INTERACTIONS BETWEEN UPLAND CATCHMENT AND LOWLAND RIVERS - AN APPLIEDAUSTRALIAN CASE-STUDY

Persistent allegations have been made, mainly by Victorian farmers, th at channel and floodplain aggradation are occurring on die floodplain of the Snowy River in Victoria as a consequence of accelerated erosion of degraded agricultural land in parts of the New South Wales upland catchment. These claims prompted the Victorian Department of Water Res ources to initiate geomorphological investigations involving reviews o f historical evidence, including sequential aerial photographs, and a study of sediment sources based on environmental tracers. A qualitativ e approach set within a sediment budget framework was adopted for data integration, a detailed quantitative analysis being precluded by fina ncial, temporal and practical constraints. No compelling evidence was found to support claims of recent channel aggradation in the downstrea m Snowy River. Transfer of sediment eroded from catchment slopes in NS W to the lowland floodplain in Victoria is indirect, with some sedimen ts stored temporarily in fans and floodplains within tributary catchme nts and in the Snowy valley for long delay times. Storage and interbas in transfer of water as part of the Snowy Mountains Scheme have affect ed sediment delivery. The catchment upstream of Lake Jindabyne is effe ctively isolated by this large impoundment, and sediment transport rat es as far downstream as the Delegate River junction appear to have sig nificantly decreased as the result of the considerable reduction in di scharge.