Measurements and Analysis of Flow Velocity and Sediment Concentration at the Seabed

A review of flow velocity and sediment concentration measurements on field sites is given, but the main emphasis is on the data analysis results of near-bottom measurements of flow velocities and suspended sediment concentrations over a sandy bottom during four storms in the central North Sea. The water depth was 70 meters and the seafloor consisted of fine sand of 0.20 mm average diameter. The measurements included sediment concentrations, flow velocity in the boundary layer on the seafloor, steady current over the water column, wave heights, and photographs of the seafloor. The paper presents the variation of the sediment concentrations, waves and currents during the storms. Results from the logarithmic boundary layer flow model fit to the current measurements using the roughness (z₀) and friction velocity (u*) as fitting parameters are also given. It also gives limited comparisons of model predictions with the data. The predictions are obtained from a wave-current interaction model combined with three different moveable bed models, which predict ripple size and sediment transport effects on the bed roughness.