The aim of this study is to investigate the flow rate through the breakwater with channel and the capacity of the breakwater to exchange water under various flow conditions. First we examined the flow velocity through the breakwater with slope channel and straight channel by experiments and developed a numerical model to investigate the effect of channel in two-dimensional wave flume. Then we examined the capacity of the breakwater with channel of the model harbor in a three-dimensional wave basin. Applicability of the proposed numerical model was also examined using experimental results. Main results obtained in this study are summarized as follows:
The flow rate through the breakwater with channel can be estimated from the non-linear Darcy's law where the difference between the water surface levels in and outside of the harbor plays an important role.
The time required to change whole water in the harbor can be estimated from the water volume in the harbor, the representative current velocity around the harbor, and the opening ratio of the channel in the breakwater.
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. In the design of breakwater layout of the harbor, the first priority must be given to maintaining Wanquility. At the same time, we have to pay attention to keep the water quality in the harbor. Submerged breakwaters and floating breakwaters have an advantage of exchange of water when compared with the impermeable breakwaters. However, they are not effective to maintain harbor tranquility. We have already shown that breakwaters with slope channel and step-type channel (see Fig.l) effectively reduce transmitted wave height when compared with the breakwater with a straight channel (Morita and Deguchi, 1999).
