Improving precision in sediment source and erosion process distinction in an upland catchment, south-eastern Australia

Analysis of sediment sources is an important component in the development of catchment sediment budgets and in determining links between erosion from sources and sediment delivery to catchment outlets. In this study 137Cs and 210Pbex were used to determine surface and sub-surface source contributions of fine sediment in a small upland headwater catchment (1.6 km2) in south-eastern Australia. The findings from this analysis are employed in an adjustment procedure to better differentiate sediment source erosion processes by utilising channel survey and erosion pin data. This improved the precision of estimates of sediment-source erosion-process contributions from hillslopes and channel/gully walls. A mean of 74% of in-channel deposits and suspended sediment exiting the study catchment was derived from sub-surface sources and when adjusted for erosion process this increased to 81%, which may be attributed to channel and gully wall erosion alone. Net erosion of the channel floor was low and constitutes only a small part of the total channel source input to sediment flux. Variability in sediment source contributions within the catchment was high, with rapid transition from hillslope to channel source dominance of sediment flux with distance downstream in the study catchment.