Limits between surface and inner clogging of riverbed by fine sediment

The deposition of fine sediment on top of the riverbed affects the reproduction of spawning fishes and some species of benthos. The clogging of the substrate resulting from this deposition is a well-known issue in rivers affected by anthropogenic activity and hydraulic in-frastructures. Fine sediment can form a clogged layer inside or on top of the substrate. The latter process has not been subject to much research. The flow condition leading to surface clogging is analyzed for a single fine sediment composition. The experimental setup was prepared to create a continuously varying velocity along the length of the flume. Pictures of the deposition patterns allow the analysis of the limit between inner and surface clogging. Surface clogging was ob-served on areas with shear velocity higher than the commonly accepted critical shear velocity obtained from Shields’ diagram.