R1009 Rev 0 March 2018 Northern Agricultural Catchment Council Coastal Hazard Assessment of Islands in the Northern Agricultural Region www.coastsandports.com.au m p rogers & associates pl Coastal Hazard Assessment of Islands in the Northern Agricultural Region K1516, Report R1009 Rev 0, Page (i) m p rogers & associates pl creating better coasts and ports Suite 1, 128 Main Street, Osborne Park, WA 6017 p: +618 9254 6600 e: [email protected] w: www.coastsandports.com.au K1516, Report R1009 Rev 0 Record of Document Revisions Rev Purpose of Document Prepared Reviewed Approved Date A Draft for MRA & Client Review A Clapin C Doak C Doak 27/02/2018 0 Issued for Client Use 20/03/2018 A Clapin C Doak C Doak Form 035 18/06/2013 Limitations of this Document This document has been prepared for use by the Client in accordance with the agreement between the Client and M P Rogers & Associates Pty Ltd. This agreement includes constraints on the scope, budget and time available for the services. The consulting services and this document have been completed with the degree of skill, care and diligence normally exercised by members of the engineering profession performing services of a similar nature. No other warranty, expressed or implied, is made as to the accuracy of the data and professional advice included. This document has not been prepared for use by parties other than the Client and its consulting advisers. It may not contain sufficient information for the purposes of other parties or for other uses. M P Rogers & Associates takes no responsibility for the completeness or form of any subsequent copies of this document. Copying this document without the permission of the Client or M P Rogers & Associates Pty Ltd is not permitted. m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page i Table of Contents 1. Introduction 1 1.1 Site 1 2. Coastal Inundation Assessment 5 2.1 Sea Level Rise 5 2.2 Previous Studies 6 2.3 500 Year ARI Inundation Levels 8 2.4 Available Elevation Data 9 2.5 Inundation Hazard Assessment 10 3. Coastal Erosion Assessment 11 3.1 Available Data 13 3.2 Severe Storm Erosion Sand & Rubble Coasts - S1 Allowance 14 3.3 Historic Shoreline Movement Sand & Rubble Coasts - S2 Allowance 16 3.4 Sea Level Rise Sand & Rubble Coasts - S3 Allowance 16 3.5 Rocky Shoreline Allowance 18 3.6 Erosion Hazard Assessment 18 4. Coastal Hazard Mapping 20 5. Conclusion 21 6. References 22 7. Appendices 23 Appendix A Coastal Hazard Maps 24 m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page ii Table of Figures Figure 1.1 The Northern Agricultural Region Area 1 Figure 2.1 Storm Surge Components 5 Figure 2.2 Recommended Sea Level Rise Scenario for Coastal Planning in Western Australia (DoT 2010) 6 Figure 2.3 Model Output Showing a Tropical Cyclone Wind Field While Tracking to the Southwest of Geraldton 7 Figure 2.4 LiDAR Survey Showing Jurien Bay Islands 10 Figure 3.1 Abrolhos Island Types 12 Figure 3.2 Photograph of Typical Rubble Shoreline within the Abrolhos Islands (Image from Long Island) 13 Figure 3.3 CoastAdapt Shoreline Classification Showing Jurien Bay Islands 14 Figure 3.4 Storm Wave Attack 15 Table of Tables Table 1.1 NAR Islands Location 3 Table 2.1 Sea Level Rise Allowances 6 Table 2.2 Total Water Level During 500 Year ARI Event at the Abrolhos Islands 8 Table 2.3 500 Year ARI Storm Surge Inundation Levels for the NAR Islands 9 Table 3.1 S1 Erosion of Various NAR Island Profiles 16 Table 3.2 S3 Erosion of Various NAR Island Sandy Coasts 17 Table 3.3 S3 Erosion of Various NAR Island Rubble Coasts 18 Table 3.4 Erosion Allowances for Sandy Coasts, North, South and West Aspects 18 Table 3.5 Erosion Allowances for Sandy Coasts, East Aspect 19 Table 3.6 Erosion Allowances for Rubble Coasts, North, South and West Aspects 19 Table 3.7 Erosion Allowances for Rocky Coasts 19 m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page iii 1. Introduction 1.1 Site The Northern Agricultural Region (NAR) covers an approximately 7.5 million hectare area of Western Australia, spanning the coastline between Gingin to the south and Kalbarri to the north. The coastline and waters that form part of the region, as identified in Figure 1.1, feature over 150 islands. The majority of these islands are part of either the Houtman-Abrolhos Group (Abrolhos) or the Turquoise Coast Island Nature Reserves (Turquoise Coast NR) and are significant sites of natural resource management investment - including revegetation/invasive flora and fauna control and feral-free sanctuaries for threatened species such as Dibblers and Australian Sea Lions. Figure 1.1 The Northern Agricultural Region Area m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page 1 Given the close proximity and susceptibility to coastal processes, the risks posed to natural resources on the NAR islands from coastal hazards both now and into the future need to be considered. It is especially important to understand how changes to the climate system and projected sea level rise may impact the islands over the relevant planning timeframe. Within Western Australia, State Planning Policy 2.6 State Coastal Planning Policy (SPP2.6, WAPC 2013) provides guidance on the assessment of coastal hazard risks for infrastructure as well as natural assets located in close proximity to the coast. This guidance is in the form of a methodology to assess the potential extent of coastal hazard impacts. To provide guidance regarding the risks posed by coastal hazards, the Northern Agricultural Catchments Council (NACC) engaged specialist coastal and port engineers, M P Rogers & Associates (MRA), to prepare a coastal hazard assessment for the islands within the NAR. NACC is one of Australia’s 56 regional Natural Resource Management (NRM) organisations working to accomplish nation-wide management, restoration and protection of Australia’s natural environment by addressing national environmental priorities at the regional level. The outcomes of this assessment, in conjunction with the ecological requirements of target conservation species, will aid natural resource managers in determining the timeframes for which specific islands may become unsuitable for maintaining these species. This will in turn, guide future NRM investment decisions within the NAR. A total of 30 islands in the NAR (22 in the Abrolhos and 8 in the Turquoise Coast NR) were identified by manager stakeholders as having significant terrestrial NRM values at risk from coastal hazards. The coastal inundation and erosion assessments in Sections 2 and 3 as well as the coastal hazard mapping in Section 4 focusses on the 30 islands, as listed (south to north) in Table 1.1. m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page 2 Table 1.1 NAR Islands Location Island Location Lancelin Island Lancelin, Turquoise Coast NR Wedge Island Wedge Island, Turquoise Coast NR South Green Island Grey, Turquoise Coast NR North Green Island Escape Island Whitlock Island Jurien Bay, Turquoise Coast NR Boullanger Island Favorite Island Pelsaert Island Middle Island Gun Island Stick Island Leo Island Alexander Island Serventy Island Campbell Island Suomi Island Keru Island Wooded Island Abrolhos Islands Morley Island Rat Island Little Rat Island Long Island Beacon Island West Wallabi Island East Wallabi Island Pigeon Island Seagull Island Tattler Island North Island m p rogers & associates pl NACC, Coastal Hazard Assessment of Islands in the NAR K1516, Report R1009 Rev 0, Page 3 It is important to recognise the differences in assessing natural flora and fauna resources on offshore islands, compared to developed sections of mainland coastlines. The Turquoise Coast NR islands listed are completely uninhabited and do not contain any developed infrastructure. Human influence on these islands is limited to temporary visitors on suitable boating days. A number of the Abrolhos islands listed, including Pigeon, Little Rat, Rat and East Wallabi islands, have minimal infrastructure - generally limited to fisherman shacks, private mooring jetties and a single airport runway. Fisherman might stay for periods of time seasonally, however there is no public accommodation on the islands for visitors. Visitors are allowed to moor overnight at several locations or day trip to the islands by boat or plane, either privately or via several local charters who operate out of Geraldton. The difficulty in accessing the islands, approximately 60 km offshore, means that they are generally only accessed by experienced boaters, fisherman and charter operators. This helps to reduce the risks of public safety issues on the islands. The consequences, and therefore risks, are much lower for the natural resources assessed in following Sections of this report. The fact that significant and widespread vegetation can be identified throughout the islands today, shows that flora and fauna has historically and can potentially, over the 100 year planning timeframe, survive severe storm events. It is vital that this is considered in analysing the coastal hazard assessment and subsequent maps presented in this report. This is particularly significant as the SPP2.6 methodology should not be viewed as a prediction of future shoreline location, but rather should be viewed to provide a conservative assessment of land areas that could potentially be impacted by coastal processes over the relevant planning horizons. This coastal hazard assessment will provide a first pass assessment of the potential areas that could be impacted by inundation and erosion over a range of timeframes up to and including the “long term” 100 year planning timeframe to the year 2118 as required by SPP2.6.