Coastal Living and Flooding

Friday 9th December, 2016

Flooding is one of the most devastating phenonmenons in the world, and is the most frequent hazard compared to other natural hazards such as droughts, fires, and earthquakes. With most Australians living on the coast, and about 40% of NSW’s coastline vulnerable to recession under sea level rise [1] – we look at how flooding (exacerbated by climate change) affects the Illawarra and housing.

Coastal living provides advantages with its natural surroundings, but how are we affected during natural disasters?

The Major Climate Impacts of South East NSW is summarised in the table below (information from OEH NSW Climate Impact Profile, and [2])

Major Climate Impacts for South East NSW

– Hotter
– Rainfall shift: likely increase in summer and decrease in winter
– Snowfall: likely decrease
– Run-off and stream flow: likely decrease in spring & winter, particularly in the west, and increase during summer
– Sea level: virtually certain to continue to rise
– Erosion: likely increase on some soils
– Coastal agricultural soils: increase in inundation and acidification
– SLR with increased flooding → risk to property and infrastructure on the coast
– Changes to natural ecosystems (alpine, low-lying coastal and fire sensitive)
– Potential Changes in flora and fauna – invasive species?

There are 4 areas of the Illawarra I’ll be dividing this post into to represent the type of housing developments and how they are affected by climate change and inundation.

1 . Northern Suburbs –

They often have no issue with the flooding and tsunamis (due to the high elevation) but coastal erosion do pose an issue [3] [4]. The rocky shores do appear much more resistant against coastal erosion – but there are concerns about rock falls. Coalcliff is particularly prone to landslides due to the claystones and shales that are inter-bedded with the sandstones, and the undercutting that occurs with erosion. This type of damage on the old Lawrence Hargrave Drive results in the $52 million construction of the Sea Cliff Bridge.

2. Wollongong – 

With a population of 292,000 [5], Wollongong is a beautiful city to live in. However combination of the steep escarpment, flat coastal plains, and numerous small watercourses makes it particularly susceptible to flash flooding. Flash flooding occurs when large amounts of rain falls over a short period of time, causing watercourses to rise quickly resulting in little warning before the water enters homes, business, and roads.

If you live close to a creek, major stormwater drain or outlet, or live in a low-lying area, you may be at risk from flooding even if you haven’t experienced a flood before. Wollongong City Council is able to provide information on known flood levels recorded from historical events and from completed flood studies. For more information please refer to Council’s website.

3. Lake Illawarra –

This is a low lying area that is often affected by flooding. In events where there is high levels of rain and storm surges, water doesn’t have anywhere to move to due to the location of the lake on one side, and the ocean on the other – during high levels of rain and storm surges, this can be catastrophic for those living in this area.

The picture blow shows that the elevation between Primbee and Warilla is between 0 to 2m above sea level.

elevation
Elevation of land from Thirroul to Minnamurra (click to enlarge)

4. Kiama –

Kiama has a limited floodplain, combined with its naturally hilly topography of the area means that during heavy rain the water flows into the ocean. However, the cumulative impact of urban development increased impervious areas resulting in higher volume and velocity of surface runoff, and exposing areas to the risk of erosion and flash flooding. Recent events have also suggested that Kiama is more susceptible to damages and high winds from storm surges due to the high location and wide open plains, and spaces [6].


Below, is the Tsunami Evacuation Area map below represents the areas that should be evacuated in the event of a tsunami. It should be noted that they do not depict inundation, but is a conservative estimation of where areas should be evacuated due to water coming in from the ocean. Anything that is 1km from the coast is listed as an evacuation point, however areas near the Lake Illawarra are more prone to inundation due their low-lying elevation. This map also gives a general representation of how climate change, and sea-level rising will affect residential areas.

With a sea-level rise of 0.5 m, coastal flooding events are likely to occur hundreds of times more frequently [1]
Tsunami Evacuation Areas - taken from SES Tsunami Safe Website
Tsunami Evacuation Areas – taken from SES Tsunami Safe Website

For more detailed maps look to your council website, as they each do their own flood maps, to see how you can be affected. For Wollongong City Council, flood plain risk management studies can be found at http://www.wollongong.nsw.gov.au/services/sustainability/floodplainmanagement/Pages/catchmentstrategies.aspx.

Written by Vivian Pham (Linkedin, Twitter)
Edited by Michael Whitehouse (Facebook, Twitter, Linkedin)

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