Drag reduction in turbulent muddy seawater flows and some sedimentary consequences

Turbulent saline flows which contain low concentrations of suspended clay (< 10 g 1⁻¹) have previously been reported to possess dramatically different boundary layer characteristics from clearwater flows and to exhibit the phenomenon of drag reduction. Drag reduction causes significantly lower friction factors and higher erosion thresholds in muddy saline flows than predicted by experimental data gained from fresh‐water flows using the law of the wall to estimate bed shear stress. Confirmation is given by experimental results on drag reduction using non‐intrusive laser Doppler measurements in seawater flows with <2·2 g 1⁻¹ maximum concentration of suspended clay. Increasing the concentration of clay caused progressively lower velocities near the wall due to a gradual thickening of the buffer region of the turbulent boundary layer. Several aspects of sediment transport, deposition and bedform development in natural marine environments are thus considered to be significantly affected by the drag reduction process.