2019 Volume 75 Issue 2 Pages I_7-I_12
Installing floodgates and movable breakwaters ―such as flap gates and self-elevating seawalls at the opening of a port― are attracting attention as effective countermeasures against tsunamis and storm surges. However, a previous study revealed that inflow of seawater takes place through small gaps in the movable gates. Additionally, it is necessary to consider intrusion from the other parts, as these floodgates are used in combination with existing structures such as breakwaters and coastal dykes. In particular, a breakwater consists of a rubble mound, and thus there is a concern that tsunamis and storm surges will enter the port through the voids between stones when different water levels occur on each side of the breakwater. Because this risk has yet to be adequately recognized by engineers, an inflow rate assessment method has not been established to date. In this study, a method for evaluation of the inflow discharge through a breakwater mound by conducting a hydraulic experiment and numerical analysis is proposed. As a result, it was identified that seawater inevitably enters a port through the porous rubble mound when tsunamis and storm surges occur. In particular, it was found that a long-period wave tends to be less attenuated even if the opening is perfectly enclosed by floodgates.
