THE INCREASE OP BED SHEAR IN A CURRENT DUE TO WAVE MOTION

Abstract

As early as 1948 Exnstein [lj suggested that the approach to the calculation of the sand transportation by waves could be similar to that for uniform flow. Tests conducted by author proved that for a current, with waves being propagated m a direction perpendicular or almost perpendicular to this current, the sand transportation is a function of the intensity of bed shear in the direction of the current. Therefore, an attempt has been made to study the increase of the bed shear of a current due to wave motion. The results of this study are presented in this paper. This problem has also been studied by Jonsson and Lundgren !?l >L5] t>ut they have assumed that current and wave-propagation occurs m the same direction. As for normal beach conditions, the angle between current and wave crests is between 0° and 20°, tests have been executed in the Delft Hydraulics Laboratory for angles of 0° and 15°. For an angle of 0° between the wave crests and the direction of the current, results have been presented by Bijker in the proceedings of the seminars at the I.A.H.R. conference which was held m Leningrad in 1965. Because it is not feasible to measure the bed shear directly an indirect method had to be chosen. Determination of the bed shear by means of the velocity profile m the vicinity of the bed is not feasible m this case as the combined velocity profile is of a rather complicated nature. The bed shear is therefore determined by means of the energy slope.