The authors developed a wave dissipating caisson breakwater having a function of seawater exchange. This caisson is a permeable slit caisson with a submerged vertical plate in a water chamber. This caisson generates a one-way flow from offshore to harbour. This flow enhances the exchange between contaminated harbour water and clean offshore water. Originally, this caisson was intended for calm sea. However, the function of seawater exchange came to be required even for outer breakwaters at large harbours facing rough sea. In offshore areas the width of a caisson must be extended to resist against strong wave forces. Therefore, the caisson needs to have channels piercing itself. In order to make clear its hydraulic characteristic, a two-dimensional hydraulic model experiment was carried out. It revealed that the channels never spoiled the seawater exchange, even in the condition of smaller wave height.

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In open sea region with severe wave attacks, a breakwater covered with wave-dissipating blocks have been widely used. However, the application of this breakwater at greater depths implies the increase of construction costs because it requires a large quantity of wave-dissipating concrete blocks. Therefore, the authors developed a new type of breakwater. This breakwaterconsists of wave absorbing caisson and sloping top caisson. In this paper, through the sliding experiment of this new type breakwater using a 1/60 model, we prove the stability and define the hydraulic characteristics of this breakwater.

Recently, it has increased the case to be constructed the breakwaters where thewater depth is deeper and the wave height is greater. The authors developed a new type of breakwater.This breakwater consists of wave absorbing caisson and sloping top caisson. Through the model experiments,the wave force formula, the reflection coefficient, and the wave overtopping quantity weredefined. However, it was not defined the relation between the crown height and the transmission coefficient ofthis breakwater. When the crown height of the breakwater is higher it can be tranquil. Otherwise, thebreakwater width must be extended because of the wave force increased. Then, it is important to define therelation between the crown height of the breakwater and the transmitted wave height and find theappropriately crown height of the breakwater.In this paper, the authors carried out the experiments for several types ofbreakwaters by using irregular waves, and defined the formula for the transmission coefficient and the crown height of the breakwater to be required.

Recently, it has been necessary the purification of basin water in port and harbor for utilizations, such as live fish preservation facilities and amenity space. Therefore, various types of water-exchange breakwater by wave energy, tidal current and sea level exchange have been developed. The authors developed a wave dissipating caisson breakwater having a function of seawater exchange. This caisson is a permeable slit caisson with a submerged vertical plate in a water chamber, and generates a one-way flow from offshore to harbor.In this paper, through the field investigation, we proved the water inlet ability of this water-exchange breakwater that was constructed in MISAKI fishing port, and compared the result of the hydraulic model test with the result of the field investigation.