WAVE DECAYING DUE TO BREAKING

Abstract

In the planning and design of coastal engineering works for the control of beach characteristics, a proper and effective measure against wave must be the most important problem to be solved. When the wave generated on the open sea approaches the shallow sea area, it will be transformed under the influence of sea bottom. For the construction works of coastal structures on a shoreline or in shallow water, the estimation of the rate of wave transformation is needed. In this concern, many reports were already published by the researchers,i. e, R.L.Wiegel, M.A.Mason,H.W. Iversen and T.Kishi. Moreover, the so-called Breaker Index which shows the breaking conditions has been obtained by the Beach Erosion Bord (U.S.A.), based on the data of field observations. Furthermore, these characteristics were investigated theoretically and experimentally by H.W. Iversen, Hamada, Sato and Kishi. Though these results show the wave transformation from the deep sea to a breaking point, there are few reports dealing with the wave transformation in the process of breaking and after a breaker zone. In the execution of coastal works projected in Ministry of Agriculture and Forestry such as shore reclamation works, coastal defence works and river mouth improvement, the wave inshore from a breaker zone often should be taken into consideration. In the past design of coastal structure, the wave acting on structures in the shallow water is calculated from the deep sea wave usually by using very rough estimation that wave height is reduced by about 30 per cent after a single breaking and wave period by about 10 per cent. Consequently, in order to analyze the wave decaying due to breaking, this paper treated with the wave transformation in the vicinity of a breaking point.