Present and future tsunami and storm surge protections in Tokyo and Sagami bays

On March 11, 2011, a large earthquake that occurred offshore the northeast coast of Japan generated a large tsunami which devastated extensive areas of the Tohoku coastline and large casualties were recorded. Based on the experiences, coastal protection works in Japan are now in the process of modifications. In the present paper, Tokyo and Kanagawa are taken as examples and new methodologies are explained in the area. For the case of storm surge, a new model is applied to predict the future behavior of storm surge. For the case of tsunami, Genroku Kanto Earthquake (1703), Keicho Earthquake (1605) and Meiou Tokai Earthquake (1498) were mainly discussed in the numerical analysis, since tsunamis caused by these three earthquakes gave strong damages to coastal area of Kamakura, and left influences to Yokohama and Tokyo. New tsunami flood maps over coastal land area based on numerical simulations were presented to the residents of coastal region on April 2012 in Kanagawa prefecture. For Kamakura area, Keicho Earthqueke takes 90 minutes to reach the Kamakura coast and the height is over 12 m. But for the case of Genroku Kanto earthquake it takes 25 minutes and the height is 8 m. It appears that there are two different types of risk, 1) high wave comes but we have time for evacuation and 2) relatively small wave comes quickly and time is limited for evacuation. New countermeasures including soft and hard techniques are also required.