Modelling the Probable Maximum Precipitation for Large Catchments

Abstract

The design flood requirement for the Burdekin Falls Dam in Queensland, Australia, has under recent guidelines tightened to a one in one million years event. The usual Probable Maximum Precipitation event, as currently designed for, is estimated in existing literature as a one in ten thousand years event, so does not meet this criterion. We note that one storm event at the maximum design level for the Burdekin Falls Dam has already occurred elsewhere in Northern Queensland. We conduct a number of preliminary investigations, of extreme lake heights above the spillway lip, extreme flow volumes over the spillway, and extreme storm event in meteorologically similar lo- cations in Australia, to suggest future more intensive and thorough analyses that might be helpful. Our preliminary and tentative find- ing is the dam does not meet the extreme event requirements of the latest regulation risk levels. However evaluating extreme values is difficult and subject to considerable variation. In addition the effects of catchment flow and lake bathymetry need to be evaluated using the estimated precipitation.