Bank erosion of an incised upland channel by subaerial processes: Tasmania, Australia

The headwaters of many rivers are characterized by gullies and incised stre ams that generate significant volumes of sediment and degrade downstream wa ter quality. These systems are characterized by harsh climates, ephemeral f lows that do not reach bank top, and bare cohesive banks of clay and weathe red bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose-built groundprofiler and p hoto-electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 +/- 2 mm a(-1). Erosion is controlle d by subaerial processes that loosen bank material. Observations show that needle-ice growth is important in winter and desiccation of clays predomina tes in summer. Flows are unable to erode firm cohesive clays from the banks , and erosion is generally limited by the availability of loosened material . This produces strong hysteresis in turbidity during events. Peak turbidit y is related to the number of days with low flow between events, and not pe ak stage. Rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of cu rrent erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. Copyright (C) 2000 John Wiley & Sons, Ltd.