Channel instability in a forested catchment: a case study from Jones Creek, East Gippsland, Australia

Jones Creek, a forested sub-catchment of the Genoa River, Victoria, Austral ia has experienced channel metamorphosis induced by a series of floods sinc e 1971. In the flood of record, in 1971, the Genoa River widened by up to t wo times at the confluence with Jones Creek. This effectively shortened the course of Jones Creek, resulting in a lagged tributary response. Incision and bed steepening during floods in 1975 and 1978 triggered significant cha nges in channel form along Jones Creek. Channel changes between 1972-1997 r esulted in a four-fold increase in cross-sectional area. Channel depth incr eased by up to 1.5 m, but has subsequently refilled by around 0.6 m. Initia lly, incision resulted in increased stream power as a result of increased m ean depth, while sinuosity was maintained. This was followed by channel wid ening, a reduction in sinuosity and a continued increase in slope. Estimate d stream power remains high as the channel continues to laterally adjust. T his study highlights the dynamic nature of tributary-trunk stream relations hips in a cut-and-fill landscape, demonstrating how trunk stream adjustment s can induce profound tributary instability in a forested subcatchment. Cha nnel widening of the trunk stream primed the tributary for change. Bedlevel incision and increases in bedslope breached the threshold of landscape sta bility in this steep alluvial tributary. Three periods of channel change ca n be identified, reflecting the complex response of the system to channel i ncision. Rather than developing simple cutoffs, Jones Creek now exhibits a range of lateral adjustment and realignment features. Responses to external disturbance provide insights into 'natural' recovery mechanisms in this fo rested setting. Lateral adjustment and associated sediment deposition have been accompanied by rapid rates of vegetation colonisation and stabilisatio n of realignment features, effectively reducing the volume of sediment that is available to be reworked through the channel network. (C) 2000 Elsevier Science B.V. All rights reserved.