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September 11, 2009
Whilst walking the dogs on the beach at Encounter Bay at Victor Harbor in the mornings and evenings this week, I've been noticing the effect of the tide on the foreshore compared to the past. The erosion of the sand dunes has been quite marked from the storm surges this winter:
Gary Sauer-Thompson, erosion, Encounter Bay, Victor Harbor, 2009
I imagine that this is how the rising sea levels caused by global heating manifests itself--as a steady erosion of the sand dunes from the higher tides and the wilder weather. This erosion will continue due to warming of the oceans and the consequent thermal expansion and melting of non-polar glaciers and icecaps and the ice sheets of Antarctica and Greenland. Seawater will forced its way through sand dunes and spilled across the low-lying land
The Victor Harbor City Council will be required to protect the coastal area rather than retreat since abandonment is not usually an option. Part of adapting to rising sea levels will, presumably, involve building protective sea walls for the resort-area beaches:
Gary Sauer-Thompson, erosion + Maleleuca, Encounter Bay, Victor Harbor, 2009
Many would argue that this erosion is not unusual in that beach and sand dunes built-up during months of relative calm will be eroded during stormy seasons, only to be built-up again after the storms have passed. As well, wave action and currents are continually moving sand along the shore, often resulting in a net drift of material in one direction.
However, the storm surges and beach erosion must be more severe than usual because the City Council has placed several lines (groynes?) of sand bags from the dunes to the sea in order to protect the dunes from tidal movement. Secondly, that ignores that sea levels along the South Australian coast are expected to rise by up to 40 cm above 1990 levels by 2050 and by 90 cm by 2100, with each one centimeter of rise resulting in one meter of erosion on low-lying beaches.
That means the coastline will move inward. What is now currently a vegetated dune will become the beach. There is not that much distance (or height) from the outer edge of the sand dunes to the foreshore holiday houses along the coastline near the city. So far the Council's response to beaches shrinking as the sand is washed away is sand deposits in order to protect the beaches.
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See the National Seachange Taskforce --a national body that represents the interests of coastal councils and communities experiencing the effects of rapid population and tourism growth. They now realize that coastal areas are exposed to particular risks associated with climate change and that climate change is a critical issue for coastal communities and councils.