SIMULTANEITY OF MAXIMUM STORM SURGE AND WAVE CAUSED BY TYPHOON IN TOKYO BAY, JAPAN

摘要

In the present design of coastal defense facilities in Japan, the combination of the maximum storm surge and significant wave height by a particularly violent typhoon is often adopted as the design condition. The safety degree is evaluated by the safety factor or the wave-overtopping rate for the design condition. However, the maximum storm surge and significant wave height do not necessarily appear simultaneously. The magnitude of coastal defense failures is related to the duration of the storm. To solve these problems, the storm surges and waves in Tokyo Bay, caused by the major typhoons over the past four decades and the model ones based on the Isewan Typhoon, are simulated by numerical model. The result is such that the time difference between the maximum storm surge and significant wave height varies with the typhoon condition. The mean time difference ranges from -2 to +1 hr, being related with the location in the bay. The mean storm surge and wave duration is respectively about 10 and 15 hr in the past typhoons and about 5 and 10 hr in the model typhoons. The time difference being 1 hr, the maximum wave-overtopping rate of a typical seawall may become less than half, the amount during a storm near a quarter. As mentioned above, the time difference and the duration are very important to evaluate the performance evaluation of coastal defense facilities.