Download managing sea level rise - Lake Macquarie City Council

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.