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Fact sheet 16 MANAGING SEA LEVEL RISE What is Sea Level Rise? Scientists predict global sea levels will almost certainly rise by 0.59 metres by the end of this century as a result of climate change. This is assuming we do not significantly change our lifestyle, and continue to produce high levels of greenhouse gases. Further research by the CSIRO shows that by 2100, levels on the east coast of Australia will be about 0.12 metres higher than the global average. This is due to the additional effect of the warm East Australian Current. Most of this rise in sea level is due to expansion of the ocean water as it becomes warmer. However, sea levels may rise another 0.20 metres as glaciers and land-based ice sheets melt. This makes a total predicted sea level rise of 0.91 metres by 2100. The NSW Government has adopted a predicted rise of 0.90 metres by 2100 as a state-wide benchmark for all coastal Councils for future planning and risk management. Global measurements of sea level rise, show that they are actually rising faster than these predictions. Levels will be revised when the Inter-governmental Panel on Climate Change (IPCC) presents its next global report in 2014. Impacts on the Lake Lake water levels As ocean levels rise, Lake Macquarie will rise by roughly the same amount, so by 2100 the lake could be nearly one metre higher than it is now. This means by the end of this century foreshore areas below 1.0 metre Australian Height Datum (AHD) may be at increased risk of permanent inundation. Public land such as foreshore reserves and wetlands, as well as some privately owned waterfrontage, may be affected. Stormwater drains, roads, and sewers could be inundated and services may be disrupted. Residents in areas such as Redhead, Swansea, Belmont, and Blacksmiths that have access to fresh bore water may find the water becomes salty. What is AHD? AHD is an abbreviation for Australian Height Datum. Zero metres AHD is approximately equal to the average sea level around the coast of Australia, so AHD is similar to ‘above sea level’. Flooding The level of Lake Macquarie rises when heavy rain and run off increase the volume of water in the lake. The highest recorded flood was in 1949, when the lake was raised to 1.2 metres. A review of flooding in Lake Macquarie included the effects of sea level rise and other climate change factors. It estimates that by 2100 many foreshore areas below 3.0 metres AHD may be at increased risk of flooding. Tides Sea level rise will allow more water to enter the lake through Swansea Channel, so the range of tides will increase, and their effect will extend further into the lake. However, a recent Council study shows the effect of tides will be small compared to the effect of average sea level rise, adding an additional seven centimetres to high tide levels in the lake by 2100. Foreshore erosion As sea levels rise, the lake foreshore will shift landward due to inundation of low-lying land. At the same time, foreshore erosion will increase as beaches and the lakebed adjust to the new water levels. The rate and extent of erosion will depend on local factors, but the underlying factors (water levels, waves, soil erodibility) mean that lake foreshores may erode by several metres landward for each metre of sea level rise. eShorance Council has developed a simple method to estimate how sea level rise may affect the foreshore of estuarine lakes such as Lake Macquarie. You can access this online tool at http://www.lakemac.com.au/eshoreance/ Impacts on the Coast Coastal erosion The NSW Government’s Coastal Management Guideline predicts that, as sea levels rise, sandy beaches and dunes will tend to erode and the coastline will recede (move inland). Erosion may be accelerated by increased storm surge and bigger waves. As a general rule, sandy ocean coastlines recede by 50–100 metres for every 1 metre increase in sea level. However, this may vary depending on local conditions. Fortunately, there are very few houses in Lake Macquarie built on beach dunes, and Council has established a ‘coastal hazard zone’ to control new development in vulnerable areas. Beaches, dunes, and coastal recreational facilities such as surf clubs are most at risk from coastal sea level rise and coastline recession. The best coastal protection is provided by natural features, such as beaches and dunes, that absorb wave energy and can adjust naturally after storms. Low-lying coastal areas, such as Blacksmiths and Belmont South, rely on sand dunes for protection from ocean waves and storm surge. It is important to keep the dunes well vegetated and free from damaging activities and development. If necessary, coastal sea walls can be built to protect property, but they are expensive to build and maintain. Once built, the beaches in front of them are lost to erosion and wave energy can be transferred to other locations. At least for the next few decades, coastal sea walls will not be required to protect properties in Lake Macquarie. What is Council doing? Council is tackling sea level rise and climate change from two perspectives: adapting and preventing. Lake Macquarie was one of the first Councils in Australia to adopt a Sea Level Rise Policy, in August 2008. Other Council actions include: • Citywide planning for changes to lake foreshores with a predicted sea level rise of 0.9 metres by 2100 • Implementing guidelines setting higher floor levels for new foreshore developments in lowlying areas, and requiring them to consider sea level rise and increased flooding in the positioning and design of buildings and services • Working with communities such as Swansea and Dora Creek to plan for the impacts of climate change and sea level rise and act on their plans • Monitoring coastal recession on our beaches • Investigating the effect of sea level rise on foreshore and coastal ecosystems such as saltmarsh and mangroves • Reviewing flood management plans, coastal hazard zones, and natural disaster plans to ensure they consider the additional effects of climate change • Reducing Council’s carbon footprint by 3% each year and working with the community to reduce the City’s footprint. What can I do? Some of the actions you can take to adapt to and reduce climate change and sea level rise are: • Planning future building, renovation, or landscaping so it is suitable for changed sea levels and climate conditions (especially if you live in a low-lying area) • Planting and restoring creek banks and foreshore areas to create natural barriers to foreshore recession and erosion • Being well-prepared and well-informed to deal with emergencies, such as flood, storm, or bushfire • Participating in community activities to help raise awareness of and plan for sea level rise and other effects of climate change • Reducing your consumption of energy and goods – use energy efficient appliances, install a solar hot water heater, install solar electricity or buy Green Power, and shop modestly and wisely • Participating in community activities to help reduce our carbon footprint and to raise awareness and understanding of climate change issues. For more information www.lakemac.com.au Search for ‘sea level’ or go to the Environment/Climate Change/Sea Level Rise page for links to Council’s policy and the eShorance tool. There are links to other sites that provide information on the latest sea level rise science, State Government policy, and community activities. This project has been assisted by the New South Wales Government through its Environmental Trust.