Politicians rely on academics to explain their observations — as the public do. But have academics and the media deceived politicians in their exuberance to make a point in support of ‘global warming’? Their recent tour of the Australian coastline may be a case in point.

Coastal erosion happens constantly and has many causes. Spits and points grow too and bays and inlets shallow or disappear completely. There are a series of complex interactions that are site specific that give rise to these events — so they simply cannot be ascribed collectively to the results of global sea level change.

A Parliamentary Committee on Climate Change has just finished its tour of the Australian coastline looking at the impact of extreme weather and tidal events and sea level rise.

On The 7.30 Report last night MP Jennie George commented:

“People have to realise it’s not just the issue of sea level rise, it’s the extreme weather events — the king tides, the storm-surges, the cyclones that compound the problem…

…We saw it first-hand as we travelled around the nation, the early signs of the negative consequences. We saw beaches that had been washed away. We saw other beaches only existing because of sand renourishment. We saw beaches that were sandbagged, we saw houses precariously perched on top of the primary dunes — only a matter of time before they collapse. And it really opened our eyes to the need for urgent action…”

Another common cause of coastal erosion is the construction of groins, drains and carparks on beaches that stop the seasonal movement of sand along beachers. This is common in Port Phillip Bay.

When the winter wind is from the south the sand moves up beaches and around breakwaters that hook to the north and capture the reversed flow of sand when northerly winds occur in summer. Channel Deepening has possibly already caused increased tide heights.

Much the same is likely to be happening at Belongil Beach, Byron Bay, where the construction of a large carpark right on the beach many years ago has lead to ongoing problems. Stopping the movement of sand west to it has likely robbed the Belongil Beach periodically, depending on which way the weather comes from. Westerlys push the sand eastwards past the carpark where it is caught and maintains a wide beach adjacent to the Byron Bay township.

This problem is further aggravated by housing development and the associated clearing of dune top vegetation. This removes the root mass that stabilises the dunes, destabilising them and leading to erosion. Mowed lawns and hard surfaces that speed up the runoff after rainfall increase erosion, cutting the dunes back from the beaches and undermining houses and gardens.

The site of both a whaling station and an Abattoir before becoming beachside backpackers’ accommodation, Belongil has suffered this kind of erosion before too with houses falling into the sea.

The solution to these problems lies in making proper scale models of the coastal and engineering structures that enable the movement of sand, stopping development of dunes and revegetating lawns with deep rooted indigenous species. This may sacrifice the view but not the house — as quickly, anyway.

Similarly the ingress of saltwater into many freshwater systems is most often not due to sea level rise but the loss of streamflow, or more accurately streamflow persistence. A classic example is the Lakes Entrance system where increasing diversions of major streamflow — like the Thomson River to the Melbourne water supply and power generation — has seen saltwater penetrating ever further up into the Lakes Entrance system.

Land clearing, clearfall logging and bushfires also have dramatic impacts on streamflow that can in turn impact the coast. The less vegetation, the more soil that is less penetrable to water after bushfires, the more dramatic the impact of heavy rainfall which leads to more dramatic flooding events than the same rainfall in the past.

Many of these problems will not be affected by reducing carbon emissions. The fact that the threat of global warming and sea level rise has drawn attention to the coast is good. However these observations must lead to a more considered site and catchment specific evaluation.

Though academic involvement is essential it must be informed by local knowledge and a detailed site specific epidemiology of all the changes back in time that can be tracked. Only through this kind of evaluation can the whole rangeof problems and solutions be clearly identified.

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Peter Fray
Peter Fray
Editor-in-chief of Crikey
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