Turbidity-based erosion estimation in a catchment in South Australia

An erosion estimation technique was developed in this study based on turbidity and sediment sampling data in a small catchment in South Australia. Several data sets, derived from the time sequence in which the data were collected, were used to develop a number of turbidity and suspended sediment relationships. These relationships were then used to estimate erosion from the catchment. The variability in sediment load estimation using different relationships, and how these relationships impacted on load estimation, were analyzed in detail. The study estimates erosion on a storm basis using detailed sediment sampling and turbidity data. Storm sediment loads were then accumulated to derive annual load, which distinguishes this study from volume based sediment studies. The study found that large storms dominate erosion in the catchment, and erosion rate depends more on peak storm flow than other hydrological variables. A relatively low annual erosion rate from the catchment was found, which is consistent with studies in other Australian catchments. The study found that, to establish a sound relationship between suspended sediment and turbidity for a catchment, it requires extensive data collection of large as well as small storms at short time intervals, a storm-based erosion estimation approach, and a data set that is used for interpolation rather than extrapolation. Erosion estimation based on infrequent, non-storm based or extrapolated data is exposed to potentially large errors, and the results may only be relied upon as a general guide rather than serious estimation of catchment erosion.