Interactions between upland catchment and lowland rivers: an applied Australian case study

Persistent allegations have been made, mainly by Victorian farmers, that channel and floodplain aggradation are occuring on the floodplain of the Snowy River in Victoris as a consequence of a accelaerated erosion of degraded agricultural land in parts of the New South Wales upland catchment. These claims prompted the Victorian Department of Water Resources to initiate geomorphological investigations involving reviews of historical evidence, including the squential aerial photographs, and a study of sediment sources based on environmental tracers. A qualitative approach set within a sediment budget framework was adopted for data integration, a detailed quantitative analysis being precluded by financial, temporal and practical constrainsts. No compelling evidence was found to support claims of recent channel aggradation in the downstream Snowy River. Transfer of sediment eroded from catchment slopes in NSW to the lowland floodplain in Victoria is indirect, with some sediments stored temporarily in fans and floodplains within tributary catchments and in the Snowy valley for long delay times. Storage and interbasin transfer of water as part of the Snowy Mountains Scheme have affected sediment delivery. The catchment upstream of Lake Jindabyne is effectively isolated by this large impoundment, and sediment transport rates as far downstream as the Delegate River junction appear to have significantly decreased as the result of the considerable reduction in discharge.