Department for Environment and Heritage Adelaide’s Living Beaches A Strategy for 2005 – 2025 Technical Report www.environment.sa.gov.au Study Team Rob Tucker – Manager, Coastal Protection Branch, Department for Environment and Heritage John Parker Liz Barnett Ross Cole Stephen Cox Joseph Davis Jenny Deans Sharie Detmar Alison Eaton Doug Fotheringham Carole Hutchens Peter Johnson Sue Murray–Jones Fiona Orchard Sam Penney Ron Sandercock Leonie Scriven Murray Townsend Guy Williams Prepared by Natural and Cultural Heritage Department for Environment and Heritage For the Government of South Australia Telephone (08) 8204 1910 Email: [email protected] Web Address: www.environment.sa.gov.au All information in this report was correct at June 2005. Cover photo: Brighton II Adelaide’s Living Beaches Foreword Adelaide’s coastline is a special sand to maintain beach width Of necessity, the report adopts asset and an inspiration to many and provide for strengthened a scientific and engineering local residents and visitors. The dune buffers. approach, and the level of detail coastline is dynamic, always Effective management of the makes it particularly appropriate shifting in response to the wind coast depends on an alliance for use by the State Government and waves. However, human with an informed community and seaside councils. The impacts have altered the involved in sound decision-making. report provides a timely review dynamics of the coast to such an The issues are often complex and of knowledge about Adelaide extent that natural processes can inter-related, the solutions are coastal processes, taking no longer sustain the beaches. costly, and some members of the into account previous reports Most of the land behind the public believe that a permanent since 1972. It also provides an structural solution to the moving foreshore was developed from updated assessment of measures sands is preferable to the ongoing the early 1900s onwards. Roads, available to protect the coast. buildings, houses, recreational recycling of sand from north to areas, and their sewerage south. However, the strategy and stormwater infrastructure since 1972 of beach replenishment were often built right over and rock revetment as the last coastal dunes. Consequently, line of defence has been a dune sand is unable to erode successful and cost-effective away during storms, and so method for maintaining sandy substantial protection works beaches, rebuilding sand dunes GRAHAM FOREMAN and preventing storm damage have been put in place to retain Chair, Coast Protection Board the foreshore and beaches. to property. Early on, this protection was in In 2000, the Department for the form of seawalls. From the Environment and Heritage, on 1970s, however, protection was behalf of the Coast Protection mainly achieved by replenishing Board, initiated a review of the beaches with sand. management of Adelaide’s Adelaide’s coastline is now metropolitan beaches. Based on a highly managed one. The examination of the benefits and sand that forms the beaches costs of a range of strategies, is a scarce and moving asset. along with the results of a series of modelling and feasibility studies The strategy for the future and input from the community, management of the beaches the Department has developed cannot be static but needs an innovative strategy for to be responsive to changing managing Adelaide’s beaches conditions to ensure that called Adelaide’s Living Beaches: future generations are not A Strategy for 2005–2025. disadvantaged by our decisions now. Climate change is likely to This technical report has been gradually alter the forces that developed to accompany act on the coastline, so we must Adelaide’s Living Beaches: allow for additional supplies of A Strategy for 2005–2025. Adelaide’s Living Beaches III Contents Study Team II 1.4 Sand supply 28 2.2.4 Groundwater changes 44 Foreword III 1.4.1 Geomorphological supply 30 2.3 Stormwater and Contents IV sewage management 45 1.4.2 In situ supply 30 List of Figures VIII 2.3.1 The Barcoo Outlet 45 1.5 Coastal processes 30 List of Tables X 2.3.2 Smaller stormwater 1.5.1 Tides 30 Acknowledgments XII outfalls 45 1.5.2 Currents 31 Executive Summary 1 2.3.3 Sewage treatment 1.5.3 Wind and waves 32 discharges 45 Background 1 1.5.4 Wave set-up and run-up 32 2.4 Loss of seagrass Components of the coverage 46 future strategy 3 1.5.5 Storms and surges 33 2.4.1 Blow-outs 49 Implementation 4 1.5.6 Sand transport 33 2.5 Seabed stability 49 Economic assessment 7 1.5.7 Biological activity 35 2.5.1 Effects of changed Social impacts 8 2. Human Impacts seabed conditions 51 on the Coast 37 Environmental impacts 9 2.6 Climate change 52 2.1 Coastal development 37 Risk assessment 9 2.6.1 Global sea level rise 53 2.1.1 Dune encroachment 37 Community education 2.6.2 Changes in weather and consultation 9 2.1.2 Land fill and conditions 53 development 39 Conclusion 10 2.7 Relative sea level rise 54 2.1.3 Sand excavation 39 1. The Adelaide Coast 11 2.7.1 Tide gauge data 2.1.4 Sand impoundment 40 and sea level trends 1.1 The metropolitan beach 11 for Adelaide 54 2.2 Recent coastal 1.2 Geological setting 14 development 42 2.7.2 Land subsidence along Adelaide’s coast 55 1.2.1 St Kilda formation 14 2.2.1 The Patawalonga 42 2.7.3 Levelling surveys for 1.3 Sand attributes 24 2.2.2 Holdfast Shores marina Adelaide 56 1.3.1 Sand type 25 and the Patawalonga entrance 42 2.8 Potential impacts of 1.3.2 Sand distribution 27 climate change and 2.2.3 Adelaide Shores relative sea level rise 56 1.3.3 Effective beach boat haven 43 and dune width 28 2.8.1 Beach width loss 58 IV Adelaide’s Living Beaches 2.8.2 Increased rate 4.1.2 External replenishment 90 5.1 Investigation of of littoral drift 58 potential sand sources 107 4.1.3 Costs of historical 2.8.3 Changes in storminess beach replenishment 91 5.1.1 Ideal sand for beach due to climate change 58 replenishment 107 4.2 Sand trapping 93 3. Coastal Management 5.1.2 Offshore sand History 59 4.2.1 Semaphore South trial investigations 109 offshore breakwater 93 3.1 Early coastal 5.1.3 Land-based sand development 59 4.3 Sand bypassing 97 investigations 119 3.2 Early coast protection 4.3.1 Torrens Outlet 97 5.2 Modelling of coastal works 59 4.3.2 Holdfast Shores processes 122 3.3 Major studies and marina and Adelaide 5.2.1 Littoral zone sand reports on Adelaide Shores boat haven 98 transport 122 coast protection 61 4.3.3 North Haven 99 5.2.2 Predictive sand 3.3.1 The 1970 Culver Report 61 4.4 Seawall protection 100 transport modelling 123 3.3.2 The 1984 Adelaide 4.4.1 Design height of 5.2.3 Coastal processes Coast Protection seawalls 101 study 124 Strategy Review 65 4.4.2 Responsibility for 5.3 Seagrass rehabilitation 3.3.3 The 1985 Metropolitan and cost of seawalls 101 studies 132 Coast Protection District Management Plan 67 4.5 Dune management 102 5.4 Economic value of Adelaide’s beaches 133 3.3.4 1992 Review of 4.5.1 Sand dune Alternatives for the protective buffer 102 5.4.1 Property and beach Adelaide Metropolitan amenity value 133 Beach Replenishment 4.5.2 Sand drift and public access control 103 5.4.2 Storm protection Strategy 71 value 133 3.3.5 Report of the Review 4.5.3 Non-indigenous coastal plants 103 5.5 Activities and views of the Management of of beach users 134 Adelaide Metropolitan 4.6 Monitoring 104 Beaches, 1997 76 5.5.1 Types of beach use 135 4.6.1 Seabed monitoring 104 4. The Existing Management 5.5.2 Valued beach Strategy 83 4.6.2 Harbour bypass attributes 135 monitoring 106 4.1 Beach replenishment 85 5.5.3 Level of support for 5. Recent Studies and beach management 4.1.1 Sand recycling 89 Investigations 107 methods 136 Adelaide’s Living Beaches V 6. The Future Management 6.8 Implementation plan 154 7.2.4 Social impacts of Strategy 137 using structures to 6.8.1 Coastal slow sand 176 6.1 Coast protection management cells 155 alternatives 137 7.2.5 Social impacts of 6.8.2 Schedule of capital integrating sand 6.1.1 Evaluation of and operating costs 157 bypassing at harbours alternative strategies 139 7. Economic, Social with beach 6.2 Components of the and Environmental management 177 future management Considerations 159 7.2.6 Summary of social strategy 140 7.1 Economic evaluation 159 impact assessment 177 6.3 Continue beach 7.3 Environmental impacts 177 replenishment 142 7.1.1 Evaluation of the alternatives presented 7.3.1 Environmental 6.3.1 The importance of in the 1992 review 159 impacts of beach beach replenishment 142 7.1.2 Comparison of replenishment 177 6.3.2 Future sand capital and operating 7.3.2 Environmental recycling sources 142 costs for practical impacts of using alternatives 161 6.4 Recycle sand more sand slurry pumping effectively using sand 7.1.3 Net present value and pipelines 180 slurry pumping and of practical alternatives 167 7.3.3 Environmental pipelines 147 7.1.4 Economic benefits of impacts of adding 6.4.1 Pipeline transfer beach management sand from external system 147 and coast protection 167 sources 181 6.4.2 Sand acquisition 7.1.5 Benefit–cost analysis 168 7.3.4 Environmental systems 148 impacts of using 7.1.6 Risk assessment 168 structures to slow sand 183 6.5 Add coarse sand from external sources 150 7.1.7 Summary of economic 7.3.5 Environmental assessment 172 impacts of integrating 6.6 Build coastal structures sand bypassing at in critical locations 151 7.2 Social impacts 173 harbours with beach management 184 6.6.1 Groynes 151 7.2.1 Social impacts of beach replenishment 173 7.3.6 Summary of 6.6.2 Breakwaters 152 environmental 7.2.2 Social impacts of using impact assessment 184 6.6.3 Hybrid fields 153 sand slurry pumping and pipelines 174 8.