Erodability

Abstract: A portable benthic annular flume for thein situmeasurement of suspension feeding (biodeposition rates) and erosion potential of undisturbed intertidal cohesive sediments with benthic biota is described. The experimental procedures used during deployment are also outlined. Results showing the changes in biodeposition rates, sediment resuspension, erosion rates and critical erosion velocities associated with large-scale (km) and small-scale (m) spatial differences are presented. Comparison between laboratory andin situmeasurements demonstrated marked differences in sediment erodability if the physical and biological properties of the sediment are not maintained.

Abstract: The bed shear strength on an intertidal mudflat bordering salt marshes along the Dutch Wadden Sea coast was determined by means of an in situ erosion flume (ISEF). Characteristic erosion patterns (type I- and type II-erosion) were observed for most measurements. The critical erosion threshold varied between 0·11–0·18 (Pa) for all measurements and erosion rates varied between 5×10 −5 and 3×10 −3 (kg m −2 s −1 ). No clear relationship was found between distinct parameters like bed density, moisture content or biological activity and the critical erosion threshold. A more pronounced effect of the erodability of the mudflat was found when the erosion rate was taken into account. Basically two clusters were distinguished. High mean peak erosion rates of the substratum were found at locations which were characterized by a low mud content of the substratum (below 20% mud by weight). In these situations bed load transport is expected to be the most important process which determined erosion of the bed and erosion of predominantly the sand fraction was found. At higher rates of the mud content (over 20% mud by weight) mean peak erosion rates decreased substantially (an order 6 to 10 times lower) and both erosion of the mud and sand fraction was found.