Advances in Bank Erosion Modelling at a Catchment-Scale and Its Significance to the Sediment Budget

Abstract:

Channel bank erosion has been shown to contribute significantly to catchment sediment budgets, yet representation of this process in catchment models is often overly simplistic, or non-existent. In this study, the physically-based hydrological SHETRAN model has been modified to improve representation of channel bank erosion processes by incorporation of the influences of vegetation and channel sinuosity. The presence of vegetation on channel banks increases bank stability, reducing erosion rates. Large flood events have the potential to remove bank vegetation resulting in a sudden increase of bank erodibility, which then decreases over time as vegetation re-establishes. Within the updated model, erodibility coefficients throughout the catchment are temporally variable and respond to high magnitude discharge events to represent vegetation removal. The influence of further flood events during the vegetation recovery period is enhanced due to the increased erodibility, enabling the model to represent memory within the catchment. Meteorological conditions after high magnitude events influence the length of recovery time, which is also incorporated within the model. Channel sinuosity and channel curvature show a non-linear relationship with bank erosion due to the positioning of high-velocity flow within channels. The influence of sinuosity has been incorporated within the model by spatial variation of minimum and maximum bank erodibility coefficients according to variation of sinuosity within represented channels. The developed model has been applied to the Eden catchment, Cumbria, UK. The model has been validated using observed long-term bank erosion data from a GIS overlay methodology, indicating bank erosion contributes up to 11% of the annual catchment sediment budget. This paper will detail both the new modelling approach and accuracy of its application.