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Tweed Shire

Coastal Hazards Assessment

Prepared For: Tweed Shire Council

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

Tweed Shire Council has prepared this document with financial assistance from the NSW Government through the Office of Environment and Heritage. This document does not necessarily represent the opinions of the NSW Government or the Office of Environment and Heritage.

Offices

Brisbane Denver Mackay

Melbourne Newcastle

Perth Sydney

Vancouver

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DOCUMENT CONTROL SHEET

BMT WBM Pty Ltd BMT WBM Pty Ltd Level 8, 200 Creek Street Brisbane 4000 Queensland Australia PO Box 203 Spring Hill 4004 Tel: +61 7 3831 6744 Fax: + 61 7 3832 3627 ABN 54 010 830 421 www.bmtwbm.com.au

Document :

Project Manager :

R.B19094.001.04.docx

DCP

Client : Client Contact: Client Reference

Tweed Shire Council Jane Lofthouse EQ2012-162

Title : Tweed Shire Coastal Hazards Assessment

Author : Dean Patterson

Synopsis : The Tweed Shire Coastal Hazards Assessment report presents a summary of the regional and local coastal processes operating on the Tweed coastline. The report presents the methodology and outcomes for the definition of coastal hazards affecting the study area coastline, including a detailed assessment of shoreline recession hazard for Kingscliff, determined from local knowledge, various survey data sources, analysis of photogrammetry data and numerical modelling. The Study provides definition of the erosion hazards using a risk-based approach providing for variability and uncertainty, particularly beach erosion and recession for the immediate, 2050 and 2100 timeframes, taking account of ENSO variability and projected future sea level rise.

REVISION/CHECKING HISTORY

REVISION NUMBER

DATE OF ISSUE CHECKED BY ISSUED BY

0

01

02

03

04

22/11/12

14/12/2012

31/1/2013

30/11/2013

9/12/2013

M J Andrews

M J Andrews

M J Andrews

M J Andrews

M J Andrews

D C Patterson

D C Patterson

D C Patterson

D C Patterson

D C Patterson

DISTRIBUTION

DESTINATION REVISION 0 01 02 03 04

Tweed Shire Council BMT WBM File BMT WBM Library

PDF PDF PDF

PDF PDF PDF

PDF PDF PDF

PDF PDF PDF

PDF + hard copies PDF PDF

CONTENTS I

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CONTENTS

Contents i  List of Figures iv  List of Tables vii 

EXECUTIVE SUMMARY IX 

1  INTRODUCTION 1-1  1.1  Background 1-1  1.2  Context and Objectives of this Study 1-4 

1.2.1  Objectives of this Coastal Zone Hazards Study 1-4 

1.3  NSW Coastal Management Framework 1-5  1.4  Study Area Beaches 1-5  1.5  Historical Data and Reports 1-6 

2  REGIONAL CONTEXT 2-1  2.1  Geology and Geomorphology 2-1 

2.1.1  Geologic Context 2-1 

2.1.2  Geomorphologic Units 2-2 

2.1.3  Coastal Barrier Evolution 2-3  2.1.3.1  Shoreward Sand Supply 2-3 

2.1.3.2  Dune Formation 2-6 

2.1.3.3  Northward Longshore Sand Transport 2-7 

2.2  Regional Wave Climate 2-8  2.2.1  Storm Wave Generation Sources 2-8 

2.2.2  Measured Regional Wave Climate 2-9 

2.2.3  Extreme Waves 2-12 

2.2.4  Nearshore Waves 2-14 

2.2.5  ENSO Variability of Wave Climate 2-17  2.2.5.1  Significance of Wave Climate Variability 2-17 

2.2.5.2  Wave Climate Correlation with ENSO 2-17 

2.3  Water Levels 2-22  2.3.1  Astronomical Tide 2-22 

2.3.2  Elevated Water Levels 2-23 

CONTENTS II

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2.3.2.1  Ocean Storm Tide Levels 2-23 

2.3.2.2  Wave Set Up 2-24 

2.3.2.3  Wave Run-up 2-24 

2.3.2.4  Elevated Estuary Water Levels 2-24 

2.4  Sediment Budget and Shoreline Change 2-25  2.4.1  Previous Studies 2-25 

2.4.2  Cross-shore Sediment Transport 2-27  2.4.2.1  Storm Erosion 2-27 

2.4.2.2  Net Shore-face Supply to the Beach System 2-29 

2.4.3  New Modelling of Contemporary Shoreline Processes 2-30 

3  COASTAL HAZARDS ASSESSMENT: ISSUES AND METHODOLOGY 3-1  3.1  Coastal Hazard Components 3-1  3.2  Climate Change 3-1 

3.2.1  Sea Level Rise 3-1 

3.2.2  Wave Climate Changes 3-1 

3.2.3  Storm Surge Impacts 3-2 

3.3  Beach Erosion (Storm Bite) 3-2  3.3.1  Erosion Processes 3-2 

3.3.2  Storm Bite Assessment 3-3 

3.4  Long Term Recession 3-4  3.4.1  Assessment Approach and Issues 3-4 

3.4.2  Considerations and Uncertainties 3-5 

3.4.3  Analysis of Historical Shoreline Recession 3-6 

3.4.4  Sea Level Rise Impacts 3-7  3.4.4.1  Equilibrium Profile (Bruun Rule) Concept 3-7 

3.4.4.2  Shoreline Evolution Modelling of Sea Level Rise Effects 3-10 

3.5  Erosion / Recession Hazard Definition 3-11  3.5.1  Erosion Hazard Assessment Approach 3-11 

3.5.2  Erosion Hazard Assessment Uncertainty 3-13 

3.6  Coastal Inundation 3-15  3.6.1  Elevated Ocean Levels 3-15 

3.6.2  Design Wave Conditions 3-15 

3.6.3  Wave Run-up and Overtopping 3-16 

3.6.4  Creek Estuary Inundation 3-17 

3.7  Coastal Entrance Instability 3-18  3.8  Dune Stability & Reduced Foundation Capacity 3-18  3.9  Sand Drift 3-20 

CONTENTS III

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4  KINGSCLIFF COASTAL HAZARDS ASSESSMENT 4-1  4.1  Context 4-1  4.2  Conceptual Coastal Processes 4-1  4.3  Historical Shoreline Behaviour 4-3 

4.3.1  Impacts of Cudgen Creek Training Walls 4-3 

4.3.2  Analysis of Photogrammetry Data 4-6 

4.4  Assessment of Kingscliff Coastal Hazards 4-8  4.4.1  Coastal Hazards Affecting Kingscliff 4-8 

4.4.2  Erosion Hazard Strategy and Hazard Components 4-9 

4.4.3  Erosion Hazard Zones 4-12 

4.5  Coastal Inundation Hazard 4-17  4.5.1  Wave Run-up and Overtopping 4-17 

4.5.2  Cudgen Creek Estuary Inundation 4-18 

5  TWEED SHIRE COASTLINE HAZARDS ASSESSMENT 5-1  5.1  General Considerations 5-1  5.2  Pottsville 5-1 

5.2.1  Coastal Erosion Processes 5-1 

5.2.2  Previous Coastal Hazard Assessments 5-2 

5.2.3  Re-assessed Short Term Storm Bite 5-3 

5.2.4  Re-assessment of Long Term Shoreline Movement 5-3  5.2.4.1  Updated Photogrammetric Analysis 5-3 

5.2.4.2  Sea Level Rise Recession 5-6 

5.2.5  Erosion Hazard Assessment 5-6 

5.2.6  Coastal Entrance Instability 5-8 

5.2.7  Coastal Inundation Hazard 5-8 

5.2.8  Mooball Creek Estuary Inundation 5-8 

5.3  Hastings Point to Norries Head 5-10  5.3.1  Coastal Erosion Processes 5-10 

5.3.2  Previous Coastal Hazard Studies 5-11 

5.3.3  Re-assessed Short Term Storm Bite 5-11 

5.3.4  Long Term Shoreline Movement 5-12  5.3.4.1  Updated Photogrammetric Analysis 5-12 

5.3.4.2  Adopted Recession Trend Rates 5-14 

5.3.4.3  Sea Level Rise Recession 5-14 

5.3.5  Erosion Hazard Assessment 5-15 

5.3.6  Coastal Entrance Instability 5-15 

5.3.7  Coastal Inundation Hazard 5-18 

LIST OF FIGURES IV

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5.3.8  Cudgera Creek Estuary Inundation 5-19 

5.4  Norries Head to Sutherland Point 5-21  5.4.1  Coastal Erosion Processes 5-21 

5.4.2  Previous Coastal Hazard Studies 5-23 

5.4.3  Short Term Storm Bite 5-23 

5.4.4  Long Term Shoreline Movement 5-25  5.4.4.1  Updated Photogrammetric Analysis 5-25 

5.4.4.2  Adopted Recession Trend Rates 5-28 

5.4.4.3  Sea Level Rise Recession 5-29 

5.4.5  Erosion Hazard Assessment 5-30 

5.4.6  Coastal Inundation Hazard 5-30 

5.5  Fingal Head/Letitia Spit 5-35  5.5.1  Coastal Erosion Processes 5-35 

5.5.2  Previous Coastal Processes and Hazard Studies 5-36 

5.5.3  Short Term Storm Bite 5-37  5.5.3.1  Updated Photogrammetric Analysis 5-37 

5.5.3.2  Adopted Recession Trend Rates 5-40 

5.5.3.3  Sea Level Rise Recession 5-40 

5.5.4  Erosion Hazard Assessment 5-41 

5.6  Coastal Inundation Hazard 5-42 

6  GLOSSARY OF TERMS 6-1 

7  REFERENCES 7-1 

APPENDIX A:  KINGSCLIFF EMBAYMENT PHOTOGRAMMETRY DATA A-1 

APPENDIX B:  TWEED SHIRE COASTAL HAZARD MAPS B-1 

LIST OF FIGURES

Figure 1-1 Regional coastline system – Clarence River to Moreton Bay 1-1 

Figure 1-2 Tweed Shire coastline 1-2  Figure 1-3 Tweed Shire coastal hazards assessment study area 1-3 

Figure 2-1 Late Quaternary sea level history 2-1 

Figure 2-2 Global sea level since 1870 2-2 

Figure 2-3 Typical beach and shore-face profile in study region 2-3 

LIST OF FIGURES V

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