EXPERIMENTAL STUDY OF TIlE EFFECT OF NOURISHED BEACHES ON DAMPING OF WAVE HEIGHT (2nd Report)

Abstract

In previous paper (1st report), the effect of nourished beaches on damping of wave heightin the condition which a location of submerged breakwater is constant h1=1.5H, (hi: waterdepth at the location of submerged breakwater, Ho: wave height at deep water), have beenevaluated with respect to the relations between the volume of nourishing sand, the dampingrate of wave height and the height of a submerged breakwater.In this paper, the changes of damping rate of wave height with the variation of locationof submerged breakwater for the cases of wave steepnesses O.O1-O04 are revealed in thecondition that the ratio of water depth at location of submerged breakwater h~ and water depthat the crown of submerged breakwater h2 is constant h, /h1~O.2.And the following experimental facts are cleared from the comparison with the rates ofdamping wave height at the same distance from a submerged breakwater in cases of variablelocations of submerged breakwater, in order to do constant the effect of bottom friction.(1) The location of submerged breakwater that the damping of wave height shows themost remarkable effect, differs with wave steepness.(2) In cases of small steepness of wave, the damping of wave height shows the mostconspicuous effect at h1/H, ~LO-1.2.(3) In cases of large steepness of wave, it shows the most notable effect when submergedbreakwaters are located at offshore zone from breaking point and near point of shoreline.It is indicated that the change of wave height with the nourishment of beaches are influencedby the initial condition of incident wave at the location of submerged breakwater, travel dis-tance of breaker and the changing of water depth from these experimental results.