Sources of fine grained sediment in incised and un-incised channels, Jugiong Creek, NSW, Australia

Abstract

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 137Cs concentrations in soils and sediments to examine sources of fine sediment in incised and un-incised channels. In un-incised channels the 137Cs concentrations decreased to around 40-60% of surface hillslope values by stream order 3, whereas the 137Cs concentrations in incised channels decreased to 10-15% of surface hillslope values in the 1st 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.