A lot of important infrastructures are built just behind the seawall line such as port and harbr facilities, airport, roads, railroads and houses. Mean wave overtopping quantity used to be applied as an acceptable value for the design of the coastal protection facilities. However, the damage actually occurs in various places because the estimation accuracy is not so high. The accuracy estimation of time valying wave overtopping quantity at seawall line should be established.
　The paper proposes a new estimation method for wave overtopping damage in a harbor applying wave data observed in an offshore wave observation network NOWPHAS. In the system, the wave profile at seawall line is derived from the computation of non-linear wave transformation in shallow water. The Boussinesq equation model is applied in combination with the energy balance equation model to the numerical model. A wave overflow model is employed to obtain the overtopped water volume from the wave profile at the seawall.
　The estimated wave overtopping rate is compared with the field observation data in a typhoon attack in Kurihama Bay. The good agreement between the measured and estimated wave overtopping rate demonstrates the applicability of the system to another port and harbor using highest observed wave data of NOWPHAS for practical warning and design tools.