Predicting suspended sediment loads at a catchment scale: A comparison between models

Owing to financial and other constraints on natural resource management, comprehensive data on the physical processes that determine instream water quality are rare. Consequently, managers are looking to models as decision-making tools. One important application is to identify areas in greatest need of erosion management. There are many ways that suspended sediment loads can be assessed. The main constraints in the determination of loads are the data available and the scale at which this information can be applied. This study has used two models to estimate the suspended sediment load in a number of catchments in the mid-region of the Murrumbidgee River catchment. The load derived using an empirical estimation technique is compared to the load predicted from a semidistributed, lumped conceptual model (SedNet). Both these models can predict suspended sediment loads at a catchment scale with minimal data requirements compared to more complex physics-based models. Even so, it is important to recognise that these models predict loads at different time scales and include different assumptions, which can result in significant differences in the derived suspended sediment load. Nevertheless, managers rely on such models because of the reduction in available data to directly measure suspended sediment load and the increasing pressure for effective resource allocation. Hence, it is necessary to ensure consistency in the models used to assess water quality. Three sub-catchments in the Mid-Murrumbidgee River catchment - Tarcutta, Muttama and Jugiong creek catchments - were used for the suspended sediment load comparison. The comparison presented in Table 1 indicates that the long-term steady-state prediction from SedNet is within the statistical uncertainty for two of the catchments (Muttama and Tarcutta creek catchments) on a per area basis. However, it seems that there is a large discrepancy between the empirical model estimate and SedNet prediction for the Jugiong creek cat