Climate Change Risks for Victoria s Surf Coast

Transcription

1 Climate Change Risks for Victoria s Surf Coast Craig A, Clifton 1, Dan Ware 1, Simon Coverdale 2 and Chloe Hanson-Boyd 1 1 Sinclair Knight Merz, Melbourne, AUSTRALIA. cclifton@globalskm.com 2 Great Ocean Road Coast Committee, Torquay, AUSTRALIA. Abstract Victoria s Surf Coast includes some 55 km of coastline and supports important ecosystems, towns, tourism infrastructure and iconic beaches and surfing breaks. This region s economy is strongly dependent on its coastal amenity and its projected rapid population growth is underpinned by sea change migration. Risks to the region s coastal amenity and infrastructure from sea level rise and associated coastal recession were assessed using a GIS-based exposure analysis and a risk assessment. One key finding of the analysis was that risks posed by coastal recession and inundation on beach amenity were significant with relatively small changes in sea level. While many risks to Surf Coast infrastructure assets are posed under high range, end of century sea level rises scenarios, critical risks to many beaches will be posed by as little as 0.2m of sea level rise. This is particularly true for sandy beaches backed by sea walls or rocky cliffs. Keywords: coastal risk management, climate change adaptation. 1. Introduction The Intergovernmental Panel on Climate Change (IPCC [7]) concluded that there was unequivocal evidence of warming of the global climate system. They projected that under plausible scenarios for global change and emissions of greenhouse gases, temperatures would increase by between about 2 C and 4 C (relative to ) by the end of the century. They found that this could lead to global mean sea levels rising by up to about 0.79 m by 2100 [7]. These estimates remain uncertain and end of century sea level rises of more than 1.0 m and even as high as 1.4 m are considered to be plausible [5]. In areas with sandy or other erodible shorelines, rising sea levels may lead to coasts retreating landwards [5]. While the rate of recession is highly uncertain, a rule of thumb (the Bruun rule [3]), suggests that some coasts may retreat by m for each metre of sea level rise. As a manger of coastal land, environments and infrastructure, the Great Ocean Road Coast Committee (GORCC) is obliged to follow the Victorian Coastal Strategy [13], which states that end of century sea level rise of at least 0.8 m must be planned for. In response, GORCC initiated the Surf Coast Climate Change Vulnerability and Adaptation Project to enable it and other land, natural resource and infrastructure managers in the Surf Coast region (Figure 1) to commence such planning. This paper reports on the first stage of the project. This stage included an analysis of the current exposure of natural and built assets to coastal hazards and how this might change in response to projected climate change. An adaptation planning framework to guide future responses to the main risks associated with current and projected future coastal hazard conditions was also developed. Figure 1 Victoria s Surf Coast region. The region was divided into six sections for the risk assessment (Section 5): 1. Point Impossible-Bells Beach; 2. Bells Beach-Point Addis; 3. Point Addis-Urquharts Bluff; 4. Urquharts Bluff- Spout Creek; 5. Spout Creek-North Lorne; 6. North Lorne-Cumberland River. 2. The Surf Coast region 2.1 Overview Victoria s Surf Coast region corresponds with the Surf Coast Shire and extends from Point Impossible, near Torquay to Cumberland River, near Lorne (Figure 1). This 55 km stretch of coastline includes nature conservation reserves and important coastal ecosystems, as well as coastal towns and villages, beaches, caravan parks and recreation reserves. 2.2 Community and economy Surf Coast Shire had a population of almost 26,500 [2] in The Shire and region are among the fastest growing in Victoria and are

2 recipients of sea change migration from Melbourne and inland centres. Population is projected to grow by over 35% by 2026 [6]. Most of this growth is planned to be concentrated around Torquay. The economy of the Surf Coast region is strongly dependent on its coastal amenity. The Great Ocean Road, which runs south-west from Torquay, attracts over 2.5 million visitors annually. Over 20% of the local population work in tourism exposed employment sectors (i.e. retail trade, accommodation and food services, arts and recreation services). Sea change migration helps to drive the construction industry, which is the main industry of employment [2]. Tourism adds over $258 million annually to the local economy [1]. 2.3 Coastal landforms Between Torquay and Anglesea, the coast is dominated by dissected sedimentary plains, which either form erodible cliffs or back sandy beaches. The coast from Anglesea to Aireys Inlet is dominated by coastal barriers of windblown sand that form dunes or erodible cliffs that also back sandy beaches. From about Moggs Creek (west of Aireys Inlet) south-west, the coastline is dominated by the hard rocks of the Otway Ranges. These run to the coast as headlands or lie behind relatively narrow, sandy beaches. 2.4 Wave climate and extreme sea level conditions The region s coastline is predominantly open and is highly exposed to the wind and wave environment generated in the Southern Ocean and western reaches of Bass Strait. Extreme sea levels in the region most commonly result from the combination of high astronomical tides and storm surges. The latter are typically associated with eastward moving cold frontal systems that bring westerly to south-westerly winds to Australia s south coast [9]. High wave events are generally associated with westerly to south-westerly winds, although shoreward wave energy transport and wave set up is smallest in westerly events and greatest in southerly events [4]. This suggests that storm surges produced under westerly wind events are unlikely to be enhanced by wave set up, whereas those generated in southerly events may be [9]. 3. Climate change and coastal hazards Climate change is projected to significantly affect coastal and marine environments, including through: elevated sea levels, changes in sea temperature, increased ocean water acidity, changes in rainfall regime and riverine sediment supply and changes in the pattern of storm systems and hence coastal wave climate. The two key coastal hazards of concern to this project, inundation and recession, may both be affected significantly by climate change, particularly sea level rise. The extent of sea level rise over the course of this century is quite uncertain. Under most scenarios, sea level rise is projected to be about 0.2 m by The scenarios significantly diverge in projections for the latter half of the century. By 2100, they range between 0.82 m and as much as 1.4 m [8]. Sea level rise will result in new areas of low lying coastal land being exposed to inundation during storm surges and storm tide events and will increase the frequency of inundation of areas that are already exposed. By 2030, the 10 year average recurrence interval (ARI) storm tide for Lorne (~1.5 m above mean sea level, MSL) is projected to be equivalent to about the current 20 year event [8]. By 2100, the current 100 year ARI storm tide height would be exceeded multiple times per year [8]. The 100 year ARI storm tide for Lorne would increase to between 2.5 and 3.2 m above current MSL. Sea level rise will also increase the depth of water over shore platforms and offshore reefs. This may affect intertidal habitat availability or quality and the operation of key reef-based surf breaks (e.g. Bells Beach). Sea level rise may contribute to the recession of erodible coasts. The extent of this will vary with coastal geomorphology, wave climate, bathymetry and sediment supply. Based on Bruun s rule [3] (which is the subject of much debate), sandy and other unconsolidated coasts could retreat by up to 20 m as a result of 2030 sea level rise and by m in response to projected 2100 sea level rise. The actual rate of retreat may be much less. Hardened, rocky coasts in the south of the region will remain resistant to erosion. Beaches in these and other areas that are backed by cliffs or rock may be eroded regardless of the extent of coastal recession. Climate change is projected to increase the frequency of waves generated by easterly winds during summer and autumn, resulting in more short period waves and reduced return periods of storm wave events [9]. Such waves drive storm erosion events and long-term coastal recession. Projected change from a westerly to an easterly dominated wave regime may also alter long-shore sediment transport patterns. In winter, the projected greater frequency of winds from the south-west and west imply greater impact from larger westerly swells (which are favoured by surfers in this region). Increasing wavelength will lead to increased wave run up, further changes in

3 long and cross-shore sediment budgets and rates of coastal recession [9]. 4. Exposure of coastal assets to sea level rise and coastal recession 4.1 Approach A GIS-based analysis was undertaken of the exposure of natural and built assets located in proximity to the coast to inundation and/or coastal recession. This differs from a risk assessment in that it only considers whether the land or assets might experience inundation or coastal erosion and not what the consequence of that exposure might be. The assessment considered a variety of buildings and other coastal infrastructure on GORCCmanaged land, as well as roads, coastal native vegetation and Indigenous cultural heritage assets. Exposure to coastal inundation was based on the assets elevation and did not take account of structural or other controls on water movement. It did not account for wave set up or run up. Exposure to coastal recession was based on the upper limit of the Bruun rule, namely that unconsolidated, erodible coasts retreat by 100 m in response to each 1 m of sea level rise. Outputs of the analysis has been summarised by exposure categories as defined in Nineteen of these built assets are highly or very highly exposed to permanent inundation. Together, they represent Table Built infrastructure GORCC manages several Crown land reserves along the Surf Coast. These reserves contain much of the region s coastal recreational and tourism infrastructure, including boat ramps, car parks, caravan parks, piers and fishing platforms, playgrounds, public amenities and shopping centres. The close proximity of these assets to the coast means that many are exposed to coastal hazards and sea level rise. While some infrastructure (e.g. boat ramps, piers, fishing platforms) may be highly exposed to coastal hazards, they will not necessarily be vulnerable to them, particularly with small changes in sea level. There are nearly 276 built assets that are located on GORCC managed land for which asset values have been attributed. Their total value exceeds $150 million. Nineteen of these built assets are highly or very highly exposed to permanent inundation. Together, they represent $9.8 million in asset value and include four of the six caravan parks managed by GORCC. Almost 60 assets are highly or very highly exposed to temporary inundation, $9.8 million in asset value and include four of the six caravan parks managed by GORCC. Almost 60 assets are highly or very highly exposed to temporary inundation, representing $18.4 million in total value. These assets include the Point Grey complex and GORCC managed caravan parks at Lorne and Anglesea. Over 175 of the assessed assets, with a combined value of $130 million, are highly or very highly exposed to coastal recession. These include the Lorne, Fairhaven, Anglesea, Jan Juc and Torquay Surf Life Saving Clubs and 31 of the 51 beach access car parks located on GORCC managed land. 4.2 Indigenous cultural heritage Fifteen of over 30 known cultural heritage sites located on GORCC managed land are highly or very highly exposed to coastal recession. Four of these assets are already exposed to temporary inundation. 4.3 Native vegetation Almost 243 ha of native vegetation is highly or very highly exposed to coastal recession, much of which comprises vulnerable or depleted ecological vegetation classes (EVCs). Over 150 ha of native vegetation, mainly depleted and endangered EVCs, are highly or very highly exposed to temporary inundation. representing $18.4 million in total value. These assets include the Point Grey complex and GORCC managed caravan parks at Lorne and Anglesea. Over 175 of the assessed assets, with a combined value of $130 million, are highly or very highly exposed to coastal recession. These include the Lorne, Fairhaven, Anglesea, Jan Juc and Torquay Surf Life Saving Clubs and 31 of the 51 beach access car parks located on GORCC managed land. 4.5 Indigenous cultural heritage Fifteen of over 30 known cultural heritage sites located on GORCC managed land are highly or very highly exposed to coastal recession. Four of these assets are already exposed to temporary inundation. 4.6 Native vegetation Almost 243 ha of native vegetation is highly or very highly exposed to coastal recession, much of which comprises vulnerable or depleted ecological vegetation classes (EVCs). Over 150 ha of native vegetation, mainly depleted and endangered EVCs, are highly or very highly exposed to temporary inundation.

4 Table 1 Definition of categories of exposure of GORCC assets to permanent and temporary inundation and coastal recession and erosion. Elevations above MSL and distances from coast refer to the location of assets included in the exposure analysis. Exposure category Permanent inundation 1 Temporary inundation 2 Coastal erosion and recession 3 Very high: exposed under m elevation < m elevation <20 m from coast historical conditions High: exposed with 0.2 m m elevation m elevation m from coast sea level rise Moderate: exposed with 0.8 < m elevation < m elevation < m from coast m sea level rise Low: exposed with 1.4 m < m elevation < m elevation < m from coast sea level rise Very low: not exposed with 1.4 m sea level rise 1.6 m elevation 3.2 m elevation 160 m from coast or located on hard rock Notes: 1. Permanent inundation: exposure to inundation during typical diurnal tide cycle. 2. Temporary inundation: exposure to inundation during 100 year ARI storm tide (currently 1.69 m at Lorne). 3. Coastal erosion and recession: based on distance from MSL line. <20 m category includes assets forward of MSL line. 5.2 Risk assessment results 4.7 Roads The six sections of the Surf Coast region (Figure 1) The Surf Coast region s road network includes the iconic Great Ocean Road. In addition to its value for tourism, this road is also main road connecting coastal settlements in the region. Approximately 1.7 km of road is already exposed to temporary inundation. A further 1.9 km would be exposed to temporary inundation with just 0.2 m of sea level rise (high exposure). Over 8 km of the Great Ocean Road is highly or very highly exposed to coastal recession. differed markedly in their exposure to risk from coastal inundation and recession. This reflects the relative concentration of built assets close to the coast, coastal topography (hence exposure to inundation) and geology (hence exposure to coastal erosion and recession). The sparsely developed Bells Beach-Point Addis and Spout Creek-North Lorne sections of the coast had significantly fewer assets exposed to the main coastal hazards than the other four sections of coastline and consequently recorded fewer risks. 5. Risks to the Surf Coast resulting from coastal climate change hazards 5.1 Approach A key component of this stage of the Surf Coast Climate Change Vulnerability and Adaptation Project was to undertake an assessment of the risks coastal climate change hazards. The assessment applied standard risk assessment protocols (AS/NZS ISO 31000:2009 [12]) and drew on exposure analysis (section 4) and a stakeholder risk workshop. Unlike the exposure analysis, the risk assessment considered the implications or consequences of exposure to coastal climate change hazards. Risk was considered from the perspectives of local residents, beach users, GORCC, the Surf Coast shire and regional tourism and related business operators. The Surf Coast region was divided into six sections for the risk assessment (Figure 1), with the division reflecting settlement patterns, coastal geomorphology and the distribution of assets. The assessment considered four climate change and coastal hazard scenarios. These reflected the low to very high exposure categories described in Table 1. Characteristics of the key risks from coastal climate change hazards that were identified through the risk assessment are described in Table 2. Those relating to built assets and infrastructure are mostly concentrated in or near the main population centres (Torquay, Anglesea, Aireys Inlet-Fairhaven and Lorne). Those relating to natural or heritage assets are more widely distributed along the coast. Table 2 Characteristics of priority risks from coastal climate change hazards to the Surf Coast region. Asset class and description Beaches and associated recreational and tourism infrastructure: including beaches and the infrastructure (access tracks, car parks, playgrounds, amenity blocks, Surf Lifesaving Clubs, boat ramps etc.) that add to the safety and amenity of beach use. Environment and heritage features: intertidal and dune habitats and estuaries and dependent species. Sites and places of indigenous cultural heritage. Residential and commercial properties: private residential and commercial properties located in Key locations Torquay, Anglesea, Aireys Inlet- Fairhaven, Lorne All six sections of coast Locations at Torquay, Anglesea, Aireys Inlet-

5 areas at risk from coastal recession. Roads: including local roads, footpaths, sections of the Great Ocean Road and road bridges. Surf breaks: including reef and beach breaks. Fairhaven, Lorne Torquay, Anglesea, Aireys Inlet- Fairhaven. Great Ocean Road from Anglesea-Spout Creek All six sections of coast The majority of material risks (those assessed to be in high and extreme categories) arising from coastal climate change hazards require approximately 0.8 m of sea level rise. Risks associated with the region s beaches were they main exceptions to this. Many of these were considered to become material with coastal recession resulting from just 0.2 m of sea level rise. The risks posed were to the beaches themselves, the habitat they provide and some heritage sites. They are projected to arise because many of the region s beaches are backed by natural or constructed features that will prevent them from migrating landwards as sea levels rise. Use of or access to beaches is fundamental to the region s tourism and sea change driven economy. If this is lost or diminished with relatively small rises in sea level, then real estate values and economic activity would be adversely affected. These risks to real estate values would occur well in advance of those arising from any direct impacts on properties of coastal recession or inundation. 6. A framework for adaptation 6.1 Climate change adaptation Adaptations are the adjustments made in natural or human systems in response to experienced or projected climate conditions or their beneficial or adverse effects or impacts [11]. They may be planned measures, such the construction of groynes to hold sand on a beach or the reconstruction and the raising of a road that is regularly cut during storm tide conditions. They may also occur autonomously or without planned intervention, such as might occur as beaches backed by sand dune systems retreat inland in response to rising sea levels. The Victorian Coastal Strategy [13] has adopted a relatively simple typology of adaptation, as follows: Protect beaches, dunes, and infrastructure, land use and development from sea level rise and coastal recession. Accommodate sea level rise and coastal recession through planning and building policies and provisions, redesign and rebuild of infrastructure at risk. Retreat through relocation of infrastructure, land use and development Adaptation strategies typically also include a fourth type of adaptation, the development of adaptive capacity. As the name suggests, these types of adaptation are concerned with developing the capacity of an organisation, community or other system to understand and moderate risks from climate change and realise any benefits [11]. Different types of adaptation option will be more or less suited to particular contexts. Where the value of an asset at risk from sea level rise or recession is high relative to the cost of risk treatment, protective options may be used. In situations where asset values at risk are relatively low or asset protection is relatively expensive or ineffective, sea level rise or coastal retreat may be accommodated (e.g. by ensuring infrastructure is not developed in at-risk locations or that it is not significantly damaged by storm tide inundation). Where protective options are or will ultimately be unable to successfully mitigate risks from coastal inundation or recession, it may be necessary to relocate existing infrastructure, land use or development (i.e. retreat) to locations that are not exposed to such risks. 6.2 Adaptation pathway framework The adaptation framework proposed by the project provides for the development of flexible pathways that are responsive to experienced changes in sea levels, coastal recession and risk perception (Figure 2). The framework envisages the sequential deployment of adaptation options or tactics that are suited to particular windows of sea level rise or coastal recession. The deployment of new adaptation options or tactics is triggered by an approaching risk threshold that is based on the sea level or another limit of effectiveness of the current options.

6 Figure 2 Illustration of the proposed adaption framework. The chart shows the planned-for envelope of potential sea level rise during (based on m rise by 2100). In this illustration, four adaptation tactics are planned for deployment. Option #1 is designed to mitigate risk to about 0.25 m of sea level rise. At about 0.2 m of sea level rise, the process for deploying Option #2 is triggered (to allow time for planning, implementation and adjustment). This option mitigates risk until sea level rise reaches about 0.75 m. Deployment of Option #3 is triggered at about 0.7 m. Above 1.3 m Option #3 is no longer effective and there are no affordable options to mitigate impacts. At this point, option #4 accepting sea level rise and managing its impact or retreating from it is adopted. Risk falls outside the typically accepted range from this point. Adapted from [10]. The process of deploying the adaptations begins before the risk threshold is reached to ensure there is sufficient time for planning, finance raising and community or stakeholder engagement. Trigger points are risk-based and draw on experienced coastal hazard conditions. They are not time based and so provide flexibility to adapt to more or less rapid sea level rise while remaining within acceptable risk levels. Early options, when risks are low, may involve no more than the development of adaptive capacity through further studies and land use planning to avoid unnecessary future risk exposure. The level, type and sequence of intervention may vary between locations and with the types of asset that are at risk. Adaptation pathways are required for each of the priority risks identified by the project. 6.3 Monitoring and review Monitoring and review are critical components of any risk management process. They are particularly important for climate change risks, where the hazards will emerge over long time scales, understandings of risk are changing rapidly and adaptive planning responses are required. A framework for monitoring and review was developed to help underpin the proposed adaptation framework. It is based on the identification and use of risk-based trigger points to flag the need to initiate or modify adaptive responses. 7. Summary The natural assets and built infrastructure of Victoria s Surf Coast region face a variety of challenges from coastal climate change hazards. Many are highly exposed to inundation and/or coastal erosion and recession resulting from sea level rise. Most material risks arising from coastal climate change hazards are anticipated to arise from sea levels that are projected to occur towards the end of this century. However, beaches and their associated values and uses face significant risks over a much shorter timeframe. 8. References [1] Ainsaar M. and Riusseene M Tourism strategic plan for the Surf Coast region. Consultancy report to Surf Coast Shire. Urban Enterprises Pty Ltd. [2] Australian Bureau of Statistics. (2013), National regional profile. Surf Coast Shire. roducts/lga26490population/people ?opendocument&tabname=summary&prodno=lga 26490&issue= Accessed 31/5/2013. [3] Bruun P Sea-level rise as a cause of shore erosion. American Society of Civil Engineering Proceedings, Journal of Waterways and Harbors Division 88:

7 [4] Coastal Engineering Solutions Pty Ltd Coastal processes study. Report to Great Ocean Road Coast Committee. Draft. [5] Department of Climate Change Climate change risks to Australia s coast. A first pass national assessment. Department of Climate Change. [6] Department of Sustainability and Environment Victoria in Future population projections. [7] Intergovernmental Panel on Climate Change [IPCC] 2007a. Climate change 2007: Synthesis report. Summary for policymakers. IPCC. [8] McInnes, K., I. Macadam, and J. O'Grady The Effect of Climate Change on Extreme Sea Levels along Victoria's Coast. A Project Undertaken for the Department of Sustainability and Environment, Victoria as part of the 'Future Coasts' Program. [9] McInnes, K, J. O'Grady and M. Hemer Waves and extreme sea levels on the Great Ocean Road Coast: implications of future climate change. A report for Sinclair Knight Merz and Great Ocean Road Coast Committee. CSIRO Marine and Atmospheric Research, [10] Ministry for the Environment Coastal Hazards and Climate Change. A Guidance Manual for Local Government in New Zealand. 2nd edition. Revised by Ramsay, D, and Bell, R. (NIWA). Prepared for Ministry for the Environment. [11] Smit, B. Pilifosova O. Burton I. Challenger B. Huq S. Klein R.J.T. Yohe G Chapter 18 Adapting to climate change in the context of sustainable development and equity. IPCC Third Assessment Report, Intergovernmental Panel on Climate Change. [12] Standards Australia AS/NZSISO 31000:2009 Risk management: principles and guidelines. Standards Australia. [13] Victorian Coastal Council Victorian Coastal Strategy Victorian Coastal Council.