RIP-CURRENT AND COASTAL TOPOGRAPHY

Abstract

At the 1974 Conference on Coastal Engineering (Copenhagen), the -writer proposed a new theory on the mechanism of generation of ripcurrent and cuspidal coast that the alongshore homogeneous structure of wave field and movable sedimental bottom (that is two-dimensional wave setup and bottom topography) is unstable to a small perturbation, the motive force of instability being the radiation stresses caused by incident wave. In this paper, based on the response concept and the mathematics already presented at the previous conference some improvements in solving the fundamental equations are attempted, since the direct solution of the full system of basic equations did not necessarily result in the sufficient conclusion. The response of water-wave system to an infinitesimal perturbation in bottom boundary is quick enough compared with that of sediment system to a change occurring in water-wave system. Consequently, the water system is treated as quasi-stationary. By solving the equation of mass conservation of sediment transport under the prescribed boundary conditions, the preferred wavelength of rip-current as well as the profiles of velocity distribution and the bottom perturbation have been determined as an eigenvalue problem.