Lake Eyre Basin - Geography

Geography

During years of especially high rainfall, all the riverbeds in this vast, mostly flat, arid and semi-arid area lead inland (not towards the sea) towards Lake Eyre in central South Australia.

Lake Eyre itself lies approximately 16 metres below sea level, and usually contains only salt. In flood years it fills and for a short time undergoes a period of rapid growth and fertility: long-dormant marine creatures multiply and large flocks of waterfowl arrive to feed and raise their young before the waters evaporate once more.

None of the creeks and rivers in the Lake Eyre Basin are permanent: they flow only after heavy rain – a rare to very rare event in the arid interior of Australia. Average annual rainfall in the area surrounding Lake Eyre is 125 millimetres (5 inches), and the pan evaporation rate 3.5 metres (about 11 feet). Annualised average figures are misleading: since 1885 annual rainfall over the 1,100,000 square kilometres of the Lake Eyre Basin has ranged from about 45 millimetres (less than 2 inches) in 1928 to over 760 millimetres (30 inches) in 1974. Most of the water reaching Lake Eyre comes from the river systems of semi-arid inland Queensland, roughly 1000 kilometres to the north.

To provide a sense of scale, the Lake Eyre Basin is about the size of France, Germany and Italy combined. It is roughly the same size as the Murray-Darling basin (which drains inland eastern Australia and is responsible for a large proportion of the continent's agricultural productivity) but has vastly less water. Nevertheless, the entire flow of the Murray-Darling would be insufficient to fill Lake Eyre, merely keeping pace with evaporation. In contrast, the flow of the Mississippi could fill Lake Eyre in 22 days, that of the Amazon in just 3 days.

Other lakes in the basin include Lake Frome, Lake Yamma Yamma and Lake Hart.