Numerical Analysis on Hydraulic Characteristics of Tsunami Overtopping Caisson Breakwaters

The hydraulic characteristics of tsunami overtopping breakwater were analysed using a numerical model to obtain fundamental knowledge for investigating the measures needed against scouring of a rubble foundation and subsoil on the harbour-side of a breakwater due to overflow. Numerical computation was systematically conducted by changing the shape of the parapet, tsunami height, and the presence or absence of wave-dissipating blocks in front of the caisson. As a result, it was clarified that the discharge coefficient of a caisson with parapet is up to about 1.7 times of a rectangular caisson. Wave-dissipating blocks in front of caisson suppress increase in discharge coefficient of a caisson with parapet. An estimation method for the discharge coefficient and the trajectory of the overflow nappe is proposed. Dimensionless parameters used for the estimation were obtained from numerical analysis, and they are summarized in calculation diagrams. An estimation method for the flow velocity impinging to the harbour-side mound based on the theory of the plane turbulent free jet is also presented.