This paper first reviews (1) the storm surge and wave disasters in the coastal and port areas of Osaka Bay and Tokyo Bay in Japan in 2018 and 2019, respectively and (2) two intensity levels of typhoons for coastal defense design and evacuation planning. Then, the paper summarizes their technical issues, such as, the radius of maximum wind speed in worst-case storm surge and wave-overtopping flood simulations. Finally, the paper presents climate change related issues, such as: (1) past mean sea level, typhoon, wave, and storm surge trends, and (2) future climate change adaptation.
Fig. 1 shows that Japan has many cities of more than million people on low plains that extend from the coast of very enclosed bays. These bays are several tens of kilometers from the mouth to the head and have maximum depths of a few tens of meters. They are usually calm but meet storm surges and high waves during typhoon events. In addition, ground-water pumping has caused some parts of the land to sink below the mean monthly-highest water level (hereinafter, HWL) and increased the risk of flooding. The ports on the coast play a core role in international shipping and the country's economy.
Two major storm surge disasters occurred in the 1950s. The 1953 Typhoon Tess crossed the mouth of Ise Bay and triggered storm surge flooding along the southern and eastern coast. This event led to the enactment of the 1956 Coast Act, which requests each prefectural governor to protect coastal areas from tsunamis, storm surges, and high waves. The 1959 Typhoon Vera caused a landfall on Honshu Island (central pressure: 929 hPa) and passed by Ise Bay (940 hPa), generated a storm surge in the bay, recorded 3.5 m at Nagoya Port, causing the collapse of the coastal dike and flooding over the area of 30 km inlands that lasted for 120 days, eventually claiming 5,000 lives. The flood carried much lauan logs from lumberyards in the port and destroyed many buildings. The event prompted the national and local governments to start building massive coastal defense in the 1960s on the coast of Tokyo Bay, Ise Bay, and Osaka Bay for the storm surge of the Vera-class design typhoon (Kawai, 2019).
