In the design of breakwater layout of the harbor, the first priority must be given to maintain tranquility. At the same time, we have to pay attention to keep the water quality in the harbor. We have investigated the functions of breakwaters with channel to exchange water in harbors. In this study, we examined the performance of the breakwater layout and the breakwater with channel in small harbor to maintain tranquility and exchange water in the obliquely incident wave and tidal current. In a three-dimensional wave basin we examined the several cases of the breakwater layout in the model harbor, that is, the width, shape of the entrance, water area in harbor, and so on. We also examined the possibility for predicting waves in harbors of various shape numerically by using experimental results.
In the design of breakwater layout of the harbor, we have to pay attention to some subjects. Those are the tranquility and the water quality, the motion of moored ship in the harbor. The behavior of long period waves also becomes severe problem in some harbors. 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 (Morita and Deguchi, 2001). We also investigated the capacity of the breakwater with channel in the model harbor to exchange water in a longshore current generated by obliquely incident waves (Morita, Yoon and Deguchi, 2003). In this study, we examined the performance of the breakwater layout and the breakwater with channel in small harbor to maintain tranquility and exchange water in the waves and tide in a three-dimensional wave basin (Fig.1).