Coastal Vulnerability Assessment of the Wedge and Grey Coast 1189_001/1 September 2015 P:\DPW\1189_CoastalVulnerability\001_OriginalScope\Reports\WedgeGreyCVA_1189_0011_Rev0_20150827.docm Coastal Vulnerability Assessment of the Wedge and Grey Coast Prepared for Department of Parks and Wildlife Prepared by BMT Oceanica Pty Ltd In association with BMT JFA Pty Ltd and Damara WA Pty Ltd September 2015 Report No. 1189_001/1 Client: Department of Parks and Wildlife Document history Distribution No. copies Revision Author Recipients Organisation Date & format S. Green A M. Eliot B. Hegge BMT Oceanica 1 x docm 17/07/15 H. Fanai B S. Green B. Hegge BMT Oceanica 1 x docm 22/07/15 Department of Parks and C S. Green N. Greenhill 1 x pdf 22/07/15 Wildlife D S. Green B. Hegge BMT Oceanica 1 x docm 31/08/15 Department of Parks and 0 S. Green N. Greenhill 1 x pdf 1/09/15 Wildlife Review Revision Reviewer Intent Date A B. Hegge Technical 17/07/15 B B. Hegge Technical 22/07/15 N. Greenhill Department of Parks and Wildlife C K. Illich Department of Transport 20/08/15 V. Panizza Department of Planning D B. Hegge Technical 31/08/15 Status This report is 'Draft' until approved for final release, as indicated below by inclusion of signatures from: (i) the author and (ii) a Director of BMT Oceanica Pty Ltd or their authorised delegate. A Draft report may be issued for review with intent to generate a 'Final' version, but must not be used for any other purpose. Approved for final release: Author Director (or delegate) Date: 1/09/2015 Date: 1/09/2015 Cover Main image: Wedge shacks (BMT Oceanica Pty Ltd) Minor images: Collecting sediment samples at Wedge (BMT Oceanica Pty Ltd) North Grey Coast (BMT Oceanica Pty Ltd) Disclaimer This report has been prepared on behalf of and for the exclusive use of Department of Parks and Wildlife, and is subject to and issued in accordance with the agreed terms and scope between Department of Parks and Wildlife and BMT Oceanica Pty Ltd. BMT Oceanica Pty Ltd accepts no liability or responsibility for it in respect of any use of or reliance upon this report by any third party. Copying this report without prior written consent of Department of Parks and Wildlife or BMT Oceanica Pty Ltd is not permitted. © Copyright 2015 BMT Oceanica Pty Ltd Contents Executive Summary .................................................................................................................. iii 1. Introduction ....................................................................................................................... 1 2. Desktop Review ................................................................................................................. 2 2.1 Available information ............................................................................................ 2 2.2 Sediment cells ........................................................................................................ 3 2.3 Sediment transport ................................................................................................ 8 3. Coastal Vulnerability Assessment ................................................................................. 10 3.1 Coastal classification .......................................................................................... 10 3.1.1 Wedge .........................................................................................................10 3.1.2 Grey ............................................................................................................10 3.2 Planning timeframes ............................................................................................ 11 3.3 Allowance for the current risk of storm erosion (S1) ........................................ 11 3.3.1 Profiles ........................................................................................................12 3.3.2 Grain size ....................................................................................................13 3.3.3 Storm characteristics ...................................................................................13 3.3.4 Model results ...............................................................................................13 3.4 Allowance for historic shoreline movement trends (S2) ................................... 14 3.4.1 Shoreline mapping .......................................................................................14 3.4.2 Shoreline movement analysis ......................................................................14 3.4.3 Shoreline movement trends .........................................................................17 3.5 Allowance for erosion caused by sea level rise (S3) ......................................... 21 3.6 Erosion Hazard Mapping ..................................................................................... 21 3.7 Allowance for the current risk of storm surge inundation (S4) ........................ 25 4. Summary and Recommendations .................................................................................. 28 5. References ....................................................................................................................... 29 BMT Oceanica: Department of Parks and Wildlife: Coastal Vulnerability Assessment of the Wedge and Grey Coast i List of Figures Figure 2.1 Secondary cells and tertiary cell points adjacent to at Wedge and Grey ................ 4 Figure 2.2 Secondary cells and tertiary cell points north of Grey ............................................ 5 Figure 3.1 The Wedge salient forming a tombolo in December 1994 (left) and skewed north in February 1998 (right) ...............................................................................10 Figure 3.2 Limestone outcrops throughout the Grey settlement ............................................11 Figure 3.3 Nearshore bathymetry profile locations at Wedge ................................................12 Figure 3.4 Nearshore bathymetry and profile location at Grey ...............................................13 Figure 3.5 Transects used for Wedge shoreline change analysis using the Digital Shoreline Analysis System ...................................................................................15 Figure 3.6 Transects used for Grey shoreline change analysis using the Digital Shoreline Analysis System ...................................................................................16 Figure 3.7 Rate of change in shoreline position (m/yr) at Wedge from 1960 to 2013 .............18 Figure 3.8 Rate of change in shoreline position (m/yr) at Grey from 1960–2013 ...................20 Figure 3.9 Wedge coastal erosion hazard .............................................................................23 Figure 3.10 Grey coastal erosion hazard ................................................................................24 Figure 3.11 Inundation risk area at Wedge for 500 yr ARI storm event and 0.9 m sea level rise ...............................................................................................................26 Figure 3.12 Inundation risk area at Grey for 500 yr ARI storm event and 0.9 m sea level rise .......................................................................................................................27 List of Tables Table 2.1 Key data sets used to assess the coastal vulnerability of Wedge and Grey........... 2 Table 2.2 Key reports contributing to knowledge of coastal processes at Wedge and Grey ...................................................................................................................... 2 Table 2.3 Sediment Cells along the Midwest Coast .............................................................. 6 Table 2.4 Primary Cell Boundaries ........................................................................................ 7 Table 2.5 Secondary Cell Boundaries ................................................................................... 7 Table 2.6 Tertiary Cell Boundaries ........................................................................................ 8 Table 3.1 SPP 2.6 coastal classifications .............................................................................10 Table 3.2 Allowance for the current risk of storm erosion .....................................................14 Table 3.3 Shoreline records used to determine the historic position of the vegetation line .......................................................................................................................14 Table 3.4 Wedge allowance for historic shoreline movement (S2) .......................................17 Table 3.5 Grey allowance for historic shoreline movement (S2) ...........................................19 Table 3.6 Erosion allowance for sea level rise .....................................................................21 Table 3.7 Wedge allowances for erosion .............................................................................21 Table 3.8 Grey allowances for erosion .................................................................................22 Table 3.9 Storm surge inundation levels including wave setup and run-upnundation levels including wave setup and run-up ................................................................25 ii BMT Oceanica: Department of Parks and Wildlife: Coastal Vulnerability Assessment of the Wedge and Grey Coast Executive Summary An understanding of future coastal processes is required to aid planning at the Wedge and Grey shack