified by 32%; with

○ Ultimate (Developed) levels of development.

Table 1-1 Required Modelling Scenarios

Scenario AEP

20% 10% 5% 2% 1% 0.5% 0.2% PMP

Base

Developed

Climate Change A

Climate Change B

1.3 Study Approach The study involved the following five key stages:

data collection;

hydrological modelling;

hydraulic modelling;

flood mapping and deliverables; and

reporting.

Shepparton East Overland Flow Urban Flood Study – Final Report 6 Data Collation


2 Data Collation This section documents the data that has been collated by BMT WBM to date for the Study. BMT WBM has obtained information from a number of agencies and sources, including:

Goulburn Broken Catchment Management Authority (GBCMA);

Goulburn-Murray Water (GMW);

Greater Shepparton City Council (GSCC);

Bureau of Meteorology (BoM); and

Department of Environment, Land, Water and Planning (DELWP).

2.1 Topographic Data For the Study 0.5m gridded LiDAR was provided by GBCMA to form the basis of the Digital Elevation Model (DEM) which was used for both the hydrologic and hydraulic modelling components of the Study. The extent of the available LiDAR was less than the hydrologic catchment boundaries and formed the basis of the extent of the hydraulic model. The extent of the available LiDAR is shown in Figure 2-1.

2.2 Aerial Photography Aerial Photography of the catchment is an important tool for verifying catchment characteristics such as land use, building footprints and other structures. During the hydrologic modelling stage this information was used, along with the planning scheme overlays, to estimate the fraction imperviousness of the catchment. Similarly, when developing the hydraulic model this information was used to assign the Manning’s values (roughness) to the catchment and any blockages caused by buildings.

For the Study one geo-referenced tile covering the Shepparton was provided by GBCMA.

2.3 Planning Scheme The planning scheme layers were used in conjunction with the aerial photography and on-ground photography to define the current land use of the catchment. The planning scheme layers were used in both the hydrologic and hydraulic model to define factors such as fraction impervious and Manning's values (roughness). This was supplied by GBCMA and covers the study area.



2.4 Drainage Infrastructure Underground drainage, as well as culvert and open channel information, was used during the hydraulic modelling component of the flood study. It is important to incorporate any assets in the hydraulic model using as accurate information as possible. Locating the asset in the wrong location may disconnect it from the main flow channel. Whilst applying incorrect attributes (width/height/inverts/weirs/drops/etc) may result in incorrect flows passing through the structure. This may result in either elevated or depressed flooding upstream and over the road as well as elevated or depressed water levels downstream depending on which attributes are incorrect.

For the Study two asset collection surveys were undertaken to collate an accurate as possible GIS dataset of the existing drainage network. These were undertaken by Chris Smith Survey and Think Spatial. The survey by Chris Smith Survey captured details of the open channel drainage network whereas the survey by Think Spatial captured details of the underground drainage network.

The provided survey represented a significant improvement on the existing dataset. However many pits could be accessed and as such substantial infilling of the data was required, this is discussed in greater detail in Section 4.4.1.

Within the catchment there are currently 47 retarding basins. The location and details were provided by Greater Shepparton City Council.

2.5 Historic Flooding Due to the lack of stream or flow gauges within the catchment it was not possible to undertake a traditional model calibration. Fortuitously, a significant flood event occurred during the study. This allowed flood marks to be collected throughout the catchment, together with sub-daily rainfall information.

Immediately following the flood event that occurred on the 27th and 28th of February 2013 BMT WBM and GBCMA undertook a site inspection of the catchment. Soon after a flood level survey was commissioned and undertaken by Spiire. In total 120 flood marks were surveyed and these together with the rainfall information formed the basis of the joint verification of the hydrologic and hydraulic models.

2.6 Streamflow Data There are no stream flow gauges available within the catchment that could be used to calibrate or verify the hydrologic and hydraulic models.

2.7 Rainfall Data Rainfall data was used during the verification process whereby the hydrologic and hydraulic models underwent a joint verification of the February 2013 flood event. Both daily and pluviograph rainfall data was obtained from the Bureau of Meteorology as well as a number of privately owned and operated rain gauges within the Study area. The obtained rainfall gauges details are tabulated in Table 2-1 and presented spatially in Figure 2-2.



Table 2-1 Rainfall Data Collected

Station No. Station Name Station Type Provider

81034 Mooroopna Daily Bureau of Meteorology

81095 Murchison (Arcadia (Sunnyville)) Daily Bureau of Meteorology

81013 Dookie Agricultural College Daily Bureau of Meteorology

81114 Tatura (Thiess Services) Daily Bureau of Meteorology

81007 Caniambo Daily Bureau of Meteorology

81125 Shepparton Airport Daily Bureau of Meteorology

Pluviograph Bureau of Meteorology

81049 Tatura Institute for Sustainable Agriculture

Daily Bureau of Meteorology

Pluviograph Bureau of Meteorology

N/A Archer St, Shepparton Daily Private Individual

N/A Midland Hwy, East Shepparton Daily Private Individual

N/A Bregan Court, Grahamvale Daily Private Individual

N/A Dobson Road, Grahamvale Daily Private Individual

N/A Hicken Crescent, Shepparton Daily Private Individual

N/A Ebbott Road, East Shepparton Daily Private Individual

N/A Old Dookie Rd, Shepparton East Daily Private Individual

N/A Doyles Road, Shepparton East Daily Private Individual

N/A Kensington Gardens, Channel Road, Shepparton Daily Private Individual

N/A 540 New Dookie Road, Lemnos Daily Private Individual

N/A Kialla Daily

Private Individual Pluviograph

N/A Grahamvale Daily

Private Individual Pluviograph

shepparton east overland flow urban flood study – final report · the purpose of this report is...

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