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, Australia has experienced channel metamorphosis induced by a series of floods since 1971. In the flood of record, in 1971, the Genoa River widened by up to two 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 changes in channel form along Jones Creek. Channel changes between 1972-1997 resulted in a four-fold increase in cross-sectional area. Channel depth increased by up to 1.5 m, but has subsequently refilled by around 0.6 m. Initially, incision resulted in increased stream power as a result of increased mean depth, while sinuosity was maintained. This was followed by channel widening, a reduction in sinuosity and a continued increase in slope. Estimated stream power remains high as the channel continues to laterally adjust. This study highlights the dynamic nature of tributary-trunk stream relationships in a cut-and-fill landscape, demonstrating how trunk stream adjustments can induce profound tributary instability in a forested subcatchment. Channel widening of the trunk stream primed the tributary for change. Bedlevel incision and increases in bedslope breached the threshold of landscape stability in this steep alluvial tributary. Three periods of channel change can be identified, reflecting the complex response of the system to channel incision. 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 forested setting. Lateral adjustment and associated sediment deposition have been accompanied by rapid rates of vegetation colonisation and stabilisation 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.