154. Sources of Fine Grained Sediment in Incised and Un-incised Channels, Jugiong Creek, NSW, Australia

In southeastern Australia land-use changes due to European settlement (∼180 years ago) triggered widespread channel incision, and erosion from these features delivered massive volumes of sediment to rivers. It is proposed that the channels remain a major source of sediment. We use measurements of Cs concentrations in soils and sediments to examine sources of fine sediment in incised and unincised channels. In un-incised channels the ¹³⁷Cs concentrations decreased to around 40–60% of surface hilllslope values by stream order 3, whereas ¹³⁷Cs concentrations in incised channels decreased to 10–15% of surface hillslope values in the 1^st order streams. In both cases we attribute the decreases in ¹³⁷Cs concentrations to input of sediment from the channel walls; the input is four times greater in the incised channels. It is concluded that erosion from the walls of incised channels remains a significant source of sediment to rivers in southeastern Australia.