Investigation on the erosion stability of cohesive sediment deposits in the weir channel of the barrage Iffezheim, River Rhine

摘要

To investigate the erosion stability of deposited fine sediment in the barrage Iffezheim on the Upper Rhine River, a combined measuring strategy was applied. Next to in situ measurement, sediment cores were extracted and analysed in the laboratory. At 12 sampling points, the in situ device was used to measure the critical bed shear stresses at the sediment surface. At the same time, sediment cores were withdrawn at each site to perform depth-orientated investigations in the hydraulic laboratory. The objective of this study was to investigate the remobilisation potential of the deposited fine sediments. Next to critical shear stresses and erosion rates, additional sedimentary and biological parameters were examined such as bulk densities, particle size distributions, TOC-contents and chlorophyll-a concentrations. Moreover, different methods were tested and compared to determine the critical shear stresses for the deposited fine sediments.The results generally reveal a very low erosion stability, especially at the sediment surface and in the upper sediment layers. Deeper sediment layers are characterised by consolidation effects and display a higher erosion resistance. High clay contents result in increased stability while high sand contents show a high remobilisation potential. No significant relation to the parameters TOC-content or chlorophyll-a concentration can be identified. A comparison between the different techniques applied to determine the critical bed shear stresses reveals values in the same order of magnitude; however, some significant variations occur in this extent.