Thursday, January 21, 2010

Southwest Tasmania

The Gordon Dam is a sight to behold – an enormously high dam wall holding back water many times the volume of water in Sydney Harbour. It is built in a very deep and narrow gorge and the design of it is an arch dam.

Arch dams need much less material to achieve the strength than normal gravity dams. The enormous upstream load is transferred through the curves of the dam and into the rock of the abutments and foundation. Furthermore, the Gordon Dam is an arch dam with a double curve. As well as the obvious side to side curve, the dam is also curved top to bottom – the crest overhangs the base several metres.

The Gordon River above the dam.

And an arch of a different kind. Tasman’s Arch at Eaglehawk Neck on the Tasman Peninsula is what is left of the roof of a large sea cave, or tunnel, that was created by wave action over many thousands of years. This immensely slow process or erosion is continuing and the arch will eventually collapse. It will end up like the photo below which is of the Devil’s Kitchen.

The rock afces without the arch.
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