Water flows on Cooper Creek in arid Australia determine 'boom' and 'bust' periods for waterbirds

Cooper Creek is probably the longest and most important dryland river in Australia and one of the largest endorheic catchments in the world. Long dry periods (`busts') are punctuated by floods of high productivity (`boom' periods). Data on waterbird distribution and abundance were collected during a boom period (1989/1990 flood) when Cooper Creek ran into Lake Eyre and overflowed into Strzelecki Creek to fill Lake Blanche. There were about 500 000 waterbirds in December 1990: Lower Cooper (138 000), Lake Eyre (325 000), Lake Blanche (40 000). Given underestimates of aerial surveys, conceivably there were one million waterbirds, making the area one of the most important for waterbirds in Australia. Colonies of Australian pelicans, cormorants, black swans, terns and silver gulls established during this flood. We used flow data and rainfall to estimate how often such habitat (boom periods) is created over a 100-year period, 1885-1995. Rainfall (cumulative index of four rainfall stations--Muttaburra, Tangorin, Isisford and Innamincka), was significantly related to total annual flow (ML), measured at Cullamurra (R super(2)=0.86). We estimated that the Lower Cooper (south of Lake Hope) receives water about every 4.5 years but these floods seldom reach Lake Eyre (8 years in 100 years). There is water in Lake Hope and the Lower Cooper Creek: respectively, 62% and 39% of the time. Cooper Creek overflowed into Strzelecki Creek when there were large floods (1906, 1950, 1974) or two or more consecutive years of high flows (1916-1918, 1955-1956, 1989-1990). Lake Blanche filled six times and Lake Callabonna filled four times in 100 years. Occasionally, local rainfall also fills lakes (e.g. Lake Callabonna in 1931). Like all terminal river systems, these wetlands depend predominantly on upstream flows of water. Potential irrigation developments in the catchment will divert water from the river and decrease the frequency and flooding of wetlands of the Lower Cooper. There will be fewer feeding areas and less breeding opportunities for waterbirds. Boom periods will be shorter and bust periods longer.