At Waku fishing port in Yamaguchi pref., which has a vertical breakwater at the mouth of the port, dissipation blocks were installed in front of the breakwater to reduce the sea water spray caused at the breakwater. In this study, to clarify the effect of dissipation blocks on the reduction of the spray caused at the vertical breakwater, field observations were conducted at Waku fishing port in the winter seasons before and after the construction: the wave run-ups (heights and frequency), the wind (velocity and direction) and the salinity concentrations of the spray at 30 observation points were measured. The observed data showed that the dissipation blocks can effectively reduce the sea water spray caused at a vertical breakwater.
