F I N a L D R a F T 11/11/2008 Wrl Technical Report 2008/04 Es.2

COASTAL PROCESSES, COASTAL HAZARDS, CLIMATE CHANGE AND ADAPTIVE RESPONSES FOR PREPARATION OF A COASTAL MANAGEMENT STRATEGY FOR CLARENCE CITY, TASMANIA

by

J T Carley, M J Blacka, W A Timms, M S Andersen, A Mariani L D S Rayner, J McArthur and R J Cox A T N F 1 I A N F IO Technical Report 2008/04 R IS V October 2008 D E R

THE UNIVERSITY OF NEW SOUTH WALES SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING WATER RESEARCH LABORATORY

COASTAL PROCESSES, COASTAL HAZARDS, CLIMATE CHANGE AND ADAPTIVE RESPONSES FOR PREPARATION OF A COASTAL MANAGEMENT STRATEGY FOR CLARENCE CITY, TASMANIA

WRL Technical Report 2008/04 October 2008

by

J T Carley, M J Blacka, W A Timms, M S Andersen, A Mariani, D S Rayner, J McArthur and R J Cox

Water Research Laboratory School of Civil and Environmental Engineering Technical Report No 2008/04 University of New South Wales ABN 57 195 873 179 Report Status Final Draft Revision 1 King Street Date of Issue October 2008 Manly Vale NSW 2093 Australia

Telephone: +61 (2) 9949 4488 WRL Project No. 06071.02 Facsimile: +61 (2) 9949 4188 Project Manager James Carley

Title Coastal Processes and Hazards for Preparation of a Coastal Management Strategy for Clarence City, Tasmania

Author(s) J T Carley, M J Blacka, W A Timms, M S Andersen, A Mariani, D S Rayner, J McArthur and R J Cox

Client Name Clarence City Council

Client Address PO Box 96 Rosny Park TAS 7018 Client Contact Phil Watson

Client Reference

The work reported herein was carried out at the Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales, acting on behalf of the client.

Information published in this report is available for general release only with permission of the Director, Water Research Laboratory, and the client.

WRL TECHNICAL REPORT 2008/04 ES.1

EXECUTIVE SUMMARY

ES.1 CLIMATE CHANGE AND SEA LEVEL RISE

Climate change is occurring now and is expected to accelerate. Consideration has been given to six primary climate change variables in this report and 13 secondary climate change variables. Global sea level rise is the climate change variable most relevant to coastal management for which well accepted, quantified projections are available. Changes to atmospheric circulation, storm intensity and frequency are also of high importance to the coastal zone, however, well accepted quantification of likely changes is not available. The latest Intergovernmental Panel on Climate Change (IPCC, 2007a, b) Report provides numerous sea level rise scenarios for 2100. Simplified “mid” and “high” sea level rise scenarios developed by WRL for engineering application are shown in Table ES.1. Similar engineering scenarios were developed in NCCOE (2004). It should be noted that IPCC (2007a, page 17) addresses the doomsday scenario involving the total melting of the Greenland ice sheet (suggested timescale is millennia) which it estimates would elevate global sea levels by a further 7 m. Even more extreme postulations exist, including a rise of up to 70 m (GACGC, 2006) if all the world’s ice sheets were to melt, however, the timescale is considered to be millennia. The IPCC represents an international consensus position for planning purposes and has been used for this study. The maximum sea level rise scenario examined in this study, over the planning period to 2100, is 0.9 m.

Table ES.1 Simplified Engineering Estimates of Global Sea Level Rise (by WRL) based on IPCC (2001, 2007) and NCCOE (2004) Scenario Year 2050 2100 Adopted “Mid” scenario 0.2 0.5 Adopted “High” scenario 0.3 0.9

ES.2 COASTAL PROCESSES AND HAZARDS

The following coastal processes were considered within the constraints of available data and project resources for the Clarence coast:  Astronomical tides (predicted tides)  Tidal anomalies, through: o Barometric setup o Wind setup o Coastally trapped waves  Ocean swell waves F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 ES.2

 Local wind waves  Wave setup  Wave runup and overtopping  Longshore sand transport (littoral drift)  Onshore-offshore sand transport (beach erosion and recovery).

The following coastal hazards were considered within the constraints of available data and project resources:  Beach erosion and dune stability  Shoreline recession (long term change due to waves or sediment budget)  Beach rotation  Unstable creek or lake entrances  Wind blown sand  Coastal inundation  Stormwater erosion  Climate change, including sea level, changes to waves, wind and rainfall  Seawater ingress into groundwater table causing displacement of fresh water.

The following coastal hazards were not assessed in this study:  Slope, cliff or bluff instability (except for an allowance for houses on sand dunes)  Potential acid sulfate soils  Tsunami  Ecological change and threats.

Hazards have generally been assessed for 100 year average recurrence interval (ARI), 1% Annual Exceedance Probability (AEP) events, in line with most flood policies. Higher ARI events need to be considered for infrastructure of higher importance than private houses.

ES.3 ASSETS AT RISK

Figures showing potential inundation and erosion/recession have been derived from LIDAR surveys and the modelling undertaken, to indicate possible properties at risk. Indicative numbers of houses at risk are provided as an order of magnitude estimate. Individual properties that may have been identified at possible risk need to have detailed assessment undertaken, which (subject to the triggers adopted) may be at the time of proposed redevelopment. Indicative numbers of houses at risk due to erosion/recession are shown in Table ES.2, with indicative houses at risk due to inundation shown in Table ES.3. Some F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 ES.3

properties are at risk from both hazards, however, for this study, the hazards are treated separately, and may eventuate from different storm events. It is acknowledged that other infrastructure is also at risk, however, most of this services the houses which are present. The occurrence of inundation may result in no damage, or range from nuisance flooding for some properties to major damage. The amount of damage is dependent on the inundation level, floor level and construction materials and fittings. The values presented indicate the market value of the properties at risk, and provide an upper limit on potential losses if no adaptation is undertaken.

Table ES.2 Indicative Houses/Buildings at Risk due to Coastal Erosion and Recession Present 2050 mid 2050 high 2100 mid 2100 high SLR SLR SLR SLR Bellerive* 2 5 5 6 12 Howrah and Little Howrah Beach* 10 11 11 18 27 Seven Mile Beach west 1 1 2 3 11 Roches Beach, Lauderdale 19 108 108 125 195 Mays Beach 2 4 4 4 8 Cremorne (Ocean) Beach 9 36 38 44 53 Clifton (Ocean) Beach, west 3 7 7 10 12 South Arm Beach – Halfmoon Bay 9 13 18 23 43 Glenvar Beach *0 *0 *0 *0 *0 Opossum Bay *0 *0 *0 *0 *0

TOTAL NUMBER 55 185 193 233 361 POTENTIAL IMPROVED VALUE ($M) 28 93 97 117 181 * The likely presence of rock and/or a seawall may protect properties from erosion and recession, however, this has not been quantified. Such properties may also be vulnerable to wave impacts. Rock level needs to be mapped. Higher values cannot be excluded until this is undertaken

F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 ES.4

Table ES.3 Indicative Houses/Buildings at Risk due to Inundation Present Present 2100 high day depth day all SLR all > 0.3 m depths depths Montagu Bay 0 0 0 Kangaroo Bay 0 8 23 Bellerive 2 13 61 Little Howrah Beach 0 2 9 Rokeby Waste Water Treatment Plant 0 0 0 Roches Beach, Lauderdale – from South Arm Road, Ralphs Bay 101 161 491 Seven Mile Beach west 0 0 84 Roches Beach, Lauderdale * * * Mays Beach 0 0 0 Cremorne (Ocean) Beach * * * Cremorne – Pipe Clay Esplanade 15 95 118 Clifton – Bicheno St, Pipe Clay Lagoon 9 21 26 Clifton (Ocean) Beach, west * * * South Arm Neck – Ralphs Bay side Road Road Road Hope Beach, South Arm Neck - ocean side * * * South Arm Beach – Halfmoon Bay 2 5 8 Glenvar Beach ** ** ** Opossum Bay ** ** **

TOTAL NUMBER 129 305 820 POTENTIAL IMPROVED VALUE ($M) 65 153 410

* Inundation is possible from this side, but is potentially less severe than from the other side of the isthmus. ** Inundation is unlikely, but direct wave impacts are possible on beachfront structures.

ES.4 ADAPTIVE MANAGEMENT OPTIONS

IPCC (2001) listed three classes of adaptive management options, namely:

 Retreat  Accommodate  Protect

Practical management options include:  Planning controls, which deal with: o Building setbacks o Minimum floor levels o Appropriate engineering assessments o Appropriate construction techniques (e.g. piled buildings, flood resistant materials)  Planning controls which may also consider a development freeze in some locations  Physical works such as seawalls, groynes, dune management or sand nourishment, offshore breakwaters and/or surfing reefs  Ongoing monitoring, analysis and review of findings F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 ES.5

 Additional data collection or studies  A timeframe for review – currently 5 years for Council planning schemes.

This study was undertaken for most of the coast of the Clarence local government area. Therefore, broad and rapid assessment techniques were used which need to be followed with further detailed studies and monitoring. This study was not undertaken down to the level of quantified risk to single houses, however, numbers are presented to provide an order of magnitude. That is, costings provide an order of magnitude estimate only.

With the philosophy of managed/adaptive approach with multiple interventions, it is conservative to construct protective works now for high sea level rise in 2100, particularly if the provision to upgrade is incorporated in their design. It is prudent, however, to consider a range of sea level rise scenarios for future planning, as most of the present day risk is due to inadequate past planning.

Hard protection (in the form of seawalls) and soft protection (through sand nourishment, supplemented with groynes) are technically feasible (subject to additional studies). The cost of these protection options is generally less than the value of the assets protected for most locations, and for all sea level rise scenarios to 2100. The economic factors of adaptive management need to be balanced against environmental and social factors to achieve the optimum outcome. An example of a social factor is the continued availability of a recreational beach for use by non-beachfront residents. In reality, successful coastal management will usually combine elements of retreat, accommodate and protect.

ES.5 POTENTIALLY FEASIBLE ADAPTIVE MANAGEMENT OPTIONS

A summary of potentially feasible adaptive management options is shown in Table ES.4. Detailed development and design needs to be undertaken before implementing most of these options. Further details on the options are provided in the body of the report.

F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 ES.6

Table ES.4 Potentially Feasible Adaptive Management Options Retreat Raise Piled Seawall or Groynes and/or floors or buildings levee and/or setbacks land nourishme nt

Montagu Bay n/a  n/a present n/a Kangaroo Bay n/a  n/a present n/a Bellerive     ? Howrah and Little Howrah Beach     ? Rokeby and Droughty Point x  x  x Lauderdale - South Arm Road, Ralphs Bay ?  x  x Seven Mile Beach west    ? ? Roches Beach, Lauderdale      Mays Beach  x  x x Cremorne (Ocean) Beach      Cremorne – Pipe Clay Esplanade ?  x  x Clifton – Bicheno St, Pipe Clay Lagoon ?  x  x Clifton (Ocean) Beach, west    ? ? South Arm Neck – Ralphs Bay side x x x  x Hope Beach, South Arm Neck - ocean side x x x  x South Arm Beach - Halfmoon Bay     ? Glenvar Beach     x Opossum Bay     x  Feasible subject to detailed studies x Not feasible ? May be technically feasible, but unlikely to be economically feasible n/a not applicable (e.g. hard foreshore)

F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04

CONTENTS

1. INTRODUCTION 1 2. OVERVIEW OF COASTAL PROCESSES, HAZARDS, DATA AND LOCATIONS 2 2.1 Coastal Processes 2 2.2 Hazards 2 2.3 Available Data and Analysis 3 2.3.1 Land and Level Details 3 2.3.2 Bathymetry 4 2.3.3 Water Levels 4 2.3.4 Wave Data 4 2.3.5 Sea Level Rise 5 2.3.6 Barometric Pressure 5 2.3.7 Recession and Long Term Change 5 2.4 Locations Requiring Detailed Assessment 6 3. PROBABILITY, EXTREME EVENTS AND DESIGN EVENT 8 3.1 Overview 8 3.2 Terminology 8 3.3 Overview 9 3.4 Maritime Structures Standard 10 3.5 Building Code of Australia (2007) 11 3.6 NSW Floodplain Development Manual (2005) 11 3.7 FEMA USA (2000) 13 3.8 Tasmanian Building Act 2000 13 3.9 Extrapolation of Data to Extreme Events 13 3.10 Design Events considered in this Report 14 3.11 Freeboard for Floor Levels 14 4. CLIMATE CHANGE 16 4.1 Overview of Key and Secondary Climate Change Variables 16 4.2 Sea Level Rise 20 4.3 Sea level Rise adopted in other States 22 4.4 Quantification of Other Climate Change Variables 24 4.4.1 Climate Change Projections for Hobart 24 4.4.2 Wind Climate Change Projections and Sensitivity 24 4.4.3 DEFRA UK Allowances and Sensitivity 25 4.5 Gap Analysis 26 5. QUANTIFICATION OF EXTREME WATER LEVELS 27 5.1 Previous Analyses of Extreme Water Levels 27 5.2 Design Water Levels (Tide + Storm Surge) 28 5.3 Barometric Setup Component of Storm Surge 30 5.4 Local Effects – Local Wind Setup, Wave Setup and Wave Runup 31 6. OCEAN SWELL WAVES 32 6.1 Offshore Wave Climate Data 32 6.2 Direction of Extreme Offshore Waves 33 6.3 Extreme Offshore Waves 34 6.3.1 Background 34

i WRL TECHNICAL REPORT 2008/04

6.3.2 Other Studies 34 6.3.3 Extreme Waves Estimates for this Study 35 6.4 SWAN Modelling 37 6.5 Nearshore Extreme Swell Waves 38 6.6 Gaps and Further Analysis 40 7. LOCALLY GENERATED WIND WAVES AND BOAT WAVES 41 7.1 Procedure for Estimating Design Wind Wave Heights 41 7.2 Design Wind Speed 41 7.3 Fetch and Duration Limitations 42 7.4 Design Wind Wave Heights 42 7.5 Boat Waves 44 8. SUMMARY OF DESIGN WAVES 45 9. WIND SETUP MODELLING 46 9.1 Wind Setup Process 46 9.2 Modelling Wind Setup 46 10. WAVE SETUP, WAVE RUNUP AND INUNDATION 48 10.1 Wave Setup 48 10.2 Wave Runup 48 10.3 Wave Setup and Runup Levels 49 11. TSUNAMIS 51 12. EROSION HAZARD 53 12.1 Models Available 53 12.2 SBEACH Model 54 12.3 Statistical Models 55 12.3.1 Gordon Model 55 12.3.2 Deans et al (1994) 56 12.3.3 Thom and Hall (1991) 56 12.4 Sand Grading Curves 56 12.5 SBEACH Application to Clarence 57 12.5.1 Overview 57 12.5.2 Profiles 57 12.5.3 Water Levels 57 12.5.4 Wave Heights 58 12.5.5 Design Erosion Event and Storm Clustering 58 12.5.6 SBEACH Model Results 59 13. RECESSION HAZARD AND LITTORAL DRIFT 61 13.1 Littoral Drift Transport 61 13.2 Underlying Recession 61 13.3 Possible Causes of Underlying Recession 62 13.4 Future Recession and the Bruun Rule 63 13.4.1 Bruun Rule 63 13.4.2 Profile Closure Depth 64 13.4.3 Discussion on the Application of the Bruun Rule in other Jurisdictions 64 13.4.4 Application of Bruun Rule to Clarence 65 13.5 Gaps and Further Work 68 14. BEACH ROTATION 69

ii WRL TECHNICAL REPORT 2008/04

14.1 Description 69 14.2 Gaps and Future Studies 70 15. ENTRANCE STABILITY OF ESTUARIES 71 15.1 Overview of Entrance Stability 71 15.2 Acton Creek, Seven Mile Beach 71 15.3 Clarence Plains Rivulet, Droughty Point 71 15.4 Pipe Clay Lagoon, Cremorne 72 15.5 Un-named Creek Roches Beach North 72 15.6 Future Studies and Gaps 72 16. WIND BLOWN SAND 73 17. STORMWATER EROSION 75 18. SEAWATER INTRUSION INTO GROUNDWATER 76 18.1 Overview 76 18.2 Hydrogeological Setting 76 18.3 Groundwater Usage and Management 77 18.4 Potential Impacts of Sea Level Rise and Climate Change 78 18.5 Recommendations for Monitoring and Investigation 80 19. SUMMARY OF DESIGN WATER LEVELS 81 19.1 Overview 81 19.2 Present Day 82 19.3 2050 Design Water Levels 82 19.4 2100 Design Water Levels 84 19.5 Sensitivity to other Climate Change Variables 86 19.5.1 Overview 86 19.5.2 Peak Rainfall Intensity in Small Catchments 86 19.5.3 Offshore Wind Speed 87 19.5.4 Extreme Wave Height 87 20. SUMMARY OF ALLOWANCES FOR EROSION AND RECESSION 89 20.1 Overview 89 20.2 Allowances 89 21. RISK AREAS FOR COASTAL EROSION AND RECESSION HAZARDS 92 22. RISK AREAS FOR COASTAL INUNDATION 94 23. OVERVIEW OF ADAPTIVE MANAGEMENT OPTIONS 96 23.1 Overview of Adaptive Management Options 96 23.2 Risk and Timing of Adaptive Management Options 96 23.3 Clarence-Wide Adaptation Strategies 98 23.4 Adaptation Strategies and Costing 99 24. SITE SPECIFIC ADAPTATIVE MANAGEMENT OPTIONS 102 24.1 Opossum Bay 102 24.2 Glenvar Beach, Opossum Bay 104 24.3 Roches Beach, Lauderdale 106 24.4 Cremorne Ocean Beach, Pipe Clay Esplanade and Cremorne Avenue 109 24.5 Clifton Beach 112 24.6 Bicheno Street, Clifton 113 24.7 Howrah – Little Howrah Beach 114

iii WRL TECHNICAL REPORT 2008/04

24.8 Seven Mile Beach 115 24.9 South Arm Road at South Arm Neck 115 24.10 Bellerive – Bellerive Beach 116 24.11 Rokeby Sewage Treatment Works and Droughty Point, Rokeby 116 24.12 South Arm Beach – Half Moon Bay 117 24.13 Mays Beach 117 24.14 Montagu Bay and Kangaroo Bay 118 24.15 Other Potentially Vulnerable Areas not considered in this Study 118 25. CONCLUSIONS 119 25.1 Climate Change and Sea Level Rise 119 25.2 Coastal Processes and Hazards 119 25.3 Assets at Risk 120 25.4 Adaptive Management Options 122 25.5 Potentially Feasible Adaptive Management Options 123 26. REFERENCES AND BIBLIOGRAPHY 125

APPENDICES

A. SWAN MODELLING B. INUNDATION DEPTHS AND AVERAGE RECURRENCE INTERVALS

iv WRL TECHNICAL REPORT 2008/04

LIST OF TABLES

2.1 Matrix of Locations and Requirements 3.1 Probability of Exceedance for Given ARI Event and Project Life 3.2 Design ARI Event for Given Accepted Risk of Exceedance and Project Life 3.3 Design ARI Event for Various Structures (reproduced from AS 4997-2005 Table 5.4) 4.1 Interaction Matrix of Climate Change Variables for Clarence 4.2 IPCC (2007) Global Sea Level Rise Scenarios 4.3 Simplified Engineering Estimates of Global Sea Level Rise (by WRL) 4.4 Summary of Formal Policy or Common Practice Regarding Sea level Rise for Planning Purposes 4.5 Projected Climate Change for Hobart (from CSIRO, 2007) 4.6 Indicative Sensitivity Range of Climate Change Parameters (from DEFRA, 2006) 5.1 Published Tidal Planes for Hobart and Indicative Future Levels 5.2 Design Water Levels using Mid and High Range Sea Level Rise (SLR) Scenarios 5.3 Equivalent Present Day Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels and Future 100 year ARI event 5.4 Equivalent Future Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels Present Day 100 year ARI event 5.5 Extreme Low Barometric Pressures and the Tidal Anomalies they would Generate (for present day sea level) 6.1 Directional Order of Largest Waves to south-west of Tasmania from C-ERA-40 Dataset 6.2 Summary of Extreme Offshore Wave Heights 6.3 Summary of Extreme Offshore Wave Heights adopted for this Study 6.4 Summary of Nearshore Wave Coefficients modelled with SWAN (Hs = 1 m, Tp = 15 s) 6.5 Summary of Nearshore Wave Coefficients modelled with SWAN (Hs = 1 m, Tp = 20 s) 7.1 Design Wind Velocities (3 second Gust) 7.2 Fetch and Directional Wind Velocity Multipliers 7.3 Design Local Wind Waves 7.4 Typical Boat Wave Characteristics 8.1 Summary of 100 year ARI Design Waves 9.1 Local Wind Setup in Estuaries 10.1 Present Day 100 year ARI Wave Setup and Runup Levels 11.1 Notable Tsunami Events reaching Tasmanian or East Australian Coast 1858 to 2006 13.1 Commonly Used Input Parameters for Bruun Rule Application 13.2 Estimated Bruun Rule Profile Gradients 18.1 Bore Search of Mineral Resources Tasmania Database

v WRL TECHNICAL REPORT 2008/04

18.2 Potential Impacts of Climate Change on Groundwater Systems 19.1 Present Day 100 year ARI Wave Setup and Runup Levels 19.2 100 year ARI Wave Setup and Runup Levels for 2050 Mid Range Sea Level Rise 19.3 100 year ARI Wave Setup and Runup Levels for 2050 High Range Sea Level Rise 19.4 100 year ARI Wave Setup and Runup Levels for 2100 Mid Range Sea Level Rise 19.5 100 year ARI Wave Setup and Runup Levels for 2100 High Range Sea Level Rise 20.1 Allowances for Erosion and Recession (sandy ocean beaches only) 21.1 Indicative Houses/Buildings at Risk due to Coastal Erosion and Recession 22.1 Indicative Houses/buildings at Risk due to Inundation 23.1 Equivalent Present Day Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels and Future 100 year ARI event 23.2 Equivalent Future Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels Present Day 100 year ARI event 24.1 Summary of Adaptive Management Options for Opossum Bay 24.2 Summary of Adaptive Management Options for Glenvar Beach, Opossum Bay 24.3 Summary of Adaptive Management Options for Roches Beach, Lauderdale 24.4 Summary of Adaptive Management Options for Cremorne Ocean Beach 24.5 Summary of Adaptive Management Options for Clifton Beach 25.1 Simplified Engineering Estimates of Global Sea Level Rise (by WRL) 25.2 Indicative Houses/Buildings at Risk due to Coastal Erosion and Recession 25.3 Indicative Houses/buildings at Risk due to Inundation 25.4 Potentially Feasible Adaptive Management Options

vi WRL TECHNICAL REPORT 2008/04

LIST OF FIGURES

1.1 Location 2.1 Rock Foreshores 2.2 Council Survey Program, Roches Beach, Lauderdale 2.3 Bathymetry of Clarence Region 2.4 a-j Locations of Swell and Wind Wave Modelling 3.1 Balance between Risk and Construction Cost 4.1 Sea Level Rise Scenarios 5.1 Extreme Water Levels for Hobart (Present Day) 5.2 Change in ARI of Extreme events with Future Sea level Rise 5.3 Extreme Low Barometric Pressure for Hobart 6.1 Wave Buoy Locations 6.2a C-ERA-40 Data Area and Directional Probabilities 6.2b ERA-40 Wave Heights and Directions 6.3 Extreme Wave Heights – Global, Cape Sorell, Wedge Island and Eden 6.4 SWAN Modelling Domains for Coarse and Fine grid Models 6.5a,b SWAN Nearshore Wave heights for Select Locations 9.1 Illustration of Wind Setup and Barometric Setup 9.2 Wind Setup Modelling 12.1 Sand Grading Curves 12.2 Example of SBEACH Input and Output 13.1 Past Global Sea Level and Evolution of a Zeta Curve Beach Planform 13.2 Beach Change, Little Howrah Beach 13.3 Bambra Reef, Roches Beach, Lauderdale and Effect of Reduced Salient Control 13.4 Bruun Rule 13.5 Beach Profiles of Clarence 15.1 Unstable Sand Spits near Estuary and Creek Mouths 15.2 Acton Creek, Seven Mile Beach 15.3 Clarence Plains Rivulet, Droughty Point and Rokeby Beach 15.4 Pipe Clay Lagoon Cremorne Protection Works 15.5 Access along Pipe Clay Lagoon to Southern Cremorne Properties 15.6 Un-named Creek, Roches Beach North, Lauderdale 16.1 Beach Access Points at Roches Beach, Lauderdale 17.1 Stormwater Infrastructure, Bellerive and Howrah 17.2 Damaged Stormwater Outfall, Roches Beach, Lauderdale 21.1 Dune Stability Scheme 21.2 Erosion and Recession Hazard Lines – Bellerive 21.3 Erosion and Recession Hazard Lines – Little Howrah 21.4 Erosion and Recession Hazard Lines – Seven Mile Beach west 21.5a-d Erosion and Recession Hazard Lines – Roches Beach Lauderdale

vii WRL TECHNICAL REPORT 2008/04

21.6 Erosion and Recession Hazard Lines – Mays Beach 21.7 Erosion and Recession Hazard Lines – Cremorne (Ocean) Beach 21.8 Erosion and Recession Hazard Lines – Clifton (Ocean Beach), south 21.9 Erosion and Recession Hazard Lines – Hope Beach, South Arm Neck – ocean side 21.10 Erosion and Recession Hazard Lines – South Arm Beach – Halfmoon Bay 22.1 Potential Inundation Areas – Montagu Bay 22.2 Potential Inundation Areas – Kangaroo Bay 22.3 Potential Inundation Areas – Bellerive 22.4 Potential Inundation Areas – Howrah and Little Howrah 22.5 Potential Inundation Areas – Rokeby and Droughty Point 22.6a-d Potential Inundation Areas – Lauderdale from Ralphs Bay Side 22.7 Potential Inundation Areas – Seven Mile Beach, west 22.8a-c Potential Inundation Areas – Roches Beach, Lauderdale from ocean side 22.9 Potential Inundation Areas – Mays Beach 22.10 Potential Inundation Areas – Cremorne (Ocean) Beach from ocean side 22.11 Potential Inundation Areas – Cremorne Pipe Clay Esplanade 22.12 Potential Inundation Areas – Clifton, Bicheno Street, Pipe Clay Lagoon 22.13 Potential Inundation Areas – Clifton (Ocean) Beach, south from ocean side 22.14 Potential Inundation Areas – South Arm Neck – Ralphs Bay side 22.15 Potential Inundation Areas – South Arm Beach – Halfmoon Bay 23.1 Adaptive Management Options 23.2 Examples of Raised Houses 23.3 Examples of Seawalls 23.4 Examples of Groynes 23.5 Example of Dune Management 23.6 Example of Sand Nourishment 23.7 Risk and Timing of Adaptive Management Options

viii WRL TECHNICAL REPORT 2008/04 1.

1. INTRODUCTION

The City of Clarence is located to the east of Hobart as shown in Figure 1.1. The purpose of this study is to identify localities and infrastructure within Clarence City which may be vulnerable to coastal hazards, both at present, and due to sea level rise and climate change into the future. Coastal hazards have been assessed for the present day, 2050 and 2100. Figures showing potential inundation and erosion/recession have been derived from LIDAR surveys and the modelling undertaken, to indicate possible properties at risk. Indicative numbers of houses at risk are provided as an order of magnitude estimate. Individual properties that may have been identified at possible risk need to have detailed assessment undertaken, which (subject to the triggers adopted) may be at the time of proposed redevelopment. The study also investigates adaptive management options in response to present and future coastal hazards.

1 WRL TECHNICAL REPORT 2008/04 2.

2. OVERVIEW OF COASTAL PROCESSES, HAZARDS, DATA AND LOCATIONS

2.1 Coastal Processes

There is some overlap as to what may be defined as a coastal process versus a coastal hazard. In this report, coastal hazards are defined as the consequences of coastal processes which affect the built environment or the safety of people. The following coastal processes are applicable to the study area and are assessed or discussed in subsequent sections:

 Astronomical tides (predicted tides)  Tidal anomalies, through:

o Barometric setup o Wind setup o Coastally trapped waves  Ocean swell waves  Local wind waves  Wave setup  Wave runup and overtopping  Longshore sand transport (littoral drift)  Onshore-offshore sand transport (beach erosion and recovery).

2.2 Hazards

The following coastal hazards may impact the study area:

 Beach erosion  Shoreline recession (long term change due to waves or sediment budget)  Unstable creek or lake entrances  Wind blown sand (if it affects buildings or infrastructure)  Coastal inundation  Slope, cliff or bluff instability (not assessed – see below)  Stormwater erosion

2 WRL TECHNICAL REPORT 2008/04 3.

 Climate change, including sea level, changes to waves, wind and rainfall  Tsunami (see below)  Seawater ingress into groundwater table causing displacement of fresh water  Potential acid sulfate soils (not assessed in this study).

The list is not exhaustive. An further example of a hazard not assessed in this study is sedimentation of marinas and navigation channels. Considerable discussion was provided in Sharples (2006) on slope instability, including citing previous landslide risk studies undertaken. A separate detailed geotechnical assessment could be undertaken as resources become available, but was not part of this study. It is noted that many of the soft rock foreshores around Clarence are eroding (Figure 2.1), which needs to be considered in the geotechnical assessment.

Tsunami hazard is being assessed by the SES, BOM and Geoscience Australia. An overview of tsunami history is presented in this report but quantification of the risk has not been undertaken.

2.3 Available Data and Analysis

An overview of available data is provided below, with more detailed discussion in the relevant section of the report.

2.3.1 Land and Level Details

Land levels were initially predominantly obtained from Council’s GIS system which provided contours at 2 m intervals for most locations. Additional data was available from Council’s survey program of Roches Beach (Figure 2.2).

The 2 m contour interval data is better than most areas of Australia and is suitable for an initial “second pass” assessment, but is still coarse for detailed coastal assessment, particularly when it is proposed to incorporate the results into Council’s planning scheme. High quality data to a resolution of between 0.2 and 0.5 m or better is desirable. There was insufficient initial data available for detailed modelling of the inundation depth on roads.

In light of the limitations, during the progress of this study, the state government undertook detailed surveys of land areas using LIDAR (Light Detection and Ranging) to an accuracy of 0.20 m vertical and 0.4 to 1.0 m horizontal. The “bare earth” layer from the LIDAR data

3 WRL TECHNICAL REPORT 2008/04 4.

was used for this study. This is the first major use of LIDAR data for a study of this type in Tasmania.

2.3.2 Bathymetry

Bathymetry was obtained from the TAFI (Tasmanian Aquaculture and Fisheries Institute) dataset (Figure 2.3) supplemented with bathymetric charts AUS 794 and 171. AUS 171 provides reasonable details of the shallow depths in Ralphs Bay and Pipe Clay Lagoon, which is sufficient to determine an initial inundation level, but not a water depth in shallow areas.

The TAFI dataset was comprehensive for most of the open coast locations studied. There was insufficient data inside the shallow lagoons (Ralphs Bay and Pipe Clay Lagoon) for accurate inundation modelling, so the AUS 171 chart was used there. The bathymetric surveys need to be repeated at regular intervals to map evolution of the seabed over short and long time periods.

2.3.3 Water Levels

Tide gauges exist for Hobart and Spring Bay. The Spring Bay gauge is operated by the BOM and has only been operational since 1991. Archival records indicate that tide measurements have been undertaken for Hobart since at least 1874, with the first permanent tide gauge installed in 1889 (Hunter, 2007). Digital data from the Hobart gauge is available from 1960, but has had numerous problems with the datum. These were investigated by Dr John Hunter from the University of Tasmania (Hunter, 2007), which resulted in approximately 32 years of useable data. There is little that can be done to recover past lost data beyond that reported in Hunter (2007).

The current water level data collection program is good. The only gap is for water levels inside lagoons (Pipe Clay and Ralphs Bay) which may be affected by attenuation from the ocean and/or elevation due to inflows, rainfall or local wind setup. It is understood that such measurements may be being undertaken for the proposed Ralphs Bay development, but this data is not yet publically available.

2.3.4 Wave Data

A wave buoy has been operated off Cape Sorell near Strahan by the Bureau of Meteorology since 1998. Previous CSIRO buoys have operated there from 1985 to 1992 and at other

4 WRL TECHNICAL REPORT 2008/04 5.

locations within Storm Bay for short durations. Information is provided in Reid and Fandry (1994). The Cape Sorell buoys have not measured wave direction.

A non-directional wave buoy has operated off Eden NSW since 8 February 1978 (Lord and Kulmar, 2000).

The Eden and Cape Sorell wave data is of high quality, but neither buoy is directional. No long term buoy exists off south or south-east Tasmania.

The ERA-40 and C ERA-40 dataset (Caires and Sterl, 2005; Hemer, 2007) has hindcast global wave heights from global weather models, but this has not been calibrated to or verified against southern hemisphere wave buoy data.

An HF RADAR wave monitoring system has been proposed for offshore of south-eastern Tasmania and would provide wave directional data if implemented.

2.3.5 Sea Level Rise

Historical sea level rise for Port Arthur dating back to 1841 is published in Hunter, Coleman and Pugh (2003). More recent sea level rise data for Spring Bay is available from the BOM and is updated monthly. An extensive review of Hobart’s tide gauge data was undertaken in Hunter (2007).

2.3.6 Barometric Pressure

Approximately 100 years of data are available for Ellerslie Road and 49 years of data from Hobart Airport from the Bureau of Meteorology. Low barometric pressure causes the ocean to rise at a rate of approximately 1 cm for each hPa of pressure drop, provided there is sufficient time to equilibrate.

2.3.7 Recession and Long Term Change

Long term shoreline change data has recently been derived from aerial photos for Roches Beach Lauderdale by Sharples (2007). This analysis is two dimensional only, with the plan position of shoreline features being mapped.

It would be prudent to undertake similar analyses for other developed shorelines within Clarence, however, this is beyond the scope of this project.

5 WRL TECHNICAL REPORT 2008/04 6.

The principal data limitation foreseen for assessing long term change is for Opossum Bay (and Little Howrah Beach), where development is so close to the water that it has removed all natural shoreline features which could be mapped two dimensionally. The only solution for these locations would be three dimensional photogrammetry to map the change in subaerial beach volume, however, this is beyond the scope for this project.

2.4 Locations Requiring Detailed Assessment

A list of locations for which infrastructure may be at risk from coastal hazards is shown in Table 2.1, with the modelling locations shown in Figures 2.4a-j. The list is based on WRL’s initial site inspections and discussions with Council. The priority order is approximate only.

Erosion and haphazard protection works has been reported on Barilla Bay on Pitt Water (Sharples, personal communication, 2008). This is affecting freehold land, however, the present development densities are low, and there is no public access to these foreshores. Five Mile Beach, which also fronts Pitt Water on the northern side of the Seven Mile Beach spit is also eroding (Sharples, personal communication, 2008), however, there is no development at risk. Detailed assessment for both these locations was beyond the scope of this report, but may require consideration in the future.

6 WRL TECHNICAL REPORT 2008/04 7.

Table 2.1 Matrix of Locations and Requirements Location Processes Hazard Definition Deliverables in suggested priority order

Groundwater on into

Priority Order Anomalies Tidal Tide and Waves Extreme Offshore Penetration Swell Wave Waves Local Wind Erosion Recession Stability Entrance Sand Wind Blown Inundation Open Coast Inundation Lagoon /Bay Stability Cliff/Bluff Stormwater Rise Level Sea Tsunami Intrusi Seawater Socio Economic Study Assets of Threatened Value Estimate Management Options Consultation Community Zones Hazard and Reporting SINGLE REPRESENTATIVE LOCATION   ALL LOCATIONS  o   o  o     INDIVIDUAL LOCATIONS (below) 1 Opossum Bay      2 Roches Beach, Lauderdale      3 Clifton – Bicheno St, Pipe Clay Lagoon   4 Cremorne – Pipe Clay Esplanade    5 Little Howrah and Howrah Beaches       6 Cremorne (Ocean) Beach       7 Rokeby Waste Water Treatment Plant   8 Lauderdale - South Arm Road, Ralphs Bay   9 South Arm Neck (Ralphs Bay side)   10 Hope Beach, South Arm Neck     11 Seven Mile Beach – western 1 km only       12 Mays Beach      13 Clifton (Ocean) Beach, western 500 m only     14 Glenvar Beach      15 South Arm Beach (Halfmoon Bay)      16 Bellerive Beach       17 Kangaroo Bay   18 Montagu Bay    Assessment undertaken in this study o By others in separate or future study

7 WRL TECHNICAL REPORT 2008/04 8.

3. PROBABILITY, EXTREME EVENTS AND DESIGN EVENT

3.1 Overview

This section may be skipped by the reader, unless a deeper understanding of the “design” event is sought. As a rule, a 100 year ARI (1% AEP) event (see below for definitions) has been used for assessment in this report. The theory, justification and policies behind this are provided below. Also discussed below is that a 100 year ARI (1% AEP) event may not always be the most appropriate for design.

3.2 Terminology

The following definitions are provided, adopted from Pilgrim (1987):

Average Recurrence Interval (ARI): The average time between exceedances (e.g. large wave height or high water level) of a given value Also known as Return Period.

Annual Exceedance Probability (AEP): The probability (expressed as a percentage) of an exceedance (e.g. large wave height or high water level) in a given year.

Project Life (N): Also known as planning timeframe or planning horizon.

Encounter Probability: The chance of exceedance over the project life.

The use of ARI, though superficially simple, has been criticised as misleading some stakeholders, who may believe that the event will recur only at regular intervals. This is particularly the case when it is described as Return Period, which connotes some sort of regularity in the event.

AEP has been enshrined in many policies and regulations (Sections 3.2 to 3.6), in particular a 1% AEP, which is reasonably well understood. However, AEPs less than this are harder to comprehend. For example, 0.02% AEP is generally more difficult to comprehend than the equivalent 5000 year ARI. Generally both AEP and ARI values are used in this report. Pilgrim (1987) indicated that ARI was the appropriate term for expressing probability for “partial series”, whereas AEP was the appropriate term for expressing probability for “annual series” (refer to Pilgrim, 1987; or probability texts for definitions of these).

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 9.

3.3 Overview

The most widely accepted overview of probability and risk in Australian water engineering is provided in Pilgrim (1987). Additional material is provided in British Standard 6349; Borgman, 1963; Kite, 1988. The selection of a level of risk can be expressed by the following equations (British Standard 6349; Borgman, 1963; Kite, 1988), with tabulated values presented in Tables 3.1 and 3.2. For “partial series” (the method used for wave and water level analysis in this study) but not “annual series”, Pilgrim (1987) expressed the probability as:

(3.1)

The required design ARI can be determined by manipulating equation 3.1 to

(3.2)

The equivalent AEP for an ARI is

(3.3)

For an ARI of about 10 years or more, equation 3.3 can be approximated by

(3.4) where ARI is average recurrence interval in years P is the accepted probability of exceedance (range 0 to 1, with 0 being “no chance” of exceedance and 1 being 100% probability of exceedance) N is the expected project life in years AEP is the annual exceedance probability e is the transcendental constant used as the base to natural logarithms (≈ 2.7182818).

It has been normal engineering practice in Australia to use the 100 year ARI (1% AEP) event for design of “permanent” coastal structures. The 100 year ARI event is the generally accepted balance between risk and initial capital cost, however, specific projects need to be assessed individually (see below). It is noteworthy that many of the coastal defences of the Netherlands are designed for a 10,000 year ARI (0.01% AEP) event, which has a 1% chance of being exceeded over 100 years (Delta Committee, 1962). Pilgrim (1987, p247)

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 10.

noted that encounter probability “can assist in making an essentially subjective decision about an acceptable “risk of failure””.

Table 3.1 Encounter Probability (Probability of Exceedance) for Given ARI and Project Life Probability of Exceedance (%) for Design ARI (years) ARI 1 2 5 10 20 50 100 500 1000 2000 10000 AEP 63.21% 39.35% 18.13% 9.52% 4.88% 1.98% 1.00% 0.20% 0.10% 0.05% 0.01% Project Life (years) 1 63.21% 39.35% 18.13% 9.52% 4.88% 1.98% 1.00% 0.20% 0.10% 0.05% 0.01% 2 86.47% 63.21% 32.97% 18.13% 9.52% 3.92% 1.98% 0.40% 0.20% 0.10% 0.02% 5 99.33% 91.79% 63.21% 39.35% 22.12% 9.52% 4.88% 1.00% 0.50% 0.25% 0.05% 10 100.00% 99.33% 86.47% 63.21% 39.35% 18.13% 9.52% 1.98% 1.00% 0.50% 0.10% 20 100.00% 100.00% 98.17% 86.47% 63.21% 32.97% 18.13% 3.92% 1.98% 1.00% 0.20% 50 100.00% 100.00% 100.00% 99.33% 91.79% 63.21% 39.35% 9.52% 4.88% 2.47% 0.50% 100 100.00% 100.00% 100.00% 100.00% 99.33% 86.47% 63.21% 18.13% 9.52% 4.88% 1.00%

Table 3.2 Design ARI Event for Given Accepted Risk of Exceedance and Project Life Project Required Design ARI (years) for Accepted Risk of Failure (Encounter Probability) Life (years) 1% 2% 5% 10% 20% 25% 33% 50% 75% 90% 95% 99% 1 99 49 19 9.5 4.5 3.5 2.5 1.4 0.7 0.4 0.3 0.2 2 199 99 39 19 9.0 7.0 5.0 2.9 1.4 0.9 0.7 0.4 5 497 247 97 47 22 17 12 7.2 3.6 2.2 1.7 1.1 10 995 495 195 95 45 35 25 14 7.2 4.3 3.3 2.2 20 1990 990 390 190 90 70 50 29 14 8.7 6.7 4.3 50 4975 2475 975 475 224 174 125 72 36 22 17 11 100 9950 4950 1950 949 448 348 250 144 72 43 33 22

3.4 Maritime Structures Standard

AS 4997-2005 Guidelines for the Design of Maritime Structures was first released in 2005. The recommended design event from this standard for various structures is shown in Table 3.3. Although this standard may not be directly applicable to houses and infrastructure, application of the standard for houses (normal structures or high property value) indicates that a 1000 to 2000 year ARI (0.1 to 0.05% AEP) event should be used. The standard states the need to consider freeboard but does not suggest an amount.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 11.

Table 3.3 Design ARI Event for Various Structures (reproduced from AS 4997-2005 Table 5.4) Design ARI Event for Design Working Life (years) Function Category 5 or less 25 50 100 or more category description (temporary (small craft (normal (special works) facilities) maritime structures/ structures) residential developments) 1 Structures 20 50 200 500 presenting a low degree of hazard to life or property 2 Normal structures 50 200 500 1000 3 High property 100 500 1000 2000 value or high risk to people

3.5 Building Code of Australia (2007)

The predominant development around Clarence foreshores is freestanding detached private housing. Table B1.2a of the Building Code of Australia (BCA, 2007) classifies such houses as Importance Level 2: Buildings or structures not included in Importance Level 1, 3 or 4. Table B1.2b from BCA (2007) specifies the following design average recurrence intervals (ARI) for Importance Level 2 buildings:

Wind load: 500 years ARI (0.2% AEP) Snow load: 150 years ARI (0.67% AEP) Earthquake: 500 years ARI (0.2% AEP).

No design event is specified in BCA (2007) for inundation, erosion, wave forces or tsunami.

3.6 NSW Floodplain Development Manual (2005)

The NSW Floodplain Development Manual (NSW Government, 2005) also discussed extreme events as follows:

“The 1% AEP standard is used widely in the National Flood Insurance Program in the United States of America. The special flood hazard areas are within the 100 year average recurrence interval flood boundary, or inundated to a depth of more than 1 foot (approximately 0.3 metres) in the 1% flood.

However there is concern that the 1% AEP standard, which was established as a minimum

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 12.

standard, has been interpreted by many as the level above which one does not need to worry about flooding. Historically, approximately one third of claims paid under the National Flood Insurance Program are for flood damage in areas above the 1% AEP flood level. More flood damage is sustained by property outside the area covered by the 1% AEP flood than is sustained inside the 1% AEP flood area. The 500 year (0.2% AEP) flood level is also used as a flood standard. It is the general practice for critical or high hazard facilities to be protected from or located above from the 0.2% AEP flood. Critical facilities are those properties that, if flooded, would result in severe consequences to public health and safety. Critical facilities in a town might include fire, ambulance and police stations, hospitals and nursing homes, schools, water and electricity supply installations, interstate highways, the bus station and chemical plants.”

“In the south-west of the Netherlands, the delta plan has been implemented with the aim of guaranteeing protection against the North Sea storm event which has an estimated 1 in 10,000 chance of occurring each year. For most of the river dykes along rivers such as the Rhine and the Ijssel, the accepted design event is the 1 in 1250 event. Along the Meuse, where flooding has been a lesser problem, measures are being taken to reduce the average chance of water damage in towns to 1 in 250 per year.”

The NSW Floodplain Development Manual (2005) stated that although 100 year ARI (1% AEP) has commonly been adopted as a flood planning level in Australia, higher flood planning levels may be necessary for aged care facilities and other types of developments with particular evacuation or emergency response issues. Furthermore, it stated that there can be problems with adopting a standard level of risk such as 100 year ARI (1% AEP), namely:

 It tends to preclude investigation of risk levels that may be more critical to the community, particularly in relation to evacuation and recovery strategies

 It can lead to minimal consideration or planning for larger floods, having provided a false sense of security that the 100 year ARI (1% AEP) flood event is the limit of flooding.

The NSW Floodplain Development Manual (2005) encouraged consideration of the full range of floods (up to and including the Probable Maximum Flood) when determining flood planning levels. The manual stated that flood planning levels should be determined on the basis of social, economic, cultural and environmental factors, as well as flooding considerations.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 13.

The encouragement to consider events up to and including the Probable Maximum Flood was overwritten by a Planning Circular in January 2007. NSW Planning Circular PS 07- 003 (31 January 2007) suggested that for residential development, unless there are exceptional circumstances, a flood planning level based on the 100 year ARI (1% AEP) event plus a typical freeboard of 0.5 m should be used. This is consistent with past practice.

3.7 FEMA USA (2000)

The USA Federal Emergency Management Authority (FEMA) in its Coastal Construction Manual (FEMA, 2000 page 11-16) recommends a 100 year ARI (1% AEP) design event for a “coastal residential building” and a 1000 year ARI (0.1% AEP) design event for a “high occupancy building or critical facility”. FEMA (2000) uses 1 foot (0.3 m) as freeboard in example calculations but does not specify a value.

3.8 Tasmanian Building Act 2000

The Tasmanian Building Act 2000, section 159 states that “….the floor level of each habitable room in the building is 300 millimetres or more above the prescribed designated flood level for that land”.

For a specific list of 10 watercourse floodplains (not including the study area), the Tasmanian Building Regulation 2004 prescribes a 1% AEP event (100 year average recurrence interval – ARI). For oceanic inundation, the most relevant clause of the Tasmanian Building Regulation 2004 (S.R. 2004, No. 43) is 12 (c) which states that the designated flood level is “600 millimetres above the ordinary high-water mark of the spring tide for land on which flooding is affected by the rise and fall of the tide”. This terminology (ordinary high-water mark) in no longer in common use, but has been interpreted as mean high water springs (MHWS) or mean higher high water (MHHW).

While not stated in the legislation, the reason for freeboard is usually to allow for uncertainty in the calculations, localised effects and local wind waves. In some jurisdictions, the legislated freeboard also allows for future sea level rise.

3.9 Extrapolation of Data to Extreme Events

The greatest difficulty in developing a 100 to 2000 to 10000 year ARI event is that it is based on only approximately 30 years of water level data for Hobart (Hunter, 2007),

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 14.

necessitating substantial extrapolation. Numerous extreme value distributions are available, such as Weibull, Gumbel, Fisher-Tippett, Log-Pearson-3 and Log-normal. A detailed assessment of each of these techniques is beyond the scope of this report, however, the uncertainties in such extrapolation are addressed through the addition of an appropriate freeboard or factor of safety on the design condition. Pugh (1987, page 272) suggested that as a general rule, extrapolation should be limited to three to four times the record length, which was repeated in Hunter (2007) and equates to a 90 to 120 year ARI event when the data set is limited to 30 years.

3.10 Design Events considered in this Report

In the absence of BCA (2007) specifications for inundation or wave forces, design conditions for a 100 year ARI (1% AEP) event (for inundation and erosion) are presented in this report for a 50 to 100 year design life and planning period. It is emphasised that a 100 year ARI event has a 40% chance of being exceeded over a 50 year planning period and a 63% chance of being exceeded over a 100 year planning period. The justification for the use of a 100 year ARI (1% AEP) design event is shown in Figure 3.1 from Kite (1988). The capital cost of building structures to withstand larger events increases, whereas, where lives are not at risk, the cost of damages is highest for structures designed only for minor events. The hypothetical example from Kite (1988) shows that when the capital cost and damages are summed, the 100 year ARI (1% AEP) event has the lowest overall cost. Kite (1988) added that there are few real world situations where such costing can be, or is, undertaken comprehensively due to the complexity.

More extreme events having 2000 and 10000 year ARIs are also presented so that the sensitivity and uncertainty can be considered, however, due to the short record of available data, the quantification of these rare events is speculative.

Episodic inundation or wave attack may not be catastrophic for a development designed to cope with such conditions.

3.11 Freeboard for Floor Levels

As stated above, the design floor level for houses and other development needs to be above the calculated design inundation water level through the incorporation of freeboard. The reason for freeboard is usually to allow for uncertainty in the calculations, localised effects and local wind waves. Specified freeboard in various jurisdictions is generally 0.3 to 0.5 m.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 15.

The Tasmanian Building Act 2000, section 159 specifies a 0.6 m freeboard above the “ordinary high-water mark”. The “ordinary high-water mark” (interpreted as MWHS by WRL) is less than highest astronomical tide and a 100 year ARI (1% AEP) water level. Presumably the 0.6 m freeboard specified in this case is to allow for more elevated water levels.

For the case where the calculated (“designated”) flood level is known, the current Tasmanian Building Act 2000, section 159 prescribes a freeboard of 0.3 m above the calculated (“designated”) flood level. This 0.3 m freeboard value is within the range adopted in other jurisdictions and has been adopted for this study.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 16.

4. CLIMATE CHANGE

4.1 Overview of Key and Secondary Climate Change Variables

NCCOE (2004) lists six key environmental variables applicable to coastal engineering, namely:

1. Mean Sea Level 2. Ocean Currents and Temperature 3. Wind Climate 4. Wave Climate 5. Rainfall/Runoff 6. Air temperature.

A growing body of research has found that ocean acidification (pH lowering) may be occurring, and this could be considered an additional key variable.

NCCOE (2004) also lists 13 secondary or process variables applicable to coastal engineering, namely:

1. Local Sea Level 2. Local Currents 3. Local Winds 4. Local Waves 5. Effects on Structures 6. Groundwater 7. Coastal Flooding 8. Beach Response 9. Foreshore Stability 10. Sediment Transport 11. Hydraulics of Estuaries 12. Quality of Coastal Waters 13. Ecology.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 17.

The key and secondary variables can be combined into a matrix for project assessment as shown in Table 4.1. Detailed assessment where indicated in Table 4.1 is presented in Sections 5 to 10. There is high uncertainty in the quantification (or no quantification) of many of the variables or their change, so the use of a high ARI event (e.g. 100, 2000 or 10000 year) and factors of safety (such as freeboard) need to be introduced to manage the risk of uncertainty.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 18.

Table 4.1 Interaction Matrix of Climate Change Variables for Clarence Key Variable Mean Sea Level Ocean Currents Wind Climate Wave Climate Rainfall / Runoff Air temperature Ocean Acidity and Temp Local Sea Level - assessed in detail - not quantified - quantified with - quantified with - not quantified - minor effect - no effect - possible sensitivity analysis sensitivity analysis - considered additional or - possible seasonal - managed through qualitatively in seasonal changes to and extreme large ARI design lagoon processes water level changes event and freeboard - managed through - managed through large ARI design large ARI design event and freeboard event and freeboard Local Winds - no effect - minor effect - change not - no effect - no effect - minor sea breeze - no effect quantified effects - managed through large ARI design event and freeboard Local Waves - minor effect - minor effect - quantified with - assessed in detail - no effect - minor sea breeze - no effect sensitivity analysis - managed through wind wave effects - managed through large ARI design large ARI design event and freeboard event and freeboard Effects on - effects on - minor effect - change not - major effect on - runoff change - no direct effect - possible long term Structures overtopping quantified the design of future needs consideration changes to considered - managed through protection works in design of durability of large ARI design stormwater and structures, but not event and freeboard sewer, but not assessed quantified

F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 19.

Mean Sea Level Ocean Currents Wind Climate Wave Climate Rainfall / Runoff Air temperature Ocean Acidity and Temp Groundwater - assessed - minor indirect - minor indirect - minor effect - assessed - minor indirect - may change qualitatively effect effect qualitatively effect groundwater pH Coastal Flooding - assessed in detail - minor effect - quantified with - change not - assessed - minor indirect - no effect sensitivity analysis quantified qualitatively effect - managed through - managed through - runoff needs large ARI design large ARI design consideration in event and freeboard event and freeboard design of stormwater system Beach Response - assessed in detail - minor effect - assessed - assessed - minor effect - minor effect - no effect qualitatively qualitatively - future studies - future studies recommended recommended Foreshore - assessed in detail - minor effect - assessed - assessed in detail - assessed - no direct effect - no effect Stability qualitatively - future studies qualitatively recommended - minor effect around outfalls and creeks

Sediment - assessed in detail - minor effect - assessed in detail - assessed in detail - no effect - no effect Transport - future studies - future studies recommended recommended Hydraulics of - qualitative - qualitative - qualitative - qualitative - qualitative - minor effect - no direct effect Estuaries comment only comment only comment only comment only comment only - studies, modelling - studies, modelling - studies, modelling - studies, modelling - studies, modelling and monitoring and monitoring and monitoring and monitoring and monitoring needed needed needed needed needed Quality of Coastal - not in this study - not in this study - not in this study - not in this study - not in this study - not in this study - not in this study Waters Ecology - not in this study - not in this study - not in this study - not in this study - not in this study - not in this study - not in this study

F I N A L D R A F T 11/11/2008 WRL TECHNICAL REPORT 2008/04 20.

4.2 Sea Level Rise

The Intergovernmental Panel on Climate Change (IPCC) have produced major reports in 1990, 1996, 2001 and 2007. Hence the 2007 report is known as the Fourth Assessment Report (AR4) and the 2001 report the Third Assessment Report (TAR). The latest IPCC Summary for Policymakers Report (IPCC SPM, 2007a) and Working Group 1 Report (IPCC, 2007b) provide numerous sea level rise scenarios for 2090 to 2100. Values for 2050 are not available in the Summary Report or Working Group 1 2007 reports. The IPCC (2007b) scenarios have been reproduced in Table 4.2.

Simplified “mid” and “high” sea level rise scenarios developed by WRL for engineering application are shown in Table 4.3. Similar engineering scenarios were developed in NCCOE (2004) (reproduced in Figure 4.1 of this report) based on the IPCC (2001) scenarios and are almost identical when ice melt is included and the end date is extended to 2100. As such, the NCCOE (2004) values for 2050 have been used (since no IPCC, 2007a, b values are available).

IPCC SPM (2007a) stated, “TAR projections were made for 2100, whereas projections in this Report are for 2090-2099. The TAR would have had similar ranges to those in Table SPM-2 if it had treated the uncertainties in the same way.”

The 2100 “mid” sea level scenario shown in Table 4.3 was estimated using the following assumptions detailed in Table 4.2 and IPCC (2007b, Table 10.7):

 Averaging the central values for the six emission scenarios: 0.34 m  Adding a central value for ice melt: 0.06 m  Extending to from 2095 to 2100 (by 5 years at 5.6 mm/year) 0.03 m  Which gives an actual total of 0.43 m, which was round to: 0.5 m.

The “high” sea level scenario shown in Table 4.3 was estimated using the following assumptions detailed in Table 4.2 and IPCC (2007b, Table 10.7) for the A1FI emission scenario:

 Sea level rise (excluding accelerated ice melt): 0.59 m  Upper value for ice melt: 0.17 m  Extending to from 2095 to 2100 (by 5 years at 13.6 mm/year) 0.07 m  Which gives an actual total of 0.83 m, which was round to: 0.9 m.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 21.

IPCC (2007a, page 17) addresses a doomsday scenario involving the total melting of the Greenland ice sheet (suggested timescale is millennia) which it estimates would elevate global sea levels by a further 7 m. Even more extreme postulations exist, including a rise of up to 70 m (GACGC, 2006) if all the world’s ice sheets were to melt, however, the timescale is considered to be millennia. The IPCC represents an international consensus position for planning purposes.

Table 4.2 IPCC (2007b) Global Sea Level Rise Scenarios IPCC Scenario or Rise Rate of Rise Component

Lower Upper Central Lower Upper Central (5%) (95%) (by (5%) (95%) (by WRL) WRL) Starting year (1980 to 1999) 1990 Final year (2090 to 2099) 2095 Sea level rise excluding (m) (m) (m) “scaled up dynamical ice sheet melt” B1 scenario 0.18 0.38 0.28 1.5 3.9 2.7 B2 scenario 0.20 0.43 0.32 2.1 5.6 3.9 A1T scenario 0.20 0.45 0.33 2.1 6.0 4.1 A1B scenario 0.21 0.48 0.35 1.7 4.7 3.2 A2 scenario 0.23 0.51 0.37 3.0 8.5 5.8 A1FI scenario 0.26 0.59 0.43 3.0 9.7 6.4 Average of scenarios 0.34 4.3

Scaled up dynamical ice sheet melt component B1 scenario 0.00 0.09 0.05 0 1.7 0.9 B2 scenario 0.00 0.11 0.06 0 2.3 1.2 A1T scenario -0.01 0.13 0.06 0 2.6 1.3 A1B scenario -0.01 0.13 0.06 0 2.3 1.2 A2 scenario -0.01 0.13 0.06 -0.1 3.2 1.6 A1FI scenario -0.01 0.17 0.08 -0.1 3.9 1.9 Average of scenarios 0.06 1.3

Total (by WRL) B1 scenario 0.18 0.47 0.33 1.5 5.6 3.6 B2 scenario 0.20 0.54 0.37 2.1 7.9 5.0 A1T scenario 0.19 0.58 0.39 2.1 8.6 5.4 A1B scenario 0.20 0.61 0.41 1.7 7.0 4.4 A2 scenario 0.22 0.64 0.43 2.9 11.7 7.3 A1FI scenario 0.25 0.76 0.51 2.9 13.6 8.3 Average of scenarios 0.40 5.6

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 22.

Table 4.3 Simplified Engineering Estimates of Global Sea Level Rise (by WRL) based on IPCC (2001, 2007) and NCCOE (2004) Sea Level Scenario Year 2050 2100 Adopted “Mid” scenario 0.2 0.5 Adopted “High” scenario 0.3 0.9

No reliable information is yet available for local sea level rise for Clarence which differs substantially from the global projections. Hunter et al. (2003) estimated that the land at Port Arthur (approximately 50 km east of Hobart) is rising at 0.2 ±0.2 mm/year upwards. There is no documented evidence of substantial subsidence of coastal land around Clarence, which could justify higher levels of relative sea level rise, than the global average values reported in IPCC.

4.3 Sea level Rise adopted in other States

A list of sea level rise adopted in various state policies or as accepted practice is shown in Table 4.4. This list is not exhaustive. It is subject to revision and there may be additional state policies or legislation which contradict or supersede those shown. All are broadly based on various interpretations or scenarios from recent IPCC projections. The values adopted for this project are broadly consistent with those used in other states, although some states only specify “mid” range rather than “high” range scenarios, as these represent the “best estimate”.

Notes relevant to Table 4.4 are: 1. Most (all) states, require the sea level at the end of the planning period – this is somewhat conservative (see Section 22). Technically, it may be more correct to use the level at the middle, or some weighted point in the planning period, but this is not done in practice. The argument supporting the end of the planning period is that the accepted risk (generally 1% AEP) should apply at the end of the project life. 2. IPCC is relative to 1990 (or 1980 to 1999) sea level. Most jurisdictions or analyses of extremes haven’t corrected for interim change 1990 to 2007. 3. IPCC (2007) blurs some of the parameters, e.g. start and finish date compared with IPCC (2001), and doesn’t provide values for 2050. IPCC (2001)/NCCOE (2004) engineering estimates are still frequently used and are virtually identical for 2100 when ice melt is included. 4. The use of the present day hazard largely covers the low range IPCC sea level rise scenarios. 5. Because people think in rounded numbers, most projections are for 2050 and 2100 (not 2057 etc), but this may invoke greater errors around 2100 when the rate of sea level rise is predicted to be higher.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 23.

Table 4.4 List of Formal Policy or Common Practice Regarding Sea level Rise for Planning Purposes State/body Formal policy Description/comment Year Sea level rise NSW NSW Coastal Policy (1997) and IPCC mid and high range 2050 0.2, 0.3 NSW Coastline Management scenarios for 2050 and 2100 m Manual (1990) state the need to 2100 0.5, 0.9 consider sea level rise but no policy m specification. Up to the professional judgement of consultant. State-provided peer review suggests the following Ranasinghe et al. (2007) indicate 2050 0.18 m the following values are used 2100 0.49 m QLD No policy specification. Up to the professional judgement of consultant.

Operational policy, Coastal 2050 0.3 m Development, Building and engineering standards for tidal works Maritime Structures (Queensland Government, 2004) specifies VIC Draft Victorian Coastal Strategy 2100 0.4 m (October, 2007) to 0.8 m Ranasinghe et al. (2007) indicate IPCC high range scenario 2050 0.3 m the following values are used for 2050 SA Coastal Protection Board Formal 2050 0.3 m policy 2100 1.0 m WA WA Planning Commission The mean of the median 2100 0.38 m Statement Of Planning Policy No. model of the latest from 2.6 State Coastal Planning Policy Assessment Report of the IPCC Prepared Under Section 5aa Of The IPCC Working Group 2001 Town Planning And Development Act 1928 Standards AS 4997-2005 Guidelines for the Cautions that IPCC +25 yr 0.1 m Australia Design of Maritime Structures findings are updated, with +50 yr 0.2 m latest update to be +100 yr 0.4 m considered

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 24.

4.4 Quantification of Other Climate Change Variables

4.4.1 Climate Change Projections for Hobart

The latest climate change projections for Hobart from CSIRO (2007) are shown in Table 4.5. These are for a range of emissions scenarios from IPCC (2007) which are also shown in Table 4.1. The values shown are those exceeded by the lowest 10%, 50% and 90% of modelling projections.

The scale of the modelling (grid size) used, means that the values are for the greater Hobart area, so that localised variations cannot be determined. Therefore, within the context of this WRL report, the projections for future climate change for variables such as rainfall and temperature are equal throughout greater Hobart, though the consequences may differ. There are no projections in CSIRO (2007) for (extreme low) barometric pressure change.

4.4.2 Wind Climate Change Projections and Sensitivity

CSIRO (2007) stated that for 2030: “A consequence of global warming is for the westerlies which are associated with the southern hemisphere storm track to strengthen but contract further polewards. …... in the south-east of the continent where increases in wind speed occur over southern Victoria, Tasmania and Bass Strait (-2% to +7.5% with a best estimate change of +2% to +5%).”

CSIRO (2007) stated that for 2050 to 2070: “In winter, Tasmania and much of the north of the continent (except the north-west shelf) have a greater than 70% chance of experiencing wind speed increase.”

The CSIRO (2007) wind speed projections are for average wind, whereas for design purposes, extreme winds are of more relevance. CSIRO (2007) also presented limited projections of change to extreme wind speeds (exceeded 1% of the time) versus change in average wind speed. For winter projections, the best fit line for a change of ±10% in mean wind speed for mid latitude Australia produced a change of ±3% in extreme wind speed. The caution on these modelling projections (using the wind speed exceeded 1% of the time) is that most conservative design wind speed used in this report would occur for 3 seconds in 10000 years (exceeded 0.00000000095% of the time).

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 25.

This CSIRO modelling is for westerly winds. North-west is the strongest design direction for Hobart, followed by west, then south-west (AS 1170.2:2002).

The worst Hobart case shown in CSIRO (2007) for an increase of the average wind speed (Table 4.5) is +34% (in winter). Using CSIRO (2007, Figure 5.42 b), a change of +10% in average wind speed is estimated to increase extreme wind speeds by up to 3%, and when scaled up to the +34% increase in average, would yield a +10% increase in extreme wind speed. Table 4.5 Projected Climate Change for Hobart (from CSIRO, 2007) Variable Season 2030 2030 2030 2070 2070 2070 2070 2070 2070 A1B A1B A1B B1 B1 B1 A1FI A1FI A1FI 10%50% 90% 10% 50% 90% 10% 50%90% Temperature Annual 0.4 0.6 0.9 0.7 1.1 1.5 1.4 2.1 2.9 (ºC) Summer 0.5 0.7 1 0.8 1.1 1.6 1.5 2.2 3.1 Autumn 0.4 0.7 1 0.7 1.1 1.6 1.4 2.2 3.1 Winter 0.4 0.6 0.9 0.7 1 1.4 1.3 1.9 2.8 Spring 0.4 0.6 0.9 0.6 1 1.5 1.2 1.9 2.9 No days over 35 ºC (current 1.4) Annual 1.6 1.7 1.8 1.7 1.8 2.0 2.0 2.4 3.4 Rainfall (%) Annual -6 -1 +3 -10 -3 -4 -19 -6 +8 Summer -11 -3 +4 -17 -5 +14 -31 -10 +13 Autumn -7 +1 +4 -11 -2 +7 -20 -4 +14 Winter -5 0 +6 -8 0 +9 +15 0 +18 Spring -11 -4 +3 -18 -6 +6 -31 -12 +11 Potential evaporation (%) Annual +1 +3 +6 +2 +5 +9 +4 +10 +18 Summer +1 +3 +5 +2 +5 +8 +3 +9 +16 Autumn +2 +4 +7 +4 +7 +12 +7 +14 +24 Winter -14 +12 +45 -23 +20 +75 -44 +38 +145 Spring +1 +3 +6 +1 +5 +10 +2 +9 +19 Wind speed (%) [Average] Annual -2 +1 +5 -4 +2 +8 -7 +4 +16 Summer -11 -2 +5 -19 -3 +9 -36 -6 +17 Autumn -6 -1 +5 -10 -1 +8 -20 -2 +15 Winter 0 +5 +11 0 +8 +18 -1 +15 +34 Spring -2 +2 +7 -3 +3 +11 -6 +7 +22 Relative Humidity (%) Annual -0.5 -0.2 +0.1 -0.8 -0.3 +0.1 -1.5 -0.6 +0.2 Solar radiation (%) Annual -0.3 +0.5 +1.5 -0.5 +0.9 +2.4 -1.0 +1.7 +4.7

4.4.3 DEFRA UK Allowances and Sensitivity

DEFRA (Department for Environment, Food and Rural Affairs) UK (2006) specified allowances for sea level rise as this has well developed scenarios. DEFRA specified only sensitivity ranges for other parameters such as extreme wave height, because “… the degree of certainty in the figures is lower as we require further evidence and research to understand local and regional variations, and develop our management of uncertainty.” Indicative sensitivity ranges from DEFRA (2006) are shown in Table 4.6, which include a

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 26.

sensitivity of +5% in offshore wave height to 2055. It is stressed that these values are for the UK, not Tasmania. Substantial discussion and caveats on the values are contained in DEFRA (2006). Table 4.6 Indicative Sensitivity Range of Climate Change Parameters (from DEFRA, 2006) Parameter 1990- 2025 2025-2055 2055-2085 2085-2115 Peak rainfall intensity (preferably +5% +10% +20% +30% for small catchments) Peak river flow (preferably for +10% +20% +20% +20% larger catchments) Offshore wind speed +5% +5% +10% +10% Extreme wave height +5% +5% +10% +10%

4.5 Gap Analysis

Global sea level rise (and temperature) are the only components of climate change of high relevance to the coastal zone, for which well developed scenarios are available in the IPCC. There are still major uncertainties in both the modelling and future scenarios for sea level rise. There is high uncertainty in quantifying most other climate change variables, such that at present, they are best considered through sensitivity analyses as stated above (DEFRA, 2006).

Ongoing monitoring of credible climate change projections (e.g. IPCC) is needed, together with monitoring of local processes such as water level and beach change. The findings of this report should be revised within 10 years or following major revisions to climate change projections.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 27.

5. QUANTIFICATION OF EXTREME WATER LEVELS

5.1 Previous Analyses of Extreme Water Levels

Water levels consist of (predictable) tides which are forced by the sun, moon and planets (astronomical tides), and a tidal anomaly. Tidal anomalies result from factors such as wind setup or setdown, barometric effects, seasonal changes and coastally trapped waves. The largest positive anomalies are associated with major storms and are driven by barometric setup (associated with low barometric pressure) and coastal wind setup, which are often combined as “storm surge”. Water levels within the surf zone are also subject to wave setup and wave runup. Water levels within the lagoons and creeks may be influenced by runoff of rainfall, particularly if the entrance is blocked or constricted.

The Australian National Tide Table values for the port of Hobart are reproduced in Table 5.1. Australian Height Datum (AHD) is approximately mean sea level. Chart datum, which is used in bathymetric charts and tidal predictions was changed for Hobart on 1 January 2006. The new Hobart chart datum is approximately -0.83 m AHD. The old Hobart chart datum was approximately -1.20 m AHD. As the data analysed by Hunter (2007, Page 6) covered to the end of 2004, he correctly used the old chart datum of -1.20 m AHD. Due to tidal anomalies (barometric setup, wind setup, trapped waves), extreme water levels will exceed the highest astronomical tide.

Also shown in Table 5.1 are the predicted future tidal levels due to sea level rise using the simplified scenarios from Table 4.3. There is some speculation that astronomical tides could change with increased sea level (Flick et al, 2003; Jay et al, 2004; Colosi and Munk, 2006), but no accurate quantification of this is currently available.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 28.

Table 5.1 Published Tidal Planes for Hobart and Indicative Future Levels Astronomical Tidal Planes Datum HAT MHWS MHWN MSL MLWN MLWS LAT Old Chart datum 2.1 1.9 1.4 1.3 1.1 0.6 0.4 New Chart Datum 1/1/06 1.7 1.5 1.0 0.9 0.8 0.3 0.0 AHD 0.8 0.6 0.1 0.0 -0.1 -0.6 -0.9

2050 Mid scenario AHD 1.0 0.8 0.3 0.2 0.1 -0.4 -0.7 2050 High scenario AHD 1.1 1.0 0.5 0.3 0.2 -0.3 -0.6 2100 Mid scenario AHD 1.3 1.1 0.6 0.5 0.4 -0.1 -0.4 2100 High scenario AHD 1.7 1.5 1.0 0.9 0.8 0.3 0.0 Notes: AHD: Australian Height Datum (approximately present mean sea level) HAT: Highest Astronomical Tide MHWS: Mean High Water Springs MHWN: Mean High Water Neaps MSL: Mean Sea Level MLWN: Mean Low Water Neaps MLWS: Mean Low Water Springs LAT: Lowest Astronomical Tide Source: Royal Australian Navy Hydrographic Service (1999, 2006)

5.2 Design Water Levels (Tide + Storm Surge)

Numerous extreme value distributions exist, with the most common for water levels being Gumbel (FT-1) and Log-Pearson-3. Mai et al (2002) found that a Gumbel distribution gave slightly higher predicted water levels for long recurrence intervals (10000 year ARI) for sites with approximately 100 years of data. Pugh (1987, 2004) stated that a Gumbel distribution is the most widely used for extrapolation of water levels.

An extensive analysis of the Hobart tide gauge data was undertaken by Hunter (2007). Hunter’s analysis found that while the gauge spanned 43 years of data (1/1/1960 to 31/12/2004 at the time of analysis), only 31.8 years of data were useable. Hunter’s analysis covered measured water levels (astronomical tide plus tidal anomaly) and did not separate out the tidal anomaly. There may be circumstances where a major positive tidal anomaly (“storm surge”) occurs at the time of small (neap) tides, in which case it would not register as an extreme water level event if only the total water level is considered.

The Port of Hobart (2005) listed the four largest recorded tides for Hobart as follows:

1. 1.350 m AHD: 25/07/1988 2. 1.305 m AHD: 26/05/1994 3. 1.295 m AHD: 08/08/1991 4. 1.235 m AHD: 31/12/1971.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 29.

All the Port of Hobart dates are within the useable data dates deduced by Hunter (2007), so for plotting purposes, a total of 31.8 years of useable data from the Port of Hobart was assumed by WRL as done by Hunter. This 31.8 year data span formed the base for allocating the average recurrence interval for the Port of Hobart data.

A plot of extreme water levels for Hobart using the results of Hunter (2007, Table 3) and extrapolated in accordance with Pugh (1987) is shown in Figure 5.1, together with the Port of Hobart (2005) data points. Also shown are published levels for Sydney and Fremantle (Haradasa et al, 1991; Lord and Kulmar, 2000; Fremantle in DPI, 2004). It is acknowledged that Sydney and Fremantle have different tides and storm surges to Hobart, but they have long records (of the order of 100 years) and approximately bound the shorter Hobart data. Also stated in Pugh (1987, page 272) is that extrapolation should be limited to three to four times the record length, which limits the valid extrapolated ARI for Hobart to approximately 120 years. This limit is marked on Figure 5.1, so that water levels for ARIs above 120 years are speculative. Nevertheless, indicative values for more extreme water levels are needed, and have been tabulated in Table 5.2 (shown in italics). Extrapolation of the Port of Hobart (2005) data points (Figure 5.1) yields almost identical water levels for 100 year ARI (1.44 m AHD) to the Hunter (2007) data (using WRL’s fitting).

Table 5.2 Design Water Levels using Mid and High Range Sea Level Rise (SLR) Scenarios (excludes local effects such as local wind setup, wave setup and wave runup) Water level (m AHD) ARI (years) AEP Mid range SLR High range SLR 2000 2050 2100 2050 2100 Sea level rise 0.0 0.2 0.5 0.3 0.9 1 63% 0.97 1.17 1.47 1.27 1.87 50 2% 1.37 1.57 1.87 1.67 2.27 100 1% 1.44 1.64 1.94 1.74 2.34 Speculative 1000 0.1% 1.67 1.87 2.17 1.97 2.57 2000 0.05% 1.73 1.93 2.23 2.03 2.63 10000 0.01% 1.90 2.10 2.40 2.20 2.80

The data from Figure 5.1 and Table 5.2 is further analysed in Figure 5.2. For the Gumbel fit adopted for Hobart, Figure 5.2 shows the changes to Average Recurrence Intervals with future sea level rise as shown in Tables 5.3 and 5.4. The caution on these tables is that reliable extrapolation should only be undertaken to about 120 years, and very short ARI events (e.g. 0.01 year) would be influenced by the spring-neap tide cycle). However, if the extrapolation is accepted, it can be seen that a present day 100 year ARI (1% AEP) water level would occur approximately every 3 days in 2100 with a 0.9 m rise in sea level.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 30.

Table 5.3 Equivalent Present Day Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels and Future 100 year ARI event Year SLR (m) 100 year ARI Equivalent (1% AEP) present day Level ARI (years) present 0.0 1.44 100 2050 0.2 1.64 800 2050 0.3 1.74 2,000 2100 0.5 1.94 15,000 2100 0.9 2.34 850,000

Table 5.4 Equivalent Future Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels Present Day 100 year ARI event Year SLR (m) Present day Equivalent 100 year ARI Future ARI (1% AEP) (years) Level present 0.0 1.44 100 2050 0.2 1.44 20 2050 0.3 1.44 4 2100 0.5 1.44 0.7 2100 0.9 1.44 0.01

5.3 Barometric Setup Component of Storm Surge

Hunter (2007) did not specifically analyse tidal anomalies (actual minus predicted tide). A full assessment of tidal anomalies is beyond the scope of this report, however, a basic analysis of available barometric pressure data was undertaken.

Approximately 114 years of data are available for Ellerslie Road, Hobart (1/1/1894 to present) and 49 years of data from Hobart Airport (1/6/1958 to present) from the Bureau of Meteorology. As noted above, low barometric pressure causes the ocean to rise at a rate of approximately 1 cm for each 1 hPa of pressure drop, provided there is sufficient time to equilibrate.

It is noted that meteorology is not the primary expertise of WRL, however, a basic analysis of the data was undertaken. The long term average sea level barometric pressure for Hobart is 1013 hPa. Low barometric pressure events (separated by more than 1 day) were ranked for both Ellerslie Road and Hobart Airport as shown in Figure 5.3, with a Gumbel extrapolation. It was noted that the lowest pressure events were generally accompanied by

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 31.

winds from the westerly quadrant (north-west to south-west). A detailed analysis of all these variables is beyond the scope this study.

Extrapolated low barometric pressures are shown in Table 5.5, together with the estimated positive tidal anomaly they would cause. As noted above, tidal anomalies can result from other factors, and therefore contain additional contributions, but also shown in Table 5.5 is the barometric setup added to a present day mean higher high water (MHHW) tide. Speculative values due to extrapolation beyond three to four times the record length are shown in italics. Additional analysis by a meteorologist on factors such as “probable maximum intensity” of low pressure systems could be undertaken.

Table 5.5 Extreme Low Barometric Pressures and the Tidal Anomalies they would Generate (for present day sea level) ARI (years) AEP Hobart Airport Ellerslie Road, Hobart Ellerslie Road (49 years data) (114 years data) setup plus MHHW Pressure Barometric Pressure Barometric 2000 Water (hPa) Setup (m) (hPa) Setup (m) Level (m AHD) 1 63% 982 0.31 982 0.31 0.91 100 1% 969 0.44 967 0.46 1.06 Speculative 2000 0.05% 963 0.50 959 0.54 1.14 10000 0.01% 960 0.53 955 0.58 1.18

5.4 Local Effects – Local Wind Setup, Wave Setup and Wave Runup

Local water levels are further influenced by local wind setup, wave setup and wave runup. These are calculated separately for individual locations in Section 10.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 32.

6. OCEAN SWELL WAVES

6.1 Offshore Wave Climate Data

An overview of available data was presented in Section 2. As stated, the wave buoy data described below has been utilised. Additional data is available, such as satellite, ship observations, lighthouse observations and numerous global wave models, however, these have not been analysed in this report as they are usually of lower quality or capture rate than the reliable sources described below.

A wave buoy has been operated off Cape Sorell (Figure 6.1) by the Bureau of Meteorology since 1998. Previous CSIRO buoys have operated there from 1985 to 1992 and at other locations within Storm Bay for short durations (Figure 6.1). Information is provided in Reid and Fandry (1994). None of these buoys were directional.

A non-directional wave buoy has operated off Eden NSW since 8 February 1978 (Lord and Kulmar, 2000; Kulmar et al, 2005) and has a 81% data capture rate.

The ERA-40 dataset has hindcast global wave heights from global weather models for 45 years, but Caires and Sterl (2005) reported that this has not been calibrated to southern hemisphere wave buoy data. Hemer et al, (2007) carried out a comparison between Australian wave buoy data and ERA-40 and C-ERA40 wave output. They found that the ERA-40 model significantly underestimated the large wave events, particularly in the Southern Ocean. They found that the C-ERA-40 model improved this error, but still displayed a slight underestimation of the southern ocean wave heights.

The Eden and Cape Sorell wave data is of high quality, but as stated above, neither buoy is directional. No long term buoy exists off south or south-east Tasmania. A bivariate analysis presented in KNMI (2008) using C-ERA-40 data from 1971 to 2000 was used to confirm feasible directions for offshore of southern Tasmania. This data had wave direction in 45º bins and 1 m height bins.

As shown below, the largest waves for the Cape Sorell buoy have a south-west to north- west direction. Such waves would lose substantial height in reaching the Clarence coast through refraction and diffraction (see Section 6.4 below). The largest waves for the Eden buoy have a south to south-east direction. Such waves would not undergo substantial refraction to reach the most exposed beaches on the Clarence coast (see below), but as shown below, the south to south-east waves are smaller offshore.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 33.

It is noted that an HF RADAR wave monitoring system has been proposed for off south- eastern Tasmania which would provide additional directional wave data.

6.2 Direction of Extreme Offshore Waves

In this section, the C-ERA-40 wave modelling data is used to provide directional probability to the observed wave buoy data. The tabular data for an area bounded by longitude 135º to 144º and latitude -54º to -45º (Figure 6.2a, to the south west of Tasmania) from KNMI (2008) using C-ERA-40 data from 1971 to 2000 was processed by WRL as shown in Figure 6.2 and summarised in Table 6.1. This shows that the direction with the largest observed significant waves (Hs = 12 to 13 m) was WSW (235º to 270º bin), and the direction with the second largest observed waves (Hs = 11 to 12 m) was WNW (270º to 315º bin). These directions would reach the Cape Sorell wave buoy unimpeded.

The largest significant waves observed from the SSE (135º to 180º bin) which is representative of those which would reach the Eden buoy were 7 to 8 m.

Figure 6.2b shows directional storm wave heights from the C-ERA-40 model combined with directions from the ERA-40 model for a grid cell centred on 142.5º East, 47.5º North. This again shows that the largest waves are associated with storms from the north-west to south-west, with much smaller storm waves from the south-west to south-east.

Table 6.1 Directional Order of Largest Waves to south-west of Tasmania from C-ERA-40 Dataset Ranking Direction Direction bin Largest significant (degrees true wave height band north) (m) 1 WSW 225 to 270 12 to 13 2 WNW 270 to 315 11 to 12 3 NNW 315 to 360 9 to 10 4 SSW 180 to 225 9 to 10 5 NNE 0 to 45 7 to 8 6 SSE 135 to 180 7 to 8 7 ESE 90 to 135 6 to 7 8 ENE 45 to 90 6 to 7

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 34.

6.3 Extreme Offshore Waves

6.3.1 Background

The purpose of this analysis is to provide estimates of extreme beach erosion. The results should not be used for the design of structures subject to wave forces.

Offshore waves are typically defined by the significant wave height (Hs), which is the average of the one-third highest waves, and approximates the height observed by an experienced mariner. The largest waves (Hmax) may be up to twice the significant wave height (Hs), with rare rogue or freak waves being more than twice the significant wave height.

6.3.2 Other Studies

Analysis of extreme wave heights involves identifying extreme events and applying a “peak over threshold” method to an extreme value distribution. You (2007) examined the fit of nine extreme value distributions to long term wave data for the NSW coast. These included Exponential, Lognormal, Weibull, FT-I, FT-II, FT-III, GPD-I, GPD-II and GPD-III. You (2007) found that a Gumbel (FT-I) distribution best fitted the observed data for 19 years of data from the Sydney wave buoy. You did not analyse the sensitivity to the threshold, however, he undertook his analysis for events with a threshold of approximately twice the median significant wave height.

Caires and Sterl (2005) found a best fit with a threshold of 93% to 97% quantile, which would equate to a 2.5 to 3 m threshold for Eden NSW, that is, 1.5 to 2 times the median significant wave height. The latest data for Eden NSW is presented in Kulmar (2005) and uses what appears to be a Gumbel distribution with a threshold Hs of 3.5 m and a duration of 1 hour.

Reid and Fandry (1994) produced an extensive 118 page report on the Cape Sorell wave buoy. A detailed updated analysis would require a report of similar scope which would detract from the primary purpose of this report.

Hemer et al. (2008) analysed wave buoy data from four Australian sites subject to southern ocean waves, namely Rottnest Island (WA), Cape Naturaliste (WA), Cape de Couedic (SA) and Cape Sorell (TAS). They fitted a Generalised Pareto Distribution to the full Cape Sorell data set and found a best estimate of 100 year ARI (1% AEP) Hs of 12.8 m.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 35.

6.3.3 Extreme Waves Estimates for this Study

Since 7 years of extra data was available for Cape Sorell compared with Reid and Fandry (1994), a brief reanalysis using contemporary techniques was undertaken. The Cape Sorell data from both CSIRO and BOM was combined and a time series plotted. For the CSIRO data, the buoy in 100 m of water was given precedence, however, where data gaps occurred, the 50 m buoy data was used when available. Various threshold Hs values were investigated in 0.5 m increments between 5 m and 9 m. The peak significant wave height of storm events was extracted. Individual storm events were identified visually from time series plots of the data, with an additional condition that only a single storm event (peak Hs) could occur within a 48 hour period. A Gumbel distribution was fitted to the data points as shown in Figure 6.3. It is noted that a peak Hs of 13.15 to 13.59 m was measured by the CSIRO buoys at 20:00 hours on 29 July 1985, which slightly exceeds WRL’s estimate of 13 m for 100 year ARI (1% AEP) (Figure 6.3), however, the second highest event had a peak Hs of 10.5 m. Reid and Fandry (1994) devoted a section to the discussion of the 29 July 1985 event and believed the readings (especially the Hs of 13.15 m) to be credible.

Although only approximately 6 months of data was collected in 1993 for the Wedge Island Buoy, a similar procedure to Cape Sorell was used.

A summary of wave data and statistics is shown in Table 6.2. It can be seen that Reid and Fandry (1994) estimated larger 100 year ARI (1% AEP) wave heights for Cape Sorell than WRL’s analysis found. The following reasons partially explain this discrepancy:

 The storm event having an Hs of 13.15 to 13.59 m on the CSIRO buoys at 20:00 hours on 29 July 1985 referred to above makes the distribution very sensitive to the total record length used. WRL analysed an additional 7 years of data from BOM using hourly readings, with the second largest event having an Hs of 10.5 m.

 As shown in Figure 52 of Reid and Fandry (1994), they did not use a high threshold wave height for the Gumbel distribution. They commented that the extreme wave heights “dropped away” at low probabilities. For the threshold Hs of 7 m used in WRL’s analysis (Figure 6.3), the extreme wave heights did not “drop away”.

 Some of the peak Hs values reported in Reid and Fandry were for a 20 minute duration, whereas the Eden and WRL Cape Sorell values are for 1 hour duration.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 36.

Table 6.2 Summary of Extreme Offshore Wave Heights Threshold Start date Finish of Years of Hs Hs in analysed data 100 yr analysis data ARI (m) Eden NSW Kulmar (2005) 3.5 08/02/1978 31/12/2004 27 8.5 ERA-40 and C-ERA-40, (Caires 93% September August 45 12.5 and Sterl, 2005; KNMI, 2008) to 97% 1957 2002 from quantile WSW Adopted value for Eden 8.5

Wedge Island TAS 3.0 27/05/1993 14/12/1993 0.5 9.0 (WRL analysis of CSIRO data)

Cape Sorell TAS CSIRO 11/07/1985 24/09/1993 8 BOM 07/01/1998 31/12/2004 7 Combined CSIRO and BOM 15 Reid and Fandry (1994) Weibull - 12.4 and Gumbel fit using regression to 14.6 Reid and Fandry (1994) Gumbel - 14.7 fit using moments, 20 minute to to 15.7 3 hour duration Hemer et al (2008) combined 6.5 12.8 analysis, best estimate WRL combined analysis, 1 hour 7.0 13.0 duration ERA-40 and C-ERA-40, Caires 93% 12.5 to and Sterl (2005) to 97% 15.5 quantile Adopted value for Cape Sorell 13.0

A summary of average recurrence interval (ARI) peak Hs values for 1 hour duration adopted for this study are shown in Table 6.3. As described in Section 5, Pugh (1987) stated that extrapolation (of extreme water levels) should be limited to three to four times the record length. This value is shown in Table 6.3, with Hs values for ARIs above this shown in italics. That is, the italics values are speculative, but are the best available using current data and techniques. It can be seen that although there is only 1 year of data, the values for Wedge Island are similar to Eden NSW.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 37.

Table 6.3 Summary of Extreme Offshore Wave Heights adopted for this Study (Values derived with excessive extrapolation are shown in italics) ARI (years) AEP Eden NSW Cape Sorell Wedge Island Record length 25 years 15 years 0.5 year Maximum reliable ARI 100 years 60 years 2 years (4 times record length) Hs (m) Hs (m) Hs (m) 1 63% 5.3 9.0 5.5 5 18% 5.8 10.5 6.0 10 9.5% 6.4 11.0 6.8 20 4.9% 7.4 11.5 7.9 50 2% 8.1 12.3 8.5 100 1% 8.5 13.0 9.0 Speculative 200 0.5% 9.1 13.5 500 0.2% 9.7 14.2 1000 0.1% 10.2 14.8 2000 0.05% 10.7 15.5 10000 0.01% 11.8 17.0

6.4 SWAN Modelling

Offshore swell waves reaching the Clarence coast may be modified by the processes of refraction, diffraction, bed friction and breaking. The model SWAN (Simulating WAves Nearshore) was used to quantify the change in wave conditions from a deepwater boundary beyond Storm Bay to the nearshore zone of the Clarence coast. Details of SWAN can be found in Booij et al. (1999a, 1999b).

SWAN was used to propagate swell waves to the Clarence coast. It was not used to generate local wind waves. The combined presence of swell and local wind waves may have consequences for boats, offshore structures and long term coastal sediment transport. However, for factors such as wave runup and setup on natural beaches, the application of the Ochi-Hubble six parameter spectrum (Ochi and Hubble, 1976) shows that where sea and swell are both present, the long period ocean swell wave conditions are dominant during extreme conditions.

Furthermore, to limit complexity, refraction through currents was not modelled – this may be of relevance in some circumstances between Opossum Bay and Bellerive (Figure 2.4). A coarse 250 m grid was set up from South East Cape to Cape Pillar (Figure 6.4). A finer 100 m grid was then set up from Adventure Bay to Wedge Island using input from the coarse model. As described previously, bathymetry in the model was obtained from the following sources:

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 38.

 AUS 794 and 171 bathymetric charts  TAFI seabed mapping dataset  Clarence City Council’s GIS system and LIST (Land and Information Systems Tasmania) MHWM and MLWM data sets to define the shoreline.

Generally, the TAFI data sets provided a good resolution of seabed information for the shallower regions of the model, with the admiralty charts used to extend the bathymetric data into deeper water (out to the 500 fathoms (914.4 m) contour). Triangular interpolation was used to develop the coarse and fine resolution bathymetric grids.

An example of modelling runs is shown in Figure 6.4.

6.5 Nearshore Extreme Swell Waves

SWAN modelling was undertaken for most combinations of the following conditions:

 Offshore significant wave heights of 1, 5, 10 and 15 m  Spectral peak wave periods of 10, 15, 20 and 25 seconds  Offshore wave directions from east clockwise to west in 22.5 degree increments, that is, 9 directions (E, ESE, SE, SSE, S, SSW, SW, WSW and W).

Detailed SWAN modelling parameters are shown in Appendix A. A summary of wave height coefficients for locations shown in Figure 2.4 for an offshore Hs of 1 m and Tp of 15 seconds is shown in Table 6.4, with the results presented graphically for selected locations in Figures 6.5a-b. The coefficients incorporate refraction, diffraction, friction and shoaling, but not reflection. For larger wave heights the wave coefficients generally reduce due to additional frictional loss and non linear effects (Appendix A). The coefficients shown in Table 6.4 may be multiplied by larger offshore wave heights to determine the nearshore wave heights as a slightly conservative first approximation. The locations of model output (Table 6.4) were initially selected to be in 15 to 20 m of water, which is outside the surf zone for all of the beaches in the study area. Following initial analysis, this was later reduced to 5 to 10 m for some lower energy locations where the water was shallow offshore (e.g. Roches Beach) so that representative wave heights reaching the beach could be determined. The water depths for the indicated local wave conditions at the various locations are indicated in Figures 6.5a-b.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 39.

Table 6.4 Summary of Nearshore Wave Coefficients modelled with SWAN (Hs = 1 m, Tp = 15 s)

Location Easting North Depth E ESE SE SSE S SSW SW WSW W S1 Bellerive West 530495 5251880 15 0.00 0.01 0.02 0.04 0.03 0.01 0.00 0.00 0.00 S2 Bellerive Centre 530708 5251880 15 0.00 0.01 0.02 0.04 0.03 0.01 0.00 0.00 0.00 S3 Bellerive East 531021 5251900 15 0.00 0.01 0.02 0.04 0.03 0.01 0.00 0.00 0.00 S4 Howrah off Salacia Ave 531941 5251720 15 0.00 0.01 0.03 0.06 0.04 0.02 0.01 0.00 0.00 S5 Howrah off Silwood Ave 532214 5251660 15 0.00 0.01 0.03 0.05 0.04 0.01 0.01 0.00 0.00 S6 Howrah off Boat Ramp 532390 5251637 15 0.00 0.01 0.03 0.06 0.04 0.02 0.01 0.01 0.00 S7 Howrah off Bingley St 532410 5251630 15 0.00 0.01 0.03 0.06 0.04 0.02 0.01 0.01 0.00 S8 Howrah off Howrah Point Ct 532655 5251480 15 0.00 0.02 0.03 0.06 0.05 0.02 0.01 0.01 0.00 S9 Opossum Bay North 532650 5240774 10 0.01 0.04 0.08 0.13 0.11 0.05 0.03 0.02 0.01 S10 Opossum Bay Centre 532580 5240336 10 0.01 0.03 0.06 0.10 0.09 0.04 0.02 0.01 0.01 S11 Opossum Bay South 532490 5240177 10 0.01 0.02 0.03 0.07 0.07 0.03 0.02 0.01 0.00 S12 Glenvar 532410 5239578 10 0.02 0.05 0.10 0.15 0.14 0.06 0.03 0.02 0.01 S13 Halfmoon Bay North 532921 5237890 10 0.02 0.05 0.09 0.13 0.11 0.05 0.02 0.02 0.01 S14 Halfmoon Bay Centre 533091 5236760 10 0.01 0.04 0.08 0.10 0.10 0.04 0.02 0.01 0.01 S15 Halfmoon Bay South 533100 5236365 10 0.01 0.04 0.07 0.09 0.09 0.04 0.02 0.01 0.01 S16 Hope Beach, South Arm Neck 537175 5234070 20 0.06 0.20 0.53 0.73 0.73 0.34 0.17 0.11 0.06 S17 Clifton Beach West 544272 5237870 20 0.06 0.13 0.32 0.63 0.63 0.43 0.22 0.16 0.07 S18 Clifton Beach East 544315 5237950 20 0.05 0.13 0.32 0.62 0.62 0.43 0.22 0.15 0.07 S19 Cremorne Beach South 544810 5243900 10 0.04 0.08 0.20 0.46 0.44 0.28 0.15 0.11 0.05 S20 Cremorne Beach Centre 544770 5243976 10 0.03 0.08 0.19 0.45 0.43 0.28 0.15 0.10 0.05 S21 Cremorne Beach North 544760 5243989 10 0.03 0.08 0.19 0.45 0.43 0.27 0.15 0.10 0.05 S22 Mays Beach 542650 5247636 5 0.01 0.03 0.06 0.14 0.15 0.10 0.05 0.04 0.02 S23 Roches Beach South 541490 5249064 5 0.01 0.03 0.06 0.15 0.16 0.10 0.06 0.04 0.02 S24 Roches Beach at Canal 541410 5249147 5 0.01 0.03 0.06 0.15 0.16 0.10 0.06 0.04 0.02 S25 Roches Beach Mid 540890 5250355 5 0.01 0.03 0.06 0.15 0.16 0.10 0.06 0.04 0.02 S26 Roches Beach at Reef 541170 5250873 5 0.01 0.03 0.07 0.17 0.19 0.12 0.06 0.05 0.02 S27 Roches Beach North 541190 5251074 5 0.01 0.03 0.07 0.17 0.19 0.12 0.07 0.05 0.02 S28 Seven Mile Beach West 547436 5249450 15 0.02 0.05 0.12 0.30 0.45 0.30 0.16 0.11 0.05 S29 Seven Mile Beach East 547348 5249670 15 0.02 0.05 0.12 0.30 0.45 0.29 0.16 0.11 0.05

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 40.

6.6 Gaps and Further Analysis

The following are gaps and analysis in ocean swell wave data and its propagation to the Clarence beaches.

There is no directional wave buoy data. In other locations without directional buoys this has been incorporated by hindcasting direction from weather charts. A directional wave recording instrument is the best future solution. As stated previously, an HF radar has been proposed for south-east Tasmania which would measure wave direction.

The nearshore wave heights estimated by SWAN are not calibrated or verified. It was hoped that the CSIRO buoy deployed off Wedge Island could provide some wave calibration data, however, this deployment appears to have used the same buoy which had been deployed off Cape Sorell. That is, there is no simultaneous data. SWAN is a well regarded and widely used model for wave propagation, and the results concur with the authors’ observations from numerous site visits, and provide reasonable agreement with the typical wave climates estimated for the more exposed Clarence beaches in Short (2006). A program of systematic visual observation or instrument measurement of wave heights on key Clarence beaches (such as Roches) and relating this to offshore waves would improve the certainty of SWAN modelling.

Following the above tasks, the creation of a time series of nearshore wave heights for key Clarence beaches to develop a long term wave climate would be worthwhile. This would be undertaken by combining the SWAN modelling with the offshore wave climate. This would be valuable to better define the nearshore wave climate and as input for shoreline change models.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 41.

7. LOCALLY GENERATED WIND WAVES AND BOAT WAVES

7.1 Procedure for Estimating Design Wind Wave Heights

Wind wave heights were estimated using the principles of SPM (1984), the US Army Coastal Engineering Manual (CEM: EM 1110-2-1100, 2002) and the software ACES version 4.0.3.1) as described below.

7.2 Design Wind Speed

Australian Standard AS/NZS 1170.2:2002 Structural Design Actions Part 2: Wind Actions gives design wind velocities for Australia excluding tornadoes. Design wind velocities (3 second gust, 10 m elevation, Terrain Category 2) for average recurrence intervals applicable to coastal engineering assessments are shown in Table 7.1.

Table 7.1 Design Wind Velocities (3 second Gust) Average Recurrence Interval Design Wind Velocity (years) (not adjusted for direction) 3 second gust m/s knots 1 26 51 50 39 76 100 41 80 1000 46 89 2000 48 93 10000 51 99

The wind actions standard also contains directional multipliers for wind speed for Hobart, which vary from 0.80 for four directions from north-east to south, to 1.0 for the north-west octant as shown in Table 7.2.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 42.

Table 7.2 Fetch and Directional Wind Velocity Multipliers Direction Directional Multiplier for velocity shown in Table 7.1 N 0.85 NE 0.80 E 0.80 SE 0.80 S 0.80 SW 0.85 W 0.90 NW 1.00

7.3 Fetch and Duration Limitations

For the locations shown in Figure 2.4, wind wave fetches were defined. As described in the SPM (1984, p 3-42), due to the irregular shoreline, the fetch for each primary direction was defined by using nine separate radials spaced at 3 degrees (centred on the primary direction) which were then averaged to define the fetch length shown in Table 7.3.

The design (3 s gust) wind speeds for terrain category 2 are shown in Table 7.1. For terrain category 2 (AS 1170.2:2002) and a design local elevation of 10 m (used as input into wave equations), there is no adjustment needed to these wind speeds. The equivalent average wind speeds for other durations (which ranged from 10 minutes to 1 hour) were calculated as per SPM (1984, Figure 3-13).

The US Army Coastal Engineering Manual (CEM: EM 1110-2-1100, 2002, p II-2-45) recommends that the deepwater wave forecasting equations now be used even in relatively shallow water, provided that the wave period does not exceed a limiting value (5.4 s for 3 m water depth).

7.4 Design Wind Wave Heights

Using the design wind data presented in Tables 7.1 and 7.2, and the wave hindcasting techniques of SPM (1984), CEM (2003) and software ACES (Version 4.0.3.1), extreme local wind wave conditions were estimated for 15 locations as shown in Table 7.3. Hs is the significant wave height, which is defined as the average of the one-third highest waves and correlates with the visual observations of an experienced mariner. Tp is the spectral peak wave period – period being the time in seconds between successive wave crests. Wind waves would be smaller from other directions.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 43.

Table 7.3 Design Local Wind Waves Location m E m N Dirn Fetch ARI (years) and AEP 1 50 100 1000 2000 10000 63% 2% 1% 0.1% 0.05% 0.01% (m) Hs Tp Hs Tp Hs Tp Hs Tp Hs Tp Hs Tp W1 Montagu Bay 528958 5253968 W 1640 0.4 2.1 0.6 2.6 0.7 2.7 0.8 2.9 0.8 3.0 0.9 3.1 W2 Kangaroo Bay 529687 5252916 SW 3690 0.5 2.5 0.9 3.2 0.9 3.2 1.1 3.5 1.1 3.6 1.2 3.7 W3 Bellerive 530700 5252566 S 22730 1.2 4.2 2.1 5.3 2.2 5.5 2.6 5.9 2.8 6.0 3.0 6.2 W4 Howrah Pt (& Little Howrah & Tranmere) 532877 5251535 SW 17520 1.5 4.7 2.6 5.8 2.8 6.0 3.3 6.4 3.5 6.6 3.9 6.9 W5 Rokeby Waste Water Treatment Plant 535962 5249307 S 11570 0.8 3.3 1.3 4.2 1.4 4.3 1.7 4.6 1.8 4.7 1.9 4.9 W6 Lauderdale - South Arm Road, Ralphs Bay 539134 5249450 SW 13730 1.3 4.2 2.3 5.4 2.5 5.6 2.9 6.0 3.2 6.2 3.4 6.4 W7 South Arm Neck (Ralphs Bay side) 536906 5235456 NW 10670 0.9 3.5 1.6 4.6 1.7 4.6 1.9 4.9 2.0 5.0 2.2 5.2 W8 Seven Mile Beach 541370 5254381 SE 23610 1.1 4.1 2.0 5.2 2.1 5.4 2.5 5.8 2.6 5.9 2.8 6.1 W9 Roches Beach, Lauderdale & Mays Beach 540408 5248937 E 22420 1.2 4.1 2.0 5.3 2.2 5.4 2.6 5.8 2.7 6.0 3.0 6.2 W10 Cremorne (Ocean) Beach 543575 5243858 E 19320 1.0 3.9 1.8 5.0 1.9 5.1 2.3 5.5 2.4 5.6 2.6 5.8 W11a Cremorne – Pipe Clay Esplanade east 543677 5243464 NW 1870 0.4 2.2 0.7 2.7 0.7 2.9 0.9 3.1 0.9 3.2 1.0 3.3 W11b Cremorne – Pipe Clay Esplanade west 543009 5243799 S 2980 0.4 2.3 0.7 2.9 0.7 2.9 0.9 3.2 0.9 3.3 1.0 3.4 W12 Clifton – Bicheno St, Pipe Clay Lagoon 542860 5240658 NW 3190 0.5 2.5 0.8 3.1 0.9 3.2 1.0 3.5 1.1 3.5 1.2 3.7 W13 South Arm Beach (Halfmoon Bay) 533832 5236962 NW 8260 0.9 3.4 1.5 4.4 1.6 4.5 1.9 4.8 2.0 4.9 2.2 5.1 W14 Opossum Bay and Glenvar 532985 5240276 NW 6110 0.8 3.3 1.3 4.0 1.5 4.2 1.7 4.5 1.8 4.6 2.0 4.8

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 44.

7.5 Boat Waves

Power boats, including pleasure and commuter craft, can generate a range of wave conditions which impact a fixed shoreline position for only a brief duration as the boat passes, however, it is unlikely that many vessels would be at sea during extreme storm events which cause elevated water levels. Walker (1999) reported on typical boat wave characteristics from Sydney Harbour which cited wave heights of up to 0.3 m as listed in Table 7.4. Wave periods of up to 2.5 s were reported for vessels up to 9 m length and speeds of up to 20 knots. For high speed ferries, wave periods of up to 7 s were reported. Measurements of a police launch travelling at 8 knots within the low wash area of Church Point, Sydney found waves of up to 0.3 m and 2.5 s. Boat waves (including long period, high speed ferry waves) may need to be considered in the design of maritime structures and for low energy portions of the Clarence foreshore, hence their inclusion in this report.

Table 7.4 Typical Boat Wave Characteristics Vessel Type Vessel Speed Wave Period Wave Height (knots) (seconds) (m) 4 m Dinghy 5 1 0.05 5 m Speed Boat 20 1.5 0.11 6 m Skyliner 5 1.7 0.17 9 m Flybridge 8 2.5 0.30 6 m Workboat 10 2 0.10 Small Tug 3 2 0.15 High Speed Large Ferries 15 Up to 7 Up to 0.30

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 45.

8. SUMMARY OF DESIGN WAVES

A summary of 100 year ARI (1% AEP) design waves for the various locations is shown in Table 8.1. This summary shows either swell or wind waves where one condition is clearly dominant, and both swell and wind waves when their magnitude is comparable. For the swell condition the 100 year ARI (1% AEP) nearshore condition is the greater of the Eden NSW value times the largest wave coefficient for south-south-west to south-east waves, and the Cape Sorell Tasmania value times the largest wave coefficient for south-west to west waves. The wave heights shown are representative for each precinct for planning purposes. For detailed studies of individual precincts, local gradients in wave heights may need to be considered, such as those near headlands. The swell wave heights given are in 5 to 20 m of water depth, which is generally beyond the surf zone and may be outside the local influence of headlands. The depth chosen (Section 6) was based on local bathymetry and the need to acquire a representative wave height for the subject beach.

Table 8.1 Summary of 100 year ARI Design Waves Location Label Swell Wind Hs Tp Hs Tp Dirn Montagu Bay W1 - - 0.7 2.7 W Kangaroo Bay W2 - - 0.9 3.2 SW Bellerive W3, S2 0.3 15 2.2 5.5 SW Howrah Pt (& Little Howrah & Tranmere) W4, S6 0.5 15 2.8 6.0 SW Rokeby Waste Water Treatment Plant W5 - - 1.4 4.3 S Lauderdale - South Arm Road, Ralphs Bay W6 - - 2.5 5.6 SW Seven Mile Beach west W8, S29 3.8 15 2.1 5.4 SE Roches Beach, Lauderdale (Bambra reef) W9, S26 1.6 15 2.2 5.4 E Mays Beach W9, S22 1.3 15 2.2 5.4 E Cremorne (Ocean) Beach W10, S20 3.8 15 1.9 5.1 E Cremorne – Pipe Clay Esplanade W11a, b - - 0.7 2.9 NW,S Clifton – Bicheno St, Pipe Clay Lagoon W12 - - 0.9 3.2 NW Clifton (Ocean) Beach, west S17 5.4 15 - - South Arm Neck – Ralphs Bay side W7 - - 1.7 4.6 NW Hope Beach, South Arm Neck - ocean side S16 6.2 15 - - South Arm Beach - Halfmoon Bay W13, S13 1.1 15 1.6 4.5 NW Glenvar Beach W14, S12 1.3 15 1.5 4.2 NW Opossum Bay W14, S19 1.1 15 1.5 4.2 NW

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 46.

9. WIND SETUP MODELLING

9.1 Wind Setup Process

The wind setup process is illustrated in Figure 9.1. During times of high wind, surface water is transported downwind through surface drag. In an enclosed bay, this water may “pile up” at the downwind end of the bay. Some of this piled up water may return as bed flow, however, if the bay is shallow, the shear between the bed return flow and the surface water may restrict return flow, resulting in noticeable elevated water levels, known as wind setup.

The process occurs at different scales. The regional scale process is included in measurements on the Hobart tide gauge (Section 5). The relatively steep and deep bathymetry around the Port of Hobart means that local wind setup in excess of the regional scale process is small at the Hobart tide gauge. Local wind setup in Clarence in excess of the regional scale process would be restricted to shallow bays such as Pipe Clay Lagoon and Ralphs Bay.

Wind setup is somewhat self limiting, in that its magnitude decreases as water levels increase. This has been noted in studies for Adelaide (Wynne et al. 1984) where it has been found that wind setup is far less at high tide than at low tide.

9.2 Modelling Wind Setup

Sophisticated 2- and 3-dimensional hydrodynamic models are available to model wind setup. Such a modelling exercise to model only Ralphs Bay would require approximately half of the total resources available for this entire study of most of the Clarence coastline. In lieu of this, simple 1-dimensional modelling using approximated profiles was undertaken to gauge the magnitude of wind setup.

The software CRESS (Version 4.0.2) and equations from Dean and Dalrymple (1991, p 160) was used to model wind setup. The fetch lengths and wind speed were as used for wind wave modelling, with the duration adjusted to the travel time of a shallow water wave. The results are shown in Figure 9.2 and summarised in Table 9.1. Also shown in Table 9.1 is the present day 100 year ARI (1% AEP) water level (excluding local wind setup) which is projected to be 2.34 m AHD in 2100 under the high range sea level rise scenario (Section 4). The effect of wind setup on the present day 100 year ARI (1% AEP) water level is to increase it approximately a further 0.3 m at South Arm neck, 0.13 m at the Ralphs Bay end

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 47.

of Lauderdale Canal and 0.13 m at Bicheno Street Clifton. Note that wave setup and runup are additional to this (Section 10).

Long term change to the bays, such as progressive infilling or deepening would alter the wind setup values calculated in this report. Ongoing monitoring is the only method of observing such change.

Table 9.1 Local Wind Setup in Estuaries (excludes wave setup) Hobart South Arm neck Bicheno St Clifton Ralphs Bay at water level (N wind) (N wind) Lauderdale Canal (m AHD) (W wind) 100 year WL incl 100 year WL incl 100 year WL incl ARI wind wind setup ARI wind wind setup ARI wind wind setup setup (m AHD) setup (m AHD) setup (m AHD) 0 0.78 0.78 0.23 0.23 0.20 0.20 1.0 0.33 1.33 0.16 1.16 0.14 1.14 1.5 0.27 1.77 0.12 1.62 0.13 1.63 2.0 0.23 2.23 0.11 2.11 0.12 2.12 2.5 0.20 2.70 0.09 2.59 0.10 2.60 3.0 0.18 3.18 0.08 3.08 0.09 3.09

100 year ARI (1% AEP) 1.44 0.28 1.72 0.13 1.57 0.13 1.57 Present 2.34 0.21 2.55 0.10 2.44 0.11 2.35 2100 high SLR

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 48.

10. WAVE SETUP, WAVE RUNUP AND INUNDATION

10.1 Wave Setup

Wave setup is defined as the quasi-steady increase in water level inside a surf zone due to the conversion of part of the waves’ kinetic energy into potential energy. Numerical models such as Dally, Dean and Dalrymple (1984) are available to calculate wave setup. For an initial engineering approximation on a sandy beach (but not a reflective rocky shore or seawall), wave setup at the shore is typically 15% of the significant wave height at the outer limit of the surf zone (breaker height). Present day wave setup levels are incorporated with wind setup in the still water levels presented in Table 10.1.

10.2 Wave Runup

Mase (1989) presented predictive equations for irregular runup on plane, impermeable beaches (slopes 1:5 to 1:30) based on laboratory data. Field measurements of runup (Holman, 1986; Nielsen and Hanslow, 1991) have found lower values than those predicted by Mase, however, this is partly because they have used the upper beach face as a slope rather than the entire surf zone (from break point to runup limit). Unpublished work by WRL has successfully verified the Mase equations against recorded runup reported at numerous beaches in Higgs and Nittim (1988) if the entire surf zone slope is used. This approach has also been used within the SBEACH erosion model which has successfully predicted the upper limit of profile change at numerous Australian beaches (Carley and Cox, 2003).

Wave runup is generally calculated on a two-dimensional cross sectional basis, which can change over short distances where structures (e.g. road embankments) are present. Calibration or verification of runup calculations on beaches is best undertaken with either field measurements, a physical model, or surveys of debris lines (Higgs and Nittim, 1988) following major storm events. Prediction of wave runup on structures is best undertaken with a physical model. For wave runup on beaches, the R2% value is the most commonly used, which is the runup exceeded by 2% of waves. That is, two waves out of 100 will exceed the runup limit quoted.

The wave runup calculations implicitly include wave setup. There are several cases of wave runup which need consideration in detailed studies for each precinct:

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 49.

 The wave setup level is the most representative inundation level for areas located away from the foreshore – generally those properties which are not in the front row facing the water.

 The wave runup level is a predictor of dune overtopping and wave impacts on beachfront structures.

 If the dune crest is maintained above the wave runup level, is continuous and contains sufficient sand buffer, the seaward water level (wave setup level) may not extend to the landward side of the dunes.

 In some circumstances, dune overwash or erosion may cause breaching, which may result in additional inundation of backshore areas, however, calculating the magnitude of this would require complex numerical modelling.

10.3 Wave Setup and Runup Levels

Present day wave setup levels are shown in Table 10.1 together with the R2% wave runup levels calculated from the methods of Mase (1989). The setup levels have not been calculated for areas with rocky or seawall protected shores such as Kangaroo Bay (with the exception of Opossum Bay). The runup levels are for sandy beaches and would increase if seawalls were built or are present (e.g. Opossum Bay). The wave runup level has not been calculated for the extremely flat gradients within Ralphs Bay. This would be the subject of an additional detailed study as it is highly dependent on the variable road embankment slopes.

The values shown in Table 10.1 may be slightly conservative, as it has been assumed that extreme water levels are accompanied by extreme wind conditions. This is not unreasonable though, since both phenomena are caused by intense low pressure systems. More sophisticated joint probability analyses could be undertaken for critical sites as part of future detailed studies.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 50.

Table 10.1 Present Day 100 year ARI Wave Setup and Runup Levels Location Label Swell Wind Still water Local Wave Still water R2% R2% level (excl wind setup level (incl wave wave wave setup wave and runup runup setup) wind level setup) Hs Tp Hs Tp (m, AHD) (m, AHD) (m, AHD) SWL ηwind ηwave = SWL + R2% = SWL + ηwind + R2% ηwind Montagu Bay W1 - - 0.7 2.7 1.44 - - - Kangaroo Bay W2 - - 0.9 3.2 1.44 - - - Bellerive W3, S2 0.3 15 2.2 5.5 1.44 - 0.33 1.8 1.9 3.3 Little Howrah Beach W4, S6 0.5 15 2.8 6.0 1.44 - 0.42 1.9 1.2 2.6 Rokeby Waste Water Treatment Plant W5 - - 1.4 4.3 1.44 0.10 0.21 1.8 - - Lauderdale - South Arm Road, Ralphs Bay W6 - - 2.5 5.6 1.44 0.10 0.38 2.0 - - Seven Mile Beach west W8, S29 3.8 15 2.1 5.4 1.44 - 0.57 2.0 1.2 2.6 Roches Beach, Lauderdale W9, S26 1.6 15 2.2 5.4 1.44 - 0.33 1.8 1.4 2.8 Mays Beach W9, S22 1.3 15 2.2 5.4 1.44 - 0.33 1.8 1.2 2.5 Cremorne (Ocean) Beach W10, S20 3.8 15 1.9 5.1 1.44 - 0.57 2.0 3.3 4.7 Cremorne – Pipe Clay Esplanade W11a, b - - 0.7 2.9 1.44 0.10 0.11 1.6 - - Clifton – Bicheno St, Pipe Clay Lagoon W12 - - 0.9 3.2 1.44 0.13 0.14 1.8 - - Clifton (Ocean) Beach, west S17 5.4 15 - - 1.44 - 0.81 2.3 4.5 5.9 South Arm Neck – Ralphs Bay side W7 - - 1.7 4.6 1.44 0.28 0.26 2.3 - - Hope Beach, South Arm Neck - ocean side S16 6.2 15 - - 1.44 - 0.93 2.4 4.7 6.1 South Arm Beach - Halfmoon Bay W13, S14 1.1 15 1.6 4.5 1.44 - 0.24 1.7 2.5 3.9 Glenvar Beach W14, S12 1.3 15 1.5 4.2 1.44 - 0.23 1.7 3.5 4.9 Opossum Bay W14, S10 1.1 15 1.5 4.2 1.44 - 0.23 1.7 3.1 4.5

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 51.

11. TSUNAMIS

Tsunamis are generated by major displacements in the sea bed or surface, which are caused by earthquakes, landslides, volcanoes or a major meteorite strike (asteroids or comets). Tsunamis are also referred to as tidal waves. The word tsunami means “harbour wave” in Japanese. Eastern Australia is relatively remote from the most active seismic areas of the world, and is partially sheltered by New Zealand and Pacific islands. Nevertheless, tsunami events have reached the Australian coast and have been documented in several places including by Dominey-Howes (2007 in press) and Rynn and Davidson (1999).

Rynn and Davidson (1999) identified 34 tsunamis reaching the NSW coast between 1788 and 1995, though most were too small to notice except on tide gauge records. Dominey- Howes (2007 in press) catalogued 57 tsunamis reaching the Australian coast, comprising 10 paleo-tsunamis (those occurring prior to European occupation of Australia in 1788) and 47 historic tsunamis since 1858. The historic tsunami database is biased towards those locations with the longest colonial history and written accounts (e.g. newspapers, harbourmaster journals, tide gauges), that is, the NSW coast in the 20th century. Of the 47 historic tsunamis reported, Dominey-Howes (2007) found that 75% were caused by earthquakes, 4% by volcanoes and 21% of unknown origin. Landslides and asteroid strikes are other known mechanisms of tsunami generation. Approximately 20% of historic tsunamis were reported to affect Tasmania.

Minor to moderate tsunamis have been recorded on Sydney’s Fort Denison tide gauge which has been operational since 1867. A summary of notable tsunamis observed in Tasmania and Eastern Australia between 1788 to 2006 is shown in Table 11.1. The 1960 tsunami caused the water level at Fort Denison Sydney to oscillate through a range of 0.84 m over a 45 minute period (compared with a tidal oscillation of 1 m to 2 m over approximately 6 hours). Such a rapid water level change within the enclosed water body of Sydney Harbour induced strong currents which caused damage to moored boats and shoreline structures.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 52.

Table 11.1 Notable Tsunami* Events reaching Tasmanian or East Australian Coast 1858 to 2006 Date Origin Height on Runup height on Comment/Source tide gauge open coast above (m) sea level 06/02/1858 Unknown ? Dominey-Howes (2007) 15/08/1868 Chile 1.07 1.2 m NSW Government (1990) Fort Denison Dominey-Howes (2007) 13/10/1874 Unknown ? Reported at Port Davey, TAS Dominey-Howes (2007) 10/05/1877 Chile 1.07 0.8 m NSW Government (1990) Fort Denison Dominey-Howes (2007) 28/08/1883 Krakatoa, 1.5 m (WA?) Dominey-Howes (2007) Indonesia 26/06/1924 Macquarie Is 0 m Dominey-Howes (2007) 22/05/1960 Chile 0.84 1 to 2 m NSW Government (1990), Fort Denison 1.72 m Eden NSW Rynn and Davidson (1999), 0.32 m Hobart Bryant (2001) 23/05/1989 Macquarie Is 0.22 0.3 m Rynn and Davidson (1999), Port Kembla Dominey-Howes (2007) 26/12/2004 Sumatra 1.1 m (WA?) Dominey-Howes (2007) Indonesia 28/03/2005 Nias Island 0.2 m (WA?) Dominey-Howes (2007) Indonesia 03/05/2006 Tonga 0.2 m Dominey-Howes (2007) * Bryant (2001) considers tsunami to be both singular and plural

Geological evidence of “mega-tsunami” or “paleo-tsunami” on the Illawarra NSW coastline has been presented by Bryant (2001). The high likelihood (short ARI) of these presented by Bryant is disputed by other experts (e.g. Rynn and Davidson, 1999; Satake, 2002; Dominey-Howes, 2007). Quantification of this is not currently known.

Tsunamis occur on a random and infrequent basis and are independent of all other effects causing elevated ocean water levels. The maximum tsunami runup recorded in eastern Australia since 1858 has been approximately 2 m, however, the risk of larger events cannot be dismissed. It is understood that detailed studies and modelling on tsunami risk are being undertaken by Emergency Services Tasmania and Geoscience Australia.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 53.

12. EROSION HAZARD

12.1 Models Available

Numerous numerical models and desktop techniques have been developed to assess beach erosion during storms. Couriel, Cox and Carley (1992) reviewed cross-shore beach profile models and classified them into four main groups, namely:

 Statistical;  Static equilibrium  Dynamic equilibrium  Hydrodynamic.

Static equilibrium models involve an "instantaneous" profile change to a reference post storm profile. The shape and extent of the post storm profile typically is determined by factors such as grain size, wave height and water level. Examples include the models of Dean (1977, 1984), Swart (1974) and Vellinga (1986). A common criticism of these models is that the time scale of variations in the applied hydrodynamic forcing conditions is generally faster than the time needed to develop a new equilibrium profile. An equilibrium profile based on the peak conditions during a storm event may dramatically overestimate erosion. The two approaches to circumvent this limitation have traditionally been to allow for a fixed event duration (Vellinga, 1986) or to extend the models to the dynamic equilibrium class.

Dynamic equilibrium models involve a time dependent evolution towards an equilibrium- based profile. Simple models of this class involve desktop techniques for the time dependency (e.g. Kriebel, Kraus and Larson, 1991). However, most involve a computer utilising numerical methods. An early model of this class is that of Kriebel and Dean (1985) though it did not predict the formation of an offshore bar, as later models of this class such as SBEACH (described later) do. SBEACH also incorporates many features which place it in the hydrodynamic class.

Hydrodynamic models attempt to consider more fully the physical processes occurring in the surf zone and are the focus of much ongoing research. Many major European and Japanese laboratories have developed such models, some of which are available on a commercial basis. Examples of such models include NPM or COSMOS from HR Wallingford UK, LITCROSS from the Danish Hydraulics Institute and UNIBEST-TC from Delft Hydraulics. Much of the development work involved in these models is F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 54.

undertaken in wave flumes, in which conditions are more two-dimensional than natural beaches and wave heights are much smaller than during extreme ocean events. These models are computationally intensive, but commercially-available versions for engineering use still involve time averaging over time scales many times larger than a single wave period. Such models are likely to improve with further development, however, for engineering applications they do not necessarily possess better predictive capabilities than the best equilibrium or probabilistic type models, particularly those which have been developed and tested using field data.

12.2 SBEACH Model

SBEACH is a numerical cross-shore sediment transport and profile change model from the United States Army Corps of Engineers, Coastal Engineering Research Center. The name is an acronym derived from Storm-induced BEach CHange. Details of the model are given in Larson and Kraus (1989) and Larson, Kraus and Byrnes (1990).

SBEACH considers sand grain size, the pre-storm beach profile and dune height, plus time series of wave height, wave period, water level.

The sediment transport module of the model can be classified as a dynamic equilibrium model, in that sediment transport is considered to be driven by local differences between the computed cross-shore wave energy dissipation and that which would occur for an equilibrium profile.

SBEACH uses the numerical breaker decay model of Dally, Dean and Dalrymple (1984) which has been tested extensively against both laboratory and field data. In this breaker decay model, waves which initially break continue to decay as they travel towards the shore. If the wave height to water depth ratio becomes small enough, the model allows the wave to become unbroken again (reform), shoal and break again in shallower water. The reforming of waves is observed commonly in bar/trough beach systems. The surf zone model calculates wave setup through the surf zone. SBEACH can predict the formation of one or more offshore bars across the surf zone.

Model development involved extensive calibration against both large scale wave tank laboratory data and field data. In an assessment of 10 cross-shore profile models, Schoonees and Theron (1995) placed SBEACH in the "best" group with regard to the extent of verification, and in the "acceptable" group with regard to the theoretical background. With the exception of UNIBEST-TC (from Delft Hydraulics, The

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 55.

Netherlands), models classified as having the "best" theoretical basis had not been extensively verified.

SBEACH has been verified extensively for measured storm erosion on the Australian east coast, including at Warilla, Narrabeen and Wamberal (Carley, 1992), and at the Gold Coast (Carley et al. 1998).

12.3 Statistical Models

12.3.1 Gordon Model

Gordon (1987) presented storm cut statistics for the New South Wales coast between Sydney and the Queensland border. These statistics were based on 10 years of detailed profile surveys and photogrammetric analysis of 40 years of aerial photos. Due to the limitations of photogrammetry, only eroded volumes above mean sea level were given. A distinction was made between volumes for “low demand, open beaches” and “high demand, rip heads” with the following equations presented:

VL = 5 + 30 ln(ARI) (12.1)

VH = 40 + 40 ln(ARI) (12.2)

where VL and VH are eroded volumes above AHD for “low demand, open beaches” and “high demand, rip heads” respectively (m3/m) ln is the natural (base e) logarithm ARI is average recurrence interval (years)

Due to the nature of the aerial photography program, the eroded volumes may not result from a single storm event, but rather may be the cumulative effect of several storm events. Thus the ARIs presented refer to “erosion event” eroded volumes rather than erosion arising from single storm events of a particular ARI.

Though not directly applicable to Clarence due to site specificity, the findings provide useful order of magnitude erosion volumes for the open coast. The predicted 100 year ARI erosion volumes from Gordon for the NSW open coast are 140 to 220 m3/m above AHD, for indicative maximum significant wave heights of 9 m.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 56.

12.3.2 Deans et al (1994)

Deans et al. (1994) analysed 20 years of profile data for Adelaide metropolitan beaches. Major storm erosion in Adelaide is dominated by wind waves, with 100 year ARI significant wave heights of approximately 3.4 m (Carley et al, 2001). Deans et al, (1994) found maximum erosion volumes above +1 m AHD of 30 to 40 m3/m. Converting these volumes to above AHD (by WRL) gives erosion volumes of 50 to 65 m3/m.

Again, as with the Gordon model, though not directly applicable to Clarence due to site specificity, the findings provide useful order of magnitude erosion volumes for a coast exposed to slightly larger wind waves than most of the Clarence coast.

12.3.3 Thom and Hall (1991)

Thom and Hall (1991) undertook beach surveys at monthly intervals between 1972 and 1988 on four transects at Moruya on the NSW south coast. They distinguished between “erosion dominated periods” where the beach continued to erode over a stormy period from 1972 to the end of 1974; and “accretion dominated periods” where the trend was one of accretion, particularly from 1978 to 1983. The time scale for accretion is much slower than that of erosion, with erosion (during storms) occurring at time scales of the order of 5 to 50 times faster than accretion (during mild waves) when suitable conditions prevail.

Thom and Hall related volumes to Indian Spring Low Water (ISLW) which is approximately -0.8 m AHD. They found the following erosion volumes (above ISLW) averaged over the four profiles they surveyed:

 Maximum erosion relative to the mean profile: 158 m3/m  Maximum erosion relative to the most accreted profile: 287 m3/m

Again, though not directly applicable to Clarence due to site specificity, the findings provide useful order of magnitude erosion volumes for the open coast, and are comparable to the findings of Gordon (1987), notwithstanding the slightly different vertical datum used. Furthermore, the plots of Thom and Hall (1991) illustrate the impact of sequential storms (clustering) on progressive erosion, which they termed “erosion dominated periods”.

12.4 Sand Grading Curves

Most sediment transport models require sand grain size as an input. Preliminary data for this was undertaken by taking two single sand samples from near the low water mark at

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 57.

Clifton (in line with the surf life saving clubhouse) and Roches Beach (south of Bambra Reef) on 31 January 2008. A comprehensive sampling program would involve multiple samples, locations and dates. The sand samples were oven dried and sieved to AS 1289.3.6.1-1995 in the WRL soils laboratory, with the grading curves shown in Figure

12.1. The following median grain sizes (D50) were found and were used as input for erosion modelling and defining “equilibrium” beach profiles (Section 13):

 Clifton: 0.205 mm  Roches Beach: 0.150 mm.

12.5 SBEACH Application to Clarence

12.5.1 Overview

SBEACH modelling was undertaken in a similar manner to the recommendations of Carley and Cox (2003), and Nielsen and Adamantidis (2007).

12.5.2 Profiles

SBEACH was applied to the beach profiles shown in Figure 13.5. These profiles would provide just a single snapshot, and would in fact be changing in time. Initial modelling was undertaken using the TAFI bathymetry combined with 2 m land contours from Council’s GIS system and was repeated using the LIDAR derived land profiles. Ideally, the model would be calibrated and verified against field measurements of erosion in the study area, however, these were not available. Modelling should be repeated following analysis of measured storm erosion from Council’s survey program at Roches Beach. Nevertheless, WRL has successfully utilised SBEACH at numerous locations – the model considers all the main physical processes relevant to storm erosion.

12.5.3 Water Levels

For storm erosion modelling purposes, a spring tide time series was assumed, to which a tidal anomaly was added, such that the peak water level corresponded to the ARI of the storm (1.44 m AHD for 100 year ARI, 1% AEP). For modelling purposes a symmetrical shape of the anomaly was assumed, with the peak in predicted tide and tidal anomaly assumed to coincide with the peak wave height of the storm. These assumptions are somewhat conservative but not unreasonable since intense low pressure systems are responsible for large waves, strong winds and storm surge. The assumptions could be revised with additional data and joint probability analyses.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 58.

12.5.4 Wave Heights

The peak significant wave height for each location was as shown in Section 8. It was found that for Roches Beach, the ocean swell event caused greater erosion than the wind wave event. As described below, two 100 year ARI storm events were run back to back to determine a design erosion volume.

12.5.5 Design Erosion Event and Storm Clustering

Carley and Cox (2003) found that although SBEACH could model recorded erosion events for which data was available, but when a rational 100 year ARI (1% AEP) design storm was applied, the predicted erosion volumes were less than reported values (for which reliable wave data was not available (e.g. Gordon, 1987; Thom and Hall, 1991)). This is due to sequences (clusters) of storms causing major erosion, rather than a single storm. Additional studies of clustering could be undertaken, but are not part of this study and no analysed data is readily available to feed into erosion modelling. There have been some attempts in other locations (e.g. Gold Coast and Sydney), but these can’t be applied for Clarence.

This same issue led the WA Government (2003) to specify that three back to back “design” storms (nominally 100 year ARI,1% AEP) be run through SBEACH (or similar models) to determine the storm erosion component setback for coastal planning, with a default value of 40 m for this component. The duration of each of these three WA design storms is approximately 110 hours.

Within the realms of the modelling undertaken and the paucity of historical data, there are three suggested options to define the “design” erosion event from storms:

1. A single 100 year ARI storm event 2. 2 x 100 year ARI events (less erosion than a doubling of single storm due to asymptotic behaviour) 3. 3 x 100 year ARI events (WA, 2003 policy).

Based on the experience of this report’s authors, their engineering judgement, and consultation with Clarence Council’s Technical Review Panel for this project, it was elected to model “design” erosion volumes using 2 x 100 year ARI storm events. This is a balanced position, between the use of a single storm and three storms.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 59.

Subject to the assumption made on storm clustering, the actual ARI of two closely spaced 100 year ARI storms could range from 200 to 100,000 years. However, the purpose of using two closely spaced 100 year ARI storms in SBEACH modelling is to model a sequence of lesser storms which have been observed to cause “design” erosion volumes on well monitored beaches (e.g. Gordon, 1987; Thom and Hall, 1991), while still properly considering the wave exposure of each beach.

As shown in Thom and Hall (1991), when the time gap between individual storms is small (of the order of 1 week to several months), beach recovery does not have sufficient time to progress, as it occurs at much slower timescales than erosion (Carley et al, 1998). Therefore, for SBEACH erosion modelling, defining the time gap between storms within a cluster is not needed.

12.5.6 SBEACH Model Results

An example of model input and output is shown in Figure 12.2. A summary of design erosion volumes is shown in Table 12.1. The design erosion volume was based on two back-to-back 100 year ARI design storms, to simulate multiple storm events. The differing erosion volumes can be explained by offshore steepness and wave exposure. Steeper offshore bathymetry results in increased erosion, as does larger storm wave heights.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 60.

Table 12.1 Design Erosion Volumes calculated with SBEACH Location Dune height Storm Horizontal used for erosion storm erosion (m3/m above erosion calculations AHD) allowance (m AHD) **(m) Opossum Bay*, *** 10.0 75 10 Roches Beach, Lauderdale 3.5 100 25 Little Howrah and Howrah Beaches 3.0 35 10 Cremorne (Ocean) Beach 6.0 80 15 Hope Beach, South Arm Neck 7.0 160 25 Seven Mile Beach – western 1 km only 5.0 40 10 Mays Beach 6.0 50 10 Clifton (Ocean) Beach, western 500 m only 6.0 140 25 Glenvar Beach*, *** 10.0 75 10 South Arm Beach (Halfmoon Bay) 8.0 60 10 Bellerive Beach 4.5 75 15 * May be limited by underlying rock ** Rounded to nearest 5 m *** Dune height for erosion calculations only – actual dune not present.

As discussed previously, there are few direct measurements of erosion for Clarence beaches.

Foster (1988) estimated an upper limit of 30 m3/m for Roches Beach, and acknowledged that this was based on virtually no data (other than his considerable experience).

Sharples (2007) analysed the shoreline as indicated by the vegetation line for Roches Beach from aerial/satellite photos from 1957, 1977, 1987, 2001 and 2005. The purpose of Sharples’ (2007) study was to examine long term shoreline change (Section 13). The time between successive analysed photos was too large to detect short term storm erosion, however, the maximum horizontal recession measured by Sharples was approximately 17 m, but was generally in the range of 5 to 10 m. These limited measured values do not contradict the modelled erosion value of 25 m from Table 12.1.

There are anecdotal reports of major erosion of Cremorne Spit in the 1920s, such that the erosion scarp reached the position now occupied by houses.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 61.

13. RECESSION HAZARD AND LITTORAL DRIFT

13.1 Littoral Drift Transport

Littoral drift is defined as the movement of sediment approximately parallel to the shore due to the angle of the predominant waves. On the open coast beaches of Clarence sediment transport is predominantly driven by ocean swell, however, local wind waves would have some impact on semi-sheltered beaches such as Roches, and would be the predominant cause of littoral drift transport within Ralphs Bay.

Foster (1988) and Byrne (2006) made order of magnitude estimates based on the accumulation of sand on Seven Mile Beach over the past 6000 to 7000 years. It was estimated that the littoral drift rate past Roches Beach Lauderdale was 60,000 to 70,000 m3/year northward.

Detailed littoral drift modelling is not part of this project. Output from SWAN modelling (Appendix A) indicates that at the -5 m AHD contour, near the Roches Beach canal, the wave angle varies only from 110º to 115º true north for all wave periods from 10 to 25 seconds and all offshore directions. Basic application of the CERC equation (SPM, 1984) using a median wave height of 0.3 m, a shore normal coast angle of 90º to 105º true north and breaker angles of 10º to 15º to the shore gives potential littoral drift rates of 60,000 to 90,000 m3/year northward. Additional contribution, including some southward transport, would occur due to wind waves.

13.2 Underlying Recession

Beaches such as Roches and Cremorne show a classic zeta or crenulate curve planform between the hard coastal control points (Chapman et al, 1982; Stephens et al, 1981) which is indicative of northward littoral drift. Figure 13.1 shows the evolution of zeta curve planform beaches, which shows a gradual deepening of the bay over a period of relatively stable sea level.

As discussed previously, Sharples (2007) examined ongoing change at Roches Beach for the period 1957 to 2005 using aerial photos, from 1957, 1977, 1987, 2001 and 2005. The analysis was limited to a two-dimensional analysis of the plan position of the shoreline. The limitations and inaccuracies of the techniques used were discussed by Sharples. Sharples (2007) found minimum (demonstrable) shoreline recession on Roches Beach of 4 to 6 m, increasing to 9 m south of the canal in the deepest part of the zeta curve. The best

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 62.

estimates were larger than the minima, and ranged from 5 to 10 m north of the canal, to 12.5 m south of the canal. These equate to the following average values for 1957 to 2005 (48 years):

 5 m equates to 0.10 m/year  10 m equates to 0.21 m/year  12.5 m equates to 0.26 m/year.

No analysis of other beaches within Clarence has been undertaken to date. Only Roches, Mays and Cremorne Beaches on the east coast exhibit a zeta planform, although Cremorne is further complicated by the presence of the entry to Pipe Clay Lagoon at its southern end.

Hope, Calverts and Clifton Beaches are more aligned with the predominant wave crests and do not exhibit a planform associated with net littoral drift.

There is evidence of change through erosion, recession or rotation (Section 14) at Little Howrah Beach as shown in Figure 13.2. The concrete collar of a sewer access point would have originally been poured on top of the sand or below it, and was located approximately 1 m above the sand in 17/04/2007, while on 31/01/2008 it was approximately 0.3 m above the sand.

13.3 Possible Causes of Underlying Recession

Underlying recession has only been shown through measurements to have been occurring at Roches Beach, Lauderdale. There are no significant coastal structures intercepting littoral drift on the Clarence coast. The dilapidated timber training walls at the closed mouth of Lauderdale Canal and the minor rock revetments on Roches Beach are not believed to be a major cause of recession. Likewise, the dilapidated training walls at the mouth of Pipe Clay Lagoon at Cremorne do not trap major quantities of sand.

The possible causes of recession listed below may occur at all Clarence beaches.:

 Imbalances in littoral drift, that is, more sand leaves the coastal compartment than enters it. For example, the sand supply may be slowly depleted or the bed deepening.

 Ongoing evolution (deepening) of the zeta planform (Figure 13.1), which could still be adjusting to past sea level rise or more recent sea level rise (Hunter et al, 2003; Church and White, 2006).

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 63.

 Cross shore response to recent sea level rise, such as postulated in the Bruun Rule (Section 13.4).

 Changes in the wave climate (height, direction, period) or the relative balance of wind waves and swell. SWAN modelling (Appendix A) indicates that for Roches Beach, nearshore wave direction is not sensitive to offshore direction and period, however, changes in wave height or wind waves would still alter littoral drift.

 Sediment sinks, which may include Pipe Clay Lagoon, Ralphs Bay, Seven Mile Beach and Pitt Water.

 Sand being supplied in pulses or slugs, which progress northward through the system.  Changes in seagrass colonies which may trap or liberate sand (Wallace and Cox, 2000; Hart, 1997; EPA, 1999).

 Erosion or sea level rise effects on coastal control points such as Bambra Reef (Figure 13.3), such that the extent of the salient (locally widened coastal control point in the lee of an offshore reef or island) is reduced.

13.4 Future Recession and the Bruun Rule

13.4.1 Bruun Rule

It is expected that open coast beaches will recede under conditions of accelerated sea level rise. A recession rate can be estimated using the Bruun Rule (Bruun, 1962, 1988) as the rate of sea level rise divided by the average slope of the active beach profile (Figure 13.4). This rule is based on the concept that the existing beach profile is in equilibrium with the incident wave climate and existing average water level. It is a simple concept, which assumes that the beach system is two-dimensional and that there is no interference with the equilibrium profile by headlands and offshore reefs. The Bruun rule is typically expressed as

r X R  (13.1) h  dc where R is horizontal recession (m) r is sea level rise (m)

X is the horizontal distance between h and dc h is active dune/berm height (m)

dc is profile closure depth (m, expressed as a positive number)

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 64.

13.4.2 Profile Closure Depth

For a given sea level rise and profile, the only contentious variable remaining in the Bruun rule is the closure depth (dc) for which various formulations and methods exist. Some have been verified against field data from sites such as the Great Lakes (USA) where water levels have increased over extended time periods (Hallermeier, 1981). For open coast locations on Australia’s east coast, the closure depth can range from –11 to –25 m AHD

(Nielsen, 1994). For many of these locations, when the entire term X/(h + dc) is considered (the average profile slope), it is approximately constant for any closure depth between –11 and – 25 m AHD. This has led to a “rule of thumb” of R = 50S for NSW and south-east Queensland, with 50 being referred to as the Bruun Rule factor.

Bruun (1988) suggested an ultimate closure depth of 3.5Hsb and defined Hsb for this application as the “50 to 100 year [ARI] significant breaking wave height” (the seaward limit of the surf zone for significant waves) for the subject beach. Significant waves were defined in Section 6. In a separate Danish case study however, Bruun found dc to be 2Hsb.

The method of Hallermeier (1983) is one of the most widely accepted for defining closure depths, as it is based on site specific physical characteristics and processes. Hallermeier (1983) defined three profile zones, namely the littoral zone, buffer zone and offshore zone, and surmised that the actual closure depth falls somewhere between the seaward limit of the littoral zone and the offshore zone. Hallermeier termed the depth at the seaward limit of the littoral zone do while the depth at which the offshore zone commences is termed dc. Nielsen (1994) compiled data from many studies and found that for NSW and the Gold Coast generally, two distinct sedimentological boundaries are consistently apparent at 11 m to 15 m depth and 18 m to 26 m depth (relative to AHD). For the Gold Coast, the inner sedimentological boundary lies at 14 m to 16 m depth, while the outer boundary lies at approximately ~26 m depth (Nielsen, 1994, Chapman and Smith, 1981, 1983, Smith, 1975). The seabed seaward of the inner (14 m to 16 m depth) boundary for the eastern Australian open coast is believed to be relict (Nielsen, 1994). WRL is not aware of any such studies on the Clarence coast other than the TAFI seabed mapping project.

13.4.3 Discussion on the Application of the Bruun Rule in other Jurisdictions

There are few subjects within coastal engineering/science which generate as much controversy and literature as the Bruun Rule. Most strident critics (e.g. Pilkey and Cooper, 2004) concede that there are few alternatives to the Bruun Rule, while most objective analyses (e.g. Ranasinghe et al, 2007) caution against its inappropriate application.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 65.

Ranasinghe et al, (2007) reviewed the Bruun Rule and its application around Australia. They summarised policies and/or common practice from around Australia as shown in Table 13.1.

Table 13.1 Commonly Used Input Parameters for Bruun Rule Application (Ranasinghe et al 2007, subject to update) State Sea Level Rise value Active profile slope Planning or closure depth horizon NSW 0.18 m 1V:50H* to 1V:100H based on 2050 sensitivity analysis and/or site 0.49 m specific assessment 2100 QLD 0.3 m -16 m 50 years SA 0.3 m Long term profile surveys or 50 years 1 m seagrass-sediment boundaries 100 years VIC 0.3 m Determined from applying 50 years SBEACH to a 100 year ARI storm** WA 0.38 m (2000 to 2100 mid 1V:100H 2100 range IPCC) * 1V:50H means an overall profile slope of 1 metre vertical for each 50 metres of horizontal. ** To determine the seaward limit of cross shore sand transport due to storm erosion.

13.4.4 Application of Bruun Rule to Clarence

The Bruun Rule provides an order of magnitude of long term recession due to sea level rise. The Bruun Rule is only applicable to wave dominated beaches, which precludes its application inside Ralphs Bay and Pipe Clay Lagoon. Furthermore, it is WRL’s contention that seaward profiles flatter than equilibrium (BMAP – Beach Morphology Analysis Program, version 2.0) are due to a surplus of sediment, and/or headland bypassing, and/or a profile not dominated by cross shore wave action. In these cases the closure depth as been defined as the point where the profile becomes flatter than equilibrium. The profiles used are shown in Figure 13.5, though it is noted that these are constantly changing. The representative dune crest heights used were those determined by the LIDAR survey – following Council supplied contours for interim calculations. The adopted profile slopes for input to the Bruun Rule are shown in Table 13.2. The depths in Hallermeier’s equations are calculated to mean low water (CEM, 2002) and have been adjusted to AHD in Table 13.2.

It can be seen from Table 13.2 that there is a wide scatter in the Bruun Rule factor. This may reflect differing vulnerability to sea level rise, but mostly reiterates the position of most practising coastal engineers/scientists (e.g. Ranasinghe et al, 2007) that the Bruun rule

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 66.

is an order of magnitude estimate only. It can be seen that the best estimate for most of the exposed beaches, the Hallermeier do value, or the profile evidence is generally less than 50, which conforms within the “rule of thumb” values of 50 to 100. However, some of the reflective beaches in sheltered locations have Bruun Rule factors of less than 20. For planning purposes, if a Clarence City wide value was required, the best estimate for all locations falls within an adopted value of 50 (100 was adopted in WA). If some site specificity is required it is recommended that a value of 50 (and in some cases 20) be adopted for less sensitive sites as shown in Table 13.2. For this study, a value of 50 has been used. The presence of bedrock may limit the potential recession for Opossum Bay and Glenvar Beach, but the level is unknown. Investigations in the Seven Mile Beach area have revealed approximately 13 m of unconsolidated sands overlying 70+ m of green Tertiary clay (Cromer and Sloane, 1976; Cromer, 1981; Roberts, 1988). Additional geophysical investigations would be needed for all Clarence beaches to assess the levels of underlying strata.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 67.

Table 13.2 Estimated Bruun Rule Profile Gradients Location Dune Closure depth (m, AHD) Bruun factor height*

s o o c

Profile Profile Outerd Inner d Inner d Outer d Outer Adopted Adopted SBEACH SBEACH evidence** evidence** 100 yr ARI yr ARI 100 100 yr ARI yr ARI 100 evidence ** Hallermeier Hallermeier Hallermeier Hallermeier Best estimate Bellerive 4.25 2.8 5.7 6.0 12 14 14 12 50 Little Howrah Beach 3 3.3 5.7 6.5 25 26 28 25 50 Seven Mile Beach west 5 5.3 12.9 7.5 4.5 81 358 154 55 55 50 Roches Beach, Lauderdale 2.25 2.6 5.1 4.0 3.3 25 148 120 31 31 50 Mays Beach 6 2.6 4.4 3.5 3.3 18 64 27 45 45 50 Cremorne (Ocean) Beach 6.75 5.3 12.1 8.5 43 88 66 43 50 Clifton (Ocean) Beach, west 6.5 7.7 16.0 11.5 25 68 40 25 50 Hope Beach, South Arm Neck - ocean side 7 8.0 16.0 14.0 26 33 31 26 50 South Arm Beach - Halfmoon Bay 8.75 2.1 5.7 5.0 10 13 12 10 50 Glenvar Beach 2 1.9 5.7 6.0 15 20 19 15 50 Opossum Bay 2 1.9 5.7 5.0 15 20 19 15 50 *Based on LIDAR survey data, nominal sand height used for Glenvar and Opossum since no dune present ** Only where the seaward portion of the profile becomes substantially flatter than equilibrium

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 68.

13.5 Gaps and Further Work

The study of long term recession undertaken for Roches Beach by Sharples (2007) should be extended to other beaches in Clarence with a priority order. The tracking of change through satellite photo analysis of the vegetation line could be extended or supplemented with three dimensional photogrammetry extracted from aerial photos dating back to the 1940s. This would allow long term change to be quantified, which is currently unknown for all but Roches Beach, and may provide additional data for determining storm erosion.

More detailed sediment budget and littoral drift calculations should be undertaken on the ocean beaches, particularly from Clifton through to Seven Mile – the SWAN modelling undertaken in this project would provide a nearshore wave climate. This would be a worthwhile research project, but would be of practical necessity during the design of any proposed sand nourishment and/or groyne scheme.

A process study of Pipe Clay Lagoon would determine if it is a sink for marine sand.

Bedrock depths need to be determined and mapped for Glenvar and Opossum Bay Beaches, Little Howrah and around Bambra Reef at Roches Beach, and should be extended to all Clarence beaches. WRL has sourced existing information for Seven Mile Beach, and it may exist for other Clarence locations. The level of bedrock strongly influences the erosion risk for properties located over it.

Updates to future IPCC sea level rise projections should be monitored so that the findings of this study can be appropriately updated.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 69.

14. BEACH ROTATION

14.1 Description

Beach rotation involves either a cyclic or one way change in the alignment of a beach’s planform due to changes in the wave direction over medium (weeks to months) to long (decades) term time scales. It is a well known seasonal phenomenon in Perth WA, where the beach planform alignment is influenced by north-west storms in winter and south-west seabreezes in summer.

The work on beach rotation presented by Short et al (2000) involved more than 20 years of ongoing monthly surveys at Narrabeen NSW, which is approximately 3.6 km long. Short et al found that beach rotation accounted for about 30% of beach width variation (along the 3.6 km long Narrabeen Beach). Regular long term monitoring is the only method available to properly track beach changes, so that extremes, averages, cycles and rotation can be properly identified.

Short et al (2000) looked for correlation between beach rotation at Narrabeen NSW and the Southern Oscillation Index (SOI) or el Niño / la Niña cycle. While they published lag times between SOI events and beach rotation of the order of 1 year, they concluded that there were “only weak …. relationships between SOI and beach volume and rotation indices, and no significant relationship with wave climate indicators.” Short et al, (2000) also referred to the work of others postulating links between the SOI and the generation of cyclones (low pressure systems) in the Coral Sea, Tasman Sea and Southern Ocean, however, for Sydney they found no significant relationship.

There are postulations and evidence that strong winds in the Southern Ocean are shifting towards Antarctica and developing a more westerly direction (CSIRO, 2007). Marshall (2003) investigated the Southern Annular Mode and the intensification of the southern storm belt, while Simmonds and Keay (2000) found that the number of southern ocean storms was decreasing but the intensity was increasing.

The beaches of Clarence may be influenced by changes to both swell waves and local wind waves. The changes to swell waves are indicated by the Southern Annular Mode and changes to local wind waves may be influenced by both the Southern Annular Mode and the Southern Oscillation Index.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 70.

SWAN modelling (Section 6 and Appendix A) found that for the inner ocean beaches of Cremorne, Mays, Roches and Seven Mile, the swell wave angles were relatively constant for all offshore periods and directions, but the local height was strongly influenced by offshore direction. Changes to swell and wind wave height, period and direction would still alter beach alignment. The outer Clarence beaches of Clifton, Hope and Calverts Beaches are most vulnerable to rotation due to swell wave conditions as the waves are less refracted at those locations. That is, a change in offshore wave angle leads to a change in wave angle at the beach.

14.2 Gaps and Future Studies

The potential extent of beach rotation is currently unknown for Clarence beaches. As stated above, the first stage in assessing the historical prevalence of beach rotation would be to examine aerial photos, as was done to quantify shoreline recession for Roches Beach in Sharples (2007). The frequency of historical aerial photos is poor compared with the monthly data available in Short et al (2000), however, more recent satellite photos may be available at more frequent time steps. Future rotation can be assessed with ongoing monitoring being undertaken for Roches Beach, but should be extended to other ocean beaches. This is of high practical necessity for Clarence beaches, and should be undertaken in conjunction with the recommendations from Section 13.

If credible projections for changes to the offshore wave climate can be obtained, a modelling exercise involving combining the SWAN results of this study with a beach planform model such as GENESIS could be undertaken to quantify the extent of beach rotation. This would be of high practical importance for Clarence beaches if credible projections comparable to the rigour of IPCC sea level rise projections were available. However, based on the current lack of precise quantitative projections for wave climate change, this would best be undertaken as academic research and/or sensitivity analyses.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 71.

15. ENTRANCE STABILITY OF ESTUARIES

15.1 Overview of Entrance Stability

Creek and estuary mouths discharging across sandy beaches are prone to migrate, meander, close and erode. Many eventually migrate until they reach a hard control point, however, some undergo a quasi cycle of migration and meander, and closure and breakout at other locations (Figure 15.1). This is a natural process, but may not have been considered when roads and buildings were constructed. The presence of bridges constructed close to the mouths of many creeks and lagoons constrains their position.

The following creeks and estuaries have been considered:

 Acton Creek at Seven Mile Beach  Clarence Plains Rivulet at Droughty Point  Pipe Clay Lagoon at Cremorne  Un-named Creek Roches Beach North

Other creeks discharge onto rocky shores. Pitt Water and the eastern end of Seven Mile Beach has not been considered due to the lack of development there.

15.2 Acton Creek, Seven Mile Beach

This creek is generally blocked by beach sand (Figure 15.2). The abutments associated with the bridge (Figure 15.2) effectively locate the creek mouth position, with only minor meander downstream. Provided the bridge is preserved (or rebuilt) the creek mouth position will not impact development, but its meander and breakout to the east prevents a viable dune forming at the western end of Seven Mile Beach.

15.3 Clarence Plains Rivulet, Droughty Point

This creek is generally open (Figure 15.3). The abutments associated with the bridge (Figure 15.3) and other shoreline armouring effectively locate the creek mouth position. Provided the bridge is preserved (or rebuilt) the creek mouth position will not impact development.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 72.

15.4 Pipe Clay Lagoon, Cremorne

There are no reports of the entrance blocking. The entrance on the south side is constrained by a rocky shoreline. Erosion and instability of the entrance are a threat to houses on the north side. This is evidenced by previous attempts to stabilise the entrance with (now dilapidated) timber training walls and rock protection (Figure 15.4). A substantial ebb tide shoal exists seaward of the entrance. Chapman et al, (1982) believed that almost all estuaries in eastern Australia are now a sink for marine sediments.

15.5 Un-named Creek Roches Beach North

A small un-named creek discharges just south of Lauderdale Yacht Club on Roches Beach north. The entrance is closed most of the time, but is located in the middle of a sandy beach. The pedestrian footbridge near the mouth (Figure 15.6) limits migration, and no development is immediately adjacent to the mouth.

15.6 Future Studies and Gaps

Future sea level rise may alter the foreshore flora and ecology of estuaries. Studies into this should be undertaken.

Flood studies on the creeks should be undertaken to quantify the flood hazard.

An estuary process study should be undertaken for Pipe Clay Lagoon, which should include analysis of sediments and ongoing monitoring of physical and biological indicators. As described in Section 22, a comprehensive assessment of options for stabilising the entrance of Pipe Clay lagoon needs to be undertaken – which should include a “do nothing” option.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 73.

16. WIND BLOWN SAND

Site visits and analysis of aerial photos indicates that there are no substantial hazard due to wind blown sand (aeolian drift) in Clarence. A quantity of wind blown sand will still reach the built environment during strong winds, but as all dunes are vegetated, this quantity is minor and mobile dunes are not threatening the built environment. The exception is some beach access points (Figure 16.1) where pedestrian traffic has removed vegetation, lowered the sand and forms a potential dune breach point. It is likely that weeds are present in some dune systems.

For a typical (for Clarence) median sand grain size of 0.15 mm (Roches Beach) to 0.20 mm (Clifton), sand movement is initiated for the following velocities with an anemometer elevation of 10 m (CEM, 2002):

 Dry sand ~5.5 to 6.5 m/s (~11 to 13 knots, 20 to 23 km/hour)  Wet sand ~10.5 to 11.5 m/s (~21 to 23 knots, 38 to 41 km/hour).

It can be seen that much higher wind speeds are required to mobilise wet sand compared with dry sand. Sand can become wet through waves and tide, or through precipitation. Therefore, reduced rainfall due to climate change has the potential to increase the potential for wind blown sand. The modelling of this is beyond the scope of this study.

Gaps and future studies include a botanical review of species present, followed by implementation of best practice by planting and maintaining appropriate local species. Note that a future adaptive response (Section 22) may require dunes to be raised, in which case detailed vegetation management plans and dune designs would need to be prepared. Works for dune reconstruction may need to involve detailed studies of aeolian mobilisation during the revegetation phase. Future climate change may alter the range of viable dune species.

Local Clarence community Coastcare groups listed on the web site (accessed on 14/03/2008) http://www.scat.org.au/ourGroups/ourGroups.html include:  Bellerive Howrah Coastcare Group  Friends of Rosny Montagu Bay  Seven Mile Beach Coastcare Group  South Arm Coastcare  Tranmere-Clarence Plains Land & Coastcare Inc.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 74.

Local Clarence coastal community groups listed on Council’s web site (accessed on 14/03/2008) http://www.ccc.tas.gov.au/site/page.cfm?u=365 include:  Rosny- Montagu Bay  Tranmere - Clarence Plains Landcare and Coastcare.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 75.

17. STORMWATER EROSION

Stormwater erosion is a relatively minor hazard in Clarence. There are no large conveyance structures discharging directly onto sandy beaches. There are several mid sized discharge structures on Bellerive and Howrah Beaches (Figure 17.1), however, the additional erosion resulting from these is minor and limited to within several metres of the structure. The discharge pipes along Tranmere extend into the water and/or the shoreline is generally rocky. There is documented damage to stormwater outfalls which extended out to the water at Roches Beach, Lauderdale in 2000 (Figure 17.2).

The design of future stormwater outfalls needs to consider coastal processes, such as:

 The effect of elevated ocean water levels on the hydraulic performance of the system.  Local erosion caused by stormwater discharge and/or wave scour around the outfall.

Water quality from discharged stormwater is likely to be the greatest hazard.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 76.

18. SEAWATER INTRUSION INTO GROUNDWATER

18.1 Overview

Saline intrusion is one of several impacts on groundwater systems that may be associated with sea-level rise and climate change in the Clarence City area. A first-pass desktop evaluation of these processes for groundwater systems in the Clarence area was undertaken based on limited available data.

18.2 Hydrogeological Setting

The Clarence City area is dominated by the Meehan Range that has a maximum height above sea level of 544 m, and is composed of Jurassic age dolerite. There are also outcrops of Triassic age quartz sandstone in the area. The range is vegetated mainly by dry sclerophyll woodland.

The generally narrow coastal plain consists of Quaternary age unconsolidated sands and clayey sands. To the east, there are extensive lowlands where the Hobart Airport is located, and a range of agricultural activities with viticulture, open grass and crop land. Seven Mile Beach is composed of Quaternary fine to coarse sand, clayey sands and some clay layers. Investigations in the Seven Mile Beach area have revealed approximately 13 m of unconsolidated sands overlying 70+ m of green Tertiary clay (Cromer and Sloane, 1976; Cromer 1981; Roberts 1988).

Groundwater flow systems mapping at a broad scale has identified local or intermediate systems in the Clarence area (Bacon and Latinovic, 2003). Groundwater flow systems are defined as a landscape entity that includes the recharge and discharge parts of a flowpath. The equilibrium response time for groundwater flow systems to establish a new recharge and discharge regime is assumed to be in the order of years to decades for local flow systems and up to hundreds of years for intermediate flow systems. Local flow systems in the Clarence area include coastal plains and alluvium, and undifferentiated Tertiary sedimentary rock and high-relief Jurassic dolerite. Intermediate flow systems occur within low-relief Permian and Triassic sedimentary rock.

Annual average rainfall of about 550 mm supports two river systems, a number of small watercourses and recharges groundwater systems. WRL is not aware of any formal assessment of surface-groundwater interaction or groundwater dependent ecosystems within the Clarence area.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 77.

18.3 Groundwater Usage and Management

There is very little available groundwater data for Tasmania and groundwater extraction data is not routinely collected (SKM, 2000; Bacon and Latinovic 2003). Groundwater pumping entitlements are currently not specified or capped for any area of Tasmania. The Clarence area is a small part of the South Central Unincorporated Area for groundwater management in Tasmania. The area has not been designated a specific Groundwater Management Unit and receives a low level of effective management for groundwater resources because of limited current or potential use.

Reticulated water within the City is supplied from the regional water authority Hobart Water, so there are no town groundwater supply systems in the area. It is not known whether any groundwater bores are used for domestic water supply purposes.

A regional scale assessment of sustainable yield and usage was completed for the South Central Unincorporated Area by SKM (2000). Over an area of 27,800 km2, bore usage was estimated at 10.2 GL/year from 150 bores. Estimated groundwater usage accounted for <2% of the estimated sustainable yield of 728.4 GL/year.

A search of the Mineral Resources Tasmania bore database (13/12/07) found a total of 135 bores in the Clarence area, however no stratigraphic or water quality information was available. The mapping function of the database was not functional at the time of the search, however, it would be possible to use easting and northing data for GIS mapping. The bore list provided in Table 18.1 provides a rough indication of bore distribution, but can not be considered a complete inventory of bores in the area.

Table 18.1 Bore Search of Mineral Resources Tasmania Database Area Number of Minimum Maximum bores depth (m) depth (m) Lauderdale 8 6.1 45.7 Rokeby 7 9 45.7 Seven Mile Beach 6 6 113.4 Cremorne 3 13.7 57.9 Clifton Beach 9 7.6 36.6 Sandford 39 10.7 54.9 South Arm 41 15.2 24.4 Opossum Bay 22 13.7 90

Total 135

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 78.

18.4 Potential Impacts of Sea Level Rise and Climate Change

Climate change could impact on both groundwater quantity and quality. Sea-level rise that contributes to saline intrusion or inundation is probably the most direct impact of climate change for coastal aquifer systems, particularly for shallow sandy aquifers. As noted in Section 4.1 of this report, the NCCOE (2004) lists groundwater as one of 13 secondary or process variables applicable to coastal engineering.

In broad terms, sea-level rise and climate change can impact on groundwater equilibrium in a number of ways as follows (Crosbie, 2007; Ghassemi et al, 1991):

Change in recharge e.g. rainfall, landuse, river stage Change in discharge e.g. demand for extraction, river stage Change in storage e.g. sea-level rise, change in recharge or extraction.

Table 18.2 summarises a range of other climate related processes and potential secondary impacts that could also occur. On the basis of very limited data, it is considered that seawater intrusion and seawater flooding and inundation could be highly relevant to the Clarence area. The relevance of other potential impacts of climate change on groundwater systems in the Clarence area cannot currently be determined but may include flooding of bore heads, changing recharge and discharge patterns and associated risks to groundwater dependent ecosystems. There is also a possibility that subsidence of the land surface could occur as a secondary impact of changing groundwater balance.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 79.

Table 18.2 Potential Impacts of Climate Change on Groundwater Systems Potential impact Examples and comments Possible relevance to Clarence area Raised water table causing Denmark (Andersen et al. 2003, 2006, High inundation of septic systems 2007) Seawater intrusion and lateral Saline intrusion reflects a change in High migration of the fresh-saline groundwater balance in the catchment. interface E.g. Burdekin Delta (Narayan et al. 2003) Seawater flooding and Denmark (Andersen et al. 2003, 2006, High inundation of unconfined 2007) aquifers Flooding and saline Tsunami affected areas, New Orleans Moderate contamination of bore heads (Carlson et al. 2007) Changing recharge in the May be increased or decreased recharge Moderate aquifer catchment due to depending on actual climatic variability variable rainfall and (e.g. Victorian examples by Mud et al. evapotranspiration 2006; Crosbie 2007) Increased groundwater May occur if alternative water sources to Unknown extraction and decreased drinking water are encouraged and groundwater levels. groundwater usage is not capped (e.g. Perth’s Gnangara mound Commander, 2000; Yesertnener, C. 2003) Changing discharge patterns Spring flow and baseflow in rivers and Unknown that may impact on surface stream could increase or decrease (e.g. waters and groundwater UK assessments by Faherty et al. 2007). dependent ecosystems Subsidence of land surface Secondary effect that may be related to Unknown. increased groundwater extraction in areas with compressible sediments (e.g. New Jersey - Sun et al. 1999).

In many coastal areas such as Clarence, the development and management of fresh groundwater resources are seriously constrained by the presence of seawater intrusion (Pittock 2004). Seawater intrusion is a natural phenomenon that occurs as a consequence of the density contrast between fresh and saline groundwater. If conditions remain unperturbed, the saline water body will remain stationary unless it moves under tidal influences.

However, when there is sea level change, pumping of freshwater, or changing recharge conditions, the saline body will gradually move until a new equilibrium condition is achieved (Ghassemi et al., 1996). Sustainable yield estimates for coastal aquifer systems need to account for possible seawater intrusion, which may limit increased usage of groundwater in some systems. If the sea level rises to its "best-guess" or higher predicted values (Section 4) over the next century, this would significantly increase intrusion of seawater into coastal aquifers.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 80.

18.5 Recommendations for Monitoring and Investigation

The key recommendation is to establish a network of groundwater bores in Roches Beach, Cremorne and Seven Mile Beach which are instrumented to measure groundwater levels (to AHD) and salinity – both average and extremes. As there are existing bores in the area, coordination of the data being collected needs to be undertaken in light of the recommendations in this study. Analysis of this data then needs to be undertaken.

There are a number of recommendations for a more detailed assessment of possible sea- level rise and climate change impacts on local groundwater systems which may not be the responsibility of Council. Priority desktop assessments are recommended that include the following tasks:

 Assessment of groundwater usage to determine current dependencies and strategic water supplies for future use.

 Mapping of groundwater bore locations and stratigraphic relationships to identify the most vulnerable bores in unconfined sandy aquifers.

 Mapping the projected areas over aquifer systems that may be impacted under various scenarios of sea-level rise and storm events.

It is considered important to establish baseline conditions of the saline-freshwater interface for important groundwater supply areas. This work would involve installation of a transect of nested monitoring piezometers perpendicular to the shoreline and monitoring of groundwater levels and salinity. New and existing groundwater bores close to the coastline should be sampled for electrical conductivity (EC), pH, and major ions to establish baseline conditions. An assessment of cation concentrations would also enable an assessment of how the saline-fresh interface has been moving in the past.

Increased groundwater management may be required in the future should groundwater extraction increase. Groundwater status reports at that time should consider groundwater- surface connectivity, recharge patterns, groundwater-dependent ecosystems and the potential for subsidence associated with groundwater extraction that may exacerbate the impacts of sea-level rise in coastal areas.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 81.

19. SUMMARY OF DESIGN WATER LEVELS

19.1 Overview

The levels given below are preliminary values of 100 year ARI (1% AEP) water levels for planning purposes. They are based on credible desktop techniques presented in preceding sections. As the astronomical tide is a major component, the level would persist for 1 to 2 hours at the peak of the tide. In order to reduce complexity, values are given for representative locations within individual compartments. In reality, different parts of embayments have different levels of exposure, which should be considered in detailed design studies of individual precincts. Additional complexity exists in locations such as Seven Mile Beach, where most of the frontal dune is above the wave runup level, but the western portion (and Acton Creek mouth) is below the wave runup (and possibly future wave setup) levels. This could allow inundation through three-dimensional flows, plus flooding from the creek which would need to be considered in a separate detailed study for affected locations.

The runup level shown is only realised at locations directly fronting the water, e.g. houses on the frontal dune. The following are valid circumstances for allowing habitable floor levels below the wave runup level, and in some circumstances the setup water level (both present day and under sea level rise, provided the condition is still met):

 The structure is protected by a dune barrier which has sufficient sand volume, crest height and continuity to prevent wave runup and inundation reaching it.

 The lower portions (of a building) are constructed of flood resistant materials and are designed to withstand the water forces (e.g. a boatshed, jetty or elevated house).

 For roads, alternative routes or other emergency contingency plans exist.

The runup levels shown are the 2% runup level, that is, two waves out of 100 will exceed this level. R2% is commonly used in coastal planning, however, in assessing the overtopping hazard for high speed roads to the latest EurOtop (2007) criteria, the maximum wave runup (Rmax) needs to be considered.

As discussed in Section 3.9, a freeboard of 0.3 m has been adopted for houses for this project, however, more detailed scrutiny may be needed for individual cases. This freeboard allows for uncertainty in the calculations and minor wave runup in sheltered locations, but not wave runup at locations directly fronting the water.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 82.

Calibration and verification of wave runup levels (Section 10) are recommended as part of the design process, before implementation of any dune raising works is commenced.

19.2 Present Day

Present day design inundation levels are shown in Table 19.1. Foundation stability also needs to be considered in siting structures. As stated previously, consideration needs to be given to the wave runup level for structures sited on the frontal dune.

Table 19.1 Present Day 100 year ARI (1% AEP) Wave Setup and Runup Levels Tide Still water Design R2% Design gauge level (incl floor level Wave floor level water wave and (excl wave runup (incl wave level wind runup) runup) setup) (m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD) Montagu Bay 1.44 1.5 1.8 N/A N/A Kangaroo Bay 1.44 1.5 1.8 N/A N/A Bellerive 1.44 1.8 2.1 3.3 3.6 Little Howrah Beach 1.44 1.9 2.2 2.6 2.9 Rokeby Waste Water Treatment Plant 1.44 1.8 2.1 N/A N/A Lauderdale - South Arm Road, Ralphs Bay 1.44 2.0 2.3 N/A N/A Seven Mile Beach west 1.44 2.0 2.3 2.6 2.9 Roches Beach, Lauderdale 1.44 1.8 2.1 2.8 3.1 Mays Beach 1.44 1.8 2.1 2.5 2.8 Cremorne (Ocean) Beach 1.44 2.0 2.3 4.7 5.0 Cremorne – Pipe Clay Esplanade 1.44 1.6 1.9 N/A N/A Clifton – Bicheno St, Pipe Clay Lagoon 1.44 1.8 2.1 N/A N/A Clifton (Ocean) Beach, west 1.44 2.3 2.6 5.9 6.2 South Arm Neck – Ralphs Bay side 1.44 2.3 2.6 N/A N/A Hope Beach, South Arm Neck - ocean side 1.44 2.4 2.7 6.1 N/A South Arm Beach - Halfmoon Bay 1.44 1.7 2.0 3.9 4.2 Glenvar Beach 1.44 1.7 2.0 4.9 5.2 Opossum Bay 1.44 1.7 2.0 4.5 4.8 N/A is for cases where the wave heights are small, the shoreline is rocky or armoured and development is generally set back. Individual cases may not comply with this and would need detailed assessment.

19.3 2050 Design Water Levels

Design inundation levels for 2050 are shown in Table 19.2 (mid range sea level rise scenario) and Table 19.3 (high range sea level rise scenario). Foundation stability also needs to be considered in siting structures. As stated previously, consideration needs to be given to the wave runup level for structures sited on the frontal dune.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 83.

Table 19.2 100 year ARI (1% AEP) Wave Setup and Runup Levels for 2050 Mid Range Sea Level Rise (0.2 m) Tide Still water Design R2% Design gauge level (incl floor level Wave floor level water wave and (excl wave runup (incl wave level wind runup) runup) setup) (m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD) Montagu Bay 1.64 1.7 2.0 N/A N/A Kangaroo Bay 1.64 1.7 2.0 N/A N/A Bellerive 1.64 2.0 2.3 3.5 3.8 Little Howrah Beach 1.64 2.1 2.4 2.8 3.1 Rokeby Waste Water Treatment Plant 1.64 2.0 2.3 N/A N/A Lauderdale - South Arm Road, Ralphs Bay 1.64 2.2 2.5 N/A N/A Seven Mile Beach west 1.64 2.2 2.5 2.8 3.1 Roches Beach, Lauderdale 1.64 2.0 2.3 3.0 3.3 Mays Beach 1.64 2.0 2.3 2.7 3.0 Cremorne (Ocean) Beach 1.64 2.2 2.5 4.9 5.2 Cremorne – Pipe Clay Esplanade 1.64 1.8 2.1 N/A N/A Clifton – Bicheno St, Pipe Clay Lagoon 1.64 2.0 2.3 N/A N/A Clifton (Ocean) Beach, west 1.64 2.5 2.8 6.1 6.4 South Arm Neck – Ralphs Bay side 1.64 2.5 2.8 N/A N/A Hope Beach, South Arm Neck - ocean side 1.64 2.6 2.9 6.3 N/A South Arm Beach - Halfmoon Bay 1.64 1.9 2.2 4.1 4.4 Glenvar Beach 1.64 1.9 2.2 5.1 5.4 Opossum Bay 1.64 1.9 2.2 4.7 5.0 N/A is for cases where the wave heights are small, the shoreline is rocky or armoured and development is generally set back. Individual cases may not comply with this and would need detailed assessment.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 84.

Table 19.3 100 year ARI (1% AEP) Wave Setup and Runup Levels for 2050 High Range Sea Level Rise (0.3 m) Tide Still water Design R2% Design gauge level (incl floor level Wave floor level water wave and (excl wave runup (incl wave level wind runup) runup) setup) (m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD) Montagu Bay 1.74 1.8 2.1 N/A N/A Kangaroo Bay 1.74 1.8 2.1 N/A N/A Bellerive 1.74 2.1 2.4 3.6 3.9 Little Howrah Beach 1.74 2.2 2.5 2.9 3.2 Rokeby Waste Water Treatment Plant 1.74 2.1 2.4 N/A N/A Lauderdale - South Arm Road, Ralphs Bay 1.74 2.3 2.6 N/A N/A Seven Mile Beach west 1.74 2.3 2.6 2.9 3.2 Roches Beach, Lauderdale 1.74 2.1 2.4 3.1 3.4 Mays Beach 1.74 2.1 2.4 2.8 3.1 Cremorne (Ocean) Beach 1.74 2.3 2.6 5.0 5.3 Cremorne – Pipe Clay Esplanade 1.74 1.9 2.2 N/A N/A Clifton – Bicheno St, Pipe Clay Lagoon 1.74 2.1 2.4 N/A N/A Clifton (Ocean) Beach, west 1.74 2.6 2.9 6.2 6.5 South Arm Neck – Ralphs Bay side 1.74 2.6 2.9 N/A N/A Hope Beach, South Arm Neck - ocean side 1.74 2.7 3.0 6.4 N/A South Arm Beach - Halfmoon Bay 1.74 2.0 2.3 4.2 4.5 Glenvar Beach 1.74 2.0 2.3 5.2 5.5 Opossum Bay 1.74 2.0 2.3 4.8 5.1 N/A is for cases where the wave heights are small, the shoreline is rocky or armoured and development is generally set back. Individual cases may not comply with this and would need detailed assessment.

19.4 2100 Design Water Levels

Design inundation levels for 2100 are shown in Table 19.4 (mid range sea level rise scenario) and Table 19.5 (high range sea level rise scenario). Foundation stability also needs to be considered in siting structures. As stated previously, consideration needs to be given to the wave runup level for structures sited on the frontal dune.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 85.

Table 19.4 100 year ARI (1% AEP) Wave Setup and Runup Levels for 2100 Mid Range Sea Level Rise (0.5 m) Tide Still water Design R2% Design gauge level (incl floor level Wave floor level water wave and (excl wave runup (incl wave level wind runup) runup) setup) (m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD) Montagu Bay 1.94 2.0 2.3 N/A N/A Kangaroo Bay 1.94 2.0 2.3 N/A N/A Bellerive 1.94 2.3 2.6 3.8 4.1 Little Howrah Beach 1.94 2.4 2.7 3.1 3.4 Rokeby Waste Water Treatment Plant 1.94 2.3 2.6 N/A N/A Lauderdale - South Arm Road, Ralphs Bay 1.94 2.5 2.8 N/A N/A Seven Mile Beach west 1.94 2.5 2.8 3.1 3.4 Roches Beach, Lauderdale 1.94 2.3 2.6 3.3 3.6 Mays Beach 1.94 2.3 2.6 3.0 3.3 Cremorne (Ocean) Beach 1.94 2.5 2.8 5.2 5.5 Cremorne – Pipe Clay Esplanade 1.94 2.1 2.4 N/A N/A Clifton – Bicheno St, Pipe Clay Lagoon 1.94 2.3 2.6 N/A N/A Clifton (Ocean) Beach, west 1.94 2.8 3.1 6.4 6.7 South Arm Neck – Ralphs Bay side 1.94 2.8 3.1 N/A N/A Hope Beach, South Arm Neck - ocean side 1.94 2.9 3.2 6.6 N/A South Arm Beach - Halfmoon Bay 1.94 2.2 2.5 4.4 4.7 Glenvar Beach 1.94 2.2 2.5 5.4 5.7 Opossum Bay 1.94 2.2 2.5 5.0 5.3 N/A is for cases where the wave heights are small, the shoreline is rocky or armoured and development is generally set back. Individual cases may not comply with this and would need detailed assessment.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 86.

Table 19.5 100 year ARI (1% AEP) Wave Setup and Runup Levels for 2100 High Range Sea Level Rise (0.9 m) Tide Still water Design R2% Design gauge level (incl floor level Wave floor level water wave and (excl wave runup on frontal level wind runup) dune (incl setup) wave runup) (m, AHD) (m, AHD) (m, AHD) (m, AHD) (m, AHD) Montagu Bay 2.34 2.4 2.7 N/A N/A Kangaroo Bay 2.34 2.4 2.7 N/A N/A Bellerive 2.34 2.7 3.0 4.2 4.5 Little Howrah Beach 2.34 2.8 3.1 3.5 3.8 Rokeby Waste Water Treatment Plant 2.34 2.7 3.0 N/A N/A Lauderdale - South Arm Road, Ralphs Bay 2.34 2.9 3.2 N/A N/A Seven Mile Beach west 2.34 2.9 3.2 3.5 3.8 Roches Beach, Lauderdale 2.34 2.7 3.0 3.7 4.0 Mays Beach 2.34 2.7 3.0 3.4 3.7 Cremorne (Ocean) Beach 2.34 2.9 3.2 5.6 5.9 Cremorne – Pipe Clay Esplanade 2.34 2.5 2.8 N/A N/A Clifton – Bicheno St, Pipe Clay Lagoon 2.34 2.7 3.0 N/A N/A Clifton (Ocean) Beach, west 2.34 3.2 3.5 6.8 7.1 South Arm Neck – Ralphs Bay side 2.34 3.2 3.5 N/A N/A Hope Beach, South Arm Neck - ocean side 2.34 3.3 3.6 7.0 N/A South Arm Beach - Halfmoon Bay 2.34 2.6 2.9 4.8 5.1 Glenvar Beach 2.34 2.6 2.9 5.9 6.2 Opossum Bay 2.34 2.6 2.9 5.5 5.8 N/A is for cases where the wave heights are small, the shoreline is rocky or armoured and development is generally set back. Individual cases may not comply with this and would need detailed assessment.

19.5 Sensitivity to other Climate Change Variables

19.5.1 Overview

Sea level rise is a well accepted phenomena, however, quantification of other climate change variables is less certain. In line with DEFRA (2006) suggestions (Section 4), the sensitivity to other climate change variables has been assessed as follows.

19.5.2 Peak Rainfall Intensity in Small Catchments

DEFRA (2006) suggested the following sensitivity allowances for peak rainfall intensity: 2050: +10% 2100 +30%.

This change in rainfall intensity may have the effect of changing the morphology of local streams and increase the magnitude of rainfall flooding. In conjunction with sea level rise,

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 87.

this may exacerbate the risk of a breach of the spit at Cremorne. The modelling of these processes is not part of this study.

19.5.3 Offshore Wind Speed

DEFRA (2006) suggested the following sensitivity allowances for offshore wind speed: 2050: +5% 2100 +10%.

Such changes in wind speed would have a major effect on structural loadings due to wind, which are proportional to wind speed squared. With regard to wind waves, in fetch limited situations, the increase in height is directly proportional to the increase in wind speed. That is, an increase in wind speed of 10% would increase wind wave heights by 10%. Such increased wave heights may have substantial effects on the design of coastal structures, however, for coastal planning in Clarence, the major effect would be in increased wave setup and wave runup.

For even the largest 100 year ARI (1% AEP) wind wave case in Section 10 (Little Howrah Beach: Hs = 2.8 m), the additional wave setup due to an increase in wave height of 10% would be 0.04 m, which is below the resolution of the calculation, and would be adequately covered by the adopted design freeboard of 0.3 m. Similarly, beach face runup for the most extreme wind wave case (Little Howrah) would increase by approximately 0.1 m for an increase in wave height of 10%.

19.5.4 Extreme Wave Height

DEFRA (2006) suggested the following sensitivity allowances for extreme wave height: 2050: +5% 2100 +10%.

Such changes in wave height would have a major effect on structures exposed to the full height of offshore waves, however, for coastal planning in Clarence, the major effect would be in increased wave setup and wave runup.

For the most exposed Clarence beach with development close to the foreshore (Clifton), the additional wave setup in a 100 year ARI (1% AEP) design event due to an increase in wave

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 88.

height of 10% would be 0.08 m, which is below the resolution of the calculation, and would be adequately covered by the adopted design freeboard of 0.3 m.

An increase in 100 year ARI (1% AEP) wave height of 5% (2050) at Clifton would increase wave runup on the dune by approximately 0.2 m. Similarly, an increase of 10% (2100) would increase wave runup by approximately 0.4 m. This additional design wave runup needs to be considered in future dune management for Clarence beaches open to southern ocean swells, subject to ongoing analysis of wave statistics, calibration/verification of the runup calculations and plausible revisions to future extreme wave scenarios.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 89.

20. SUMMARY OF ALLOWANCES FOR EROSION AND RECESSION

20.1 Overview

The allowances shown below are for planning purposes only and should not be used for detailed design. The values shown are representative single values for each embayment. Variations exist within embayments which could be determined with more specific assessment. Ongoing monitoring is needed to confirm and/or update the values presented. The techniques used are not applicable to protected shorelines such as those inside Ralphs Bay and Pipe Clay Lagoon.

20.2 Allowances

Allowances for setbacks for erosion and recession are shown in Table 20.1. Setback distances are from the present high water mark and comprise the following factors: S1: Allowance for storm erosion S2: Allowance for long term (underlying) recession S3: Allowance for beach rotation S4: Allowance for reduced foundation capacity (to Stable Foundation Zone) S5: Allowance for future recession (Bruun Rule).

S1 has been determined from SBEACH modelling (Section 12).

S2 has only been determined for Roches Beach (from Sharples, 2007). A single indicative value has been used (metres per year). This same value has been used for Cremorne due to its similar planform and location. A value of zero has been used for other locations.

S3 is currently unknown without further monitoring. There are no standard values which could be used due to site specificity. Modelling could be undertaken to examine sensitivity to climate change and variability, however, this would still be best supplemented with measured data. The S3 component is presented here for future incorporation.

S4 is very dependent on the individual dune height used. Detailed assessment of this can be undertaken down to the level of individual properties, however, this is beyond the scope of this study. For this study, a single representative dune height has been used for each embayment.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 90.

S5 has been calculated using Bruun Rule factors of 50 (Section 13) based on profile analysis rounded up.

For major new development such as a new subdivision, the design setback S should be the sum of S1 to S5 for 2100, with either mid or high sea level rise.

For infill development, such as new houses having similar alignment to neighbouring properties, some relaxation of the design setback may be considered, for example it could consider the sum of S1 to S5 for 2050 with a mid range sea level rise.

The design setback (DS) is defined as:

DS = S1 + N*S2 + S3 + S4 + S5 (20.1) where N is the project life in years (usually 0 for present day hazard, 50 or 100 years).

For this report, the design setback has been calculated from the seaward face of the frontal dune. Volumetric calculation for individual properties or cross sections may vary the setback line location slightly.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 91.

Table 20.1 Allowances for Erosion and Recession (sandy ocean beaches only) Location S1 S2 S3 S4 S5 Design Setbacks (DS) in suggested priority order

Priority Order (m) Horizontal storm erosion (m/year)** Underlying recession (m) for rotation Allowance zone (m) Stable Foundation factor Design Bruun rule SLR (m) 2050 mid Bruun recession 2050 high (m) Bruun recession SLR (m) 2100 mid Bruun recession (m) 2100 high SLR Bruun recession (m) present Total SLR (m) 2050 mid (m) 2050 high SLR SLR (m) 2100 mid (m) 2100 high SLR 1 Opossum Bay*, *** 10 0? ? 7 50 10 15 25 45 17 27 32 42 62 2 Roches Beach, Lauderdale 25 0.2 ? 5 50 10 15 25 45 30 50 55 75 95 3 Clifton – Bicheno St, Pipe Clay Lagoon N/A 4 Cremorne – Pipe Clay Esplanade N/A 5 Little Howrah and Howrah Beaches 10 ?? ? 7 50 10 15 25 45 17 27 32 42 62 6 Cremorne (Ocean) Beach 15 ?0.2 ? 10 50 10 15 25 45 25 45 50 70 90 7 Rokeby Waste Water Treatment Plant N/A 8 Lauderdale - South Arm Road, Ralphs Bay N/A 9 South Arm Neck (Ralphs Bay side) N/A 10 Hope Beach, South Arm Neck 25 0? ? 8 50 10 15 25 45 33 43 48 58 78 11 Seven Mile Beach – western 1 km only 10 0? ? 10 50 10 15 25 45 20 30 35 45 65 12 Mays Beach 10 0? ? 5 50 10 15 25 45 15 25 30 40 60 13 Clifton (Ocean) Beach, western 500 m only 25 0? ? 10 50 10 15 25 45 35 45 50 60 80 14 Glenvar Beach*, *** 10 0? ? 7 50 10 15 25 45 17 27 32 42 62 15 South Arm Beach (Halfmoon Bay) 10 0? ? 10 50 10 15 25 45 20 30 35 45 65 16 Bellerive Beach 15 0? ? 7 50 10 15 25 45 22 32 37 47 67 17 Kangaroo Bay N/A 18 Montagu Bay N/A * May be limited by bed rock, but the extent is not known. ** Known only for Roches – initial estimate only for other locations – studies needed. *** Dune height is for beach slope purposes only (there is no actual dune) N/A Not assessed due to predominantly hard (or non sandy) shoreline, or very sheltered location within a bay – inundation hazard predominates.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 92.

21. RISK AREAS FOR COASTAL EROSION AND RECESSION HAZARDS

Storm erosion hazard lines have been developed in accordance with the scheme of Nielsen et al (1992), which is shown in Figure 21.1. The hazard line “stable foundation line” is the seaward limit of the stable foundation zone and “line of slope adjustment” indicates the approximate line of the top of the slumped erosion scarp. The “design” storms used to define a 100 year ARI erosion event were described in Section 12. The methodology has been found to match measured erosion volumes for locations where detailed measurements have been undertaken. The erosion and recession hazard has been treated independently of the inundation hazard, though some properties may be vulnerable to both.

The erosion and recession hazard lines (the stable foundation line) are shown in Figures 21.2 to 21.10 for each area for a 100 year ARI (1%AEP) erosion event with present-day conditions and for 2050 and 2100. Detailed assessment for individual properties may generate slightly different hazard line locations. Buildings may still be permitted seaward of the hazard lines shown in this report in the following circumstances:

 Detailed assessment for an individual property by a coastal engineer varies the hazard line location;

 Rock is present beneath a veneer of sand, with the location and level of rock mapped and considered by a coastal engineer and/or geotechnical engineer

 Buildings are constructed on piles, with design input from a coastal engineer, together with a structural and/or geotechnical engineer

 A protection scheme is implemented (e.g. sand nourishment or seawall).

An estimate of the number of houses affected by the erosion and recession hazard lines is shown in Table 21.1. This has only been applied to buildings on sandy areas fronting exposed coastlines. This is an approximate estimate only, and does not consider the building type or any specific protection works. These buildings would only be lost if adaptation was not undertaken, emergency action was not taken and if the sea level rise and coastal change projections in this report eventuate. Roads and other infrastructure would also be affected.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 93.

Table 21.1 Indicative Houses/Buildings at Risk due to Coastal Erosion and Recession Present 2050 mid 2050 high 2100 mid 2100 high SLR SLR SLR SLR Bellerive* 2 5 5 6 12 Howrah and Little Howrah Beach* 10 11 11 18 27 Seven Mile Beach west 1 1 2 3 11 Roches Beach, Lauderdale 19 108 108 125 195 Mays Beach 2 4 4 4 8 Cremorne (Ocean) Beach 9 36 38 44 53 Clifton (Ocean) Beach, west 3 7 7 10 12 South Arm Beach – Halfmoon Bay 9 13 18 23 43 Glenvar Beach *0 *0 *0 *0 *0 Opossum Bay *0 *0 *0 *0 *0

TOTAL NUMBER 55 185 193 233 361 POTENTIAL IMPROVED VALUE ($M) 28 93 97 117 181 * likely presence of rock and/or a seawall may preclude protect properties from erosion and recession, however, this has not been quantified. Such properties may also be vulnerable to wave impacts. Rock level needs to be mapped. Higher values cannot be excluded until this is undertaken

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 94.

22. RISK AREAS FOR COASTAL INUNDATION

The ground areas subject to inundation under 100 year ARI (1% AEP) conditions are shown in Figures 22.1 to 22.15 with present-day conditions and for 2050 and 2100. Consideration of individual house floor levels are beyond the scope of this study. The inundation level does not include direct wave impacts which may occur for the first row of houses on the frontal dunes. Furthermore, inundation from the ocean side may be prevented if a continuous dune of sufficient height and sand volume protects the land behind it. The inundation areas presented show what happens if the dunes are breached. The inundation areas are mapped based on ground elevation (the “bare earth” LIDAR layer) and do not consider flow paths and velocities.

The potential for inundation does not necessarily preclude new development, but such inundation potential must be considered in the design of buildings and infrastructure, and in emergency planning. The peak of inundation events would persist for approximately 2 hours with the peak of the tide, however, subject to topography, substantial ponding may remain in some areas well after the peak.

Indicative numbers of houses at risk due to inundation are shown in Table 22.1. This has been presented only for present day and 2100 high sea level. It is acknowledged that other infrastructure is also at risk, however, most of this services the houses which are present. Subject to the floor level and construction type, the occurrence of inundation of the ground surrounding a house may not result in any damage to the house. The values presented indicate the market value of the potential properties at risk if no adaptation is undertaken, however, quantification of the potential damage would require extensive modelling beyond the scope of this study.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 95.

Table 22.1 Indicative Houses/buildings at Risk due to Inundation Present Present 2100 high day depth day all SLR all > 0.3 m depths depths Montagu Bay 0 0 0 Kangaroo Bay 0 8 23 Bellerive 2 13 61 Little Howrah Beach 0 2 9 Rokeby Waste Water Treatment Plant 0 0 0 Roches Beach, Lauderdale – from South Arm Road, Ralphs Bay 101 161 491 Seven Mile Beach west 0 0 84 Roches Beach, Lauderdale * * * Mays Beach 0 0 0 Cremorne (Ocean) Beach * * * Cremorne – Pipe Clay Esplanade 15 95 118 Clifton – Bicheno St, Pipe Clay Lagoon 9 21 26 Clifton (Ocean) Beach, west * * * South Arm Neck – Ralphs Bay side Road Road Road Hope Beach, South Arm Neck - ocean side * * * South Arm Beach – Halfmoon Bay 2 5 8 Glenvar Beach ** ** ** Opossum Bay ** ** **

TOTAL NUMBER 129 305 820 POTENTIAL IMPROVED VALUE ($M) 65 153 410 * Inundation is possible from this side, but is potentially less severe than from the other side of the isthmus. ** Inundation is unlikely, but direct wave impacts are possible on beachfront structures.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 96.

23. OVERVIEW OF ADAPTIVE MANAGEMENT OPTIONS

23.1 Overview of Adaptive Management Options

IPCC (2001) listed three classes of adaptive management options as shown in Figure 23.1, namely:

 Retreat  Accommodate  Protect.

Practical management options include:

 Planning controls, which deal with:

o Building setbacks o Minimum floor levels (Figure 23.2) o Appropriate engineering assessments o Appropriate construction techniques (e.g. piled buildings, flood resistant materials)

 Planning controls which may also consider a development freeze in some locations  Physical works such as seawalls (Figure 23.3), groynes (Figure 23.4), dune management (Figure 23.5) or sand nourishment (Figure 23.6), offshore breakwaters and/or surfing reefs

 Ongoing monitoring, analysis and review of findings  Additional data collection or studies  A timeframe for review – currently 10 years for Council planning schemes.

Information on the design of physical works is provided in coastal engineering texts such as the Shore Protection Manual (SPM, 1984) and the Coastal Engineering Manual (CEM, 2002). This report is limited to design concepts only.

23.2 Risk and Timing of Adaptive Management Options

DEFRA (2006, Figure 1) reproduced in Figure 23.7 (top) of this report shows the concept of a managed/adaptive approach with multiple interventions. Some indicative numbers for

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 97.

a managed/adaptive approach relevant to Clarence, based only on sea level (without considering local effects) are shown in Figure 23.7 (bottom), and tabulated in Tables 23.1 and 23.2. This analysis is illustrative and indicative only – it far exceeds the valid extrapolation of available data, but is presented so that indicative numbers can be considered for the managed/adaptive approach.

It can be seen that (within the limitations of the analysis technique) designing for a 100 year ARI (1% AEP) event in 2100 (with high range sea level rise) would provide a present day protection of the order of 850,000 years ARI, which, depending on the cost of such an adaptation, may be excessively conservative. Similarly, a present day risk level of 100 year ARI (1% AEP) would reduce to approximately 3 days ARI if no intervention was taken by 2100 with a high range sea level rise scenario, indicating the potential risk of no adaptation in the long term.

Table 23.1 Equivalent Present Day Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels and Future 100 year ARI event Year SLR (m) 100 year ARI Equivalent Level present day ARI (years) present 0.0 1.44 100 2050 0.2 1.64 800 2050 0.3 1.74 2,000 2100 0.5 1.94 15,000 2100 0.9 2.34 850,000

Table 23.2 Equivalent Future Average Recurrence Interval (Risk) of Hobart Sea Level for Various Future Sea Levels Present Day 100 year ARI event Year SLR (m) Present day Equivalent 100 year ARI Future ARI Level (years) present 0.0 1.44 100 2050 0.2 1.44 20 2050 0.3 1.44 2 2100 0.5 1.44 0.7 2100 0.9 1.44 0.01

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 98.

23.3 Clarence-Wide Adaptation Strategies

The following are recommended for the entire Clarence City.

A forecasting and warning system for prediction of inundation of roads and buildings, large waves and strong winds. Such systems already exist at the Bureau of Meteorology, but need to be better integrated into coastal planning.

A detailed survey (LIDAR) so that inundation areas and erosion volumes can be estimated more accurately – this has since been undertaken during the course of this study. Potential dune breach locations need to be identified when this data becomes available. Once available, the simple inundation modelling used in this report can be re-applied to the subject locations. Consideration needs to be given to detailed modelling of inundation (if warranted) which would cost approximately $50,000 to $100,000 per locality

An analysis of the historical change of Clarence beaches beyond Roches Beach, Lauderdale needs to be undertaken using satellite photos and/or photogrammetric analysis of aerial photos, particularly Cremorne. This is to quantify measured erosion from past storms and/or to assess any long term change.

Regular beach surveys need to be undertaken, subject to the findings of the planform analysis, which should include analysis of the collected data. Such a program is being undertaken by Council at Roches Beach, Lauderdale.

The only way to monitor changes to the lagoons and offshore areas is through regular bathymetric surveys.

The sea level rise projections in revisions to the IPCC documents need to be monitored and the implications of major revisions need to be considered.

On continuously upward sloping land (e.g. Opossum Bay) it is preferable for development to be sited above the wave runup level. This may not be practicable on low land behind higher dunes fronting the coast (e.g. Roches Beach, Seven Mile) and not necessary provided frontal dunes are preserved and maintained.

Vegetation management plans need to be prepared for all dune areas not currently maintained by community groups.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 99.

An inventory of potential sand reserves for future beach nourishment needs to be developed and investigated. Studies for access and in-principle approvals need to be initiated.

Suitable quarries for rock protection need to be identified and the suitability of their rock for coastal protection needs to be determined.

With current sea level rise projections, development proposals for any land below 10 m AHD and/or within 500 m of the coast needs at least a cursory consideration of whether more detailed assessment is required, for example by comparing the land against the figures in this report or a consequent GIS layer. The 10 m level is suggested as it is readily identifiable on Council’s GIS system and above any calculated wave runup level within the foreseeable 100 year planning period used in this report. Road access to sites also needs to be considered, for even if a site itself is above any inundation level, access to the site may be restricted during storm events.

23.4 Adaptation Strategies and Costing

Adaptation strategies are presented for preliminary consideration and have been developed on a beach by beach basis. They have not been developed down to the level of individual houses. Indicative numbers of houses at risk are provided as an order of magnitude estimate. Individual properties that may have been identified at possible risk need to have detailed assessment undertaken, which (subject to the triggers adopted) may be at the time of proposed redevelopment. The costs presented are for budgeting and comparison purposes and exclude GST. They are based on WRL’s experience from actual and planned projects, and Rawlinsons Australian Construction Handbook. The actual construction cost / tender price will depend on:

 The final detailed design, specification and contract conditions  The market conditions prevailing at the time of tendering/construction  Plant available at the time  Prospective contractors’ trading situation  Contractors’ perception of risk  Allocation of risk within the contract.

Indicative costs for rock structures are $100 per tonne, provided suitable rock is available. The rock structure cost considers future sea level rise through increased wave height on the

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 100.

structure leading to larger required rocks, and increased wave runup leading to a higher crest.

Indicative costs for nourishment sand are $15/m3 with the cost being dependent on the carting distance, the depth of the deposit (for submarine sand) and the environmental constraints. The sand price is very dependent on the source, a suitable dredge, environmental constraints and the total quantity, and could potentially range from $5 to $50 per m3.

Rock structures require ongoing maintenance, typically after large storms and/or at intervals of 10 to 20 years. As part of this maintenance, an upgrade (e.g. raising) through the addition of new armour can be readily undertaken, which fits an adaptive management framework. Sand nourishment schemes may require replenishment subject to the design and natural processes. If littoral drift sand continues to supply trapping structures (e.g. groynes), additional replenishment may not be needed. At this stage of planning, costs have not been discounted to net present costs, as there are too many uncertainties in likely future expenditure, however, this should be undertaken as part of detailed planning for options.

The retreat option has been costed in the options shown below using the following assumptions:

1. The property undergoing retreat loses all its value 2. The cost to demolish and rehabilitate the land is 10% of the current value.

The improved value of individual properties in the coastal zone has been set to $500,000. The cost of the retreat option has been set at 1.1 times the improved value of the property. In reality, should retreat be considered, there may be compensation, subsidies or incentives available to the occupants from various levels of government. However, on a society-wide basis, the factor of 1.1 is a reasonable initial estimate. This report is aimed at providing order of magnitude costs, so detailed costing of all vulnerable infrastructure has not been undertaken. Indeed, if retreat is undertaken, the needs for infrastructure would change, as it primarily services the residential properties present. Occasional inundation of roads would not necessarily cause damage beyond that of major rainfall events.

Also shown for the individual precincts are benefit to cost ratios. At this stage the benefit is simply the improved value of properties being protected. More sophisticated future studies could look at partial damage to houses and infrastructure, which is beyond this study. Although the retreat option may have a low benefit to cost ratio on economic grounds, F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 101.

consideration of environmental and social factors may favour this option in some circumstances.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 102.

24. SITE SPECIFIC ADAPTATIVE MANAGEMENT OPTIONS

24.1 Opossum Bay

There are numerous structures (houses, boatsheds and seawalls) below the present day runup limit. The steep terrain means that there is sufficient space to rebuild houses up the hill for a 100 year planning period. The steepness of the land means that there would be minimal additional cost associated with adapting the houses to any sea level rise up to 1 m. Protection from erosion and recession is believed to be provided by the presence of rock, however, this needs to be confirmed by mapping the level of the rock.

A list of possible adaptive management options is shown in Table 24.1, with only the feasible structural options presented for future scenarios. The steep beach gradient and proximity to tidal currents mean that there are doubts about the feasibility of sand nourishment, which would require additional feasibility studies. Similarly, groynes could only be considered feasible with further studies on littoral drift.

New development should be sited above the wave runup level, and sufficiently set back from the foreshore to accommodate present and future coastal hazards. The only feasible alternative to this is a seawall which would be substantially more expensive.

Community attitudes on preserving public access along the foreshore need to be tested. Subject to the findings, consideration needs to be given to planned retreat of foreshore structures and possibly repurchase or surrender of the seaward portion of allotments which intrude onto the public beach. Implementation policies and funding models for this need to be developed. Similarly, a policy on boatsheds and seawalls on the foreshore needs to be developed with consideration of community attitudes – both direct residents and other users of the beach. If these structures are to be allowed, the policy should specify that they should be designed by a coastal engineer in conjunction with a structural engineer. If existing foreshore structures are damaged, options are mandated removal or engineer design of replacements.

The preferred adaptation option needs to be chosen in the near future and design floor levels set if this is the chosen option. Suggested triggers for implementation are applications for redevelopment or damage to existing structures.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 103.

Table 24.1 Summary of Adaptive Management Options for Opossum Bay

Unit Rate $k Rate Cost $M $M Cost Quantity Feasible? Benefit/cost Present day Potential houses affected No 40 500 20.0

Seawall  m 600 5.2 3.1 6.5 Sand nourishment x Groynes x Sand nourishment plus groynes x Dune raising x House raising (of new buildings)**  No 40 30 1.2 16.7 Piled footings for reduced foundation capacity  Raise roads - Set minimum floor levels and setback  * Consider development freeze***  * Retreat  No 40 550 22.0

2050 mid SLR Seawall  m 600 6.0 3.6 5.6 House raising (of new buildings)  No 40 30 1.2 16.7 Retreat  No 40 550 22.0

2050 high SLR Seawall  m 600 6.8 4.1 4.9 House raising (of new buildings)  No 40 30 1.2 16.7 Retreat  No 40 550 22.0

2100 mid SLR Seawall  m 600 7.2 4.3 4.7 House raising (of new buildings)  No 40 30 1.2 16.7 Retreat  No 40 550 22.0

2100 high SLR Seawall  m 600 9.1 5.4 3.7 House raising (of new buildings)  No 40 30 1.2 16.7 Retreat  No 40 550 22.0 Notes: x = Unlikely to be feasible without further detailed investigation - = Probably not needed * Cost would involve Council time in developing and implementing policy. ** This would involve gradual implementation, but the costs presented show the order of magnitude. *** On low beachfront structures until a coherent strategy can be developed.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 104.

24.2 Glenvar Beach, Opossum Bay

There are numerous structures (houses, boatsheds and seawalls) below the present day runup limit. The steep terrain means that there is sufficient space to rebuild houses up the hill for a 100 year planning period. The steepness of the land means that there would be minimal additional cost associated with adapting the houses to any sea level rise up to 1 m. Protection from erosion and recession is believed to be provided by the presence of rock, however, this needs to be confirmed by mapping the level of the rock.

A list of possible adaptive management options is shown in Table 24.2 with only the feasible structural options presented for future scenarios. The steep beach gradient and proximity to tidal currents mean that there are doubts about the feasibility of sand nourishment, which would require additional feasibility studies. Similarly, groynes could only be considered feasible with further studies on littoral drift.

New development should be sited above the wave runup level, and sufficiently set back from the foreshore to accommodate present and future coastal hazards. The only feasible alternative to this is a seawall which would be substantially more expensive.

Community attitudes on preserving public access along the foreshore need to be tested. Subject to the findings, consideration needs to be given to planned retreat of foreshore structures and possibly repurchase or surrender of the seaward portion of allotments which intrude onto the public beach. Implementation policies and funding models for this need to be developed. Similarly, a policy on boatsheds and seawalls on the foreshore needs to be developed with consideration of community attitudes – both direct residents and other users of the beach. If these structures are to be allowed, the policy should specify that they should be designed by a coastal engineer in conjunction with a structural engineer. If existing foreshore structures are damaged, options are mandated removal or engineer design of replacements.

The preferred adaptation option needs to be chosen in the near future and design floor levels set if this is the chosen option. Suggested triggers for implementation are applications for redevelopment or damage to existing structures.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 105.

Table 24.2 Summary of Adaptive Management Options for Glenvar Beach, Opossum Bay

Unit Rate $k Rate Cost $M $M Cost Quantity Feasible? Benefit/cost Present day Potential houses affected No 16 500 8.0

Seawall  m 250 5.2 1.3 6.5 Sand nourishment x Groynes x Sand nourishment plus groynes x Dune raising x House raising (of new buildings) **  No 16 30 0.5 16.0 Piled footings for reduced foundation capacity  Raise roads - Set minimum floor levels and setback  * Consider development freeze***  * Retreat  No 16 550 8.8

2050 mid SLR Seawall  m 250 6.0 1.5 5.3 House raising (of new buildings)  No 16 30 0.5 16.0 Retreat  No 16 550 8.8

2050 high SLR Seawall  m 250 6.8 1.7 4.7 House raising (of new buildings)  No 16 30 0.5 16.0 Retreat  No 16 550 8.8

2100 mid SLR Seawall  m 600 7.2 1.8 4.4 House raising (of new buildings)  No 16 30 0.5 16.0 Retreat  No 16 550 8.8

2100 high SLR Seawall  m 600 9.1 2.3 3.5 House raising (of new buildings)  No 16 30 0.5 16.0 Retreat  No 16 550 8.8 Notes: x = Unlikely to be feasible without further detailed investigation - = Probably not needed * Cost would involve Council time in developing and implementing policy. ** This would involve gradual implementation, but the costs presented show the order of magnitude. *** On low beachfront structures until a coherent strategy can be developed.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 106.

24.3 Roches Beach, Lauderdale

The main Roches Beach is approximately 3500 m long and Roches Beach north, between Bambra reef and the sailing club is approximately 800 m long. A list of possible adaptive management options is shown in Table 24.3 with only the feasible structural options presented for future scenarios. New houses need to be raised above the inundation level (from the Ralphs Bay side) and those subject to erosion (from the ocean side) either constructed on piles or located in the Stable Foundation Zone. The indicative cost to pile a new house is $50,000. The indicative cost to raise a new house having a footprint of 150 m2 by 1 m (at initial construction) is $30,000.

Planned retreat may be needed in some circumstances when consideration is made of community and environmental factors, and when an economic comparison is made against physical works.

Seawalls are a technically feasible option, but may reduce beach amenity. They could be placed on the frontal dune or as a buried terminal protective structure. Community attitudes on preserving public access along the foreshore need to be tested.

Initially, minor sand nourishment in the form of dune raising could be undertaken. Indicative costs to raise the dune by 1 metre (10 m3/m of sand) would be $150 per metre of beach provided a suitable sand source can be accessed. The additional cost to revegetate the raised dune would be $150 per metre of beach.

More extensive sand nourishment into the future would be needed. For a Bruun Rule factor of 50 and an active profile height of 8 m (Section 13), the following sand quantities would be needed to counteract future sea levels rise:

 0.2 m SLR needs 80 m3/m @ $15/m3 equals $1,200 per metre of beach  0.3 m SLR needs 120 m3/m @ $15/m3 equals $1,800 per metre of beach  0.5 m SLR needs 200 m3/m @ $15/m3 equals $3,000 per metre of beach  0.9 m SLR needs 360 m3/m @ $15/m3 equals $5,400 per metre of beach.

Subject to detailed design involving net present cost scenarios, it may be prudent to retain sand on the beach with a series of groynes or artificial headlands. The littoral drift makes groynes or offshore breakwaters (in conjunction with nourishment, or standalone) a feasible option for Roches Beach. This could take the form of augmentation of the existing rock outcrops (e.g. Bambra Reef, Figure 13.3) with additional groynes needed between.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 107.

Indicative groyne length would be 100 m spaced at 500 m. At a cost of $5,000 per metre, this would amount to $500,000 per groyne, giving a total cost for groynes of $3.5M for the 3500 m long main Roches Beach and a further $1M for the 800 m long Roches Beach north. Detailed design and assessment would be needed. There may be objections to these works on environmental grounds.

Key access roads may need raising at an indicative cost of $400 per metre of road for suburban roads raised 0.5 metre and $600 per metre of road for suburban roads raised 1 metre. There are approximately 10 km of low roads in Lauderdale, giving an indicative road raising cost of $6M. A detailed study should be undertaken of South Arm Road and consideration given to raising the road and/or providing a seawall. The indicative cost for a seawall/embankment is $1500 per metre. Subject to the findings of the study, an elevated South Arm Road could form a levee against inundation from Ralphs Bay. This would also necessitate a flood gate structure to be installed at the western end of Lauderdale Canal.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 108.

Table 24.3 Summary of Adaptive Management Options for Roches Beach, Lauderdale

Unit Rate $k Rate Cost $M $M Cost Quantity Feasible? Benefit/cost Erosion and Recession Present day Potential houses affected by erosion No 19 500 9.5 Seawall  m 4300 4.3 18.0 0.5 Sand nourishment  m 4300 600 2.6 3.7 Groynes  No 9 500 4.5 2.1 Sand nourishment plus groynes  Item 7.1 1.3 Dune raising***  m 4300 0.3 1.3 7.3 Piled footings for reduced foundation capacity  No 19 50 1.0 10.0 Raise roads  Note Set minimum floor levels and setback  * Consider development freeze**  Retreat from erosion hazard  No 19 550 10.5 2050 mid SLR Potential houses affected by erosion/recession No 108 500 54.0 Seawall  m 4300 5.0 21.5 2.5 Sand nourishment plus groynes  Item 9.7 5.6 Piled footings for reduced foundation capacity  No 108 50 5.4 10.0 Retreat  No 108 550 59.4 2050 high SLR Potential houses affected by erosion/recession No 108 500 54.0 Seawall  m 4300 5.6 24.1 2.2 Sand nourishment plus groynes  Item 9.7 5.6 Piled footings for reduced foundation capacity  No 108 50 5.4 10.0 Retreat  No 108 550 59.4 2100 mid SLR Potential houses affected by erosion/recession No 125 500 62.5 Seawall  m 4300 6.0 25.8 2.4 Sand nourishment plus groynes  Item 17.4 3.6 Piled footings for reduced foundation capacity  No 125 50 6.25 10.0 Retreat  No 125 550 68.8 2100 high SLR Potential houses affected by erosion/recession No 195 500 97.5 Seawall  m 4300 7.9 34.0 2.9 Sand nourishment plus groynes  Item 27.8 3.5 Piled footings for reduced foundation capacity  No 195 50 9.75 10.0 Retreat from erosion hazard  No 195 550 107.3 Inundation (from Ralphs Bay side) Present day Potential allotments affected by inundation No 161 500 80.5 House raising (of new buildings)  No 161 30 4.8 16.8 2100 high SLR Potential allotments affected by inundation No 491 500 245.5 House raising (of new buildings)  No 491 30 14.7 16.8 Notes: * Cost would involve Council time in developing and implementing policy. * * On low beachfront structures outside Stable Foundation Zone until a coherent strategy can be developed. *** Would reduce the hazard as an interim measure, but may not remove it entirely

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 109.

24.4 Cremorne Ocean Beach, Pipe Clay Esplanade and Cremorne Avenue

There are approximately 27 houses on Cremorne spit and 25 on the beachfront north of the spit, giving a total of approximately 52 beachfront houses. Due to setbacks, not all of these are at risk from present day erosion. There are approximately 95 houses in potentially inundated areas for the present day, increasing to 118 by 2100 with high sea level rise. A summary of feasible adaptive management options is given in Table 24.4. A development freeze should be considered for properties on the spit until a comprehensive management strategy is developed. Mandatory coastal engineering assessment should be invoked for all development applications outside the Stable Foundation Zone north of the spit.

New development (not on the spit) should be sited above the inundation level. The indicative cost to raise a new house having a footprint of 150 m2 by 1 m (at initial construction) is $30,000.

Planned retreat may be needed in some circumstances when consideration is made of community and environmental factors, and when an economic comparison is made against physical works.

Consideration should be given to rebuilding the training walls at the mouth of lagoon, subject to detailed design studies and community input, unless planned retreat is to be enacted for properties on the spit.

A seawall on the beach and to protect properties on the spit and further north is a feasible option. An alternative to the seawall could be sand nourishment. Section 13 indicates than for application of the Bruun Rule to Cremorne a Bruun factor of 50 has been used, which was the basis for calculating indicative nourishment quantities. For a Bruun Rule factor of 50 and an active profile height of 10 m (Section 13), the following sand quantities would be needed to counteract future sea levels rise:

 0.2 m SLR needs 100 m3/m @ $15/m3 equals $1,500 per metre of beach

 0.3 m SLR needs 150 m3/m @ $15/m3 equals $2,250 per metre of beach  0.5 m SLR needs 250 m3/m @ $15/m3 equals $3,750 per metre of beach  0.9 m SLR needs 450 m3/m @ $15/m3 equals $6,750 per metre of beach.

In conjunction with nourishment, a minimum of two groynes/training walls would be needed – one at the southern end of Cremorne beach to prevent excessive loss of nourishment sand into Pipe Clay Lagoon, plus one at least one at the northern end to reduce

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 110.

sand loss. Indicative cost would be $5000 per m for each 100 m groyne, giving a groyne cost of $1M. Additional intermediate groynes may improve the performance of nourishment. The southern groyne may alter Cremorne Point surf break, but not necessarily detrimentally. Works on the Pipe Clay Lagoon side are discussed below.

If a protection strategy cannot be devised, retreat of houses should be considered when they become threatened by the erosion scarp.

A detailed study should be undertaken of access via Cremorne Avenue and Pipe Clay Esplanade, and consideration given to raising the road, providing a new road and/or providing a minor seawall. Council has undertaken works in the past and has surveyed the foreshore on several occasions from 1981 to 1997.

An indicative cost for suburban roads raised 1 metre is $600 per metre of road. There are approximately 4 km of low roads in Cremorne, giving a total cost of approximately $2.4M.

A seawall on the Pipe Clay lagoon side would cost approximately $2,000 per metre, and may need to extend for between 400 m and 3 km along Cremorne Avenue and Pipe Clay Esplanade. This would amount to a cost of $800k to $6M.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 111.

Table 24.4 Summary of Adaptive Management Options for Cremorne Ocean Beach

Unit Rate $k Rate Cost $M $M Cost Quantity Feasible? Benefit/cost Erosion and Recession Present day Potential houses affected by erosion No 9 500 4.5 Seawall on ocean side  m 1300 6.0 7.8 0.6 Sand nourishment  m 1300 0.6 0.8 5.8 Groynes  No 2 500 1.0 4.5 Sand nourishment plus groynes  Item 1.8 2.5 Piled footings for reduced foundation capacity  No 52 50 2.6 10.0 Set minimum floor levels and setback  * Consider development freeze**  Retreat  No 49 550 27.0 2050 mid SLR Potential houses affected by erosion/recession No 36 500 18.0 Seawall  m 1300 7.0 9.1 2.0 Sand nourishment plus groynes  Item 3.0 6.1 Piled footings for reduced foundation capacity  No 36 50 1.8 10.0 Retreat  No 36 550 19.8 2050 high SLR Potential houses affected by erosion/recession No 38 500 Seawall  m 1300 8.0 10.4 1.8 Sand nourishment plus groynes  Item 3.9 4.8 Piled footings for reduced foundation capacity  No 38 50 1.9 10.0 Retreat  No 38 550 20.9 2100 mid SLR Potential houses affected by erosion/recession No 44 500 22.0 Seawall  m 1300 8.5 11.1 2.0 Sand nourishment plus groynes  Item 5.9 3.7 Piled footings for reduced foundation capacity  No 44 50 2.2 10.0 Retreat  No 44 550 24.2 2100 high SLR Potential houses affected by erosion/recession No 53 500 26.5 Seawall  m 1300 10.0 13.0 2.0 Sand nourishment plus groynes  Item 9.8 2.7 Piled footings for reduced foundation capacity  No 53 50 2.7 10.0 Retreat from erosion hazard  No 53 550 29.1 Inundation Present day Potential houses affected by inundation No 95 500 47.5 House raising (of new buildings)  No 95 30 2.9 16.4 Raise roads  Note 2100 high SLR Potential houses affected by inundation No 118 500 59.0 House raising (of new buildings)  No 118 30 3.5 16.9 Raise roads  Note Notes: * Cost would involve Council time in developing and implementing policy. * * On properties on the spit and low beachfront structures outside Stable Foundation Zone until a coherent strategy can be developed.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 112.

24.5 Clifton Beach

There are approximately three houses presently at risk from erosion along the western 1 km of the 2.1 km beach. High sea level rise and a major storm involves some risk of a breach to Pipe Clay Lagoon, but there is presently sufficient sand buffer to prevent this.

New houses should be in the Stable Foundation Zone or engineer designed on piled footings. Consider a development freeze on properties (or portions of) seaward of the Stable Foundation Zone if a coherent strategy cannot be developed. Access to numerous properties is via Bicheno Street (discussed below).

Planning should consider relocating the surf life saving club house further landward when it reaches the end of its service life and/or it becomes damaged by storm erosion. New houses should be above the inundation level from the lagoon side and the dune crest should be monitored and maintained so that it is above the design wave runup level.

A seawall could be constructed at an indicative cost of $10,000 per metre with more precise costs shown in Table 24.5. Subject to detailed design and siting, it may need to be constructed from concrete rather than rock armour due to the likely large armour sizes needed.

Initially, minor sand nourishment in the form of dune raising could be undertaken. Indicative costs to raise the dune by 1 metre (10 m3/m of sand) would be $150 per metre of beach provided a suitable sand source can be accessed. The additional cost to revegetate the raised dune would be $150 per metre of beach.

Major sand nourishment for the western ~1000 m would be feasible, which would require the bay to be split with a groyne structure, otherwise the whole bay (2.1 km) would need to be nourished (at twice the cost of nourishing 500 m). For a Bruun Rule factor of 50 and an active profile height of 22 m (Section 13), the following sand quantities would be needed to counteract future sea levels rise:

 0.2 m SLR needs 220 m3/m @ $15/m3 equals $3,300 per metre of beach  0.3 m SLR needs 330 m3/m @ $15/m3 equals $4,950 per metre of beach  0.5 m SLR needs 550 m3/m @ $15/m3 equals $8,250 per metre of beach  0.9 m SLR needs 990 m3/m @ $15/m3 equals $14,850 per metre of beach.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 113.

The groyne would need to be approximately 200 m long and would cost approximately $15,000 per m, giving a cost of $3M. The character of Clifton beach would be altered by this groyne.

These quantities and costs are large by the standards of other Clarence beaches, due to Clifton’s higher wave climate. Additional studies would be needed to confirm these quantities.

Table 23.5 Summary of Adaptive Management Options for Clifton Beach

Unit Rate $k Rate Cost $M $M Cost Quantity Feasible? Benefit/cost Present day Houses affected by erosion No 3 500 1.5

Seawall  m 1000 8.9 8.9 0.2 Sand nourishment  m 1000 3.3 3.3 Groynes  No 1 15.0 3.0 Sand nourishment plus groynes  Item 6.3 0.2 Piled footings for reduced foundation capacity  No 3 50 0.2 7.5 Consider development freeze**  Retreat  No 3 550 1.7

2100 high SLR Houses affected by erosion No 12 500 6.0

Seawall  m 1000 14.0 14.0 0.4 Sand nourishment plus groynes  Item 32.7 0.2 Piled footings for reduced foundation capacity  No 12 50 0.6 10.0 Retreat  No 12 550 6.6 Notes: * Cost would involve Council time in developing and implementing policy.

24.6 Bicheno Street, Clifton

There are presently approximately 21 houses at risk from inundation around Bicheno Street, increasing to 26 by 2100 with high sea level rise. There are more than 100 which are either nearby or require access along the low section of Bicheno Street. Occasional inundation of Bicheno Street needs to be planned for, or the road needs to be raised at an indicative cost of $400 per metre for 0.5 m and $600 per metre for 1 m. Bicheno Street services houses in Clifton for approximately 1 km, giving a cost to raise it 1 m of approximately $600k, however, it extends for another 2 km to the north-east to provide access to numerous other rural houses, north Clifton Beach and the eastern shores of Pipe Clay Lagoon.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 114.

New development should be sited above the inundation level. A minor edge wall for the road should be considered at an indicative cost of $600 per metre. This would amount to $300k over a distance of approximately 500 m, increasing to $1.8M over 3 km.

24.7 Howrah – Little Howrah Beach

Howrah Beach is approximately 1.2 km long, while Little Howrah is approximately 200 m long. Seawalls fronting private property prevent beach access between the two beaches except at low tide. A seawall also fronts public land backing Little Howrah Beach.

There are approximately 10 houses potentially at risk due to erosion at present, increasing to 27 by 2100 with high sea level rise, though the presence of rock and/or seawalls may limit this. These buildings may also be exposed to wave impacts. There are two houses potentially at risk from inundation at present, increasing to nine by 2100 with high sea level rise.

New development should be above the design inundation level. A policy needs to be developed for the scenario where existing private seawalls fail, which could consider either planned retreat, engineer designed replacements or sand nourishment. Planned retreat should be considered should high sea level rise eventuate and physical works cannot be agreed on.

Community input should be sought on existing and future seawalls versus public access. A compromise may incorporate public access within/on a seawall design.

For the sections of beach without a seawall, minor sand nourishment in the form of dune raising could be undertaken. Indicative costs to raise the dune by 1 metre (10 m3/m of sand) would be $150 per metre of beach provided a suitable sand source can be accessed. The additional cost to revegetate the raised dune would be $150 per metre of beach.

An alternative to a seawall could be sand nourishment. For a Bruun Rule factor of 50 and an active profile height of 10 m (Section 13), the following sand quantities would be needed to counteract future sea levels rise:

 0.2 m SLR needs 100 m3/m @ $15/m3 = $1,500 per metre of beach = $2.1M

 0.3 m SLR needs 150 m3/m @ $15/m3 = $2,250 per metre of beach = $3.2M  0.5 m SLR needs 250 m3/m @ $15/m3 = $3,750 per metre of beach = $5.3M  0.9 m SLR needs 450 m3/m @ $15/m3 = $6,750 per metre of beach = $9.5M.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 115.

This is unlikely to be economically feasible due to the small number of properties at risk, which means that the only likely feasible options are seawalls or retreat.

24.8 Seven Mile Beach

Historic change (probably accretion) should be studied so that future impacts of sea level rise can be better assessed. Ongoing accretion may outpace the effects of sea level rise, however, this is not presently known.

The bridge over Acton Creek needs to consider inundation in the design of a replacement. The presence of bridge abutments prevents further meander of the mouth.

There is generally sufficient buffer and may be an accreting shoreline, so possibly only one house is at risk due to a present day 100 year ARI erosion event. This would increase to 11 by 2100 with high sea level rise.

The presence of low or no dunes at the western end makes this area vulnerable to inundation. No houses are presently at risk from inundation, however, 84 are estimated to be at risk by 2100 with high sea level rise. There may be occasional road access disruptions.

A levee and/or training wall around the creek mouth may be needed to maintain a barrier to inundation near the creek mouth. Indicative costs are $10,000 per metre for 200 m.

24.9 South Arm Road at South Arm Neck

A detailed study should be undertaken to consider raising the road or protecting it with a seawall for waves from the Ralphs Bay side. This is being undertaken by DIER.

The dune elevation and sand volume should be monitored and maintained to prevent oceanic breakthrough from Hope Beach. There is sufficient sand buffer to prevent breakthrough from the ocean side even with 0.9 m of sea level rise and a 100 year ARI (1% AEP) storm event, however, this needs to be monitored and reviewed as the consequences of such a breakthrough are serious.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 116.

24.10 Bellerive – Bellerive Beach

Approximately two houses are presently at risk due to erosion if the seawall at the west fails. This would increase to 12 by 2100 with high sea level rise.

Approximately 13 houses are presently potentially at risk due to inundation under 100 year ARI (1% AEP) storm surge, which would increase to 61 by 2100 with high sea level rise.

New development should be above the design inundation level, however, the frontal dune is the primary protection, and if it remains above the runup level, the inundation risk to houses behind it is low. The dune should be monitored and maintained so that it is above the design runup level where possible. The stormwater system should be redesigned to incorporate measures to reduce inundation.

For the sections of beach without a seawall, minor sand nourishment in the form of dune raising could be undertaken. Indicative costs to raise the dune by 1 metre (10 m3/m of sand) would be $150 per metre of beach provided a suitable sand source can be accessed. The additional cost to revegetate the raised dune would be $150 per metre of beach.

There is a short length of seawall fronting Victoria Esplanade in the western corner of the beach. Planning needs to be undertaken for replacement of this seawall at an indicative cost of $2000 per metre. The road and several houses near this are subject to inundation, which should be considered in the design of the seawall replacement.

24.11 Rokeby Sewage Treatment Works and Droughty Point, Rokeby

The design inundation level needs to be considered in future plant design and operation. Some wave runup calculations may also need to be considered. Due to the clay content of foreshore sediments, there is little potential for dynamic equilibrium or beach rebuilding following storm erosion, but rather a trend of ongoing recession. The historic rate of this recession should be estimated from aerial photos, and future long term change of the beach needs to be monitored. The low wave climate and low public usage means that a relatively minor seawall would be feasible to stop recession.

For Droughty Point, new buildings should be above the design inundation level. If existing foreshore structures are damaged, options are mandated removal or engineer design of replacements.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 117.

New seawalls (if allowed) should be designed by coastal and structural engineer. There has been some haphazard (demolition concrete) armouring of Rokeby Beach to the east, but no development is at risk. These works should be engineer designed and formalised, or removed.

Droughty Point Road is subject to inundation around the bridge over Clarence Plains Rivulet. Inundation needs to be considered in the design of a replacement. The present location and shoreline armouring prevents meander of the mouth.

24.12 South Arm Beach – Half Moon Bay

Current development is sparse for most of the beach, however, presently approximately nine houses are at risk from a 100 year ARI erosion event, increasing to 43 by 2100 with high sea level rise.

Approximately five houses are presently at risk from inundation under 100 year ARI conditions, increasing to nine by 2100 with high sea level rise.

For the houses located at the north end, a short seawall of approximately 250 m length costing approximately $1.5M could protect the at risk houses and extend from the existing headland. New houses in the central part of the bay should be set back behind the Stable Foundation Zone hazard line where there is sufficient room on the block. For the small number of sites where this is not possible, retreat may be the most feasible option, however, few of these sites are at immediate risk.

Any future sub division proposals should incorporate a detailed coastal engineering study, so that new development is sited beyond the hazard zones for the planning period.

24.13 Mays Beach

Current development is minor, though two buildings are in the immediate hazard zone, which would increase to eight with high sea level rise in 2100. There is generally sufficient room for new development to be located behind the Stable Foundation Zone hazard line, and above the wave runup level for a designated planning period (say 50 or 100 years). Any future sub division proposals should incorporate a detailed coastal engineering study, so that new development is sited beyond the hazard zones for the planning period.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 118.

24.14 Montagu Bay and Kangaroo Bay

The shoreline is generally armoured. Some areas around Montagu Bay and Kangaroo Bay are subject to inundation, including the lowest land surrounding Rosny College. The inundation level needs to be considered in future development. Wave runup needs to be considered for any structures very close to the shoreline.

24.15 Other Potentially Vulnerable Areas not considered in this Study

The following areas were not part of this study due to either low urban density or generally high land, however, consideration should be given to assessment of these locations.

 Tranmere (lowest portions);  Barilla Bay, Pitt Water  Cambridge  Five Mile Beach, Pitt Water  Lindisfarne.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 119.

25. CONCLUSIONS

25.1 Climate Change and Sea Level Rise

Climate change is occurring now and is expected to accelerate. Consideration has been given to six primary climate change variables in this report and 13 secondary climate change variables. Global sea level rise is the climate change variable most relevant to coastal management for which well accepted, quantified projections are available. Changes to atmospheric circulation, storm intensity and frequency are also of high importance to the coastal zone, however, well accepted quantification of likely changes is not available. The latest Intergovernmental Panel on Climate Change (IPCC, 2007a, b) Report provides numerous sea level rise scenarios for 2100. Simplified “mid” and “high” sea level rise scenarios developed by WRL for engineering application are shown in Table 25.1. Similar engineering scenarios were developed in NCCOE (2004). It should be noted that IPCC (2007a, page 17) addresses the doomsday scenario involving the total melting of the Greenland ice sheet (suggested timescale is millennia) which it estimates would elevate global sea levels by a further 7 m. Even more extreme postulations exist, including a rise of up to 70 m (GACGC, 2006) if all the world’s ice sheets were to melt, however, the timescale is considered to be millennia. The IPCC represents an international consensus position for planning purposes and has been used for this study. The maximum sea level rise scenario examined in this study, over the planning period to 2100, is 0.9 m.

Table 25.1 Simplified Engineering Estimates of Global Sea Level Rise (by WRL) based on IPCC (2001, 2007) and NCCOE (2004) Scenario Year 2050 2100 Adopted “Mid” scenario 0.2 0.5 Adopted “High” scenario 0.3 0.9

25.2 Coastal Processes and Hazards

The following coastal processes were considered within the constraints of available data and project resources for the Clarence coast:  Astronomical tides (predicted tides)  Tidal anomalies, through: o Barometric setup F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 120.

o Wind setup o Coastally trapped waves  Ocean swell waves  Local wind waves  Wave setup  Wave runup and overtopping  Longshore sand transport (littoral drift)  Onshore-offshore sand transport (beach erosion and recovery).

The following coastal hazards were considered within the constraints of available data and project resources:  Beach erosion and dune stability  Shoreline recession (long term change due to waves or sediment budget)  Beach rotation  Unstable creek or lake entrances  Wind blown sand  Coastal inundation  Stormwater erosion  Climate change, including sea level, changes to waves, wind and rainfall  Seawater ingress into groundwater table causing displacement of fresh water.

The following coastal hazards were not assessed in this study:  Slope, cliff or bluff instability (except for an allowance for houses on sand dunes)  Potential acid sulfate soils  Tsunami  Ecological change and threats.

Hazards have generally been assessed for 100 year average recurrence interval (ARI), 1% Annual Exceedance Probability (AEP) events, in line with most flood policies. Higher ARI events need to be considered for infrastructure of higher importance than private houses.

25.3 Assets at Risk

Figures showing potential inundation and erosion/recession have been derived from LIDAR surveys and the modelling undertaken, to indicate possible properties at risk. Indicative numbers of houses at risk are provided as an order of magnitude estimate. Individual F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 121.

properties that may have been identified at possible risk need to have detailed assessment undertaken, which (subject to the triggers adopted) may be at the time of proposed redevelopment. Indicative numbers of houses at risk due to erosion/recession are shown in Table 25.2, with indicative houses at risk due to inundation shown in Table 25.3. Some properties are at risk from both hazards, however, for this study, the hazards are treated separately, and may eventuate from different storm events. It is acknowledged that other infrastructure is also at risk, however, most of this services the houses which are present. The occurrence of inundation may result in no damage, or range from nuisance flooding for some properties to major damage. The amount of damage is dependent on the inundation level, floor level and construction materials and fittings. The values presented indicate the market value of the properties at risk, and provide an upper limit on potential losses if no adaptation is undertaken.

Table 25.2 Indicative Houses/Buildings at Risk due to Coastal Erosion and Recession Present 2050 mid 2050 high 2100 mid 2100 high SLR SLR SLR SLR Bellerive* 2 5 5 6 12 Howrah and Little Howrah Beach* 10 11 11 18 27 Seven Mile Beach west 1 1 2 3 11 Roches Beach, Lauderdale 19 108 108 125 195 Mays Beach 2 4 4 4 8 Cremorne (Ocean) Beach 9 36 38 44 53 Clifton (Ocean) Beach, west 3 7 7 10 12 South Arm Beach – Halfmoon Bay 9 13 18 23 43 Glenvar Beach *0 *0 *0 *0 *0 Opossum Bay *0 *0 *0 *0 *0

TOTAL NUMBER 55 185 193 233 361 POTENTIAL IMPROVED VALUE ($M) 28 93 97 117 181 * likely presence of rock and/or a seawall may protect properties from erosion and recession, however, this has not been quantified. Such properties may also be vulnerable to wave impacts. Rock level needs to be mapped. Higher values cannot be excluded until this is undertaken

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 122.

Table 25.3 Indicative Houses/Buildings at Risk due to Inundation Present Present 2100 high day depth day all SLR all > 0.3 m depths depths Montagu Bay 0 0 0 Kangaroo Bay 0 8 23 Bellerive 2 13 61 Little Howrah Beach 0 2 9 Rokeby Waste Water Treatment Plant 0 0 0 Roches Beach, Lauderdale – from South Arm Road, Ralphs Bay 101 161 491 Seven Mile Beach west 0 0 84 Roches Beach, Lauderdale * * * Mays Beach 0 0 0 Cremorne (Ocean) Beach * * * Cremorne – Pipe Clay Esplanade 15 95 118 Clifton – Bicheno St, Pipe Clay Lagoon 9 21 26 Clifton (Ocean) Beach, west * * * South Arm Neck – Ralphs Bay side Road Road Road Hope Beach, South Arm Neck - ocean side * * * South Arm Beach – Halfmoon Bay 2 5 8 Glenvar Beach ** ** ** Opossum Bay ** ** **

TOTAL NUMBER 129 305 820 POTENTIAL IMPROVED VALUE ($M) 65 153 410

* Inundation is possible from this side, but is potentially less severe than from the other side of the isthmus. ** Inundation is unlikely, but direct wave impacts are possible on beachfront structures.

25.4 Adaptive Management Options

IPCC (2001) listed three classes of adaptive management options, namely:

 Retreat  Accommodate  Protect.

Practical management options include:  Planning controls, which deal with: o Building setbacks o Minimum floor levels o Appropriate engineering assessments o Appropriate construction techniques (e.g. piled buildings, flood resistant materials)  Planning controls which may also consider a development freeze in some locations

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 123.

 Physical works such as seawalls, groynes, dune management or sand nourishment, offshore breakwaters and/or surfing reefs  Ongoing monitoring, analysis and review of findings  Additional data collection or studies  A timeframe for review – currently 5 years for Council planning schemes.

This study was undertaken for most of the coast of the Clarence local government area. Therefore, broad and rapid assessment techniques were used which need to be followed with further detailed studies and monitoring. This study was not undertaken down to the level of quantified risk to single houses, however, numbers are presented to provide an order of magnitude. That is, costings provide an order of magnitude estimate only.

With the philosophy of managed/adaptive approach with multiple interventions, it is conservative to construct protective works now for high sea level rise in 2100, particularly if the provision to upgrade is incorporated in their design. It is prudent, however, to consider a range of sea level rise scenarios for future planning, as most of the present day risk is due to inadequate past planning.

Hard protection (in the form of seawalls) and soft protection (through sand nourishment, supplemented with groynes) are technically feasible (subject to additional studies). The cost of these protection options is generally less than the value of the assets protected for most locations, and for all sea level rise scenarios to 2100. The economic factors of adaptive management need to be balanced against environmental and social factors to achieve the optimum outcome. An example of a social factor is the continued availability of a recreational beach for use by non-beachfront residents. In reality, successful coastal management will usually combine elements of retreat, accommodate and protect.

25.5 Potentially Feasible Adaptive Management Options

A summary of potentially feasible adaptive management options is shown in Table 25.4. Detailed development and design needs to be undertaken before implementing most of these options. Further details on the options are provided in the body of the report.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 124.

Table 25.4 Potentially Feasible Adaptive Management Options Retreat Raise Piled Seawall or Groynes and/or floors or buildings levee and/or setbacks land nourishme nt

Montagu Bay n/a x n/a present n/a Kangaroo Bay ?  n/a present n/a Bellerive     ? Howrah and Little Howrah Beach     ? Rokeby and Droughty Point x  x  x Lauderdale - South Arm Road, Ralphs Bay ?  x  x Seven Mile Beach west      Roches Beach, Lauderdale      Mays Beach  x  x x Cremorne (Ocean) Beach      Cremorne – Pipe Clay Esplanade ?  x  x Clifton – Bicheno St, Pipe Clay Lagoon ?  x  x Clifton (Ocean) Beach, west    ? ? South Arm Neck – Ralphs Bay side x x x  x Hope Beach, South Arm Neck - ocean side x x x  x South Arm Beach - Halfmoon Bay     ? Glenvar Beach     x Opossum Bay     x  Feasible subject to detailed studies x Not feasible ? May be technically feasible, but unlikely to be economically feasible n/a not applicable (e.g. hard foreshore)

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 125.

26. REFERENCES AND BIBLIOGRAPHY

Andersen M.S., Jakobsen R., Nyvang V., Christensen F.D., Engesgaard P. & Postma D. (2007): “Density driven seawater plumes in a shallow aquifer caused by a flooding event - Field observations, consequences for geochemical reactions and potentials for remediation schemes”. GQ07: Securing Groundwater Quality in Urban and Industrial Environments, Proc. 6th International Groundwater Quality Conference, Fremantle, Western Australia, 2–7 December 2007.

Andersen M.S., Christensen F.D., Engesgaard P., & Jakobsen R. (2006). „Density driven seawater plumes in a shallow aquifer caused by a flooding event - Field observations and numerical modelling”. 1st SWIM-SWICA, 19th Salt Water Intrusion Meeting & 3rd Salt Water Intrusion in Coastal Aquifers Meeting - Cagliari,Chia Laguna, Italy, September 24- 29, 2006.

Andersen, M.S., Nyvang, V, Jakobsen R and D. Postma (2003). “The geochemistry of a seawater intrusion experiment in a shallow sandy aquifer. Skansehage Denmark”. Second International Conference on Saltwater Intrusion and Coastal Aquifers- Monitoring, Modeling and Management. Mérida, México, March 30 – April 2, 2003

AS 1289.3.6.1-1995, Methods for Testing Soils for Engineering Purposes, Method 3.6.1: Soil classification tests – Determination of the particle size distribution of a soil – Standard method of analysis by sieving, Standards Australia.

AS 4997-2005, Guidelines for the Design of Maritime Structures, Standards Australia.

AS/NZS 1170.2:2002, Structural Design Actions – Wind Actions, Standards Australia.

AS/NZS 4360:2004, Risk Management, Standards Australia.

Bacon, CA and Latinovic, M. (2003). A review of groundwater in Tasmania. Department of Mineral Mineral Resources Tasmania, Tasmanian Geological Survey, Record 2003/01

Booij, N., R.C. Ris and L.H. Holthuijsen (1999a), “A third-generation wave model for coastal regions, Part I, Model description and validation”, Journal of Geophysical Research C4, 104, 7649-7666.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 126.

Ris, R.C., N. Booij and L.H. Holthuijsen (1999b), “A third-generation wave model for coastal regions, Part II, Verification”, Journal of Geophysical Research C4, 104, 7667- 7681.

Borgman, Leon E. (1963), “Risk Criteria”, Journal of the Waterways and Harbours Division, Proceedings of the American Society of Civil Engineers, WW 3, August 1963, pp 1-35.

Building Code of Australia (BCA, 2007).

Bruun, P. (1962), "Sea Level Rise as a Cause of Beach Erosion", Proceedings ASCE Journal of the Waterways and Harbours Division, Volume 88, WW1, pp 117-130, American Society of Civil Engineers.

Bruun P, (1988), "The Bruun Rule of Erosion by Sea-Level Rise: A Discussion on Large- Scale Two- and Three-Dimensional Usages", Journal of Coastal Research, 4(4), 627-648.

Bryant, E (2001), Tsunami the Underrated Hazard, Cambridge University Press, Cambridge UK.

BS 6349 : Part 1 : 1984, “British Standard Code of Practice for Maritime Structures, Part 1. General Criteria”, British Standards Institute.

Byrne, G (2006), “Roches Beach Lauderdale Coastal Erosion Study”, Vantree Pty Ltd for Clarence City Council.

Caires, S., Sterl, A., 2005. “100-year return value estimates for ocean wind speed and significant wave height from the ERA-40 data”. Journal of Climate 18, 1032–1048.

Carley J.T. (1992), "Analysis of SBEACH Numerical Beach Erosion Model", MEngSc Thesis, University of New South Wales.

Carley, J.T., Couriel, E.D. and Cox, D.R. (1998). “Numerical Modelling Sand Nourishment Profiles/Quantities and Beach Erosion due to Storms and Sea Level Rise”. WRL Technical Report 98/04, Water Research Laboratory, University of New South Wales, Australia.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 127.

Carley, J T. and Cox, R. J. (2003), “A Methodology for Utilising Time-Dependent Beach Erosion Models for Design Events”, Proceedings of Australasian Coasts and Ports Conference, Auckland, The Institution of Engineers Australia.

Carlson et al (2007). Storm-Damaged Saline-Contaminated Boreholes as a Means of Aquifer Contamination. Ground Water. Published on-line. doi: 10.1111/j.1745- 6584.2007.00380.x

CEM, Coastal Engineering Manual (2002), US Army Corps of Engineers. Chapman, D M, Geary, M, Roy, P S and Thom, B G (1982), “Coastal Evolution and Coastal Erosion in New South Wales”, Coastal Council of New South Wales.

Chapman and Smith (1981). “A Ten Year Review of Variability of an Ocean Beach”. Proceedings Fifth Australian Conference on Coastal and Ocean Engineering, pp 162-170, The Institution of Engineers, Australia.

Chapman, D M and Smith A W (1983). “Gold Coast Swept Prism - Limits”. Proceedings Sixth Australian Conference on Coastal and Ocean Engineering, pp 132-138, The Institution of Engineers, Australia.

Chapman, D M; Geary, M; Roy, P S and B G Thom (1982), Coastal Evolution and Coastal Erosion in New South Wales, a report prepared for the Coastal Council of New South Wales, Sydney, ISBN 0 7240 6582 2

Church, J.A., J.R. Hunter, K.L. McInnes and N.J. White (2006). “Sea-level rise around the Australian coastline and the changing frequency of extreme sea-level events”, Australian Meteorological magazine, 55, 253-260.

Coast Protection Board (CPB-SA, 1992), Coastline Number 26, Endorsed by the South Australian Government.

Colosi, John A and Walter Munk (2006), “Tales of the Venerable Honolulu Tide Gauge”, Journal of Physical Oceanography, Volume 36, Issue 6, June, pp. 967-996

Commander, DP (2000). Potential effects of climate change on groundwater resources in Western Australia. In Hydro, 2000 proceedings.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 128.

Couriel E.D., Cox R.J. and Carley J.T. (1992). “Methods for Storm Cut Estimation - A Review”. Proceedings New South Wales Coastal Conference, Kiama NSW Australia.

Cromer, W and Sloane, J. 1976. The Hydrology of Seven Mile Beach. Unpublished Report 1976/10, Mineral Resources Tasmania, Hobart, Tasmania.

Cromer, W. 1981. Groundwater Investigations at Seven Mile Beach for the Royal Hobart Golf Club. Unpublished Report 1981/3, Mineral Resources Tasmania, Hobart, Tasmania.

Cromer, W. (2006), “Geotechnical Risk Assessment Storm surges causing foredune erosion and flooding Roches Beach, Lauderdale”, William C. Cromer Pty. Ltd.

Crosbie, R. (2007). The Hydrological impacts of climate change on groundwater. Presentation by CSIRO Water for a Healthy Country Flagship.

CSIRO (2007), Climate Change in Australia. ISBN 9781921232947 (PDF), CSIRO, Australia.

Dally W.R., Dean R.G. and Dalrymple R.A. (1984). “A Model for Breaker Decay on Beaches”. Proceedings of the 19th Coastal Engineering Conference, pp 82-98, American Society of Civil Engineers.

Davies J.L. (1959), Sea Level Change and Shoreline Development in Southeastern Tasmania. Pap. Roy. Soc. Tasmania Vol. 93 pp 89-96 Dean R.G. (1977), "Equilibrium Beach Profiles: U.S. Atlantic and Gulf Coasts", University of Delaware, Department of Civil Engineering, Ocean Engineering Report No.12.

Dean R.G. (1984), "Applications of Equilibrium Beach Profile Concepts", Coastal Engineering Abstracts, American Society of Civil Engineers, pp 140-141.

Dean, R.G. and Dalrymple, R.A.(1991), Water Wave Mechanics for Engineers and Scientists, World Scientific, Singapore.

Deans, J. Fotheringham, D. and Wynne, A. (1995), Semaphore Park and Tennyson Foreshore Options for Protection, Technical Report 94/2, Department for Environment and Natural Resources, Coastal Management Section, Government of South Australia.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 129.

DEFRA UK (2006), Department for Environment, Food and Rural Affairs, Flood and Coastal Defence Appraisal GuidanceFCDPAG3 Economic Appraisal Supplementary Note to Operating Authorities – Climate Change Impacts October 2006 http://www.defra.gov.uk/environ/fcd/pubs/pagn/default.htm October 2006

Delta Committee (1962), Final Report, State Printing and Publishing Office, The Hague, Netherlands.

Department for Planning and Infrastructure, WA (2004), “Port Beach Coastal Erosion Study”, Technical Report, Report No. 427, July 2004, Government of Western Australia.

Dominey-Howes, Dale (2007 in press), “Geological and Historical Records of Tsunami in Australia”, Marine Geology xx (2007) xxx-xxx. doi:10.1016/j.margeo.200701.010.

EurOtop (2007), Wave Overtopping of Sea Defences and Related Structures: Assessment Manual, EA Environment Agency, UK, ENW Expertise Netwerk Waterkeren, NL, KFKI Kuratorium für Forschung im Küsteningenieurwesen, DE, August 2007. Authors: T. Pullen (HR Wallingford, UK), N.W.H. Allsop (HR Wallingford, UK), T. Bruce (University Edinburgh, UK), A. Kortenhaus (Leichtweiss Institut, DE), H. Schüttrumpf (Bundesanstalt für Wasserbau, DE), J.W. van der Meer (Infram, NL)

EPA, (1999). Semaphore Park Foreshore Protection Strategy Re-examination: Background and Alternatives. Environment Protection Agency, Government of South Australia.

Faherty et al. (2007). Effects of climate change on river flows and groundwater recharge – a practical methodology, recharge and groundwater level impact assessment. UK Water Industry Research.

(FEMA) Federal Emergency Management Agency USA (2000), Coastal Construction Manual FM55, USA

Flick, Reinhard E; Murray, Joseph F and Lesley C Ewing (2003), “Trends in United States Tidal Datum Statistics and Tide Range”, Journal of Waterway, Port, Coastal, and Ocean Engineering, Vol. 129, No. 4, 1 July, pp. 155-164

Foster D.G. (1988) and Pitt & Sherry Pty Ltd, “Report on Coast Protection Study Roches Beach Lauderdale”, Lands Department Tasmania.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 130.

Hanslow D.J. and Nielsen P. (1993), “Shoreline Setup on Natural Beaches”, Special Issue Journal of Coastal Research, Beach and Surf Zone Morphodynamics.

Hanslow D.J. and Nielsen P. (1995), “Field Measurements of Runup on Natural Beaches”, Proceedings 12th Australian Conference on Coastal Engineering, pp 189 – 193.

GACGC (2006), German Advisory Council on Global Change, The Future Oceans – Warming up, Rising High, Turning Sour, Special Report, Berlin 2006, ISBN 3-936191-14- X.

Ghassemi, F., Jacobsen, G., and Jakeman, AJ. (1991). Major Australian aquifers: potential climatic change impacts. Water International 16(1):38-44.

Gordon, A.D. (1987). Beach Fluctuations and Shoreline Change – NSW, Proceedings of 8th Australasian Conference on Coastal Engineering, Launceston, The Institution of Engineers Australia, 103-107.

Hallermeier R.J. (1981). “A Profile Zonation for Seasonal Sand Beaches from Wave Climate”. Coastal Engineering, Vol. 4, pp 253-277.

Hallermeier R.J. (1983). “Sand Transport Limits in Coastal Structure Design”. Proceedings, Coastal Structures ’83. American Society of Civil Engineers, pp 703-716

Haradasa, D., Wyllie S. and Couriel E. (1991), “Design Guidelines for Water Level and Wave Climate at Pittwater” AWACS Report 89/23, Australian Water and Coastal Studies, Sydney Australia.

Hart, D. (1997). Near-shore Seagrass Change between 1949 and 1996. Image Data Services, Resource Information Group, Department of Environment and Natural Resources, South Australia. Prepared for Environment Protection Authority, Department of Environment and Natural Resources, South Australia and SA Water.

Hemer, M.A., J.A. Church and J.R. Hunter, “Waves and Climate Change on the Australian Coast”, Journal of Coastal Research SI 50 432 - 437 ICS2007 (Proceedings) Australia ISSN 0749.0208.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 131.

Hemer, M.A., I. Simmonds, K. Keay (2008), “A classification of wave generation characteristics during large wave events on the Southern Australian margin”, Continental Shelf Research 28 (2008) 634–652, Elsevier.

Higgs, K.B. and Nittim, R. (1988), “Coastal Storms in NSW in August and November 1986”, WRL Technical Report No 88/06, Water Research Laboratory, University of New South Wales.

Holman, R. A. 1986. “Extreme Value Statistics for Wave Run-up on a Natural Beach,” Coastal Engineering, Vol 9, No. 6, pp 527-544.

Holthuijsen, L.H., Booij, N. and T.H.C. Herbers, 1989: A prediction model for stationary, short-crested waves in shallow water with ambient currents, Coastal Engineering, 13, 23- 54.

Holthuijsen, L.H., N. Booij and R.C. Ris, 1993: A spectral wave model for the coastal zone, Proc. of 2nd Int. Symposium on Ocean Wave Measurement and Analysis, New Orleans, USA, 630-641.

Hunter, J. R. (2006, Draft), “Historical and Projected Sea-Level Extremes for Hobart, Tasmania”, Commissioned by the Department of Primary Industries and Water, Tasmania. Published by Antarctic Climate and Ecosystems Cooperative Research Centre. Draft 15/15/2006.

Hunter, J. R. (2007), “Historical and Projected Sea-Level Extremes for Hobart and Burnie, Tasmania”, Commissioned by the Department of Primary Industries and Water, Tasmania Antarctic Climate & Ecosystems, Cooperative Research Centre, Private Bag 80, Hobart, Tasmania 7001.

Hunter, J., Coleman, R. & Pugh, D., (2003): “The sea level at Port Arthur, Tasmania, from 1841 to the present”, Geophysical Research Letters, vol. 30(7), 1401, doi: 10.1029/2002GLO16813, p. 54-1 to 54-4.

IPCC, (2001). Technical Summary of the Working Group I Report and Summary for Policymakers, The United Nations Intergovernmental Panel on Climate Change, Cambridge University Press, UK.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 132.

IPCC (2007a), Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

IPCC (2007b), Climate Change 2007 - The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, (ISBN 978 0521 88009-1 Hardback; 978 0521 70596-7 Paperback), [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

Jay, D A; Chisholm, TA and A Krause (2004), “Decadal-Scale Changes in Shelf Internal Tides in the Columbia River Plume Area”, American Geophysical Union, Fall Meeting 2004, abstract #OS13A-0512

Kite, G. W. (1988), “Frequency and Risk Analyses in Hydrology”, Revised edition, Water Resources Publications, Littleton, Colorado, U.S.A.

KNMI (2008), “The KNMI/ERA-40 Wave Atlas derived from 45-years of ECMWF reanalysis data”, by S. Caires, A. Sterl, G. Komen and V. Swail. http://www.knmi.nl/waveatlas

Kriebel, D.L. and Dean, R.G. (1985), “Numerical Simulation of Time Dependent Beach and Dune Erosion”, Coastal Engineering, Vol 9, Elsevier, pp 221-245.

Kriebel D.L., Kraus N.C., and Larson M. (1991), "Engineering Methods For Predicting Beach Profile Response", Proceedings of Coastal Sediments '91, American Society of Civil Engineers, pp 557-571.

Kulmar, Mark, Doug Lord and Brian Sanderson (2005), “Future Directions for wave Data Collection in New South Wales”, Proceedings of Australasian Coasts and Ports Conference, Adelaide, The Institution of Engineers Australia.

Larson M. and Kraus N.C. (1989). “SBEACH: Numerical Model for Simulating Storm- Induced Beach Change, Report 1: Theory and Model Foundation”. Technical Report

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 133.

CERC-89-9, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg USA.

Larson M., Kraus N.C. and Byrnes M.R. (1990). “SBEACH: Numerical Model for Simulating Storm-Induced Beach Change, Report 2: Numerical Formulation and Model Tests”. Technical Report CERC-89-9, US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg USA.

Lord D.B. and Kulmar M, (2000), “The 1974 Storms Revisited: 25 years Experience in Ocean Wave Measurement Along the South-East Australian Coast”, Proceedings International Conference of Coastal Engineering, pp 559-572, American Society of Civil Engineers, USA.

Mai, Stephan, Nino Ohle and Claus Zimmerman (2002), “Safety of Nuclear Power Plants against Flooding”, Proceedings of the 6th International Symposium “Littoral – The Changing Coast”, Portugal.

Marshall, G.J., 2003. “Trends in the Southern Annular Mode from observations and reanalyses”. Journal of Climate 16 (24), 4134–4143.

Mase, H. (1989), “Random Wave Runup Height on Gentle Slopes”, Journal of the Waterway, Port, Coastal and Ocean Engineering Division, American Society of Civil Engineers, pp 593-609.

MHL (1992), “Mid New South Wales Coastal Region Tide-Storm Surge Analysis”, MHL Report No. 621, Manly Hydraulics Laboratory, NSW Public Works Department.

MRT (2007). Mineral Resources Tasmania Groundwater Features on-line http://www.mrt.tas.gov.au/portal/page?_pageid=35,832436&_dad=portal&_schema=PORT AL

Mudd, GM, Jelecic, S., Ginnivan, F, Reid, M. (2006) Towards quantifying shallow groundwater-climate relationships in central and northern Victoria. In: 10th Murray-Darling Basin Groundwater Workshop, Canberra, September, 2006.

Narayan KA, C. Schleeberger C, P. B. Charlesworth PB and Bristow KL (2003). Effects Of Groundwater Pumping On Saltwater Intrusion In The Lower Burdekin Delta, North Queensland. MODSIM conference paper. Available at www.clw.csiro.au.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 134.

NCCOE, National Committee on Coastal and Ocean Engineering, Engineers Australia (2004), Guidelines for Responding to the Effects of Climate Change in Coastal and Ocean Engineering, The Institution of Engineers Australia.

Nielsen A.F. (1994). “Subaqueous Beach Fluctuations on the Australian South-Eastern Seaboard”. Australian Civil Engineering Transactions, Vol. CE36 No. 1, The Institution of Engineers, Australia, pp 57-67.

Nielsen, A.F., Lord, D.B. and Poulos, H.G. (1992), “Dune Stability Considerations for Building Foundations”, Engineers Australia, Vol CE34 No 2, June.

Nielsen, P., and Hanslow, D. J. (1991). “Wave Runup Distributions on Natural Beaches,” Journal of Coastal Research, Vol 7, No. 4, pp 1139-1152.

NSW Government (1990), Coastline Management Manual, Sydney, Australia.

NSW Government (1997), NSW Coastal Policy, Sydney, Australia.

NSW Government (2005), Floodplain Development Manual: the management of flood liable land, April, Department of Infrastructure, Planning and Natural Resources, ISBN 0 7347 5476 0, DIPNR 05_020

Ochi, M.K. and Hubble, E. N. (1976), “Six Parameter Wave Spectra”, Proceedings 15th International Coastal Engineering Conference, Vol 1, pp 301-328, American Society of Civil Engineers.

Pilgrim, D.H., (ed)., Australian Rainfall & Runoff - A Guide to Flood Estimation, Institution of Engineers, Australia, Barton, ACT, 1987.

Pilkey, O H and Cooper, J A G (2004), “Society and Sea Level Rise”, Science, 303, pp 1781-1782.

Pittock, B., (2004). Climate Change - An Australian Guide to the Science and Potential Impacts. Chapter 4. Potential impacts of climate change: Australia. Published by Australian Greenhouse Office.

Port of Hobart (2005), Excel file: “LEVELDATUMS post 2006.XLS”, compiled by Peter Fleming, 14/12/2005.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 135.

Pugh, D.T. (1987), Tides, Surges and Mean Sea-Level, John Wiley and Sons, Chichester, UK.

Pugh, D.T. (2004), Changing Sea Levels Effects of Tides, Weather and Climate, Cambridge University Press UK.

Queensland Government (2004), Operational policy Coastal Development - Building and engineering standards for tidal works. Under the (Queensland) Integrated Planning Act 1997.

Ranasinghe, Roshanka, Phil Watson, Doug Lord, David Hanslow and Peter Cowell (2007), “Sea Level Rise, Coastal Recession and the Bruun Rule”, Proceedings of Australasian Coasts and Ports Conference, Melbourne, The Institution of Engineers Australia.

Reid, J.S. and Fandry, C.B. (1994), “Wave Climate Measurements in the Southern Ocean”, CSIRO Marine Laboratories Report 223, CSIRO, Hobart Tasmania.

Ris, R.C., N. Booij and L.H. Holthuijsen, 1999, A third-generation wave model for coastal regions, Part II, Verification, Journal of Geophysical Research C4, 104, 7667-7681.

Roberts, P. (1988) Groundwater salinity at Seven Mile Beach. Unpublished Honours Thesis, University of Tasmania.

Roelvink J.A. and Broker I. (1993). “Cross-shore Profile Models”. Coastal Engineering, Vol. 21, pp 163-191.

Royal Australian Navy Hydrographic Service (RAN, 1999), “Australian National Tide Tables 2000”. Royal Australian Navy Hydrographic Service (RAN, 2006), “Australian National Tide Tables 2007”.

Rynn, Jack and Davidson, Jim (1999), “Contemporary Assessment of Tsunami Risk and Implications for Early Warnings for Australia and its Island Territories”, The International Journal of the Tsunami Society, Volume 17 Number 2, Honolulu, USA, pp 107 – 127.

Satake, Kenji (2002), “Making Waves on Rocky Ground” Book Reviews, Nature, Volume 415, 24 January 2002.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 136.

Schoonees J.S. and Theron A.K. (1995). “Evaluation of 10 Cross-shore Sediment Transport / Morphological Models”, Coastal Engineering, Vol 25, pp 1-41.

Sharples, C. (2006): “Indicative Mapping of Tasmanian Coastal Vulnerability to Climate Change and Sea Level Rise: Explanatory Report”; Report to Department of Primary Industries, Water & Environment, Tasmania, 2nd Edition, plus accompanying electronic (GIS) maps.

Sharples, C. (2007): “Shoreline Change at Roches Beach 1957 – 2006, South-Eastern Tasmania” A Report to the Antarctic Climate and Ecosystems Co-operative Research Centre, Tasmania, October 2007.

Shore Protection Manual (1984), Coastal Engineering Research Center, Department of the Army, Vicksburg, Mississippi USA.

Short, A.D. (2006), Beaches of the Tasmanian Coast and Islands, Sydney University Press.

Short, A.D. and Turner, I.L. (2000), Beach Oscillation, Rotation and the Southern Oscillation, Narrabeen Beach, Australia, Proceedings Coastal Engineering 2000, ASCE, 2439-2452.

Simmonds, I., Keay, K., 2000b. “Variability of Southern Hemisphere extratropical cyclone behaviour 1958–97”. Journal of Climate 13, 550–561. SKM, 2000. National Land and Water Audit.Groundwater Data for Tasmania. Sinclair Knight Merz Pty Ltd : Armadale, Victoria.

Smith A.W. (1975). “An Estimate of the Active Zone Determined from Properties of Natural Sediment”. Preprints 2nd Australian Conference on Coastal Engineering, Institution of Engineers, Australia, pp 136-141.

Stephens AW, Roy PS and Jones MR (1981), “Geological Model of Erosion on a Littoral Drift Coast”, Proceedings Fifth Australasian Conference on Coastal and Ocean Engineering, The Institution of Engineers Australia.

Sun, H., Grandstaff, D., Shagam, R. (1999). “Land subsidence due to groundwater withdrawal: potential damage of subsidence and sea level rise in southern New Jersey, USA”. Environmental Geology 37(4):290-296.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04 137.

Swart D.H. (1974). “Offshore Sediment Transport and Equilibrium Beach Profiles”. Doctorate Dissertation. Delft University of Technology, The Netherlands.

Tasmanian Building Regulation (2004), Tasmanian Government.

US Army Corps of Engineers (2002), EM 1110 Coastal Engineering Manual.

Vellinga, P. (1986), Beach and Dune Erosion During Storm Surges, Doctorate Dissertation, Delft University of Technology, The Netherlands. Victorian Coastal Council (2007). Draft Victorian Coastal Strategy, ISBN 978-1-74152- 889-3 (online), Draft, October 2007.

Wallace, Stephanie and Ron Cox (2000), “Effects of Seagrass on Nearshore Current and Wave Dynamics”, Proceedings of the 28th International Coastal Engineering Conference, pp 878-890, American Society of Civil Engineers.

Western Australian Planning Commission (2003), “Statement Of Planning Policy No. 2.6 State Coastal Planning Policy Prepared Under Section 5aa Of The Town Planning And Development Act 1928”, Government of Western Australia.

Walker, J.W., (1999) “Church Point – Pontoon Assessment”, WRL Technical Report No. 99/42, Water Research Laboratory, University of New South Wales, Sydney, Australia.

Wynne A.A, Fotheringham D.G., Freeman R., Moulds B., Penney S.W., Petrusevics P., Tucker R. & Ellis D.P., (1984), Adelaide Coast Protection Strategy Review. The Coastal Management Branch, Conservation Programmes Division, Department of Environment and Planning, South Australia. Prepared for The Coast Protection Board South Australia.

Yesertnener, C. (2003). Impacts of climate, land and water use on declining groundwater levels in the Gnangara Groundwater Mound, Perth WA. The Institution of Engineers, Australia, 28th International Hydrology and Water Resources Symposium, 10-14th November 2003, Wollongong. Vol 1.253-260.

You, Zai-Jin (Bob), (2007), “Extrapolation of Extreme Wave Height with a Proper Probability Distribution Function”, Proceedings of Australasian Coasts and Ports Conference, Melbourne, The Institution of Engineers Australia.

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04

APPENDIX A MODELLING COEFFICIENTS

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04

APPENDIX A – MODELLING COEFFICIENTS

SWAN modelling was undertaken using the model parameters and coefficients shown in Table A.1. Some sensitivity tests were undertaken on coefficients, with some determined based on past experience of WRL staff on wave modelling. While much of the surrounding coast has cliffs, no reflective surfaces were used in the model due to the complexity in defining reflection characteristics and the relatively low importance of wave reflections on regional scale wave propagation. Wave reflection may be of importance in specific local sites located near cliffs.

Table A.1 SWAN Modelling Setup and Parameters Coarse Computational Grid Origin 488700 m E, 5110000 m N Rotation 25 º counter-clockwise ∆X 250 m ∆Y 250 m nX 530 nY 460 Grid Size 132,500 m x 115,000 m Nested Fine Computational Grid Origin 533358.84 m E, 5209440.44 m N Rotation 25 º counter-clockwise ∆X 100 m ∆Y 100 m nX 421 nY 437 Grid Size 42,100 m x 43,700 m Directional Space Parameters Directional Range 360 º Directional Resolution 6 º Frequency Space Parameters No. Frequency Bins 24 Min. Frequency Variable Max. Frequency Variable Spectral Parameters Shape JONSWAP Period Peak Width-energy degrees Peak Enhancement Factor 3.3 Model Parameters Wave Braking Model Battjes and Janssen Α 1 Γ 0.73 Directional Spreading 5 º Bottom Friction (JONSWAP) 0.067 (default)

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04

APPENDIX B INUNDATION DEPTHS AND AVERAGE RECURRENCE INTERVALS

F I N A L D R A F T 11/11/08 WRL TECHNICAL REPORT 2008/04

APPENDIX B – INUNDATION DEPTHS AND AVERAGE RECURRENCE INTERVALS

The following tables relate to the potential inundation figures (Figures 22.1 to 22.15). They provide indicative inundation depths for the shaded areas of Figures 22.1 to 22.15 and the indicative Average Recurrence Interval (ARI) of potential inundation for the shaded areas.

The indicative ARIs for potential inundation with future sea level rise based on the shaded areas of Figures 22.1 to 22.15 are shown in Table B.1. The indicative depths of potential inundation with future sea level rise based on the shaded areas of Figures 22.1 to 22.15 are shown in Table B.2.

Table B.1 Indicative Average Recurrence Interval of Inundation of Shaded Areas Coloured Depth Indicative ARI of inundation (years) for sea level rise area Present 2050 mid 2050 high 2100 mid 2100 high SLR = 0.0 m SLR = 0.2 m SLR = 0.3 m SLR = 0.5 m SLR = 0.9 m Beige d > 0.3 m 100 15 5 0.7 0.01 Yellow d < 0.3 m 100 15 5 0.7 0.01 Purple d < 0.3 m 800 100 40 5 0.1 Orange d < 0.3 m 2,000 300 100 15 0.3 Light Blue d < 0.3 m 15,000 2,000 700 100 2 Dark Blue d < 0.3 m 800,000 100,000 40,000 5,000 100

Table B.2 Indicative Inundation Depths of Shaded Areas in 100 year ARI (1% AEP) Event Coloured Greater Indicative potential depth of inundation (m) for sea level rise area than or less than Present 2050 mid 2050 high 2100 mid 2100 high SLR = 0.0 m SLR = 0.2 m SLR = 0.3 m SLR = 0.5 m SLR = 0.9 m Beige greater than 0.3 0.5 0.6 0.8 1.2 Yellow less than 0.3 0.5 0.6 0.8 1.2 Purple less than - 0.3 0.4 0.6 1.0 Orange less than - - 0.3 0.5 0.9 Light Blue less than - - - 0.3 0.7 Dark Blue less than - - - - 0.3

F I N A L D R A F T 11/11/08