Takamatsu, Tamano and other cities were inundated by the storm surge due to Typhoon Chaba in2004, although the typhoon was not an extremely strong and large typhoon comparing to theprevious typhoons which attached Kyushu Island and the Seto Inland Sea. The combination of thestorm surge and high spring tide caused high sea level along these coastal cities.
　On-site investigations on the inundation indicated that seawater flowed into the land from theareas where the ground level and the height of defense structures were low, then moved to inlandlower-lying areas quickly, and finally gathered the lowest area. In Takamatsu city, especially, thestorm surge without high waves caused no structural damage. In Tamano city on the opposite side ofthe Seto Inland Sea, the high wave on the storm surge destroyed some facilities and houses incoastal areas.
　The numerical simulations on the storm surge were conducted with using a popular numericalmodel of storm surge. Two cases in which the variation of astronomical tide was considered or notwere calculated. The computed storm surge was, however, lower than the observed one in each case.To improve the accuracy of the storm surge, it is necessary to reproduce more accurately the windfield over the Seto Inland Sea. The coastal flooding in Takamatsu city due to the storm surge wasalso calculated with fine numerical grids of the 25m spacing. Adjusting the sea level along the coastto the observed level, the computational result on the inundation was good agreement with theactual inundation.
　To minimize the loss of human lives, we have to improve regional defense level with theintegration of structural and nonstructural measures. To integrate them, we can use effectively thenumerical simulation to express the damage due to storm surge.