Aquaculture Groundwater Resource Atlas - Leeuwin

Groundwater supplies in the Leeuwin Groundwater Province are small, localised, and commonly brackish to saline. There is little potential for further development.

The Leeuwin Complex underlies the ridge between Capes Naturaliste and Leeuwin, extending eastwards by around 10 to 15 km where it is bounded by the Perth Basin. The bedrock consists of granite, metamorphosed to granulite and gneiss which is exposed along the coast, and in scattered outcrops inland. In places the bedrock is lateritised and has a clayey weathering profile of 10 to 20 m thick.

Bore yields from the bedrock and from the base of the weathering profile are low, and success rates are poor, with records of numerous dry or abandoned bores. Groundwater ranges from brackish to saline (up to 10 ppt), and is generally used only for stock purposes.

Along the coast, the bedrock is intermittently covered by the coastal dune limestone. The limestone is likely to be as much as 50 m thick, and there is generally no groundwater owing to cave development at the base of the limestone which allows rapid drainage. Groundwater from channel flow at the base of the limestone discharges at springs along the coast. Water supplies for Augusta, Yallingup and Gracetown are drawn from such springs.

Inland of the limestone ridge, fresh groundwater may be present in colluvial and aeolian sands, and locally small supplies are developed for domestic use.

Surface water storage is commonly developed in the bedrock areas, as the soils are clayey.