DRAG REDUCTION IN TURBULENT MUDDY SEAWATER FLOWS AND SOME SEDIMENTARYCONSEQUENCES

Turbulent saline flows which contain low concentrations of suspended c lay (< 10 g l-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 signi ficantly lower friction factors and higher erosion thresholds in muddy saline flows than predicted by experimental data gained from freshwat er flows using the law of the wall to estimate bed shear stress. Confi rmation is given by experimental results on drag reduction using non-i ntrusive laser Doppler measurements in seawater flows with <2.2 g l-1 maximum concentration of suspended clay. Increasing the concentration of clay caused progressively lower velocities near the wall due to a g radual thickening of the buffer region of the turbulent boundary layer . Several aspects of sediment transport, deposition and bedform develo pment in natural marine environments are thus considered to be signifi cantly affected by the drag reduction process.