The Western Plateau is Australia's largest drainage division and is composed predominantly of the remains of the ancient rock shield of Gondwana. It incorporates two thirds of the continent; 2,700,000 square kilometres of arid land including large parts of Western Australia, South Australia, and the Northern Territory. For comparison, it is roughly four times the size of Texas, or the same size as the whole of continental Europe from Poland west to Portugal. It is Australia's largest drainage division.
Rain seldom falls in this region and aside from a handful of permanent waterholes, surface water is absent at all times except after heavy rain. Most of the territory is flat sandy or stony desert with a sparse covering of scrub or tussock grasses. Average rainfall varies from one area to another and is quoted at 100 to 350 mm per year (between 4 and 14 inches) but is highly unpredictable.
There are no permanent watercourses. The general trend is for run-off to flow inland, but there is insufficient rainfall to produce any marked drainage pattern.
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