HENRY LAWSON DRIVE UPGRADE STAGE 1A REVIEW OF ENVIRONMENTAL FACTORS AND ENVIRONMENTAL IMPACT STATEMENT FLOODING ASSESSMENT REPORT FINAL REPORT July 2021 Job No: AM513 Date: July 2021 Principal: SAB File:/Reports/HLDU S1A REFEIS-Flooding [Rev 1.5].docx Rev No: 1.5 Author: BJN Transport for NSW Henry Lawson Upgrade Stage 1A Review of Environmental Factors & Environmental Impact Statement Flooding Assessment Report TABLE OF CONTENTS Page No. ES1 EXECUTIVE SUMMARY ........................................................................................... ES1 1 INTRODUCTION ........................................................................................................... 1 1.1 Proposal background ........................................................................................ 1 1.2 Proposal location and setting ............................................................................ 1 1.3 Proposal overview ............................................................................................ 2 1.3.1 Key features of the REF proposal .......................................................... 2 1.3.2 Key features of the EIS proposal ........................................................... 3 1.4 Purpose and scope of this report ...................................................................... 5 1.4.1 Secretary’s Environmental Assessment Requirements ........................... 5 1.5 Structure of this report ...................................................................................... 6 2 LEGISLATIVE AND POLICY CONTEXT ....................................................................... 7 2.1 Relevant legislation, policies and guidelines ..................................................... 7 2.1.1 Commonwealth guidelines ..................................................................... 7 2.1.2 State legislation, policies and guidelines ................................................ 7 2.1.3 Council policies and guidelines ............................................................ 12 3 METHODOLOGY ........................................................................................................ 14 3.1 Key tasks ........................................................................................................ 14 3.2 Summary of adopted assessment criteria and standards ................................ 14 3.3 Definition of flood behaviour under pre-proposal conditions ............................ 16 3.4 Assessment of construction related impacts.................................................... 18 3.5 Assessment of operational related impacts ..................................................... 18 3.6 Impact of future climate change on flood behaviour ........................................ 18 3.6.1 Impact of future climate change on flooding to the proposal ................. 19 3.6.2 Impact of the proposal on flood behaviour under future climate change conditions............................................................................................ 19 3.7 Impact of a partial blockage of major hydraulic structures on flood behaviour .. 19 4 EXISTING ENVIRONMENT ......................................................................................... 21 4.1 Overview ........................................................................................................ 21 4.2 Catchment description .................................................................................... 21 4.2.1 Georges River ..................................................................................... 21 4.2.2 Milperra Drain ...................................................................................... 22 4.3 Description of existing flood behaviour ............................................................ 23 4.3.1 General ............................................................................................... 23 4.3.2 Georges River flooding ........................................................................ 23 4.3.3 Milperra catchment flooding ................................................................. 24 5 IMPACT ASSESSMENT .............................................................................................. 26 5.1 Impacts during construction ............................................................................ 26 5.1.1 Potential flood risks at construction work areas .................................... 26 5.1.2 Potential impacts of construction activities on flood behaviour ............. 30 5.2 Impacts during operation ................................................................................ 39 5.2.1 Potential flood risk to the proposal and its impact on flood behaviour ... 39 5.2.2 Consistency with council and state government flood related plans...... 43 5.2.3 Impact of future climate change on flood behaviour ............................. 45 5.2.4 Impact of a partial blockage of major hydraulic structures on flood behaviour ........................................................................................................ 46 Cont'd Over HLDU S1A REFEIS-Flooding [Rev 1.5].docx Page i Lyall & Associates July 2021 Rev. 1.5 Transport for NSW Henry Lawson Upgrade Stage 1A Review of Environmental Factors & Environmental Impact Statement Flooding Assessment Report TABLE OF CONTENTS (Cont'd) Page No. 5.3 Cumulative impacts ........................................................................................ 56 6 MANAGEMENT OF IMPACTS .................................................................................... 58 6.1 Approach ........................................................................................................ 58 6.2 Management of construction impacts .............................................................. 58 6.3 Management of operational impacts ............................................................... 60 7 REFERENCES ............................................................................................................ 62 LIST OF FIGURES Figure 1.1 Proposal overview Figure 4.1 (2 sheets) Catchment plan and existing drainage layout Figure 4.2 (2 sheets) Patterns of main stream flooding – Pre-proposal conditions - 10% AEP Georges River flood event Figure 4.3 (2 sheets) Patterns of main stream flooding – Pre-proposal conditions - 1% AEP Georges River flood event Figure 4.4 (2 sheets) Patterns of main stream flooding – Pre-proposal conditions – PMF Georges River flood event Figure 4.2 (2 sheets) Patterns of main stream flooding and major overland flow – Pre-proposal conditions - 10% AEP Milperra catchment flood event Figure 4.3 (2 sheets) Patterns of main stream flooding and major overland flow – Pre-proposal conditions - 1% AEP Milperra catchment flood event Figure 4.4 (2 sheets) Patterns of main stream flooding and major overland flow – Pre-proposal conditions – PMF Milperra catchment flood event Figure 5.1 (2 sheets) Indicative flood extents in vicinity of proposed construction work areas - Pre- proposal conditions – Georges River flood event Figure 5.2 (2 sheets) Indicative flood extents in vicinity of proposed construction work areas - Pre- proposal conditions – Milperra catchment flood event Figure 5.3 (2 sheets) Patterns of main stream flooding – Operational conditions - 10% AEP Georges River flood event Figure 5.4 (2 sheets) Impact of proposal operation on flood behaviour - 10% AEP Georges River flood event Figure 5.5 (2 sheets) Patterns of main stream flooding – Operational conditions - 1% AEP Georges River flood event Figure 5.6 (2 sheets) Impact of proposal operation on flood behaviour - 1% AEP Georges River flood event Figure 5.7 (2 sheets) Patterns of main stream flooding - Operational conditions – PMF Georges River flood event Figure 5.8 (2 sheets) Impact of proposal operation on flood behaviour – PMF Georges River flood event Figure 5.9 (2 sheets) Patterns of main stream flooding and major overland flow – Operational conditions - 10% AEP Milperra catchment flood event HLDU S1A REFEIS-Flooding [Rev 1.5].docx Page ii Lyall & Associates July 2021 Rev. 1.5 Transport for NSW Henry Lawson Upgrade Stage 1A Review of Environmental Factors & Environmental Impact Statement Flooding Assessment Report Figure 5.10 (2 sheets) Impact of proposal operation on flood behaviour - 10% AEP Milperra catchment flood event Figure 5.11 (2 sheets) Patterns of main stream flooding and major overland flow – Operational conditions - 1% AEP Milperra catchment flood event Figure 5.12 (2 sheets) Impact of proposal operation on flood behaviour - 1% AEP Milperra catchment flood event Figure 5.13 (2 sheets) Patterns of main stream flooding and major overland flow - Operational conditions – PMF Milperra catchment flood event Figure 5.14 (2 sheets) Impact of proposal operation on flood behaviour – PMF Milperra catchment flood event ANNEXURES A. Additional figures showing flood model results HLDU S1A REFEIS-Flooding [Rev 1.5].docx Page iii Lyall & Associates July 2021 Rev. 1.5 Transport for NSW Henry Lawson Upgrade Stage 1A Review of Environmental Factors & Environmental Impact Statement Flooding Assessment Report NOTE ON FLOOD FREQUENCY TERMINOLOGY The frequency of flood events is generally referred to in terms of their Annual Exceedance Probability (AEP) or Average Recurrence Interval (ARI). For example, for a flood magnitude having five per cent AEP, there is a five per cent probability (or 1 in 20 chance) that there would be floods of greater magnitude each year. As another example, for a flood