Measurements of threshold values for incipient motion of sediment particles with two different erosion devices

For studies on sediment transport processes experimental data on the erosion behaviour of sediments are necessary. Because of significant differences in experimental setups and subsequently in resulting values comparisons and, where possible, correlations between methods are required. This study presents measurements with two different erosion devices (straight flume and microcosm erosion chamber), which were used for the determination of critical shear stress velocities for sandy submarine sediments and sieved sediment fractions. An approach is presented to convert measured current velocities into shear stress velocities via roughness length values and drag coefficients under hydrodynamically smooth and transitional turbulent flow conditions. The results from both devices show a good agreement and the measured erosion threshold values fit to established correlations between critical shear stress velocity and grain size. In the grain size range below 200 µm results for naturally composed sediments are influenced by effects caused by the silt- and clay fraction. Sieved sediment fractions in this grain size range tend to show lowered erosion thresholds in relation to the Shields' curve.