The aim of this study is to investigate the capacity of the breakwater with channel to exchange water in longshore current generated by obliquely incident waves and to propose numerical model for predicting the capacity. We examined the performance of the breakwater with channel of the model harbor in a three-dimensional wave basin by generating the longshore currents under the incidence of regular and irregular waves. The applicability of the proposed numerical model was also examined using experimental results. It is found that the time required to exchange whole water in the harbor of the regular wave test can be estimated from the water volume in the harbor, the representative longshore current velocity induced by regular wave, and the opening ratio of the channel in the breakwater. The capacity of the breakwater with channel to exchange water induced by irregular wave can also be estimated by using the significant wave height for evaluating the velocity of longshore current.
Deterioration of water quality becomes severe problems in some harbors because the circulation of water in the enclosed region by breakwaters is weakened and exchange of water becomes inactive there. We focused on the function of breakwaters with channel to exchange water in harbors, because submerged breakwaters and floating breakwaters are not effective to maintain harbor tranquility in spite of their merit for exchanging water. We have already shown that breakwaters with slope-type channel and step-type channel effectively reduce transmitted wave height when compared with a straight-type channel (Morita and Deguchi, 1999), and the flow rate through the breakwater with channel can be estimated by applying the non-linear Darcy''s law. We also investigated the capacity of the breakwater with channel in the model harbor to exchange water in uniform flow (Morita and Deguchi, 2001).