Experimental researches on the tsunami in the laboratory have been conducted using various methods. The use and techniques of tsunami wave generator depend on the objective of the tsunami observation to be conducted. When the objective is the scouring at the downstream of a seawall, the use of a short flume with control discharge seems to be appropriate. A valve with a mechanic controller was equipped to control the discharge from a reservoir into the flume. A numerical simulation of discharge into the flume and the overflow above the seawall was conducted to determine the dimension of the tsunami flume and its generator before construction. The experiments were conducted to simulate the hydrograph of tsunami overflow above the seawall model. The numerical hydrograph is found to be comparable with the experimental hydrograph. This indicates that the tsunami wave generator is capable of simulating tsunami hydrograph and ready for further use of simulations.

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Many coastal structures or structures in coastal areas were destroyed by a tsunami attack. Such destructions were due primarily to the fact that such structures were not designed to withstand a tsunami. Those which were designed to withstand tsunami force may also have been destroyed due to some damaging factors which were not included in the design. The damage of the coastal structures is one of the important factors that have caused casualties. Especially, when the destroyed structures were originally aimed to mitigate the area against tsunami, they may cause higher fatalities. Examples of such structures are sea walls in many parts of Japan which were destroyed by the 2011 tsunami. This paper discusses the important factors relevant to the damage of seawall as tsunami mitigation structure such as impact force due to tsunami front, hydrostatic force, and hydrodynamic force, debris force and scour due tsunami. The study was carried out based on literature about the damages of seawall as tsunami protection structures and laboratory experiment reports. The destructions to the structures were divided into three classifications namely instantaneous direct destruction due to impact and drag forces, slowly direct destruction due to drag force, and slowly indirect destruction due to scour. Finally, important aspects to be considered in the design of seawall as tsunamis protection were proposed.