WAVE AND CURRENT INTERACTION IN THE NEAR BED REGION

Patrick H. Kemp, Richard R. Simons

Abstract


The question of how waves and currents interact, especially in the near-bed region is of considerable importance in relation to sediment suspension and sediment transport. Whereas empirical relationships provide useful estimates and indications in relation to the data on which they are based, a more thorough understanding of the physical processes at work is necessary for interpreting sediment transport behaviour in a more generalized way. Clearly the conditions under which flow reversal occurs near the bed, and also the extent to which wave motion may modify the current induced turbulence in the boundary layer, are both of great interest, and these and other aspects have been included in the present study. The research program was designed to look initially at the interaction between waves and currents in the absence of sediment, in order to define the mean velocity components, the structure of the turbulence, and the shear stresses. The study proceeded from experiments on waves alone, to waves propagating with the current and against the current. In all three cases the tests were carried out in the first instance with a smooth bed and subsequently with a rough bed consisting of two dimensional triangular slats. One of the main areas of interest was the height to which the water was disturbed above the bed when acted on by waves alone, and the comparable situation when a current was superimposed on the waves. Since the characteristics of the turbulent current were measured independently, it was possible to deduce whether there had been any interaction between the waves and the current, and also to infer what might happen to the distribution of the sediment which it was assumed would be put into suspension in the two cases. In the second stage of the research separate experiments were carried out in a standing wave channel and an oscillating water tunnel, using lightweight bed materials, in order to observe whether the inferences made from the clear water study were borne out by comparable changes in the distribution of the sediment in suspension.

Keywords


bed; wave/current interaction; near bed region

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