浅海における波浪スペクトルの変形と海底摩擦係数の推定について

Abstract

One of the most important problems in coastal engineering is the transformation of wavesas they approach the shore through shallow water.In this paper, from the damping of the significant wave heights and the transformationof the wave spectra observed at Izumisano Coast and Hiezu Coast, the loss of wave energy due tobottom friction is investigated quantitatively and the bottom friction factors of these coastsare estimated. In estimating the bottom friction factor by the wave spectrum method, it isassumed conveniently that each component wave propagates independently.The values of bottom friction factors at Izumisano Coast estimated are 0.14 and 0.55 by thesignificant wave method, and 0.013-0.054 and 0.25 -0.55 by the wave spectrum method. AtHiezu Coast, the values estimated are 0.027-0.16 and 0.040-0.44 respectively. It should benoted that these values are much greater than 0.01 which was given by Bretachenider to begenerally used in forecasting shallow water coean waves.It is found that the longer the significant wave period or the heigher the value of the accom-panying-wave Reynolds number is, the smallei the value of bottom friction factor estimatedby the significant wave method is, and that these values are about ten-s21venty times the theore-tical values obtained in the laminar wave boundary layer theory. In addition, the valuesestimated by the wave spectrum method seems to have the same tendency as by the significantwave method except Data No. I-I, and are about ten - one hu;ndred and twenty times thetheoretical.