Author(s): George Heritage, Neil S. Entwistle, David Milan

Linked Author(s): George Heritage, David Milan

Keywords: Gravel-bed river; Sediment transfer; DEM; Extreme event; Flood;

Abstract: We investigate gravel redistribution and morphological response of three headwater streams following the Storm Desmond floods of December 2015. Reactive management of the watercourses following the flooding concentrated on removal of gravel and clearing of vegetation, perceived as having been significant causes of local flooding. Aerial LIDAR and ortho-photography were employed to critically assess the location, type and magnitude of sediment mobilization, using an sUAV to capture imagery of lake sediment fans across the area. Whilst gravel was mobilized during the flood the volumes involved do not appear to be as high as anticipated, with little detectable change in lake fan deposits in the sink zone of the three study streams. Re-exposure of relict gravels on floodplains through stripping of surface vegetation and soils, gave the false impression of fresh deposition. Reactivation of wandering channel zones appear to have acted as buffers to large-scale sediment movement rather than acting as supply zones. Sediment accumulation through towns and villages was harder to quantify due to the rapid clean-up operation, however, the authors suggest that this may not be as large as assumed and the widespread dredging is likely to have caused more problems than it has solved as the bed of many watercourses is now highly susceptible to mobilisation following mechanical disruption of the previously strongly armoured surface.

DOI: https://doi.org/10.3850/38WC092019-1733

Year: 2019