The Margaret River has only a few large named tributaries: the Mowen River, Bramley, Yalgardup, and Ten Mile Brook. The upper river valleys of the Margaret were formed after sediments filled the sunklands left by the breakup of Gondwana. They flow westward and onto the granite of the Leeuwin Block, a remnant of the super-continent left behind by India as it pulled away to the north.
The Ten Mile Brook valley was lush and deeply forested, the result of ongoing weathering processes over millions of years. It supported one of the most diverse flora and fauna communities on earth. In 1994 the Water Authority dammed the valley to provide water for the townsites of Margaret River, Cowaramup, Gracetown, and Prevelly. However the catchment is too small to meet our requirements and the dam was originally supplemented by water pumped from the Margaret River.
Now, our scheme water is sourced directly from the Yarragadee aquifer and stored in the dam. There is some uncertainty as to whether drawing so much from the underlying aquifer could impact on the surface groundwaters supplying the base flow for the Margaret River.
We can never recover the valley. But we can be mindful of the origin of the clear sparkling water that comes from our taps.
Jinni Wilson BSc (hons) Anthropology, University of Western Australia.