MODEL TESTS ON THE BELATIONSHIP BETWEEN DEEP--WATEB WAVE CHARACTERISTICS AND LONGSHORE CURRENTS

Arthur Brebner, J.W. Kamphus

Abstract


It has Long been recognized that the movement of Littoral material takes place, in the main, in the onshore regions of a beach where breaking of waves occurs. Waves whose crests in deep water make an angLe o(a with the shore Line, and which break at an angLe C*© , are the mam source of energy for the generation of the forces which manifest themselves in Long-shore currents and the resulting LittoraL transport. This littoraL materiaL is put into motion before, during and after breaking but it is extremeLy difficult to separate the effects of the forces and currents in these three zones. In what foLlows the authors have attempted to measure the intensity of the current around the breaking zone in a highLy ideaLized beach model in which the shore Line is straight, has a constant beach sLope, 0, and is attacked by waves of constant deep-water wave-height, HQ, and period, T. During refraction and shoaLing the angLe of the wave-crests with the shore-Line is reduced from o<o to «s and during this process some of the deep-water energy being transmitted shorewards may be dissipated by friction. The exact vaLue of c*e is a function of ota , H0/L0 , and the friction Loss, but wiLL increase, both theoretscaLLy and experimentally, with increasing H0/L0 , as shown by Brebner and Kamphuis (1963). Based on the angLe of breaking, «*<B , the wave-steepness at breaking, Hg/Lg, the depth of breaking dg, and the beach sLope, 0, it is possibLe to formuLate relationships for the Long-shore current, vj^, using the prmcipLe of conservation of energy and momentum and the principle of continuity.

Keywords


model test; deep water; longshore current; littoral drift

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