Coasts and Estuaries
Coasts and Estuaries Summary
Coasts are the interface between marine and terrestrial environments. They include beaches, cliffs, intertidal zones, coastal wetlands, marshes, mangroves, lagoons, coastal floodplain forests and the estuarine portions of waterways.
Estuaries within the Glenelg Hopkins region are experiencing sea surface temperatures increasing at a rate of approximately four times the global average, which has potentially significant consequences for marine and estuarine species[i]. Temperate locations such as the Glenelg Hopkins region and cool water species are the most likely to be negatively impacted by increasing water temperature. Increased temperatures may exceed the optimal temperature range of certain species, particularly those species with limited thermal ranges.
The coastline of the Glenelg Hopkins region is subject to coastal erosion, sea level rise and flooding. With a changing climate, these impacts will be exacerbated with increases in wind speed, storm intensity and frequency, as well as changes in rainfall intensity and frequency[ii].
A 2005 CSIRO study[iii] indicated that mean sea level rise will provide the largest contribution to future flood risk. Under the worst-case, wind speed scenario, storm tide height would increase by up to 5 cm in 2030 and 20 cm in 2070. The 2030 and 2070 high-wind scenarios produce increases in storm tide height that are about 19% of the respective mean sea level rises.
The Victorian Government’s coastal policy recommends to ‘plan for sea level rise of not less than 0.8 metres by 2100, and allow for the combined effects of tides, storm surges, coastal processes and local conditions, such as topography and geology when assessing risks and impacts associated with climate change’[iv]. It is noted that as more scientific data becomes available, planning for a sea level rise of not less than 0.9 metres by 2100 is a more conservative option and maybe desirable[v].
Current Intergovernmental Panel on Climate Change (IPCC) predictions indicate that if emissions continue to track at the top of IPCC scenarios, global average sea level could rise by nearly 1 m by 2100 (0.52−0.98 m from a 1986–2005 baseline)[vi]. If emissions track along the lowest scenario, then global mean sea level, (GMSL) could rise by 0.28-0.60 m by 2100 (from a 1986–2005 baseline). The IPCC also states that ‘with regional variations and local factors, the local sea level rise can be higher than that projected for the GMSL’[vii].
Climate change will see increases in wind speed, storm intensity and frequency and changes in rainfall frequency in the Glenelg Hopkins region[viii]. These climate variables will not produce new coastal hazards, but are likely to increase the extent or frequency of existing hazards[ix]. The Glenelg Hopkins coastline is subject to coastal inundation, coastal erosion/recession, sea level rise and flooding which will be exacerbated because of a number of factors, including changes in:
mean sea level
storm climates (storm surges, storm tides and atmospheric changes)
The region’s low-lying coastal wetlands and shallow wetlands rely on direct rainfall and are affected by saltwater intrusion from the sea. Climate change will impact on these ecosystems as a result of increased drought frequency and intensity, decreases in freshwater inputs, rising sea levels and increases in coastal storm surges. These conditions may also change the character of coastal wetlands through a reduction in size, conversion to dryland or a shift from one wetland type to another (e.g. brackish to saline)[x]. The retention of coastal wetlands will require planning approaches which allow for the landward movement of wetland communities in order to avert significant loss and degradation to coastal wetlands and associated biodiversity within the Glenelg Hopkins region.
The Victorian Government has provided a package of tools to support decision making, including inundation maps, planning notes and guidelines[xi]. Some of the modelling and information on inundation and coastal erosion contained has been based on the Bruun rule[xii]. The Bruun rule may lack the complexity required to predict shoreline behaviour under a rising sea level[xiii]. The linkages between sea level rise and shoreline response are extremely complex and require a tool that will adequately address this complexity. An adaptive and flexible approach is required for planning in order to address the multiple uncertainties relating to the exact nature of coastal erosion in response to sea level rise and storm surge events.
The Glenelg Hopkins coastal wetlands are not only at risk from hydrological and climatic changes but are also subject to sea level rise and storm surge events. Coastal wetlands in the region’s urban and agricultural areas are also subject to coastal squeeze as their ability to migrate inland is restricted by surrounding land uses.
Coasts and coastal wetlands are at the interface between marine and terrestrial environments. During periods of sea level rise, coastal wetlands can persist only when they accrete soil vertically at a rate at least equal to water level rise[xiv]. Because freshwater runoff carries sediments that increase accretion, there is concern that reduced freshwater runoff decreases the supply of sediments. Saltwater intrusion as a result of rising sea levels, increases in coastal storm surges, decreases in freshwater inputs, and increased drought frequency and intensity, are very likely to expand the areas of salinisation of coastal freshwater aquifers and coastal wetlands[xv]. The region’s coastal wetlands may disappear as a result of predicted increases in shoreline erosion, made worse by dieback of shoreline plants caused by increased salinity[xvi].
[i] NJ Holbrook and J Johnson, Australia’s marine biodiversity and resources in a changing climate; a review of impacts and adaptation 2009–2012, National Climate Change Adaptation Research Facility, Gold Coast, 2012.
[ii] Department of Climate Change, Climate risks to Australia’s coasts: a first pass national assessment, Australian Government, Canberra, 2009.
[iii] KL McInnes, I Macadam, GD Hubbert, DJ Abbs, J Balthos, Climate change in eastern Victoria Stage 2 report: The effects of climate change on storm surges, CSIRO Marine and Atmospheric Research Global Environmental Modelling Systems, Aspendale, 2005.
[iv] Victorian Coastal Council, Victorian coastal strategy, Victorian Coastal Council, Melbourne, 2014.
[v] Victorian Coastal Council, Victorian coastal strategy, Victorian Coastal Council, Melbourne, 2014.
[vi] IPCC, Final Draft, IPCC WGII AR5 Chapter 5, Coastal systems and low-lying areas, 2013.
[vii] IPCC, Final Draft, IPCC WGII AR5 Chapter 5, Coastal systems and low-lying areas, 2013.
[viii] Department of Climate Change, Climate change risks to Australia’s coast: A first pass national assessment, Canberra: Australian Government, 2009
[ix] Department of Climate Change, Climate change risks to Australia’s coast: A first pass national assessment, Canberra: Australian Government, 2009
[x] C Jin, B Cant, C Todd, Climate change impacts on wetlands in Victoria and implications for research and policy, Arthur Rylah Institute for Environmental Research Technical Report Series no. 199. Department of Sustainability and Environment. Heidelberg, 2009.
[xi] Department of Sustainability and Environment, The Victorian coastal hazard guide, Department of Sustainability and Environment, Melbourne, 2012.
[xii] P Bruun, Coast erosion and the development of beach profiles. Technical Memorandum, vol 44, Beach Erosion Board, Corps of engineers, 1954.
[xiii] J Cooper and O Pilkey, Sea-level rise and shoreline retreat: time to abandon the Bruun Rule, Global and Planetary Change 43, 2004.
[xiv] DR Cahoon, DJ Reed, JW Day Jr, Estimating shallow subsidence in microtidal salt marshes of the southeastern Unite State, Marine Geology, 1995.
[xv] Victorian Coastal Council, Victorian coastal strategy, Victorian Government, Australia, 2008.
[xvi] A Lukasiewicz, CM Finlayson, J Pittock, Identifying low risk climate change adaptation in catchment management while avoiding unintended consequences, National Climate Change Adaptation Research Facility, Gold Coast, 2013.