FLOOD HISTORY OF THE LIMESTONE RANGES IN THE KIMBERLEY REGION, WESTERN-AUSTRALIA

Palaeoflood studies enable estimates to be made of the age and magnitude of past flood events. The key points are the location, stratigraphy and age of slackwater deposits. These are often best preserved in gorge sections and typically occur in association with side gorges, caves and on terraces. The slackwater deposits are allocated to specific flood events and the associated discharges are estimated from step-backwater modelling methods. Absolute dating techniques are used to assess the age of the individual slackwater deposit sequences. Studies of this kind were undertaken for Windjana Gorge in the Kimberley region of northern West Australia. The fieldwork was a contribution to the Kimberley Research Project 1988, jointly organized by the Royal Geographical and Linnean Societies. A sequence of five slackwater deposits was established and palaeodischarges calculated. Both radiocarbon and thermoluminescence dating were used to establish a chronology for the deposits, which varied in age from a few years to over 2000 years. The palaeodischarges were compared with estimates of extreme discharges obtained using other hydrological methods. For remote areas, river discharge records are of short duration and variable quality. Therefore, the use of statistical techniques based on the extrapolation of discharge and frequency are of doubtful value. The palaeodischarges for Windjana Gorge were also compared with estimates of the unit area runoff for extreme floods in Australia and worldwide. There are indications that palaeoflood studies offer a useful and independent approach to the estimation of past extreme flows. The method is especially valuable for regions that have only sparse hydrological records. © 1991.