Desert palaeofloods in central Australia

Abstract

Hydrological conditions in arid regions are notoriously difficult to characterize in time and space. The inherent variability of rainfall and the resulting runoff poses problems for both economic development and palaeoenvironntental studies. Quantitative data on past floods are especially useful because the extreme rainfalls that generate desert floods are important environmental determinants in the world's arid environments. Unfortunately these are the environments that lack long-term hydrological records. We report here on the application of a palaeohydrological procedure1,2 that utilizes flood sediments as palaeostage indicators. By determining the ages of the responsible palaeofloods it is possible to evaluate their frequency of occurrence. The magnitude and frequency of floods on major desert stream or wadi systems provide critical palaeoclimatic information by delimiting areal and temporal shifts in rainfall-inducing weather systems. Central Australia is an ideal region in which to illustrate this technique because major phases of flooding correspond to the increased extratropical influence of the north Australia monsoons and/or tropical cyclones. We demonstrate here the use of palaeoflood hydrology to evaluate the recent phase of immense floods on the Finite River near Alice Springs in arid central Australia. The method approximates the magnitudes of the three great floods of 1967, 1972 and 1974, and it proves to be useful in other desert regions where conventional hydrological information is lacking.