Variability of Sediment Discharge Relationships of Storm Events to Assess Erosion Control

The sediment rating curve is the most simple statistical model that establishes a relationship between suspended sediment concentration and discharge. The accuracy of this relationship is often low because of the scatter of the regression, particularly in small catchment. It can be attributed to space and time variations in sediment supply and sediment depletion due to various contributions of particles sources in the stream channel and over the catchment. Continuous monitoring of turbidity measurements on three agricultural catchments (5 km²) of western France during three years are used to establish a typology of this relationship for each storm event during the monitoring period, based on clockwise and anticlockwise relationships between discharge and sediment concentration and other features. It allows do distinguished in which catchment and under which conditions the sediment outflow is controlled by sediment availability, in particular due to cattle trampling and relative bank degradations in river systems on these catchments. Multicomponent statistical analysis was applied to show which hydrological and climatic component determine the supply or the depletion of sediment, and their variations according the catchment and the season. This approach based on field observations improves our understanding of the main control of sediment outflow.