Predicting the spatial patterns of hillslope sediment delivery to river channels in the Murrumbidgee catchment, Australia

Abstract

Sediment yield data derived from long-term sedimentation rates in 26 small farm dams in SE Australia were used to calibrate a spatially distributed soil erosion and sediment delivery model (WATEM/SEDEM) that takes into account contribution from gully erosion in areas of concentrated flow. For three different land use categories (poor, moderate and good vegetative cover), a sediment transport capacity coefficient was calibrated. All other parameters being equal, it was found that sediment transport capacity for cropland is 2 times higher than for degraded pasture and 20 times higher than for native forest and good pasture. Model efficiencies for the prediction of specific and total sediment yield are 0.56 and 0.89, respectively. These model efficiencies are much higher compared to those obtained when intense erosion in concentrated flow areas is not considered explicitly. Several of the catchments that were used for the calibration have very high sediment yield rates, which are attributed to the presence of gullies. The good performance of WATEM/SEDEM to all catchments suggests that the model accounts well for gully erosion. Next, the calibrated WATEM/SEDEM was applied to the Murrumbidgee River basin (30,000 km2). A mean annual sediment input into the river channels from the hillslopes of 478,000 t was predicted. The spatial pattern of hillslope-derived suspended sediment delivery in the Murrumbidgee indicates that most of the sediment originates from a few tributaries downstream of Burrinjuck Reservoir. Given the fact that high-resolution datasets (including digital elevation models) are becoming available at reasonable cost, WATEM/SEDEM provides a powerful tool to predict hillslope sediment delivery under different environments including the spatial patterns of hillslope generated sediment fluxes.