Quantification of bank erosion in a drained agricultural lowland catchment

Abstract : The long-term and current volumes of sediment exported from stream banks were calculated as potential sources of sediment in a large pond located at the catchment outlet of a small agricultural lowland basin strongly affected by anthropogenic pressure in France. Bank erosion was measured over a short period using a network of erosion pins along a small stream (1400m long) to quantify the material exported during a single winter (2012-2013). The material exported by this same stream over the last 69years was quantified using an original approach involving the comparison of a compilation of three-dimensional historical stream redesign plans that date back to 1944 with the state of the banks in 2013 (differential global positioning system and LiDAR data). The results suggest that a global trend of material loss along the stream banks monitored by erosion pins, with an average erosion rate of 17.7mmyear(-1) and an average volume of exported material of 75tkm(-1). Over 69years, this same stream exported an average of 36tkm(-1)year(-1), and the average loss of material from the banks throughout the whole catchment was estimated to be 14tkm(-1)year(-1). The contribution of bank material to the filling of the pond over the last 10years is between 46% and 52% based on an extrapolation of erosion pin dynamics or between 27% and 30% based on the comparison of LiDAR data to the average historical profile extrapolated for the catchment. These results suggest that bank erosion represents a major source of sediment in degraded waters in traditionally understudied agricultural lowland catchments, where anthropogenic pressures are high.