Proceedings of the SixteenthSeventeenth (2007) (2007) International International Offshore Offshore and and Polar Polar Engineering Engineering Conference Conference Lisbon, Portugal, July 1-6, 2007 Copyright © 2007 by The International Society of Offshore and Polar Engineers(ISOPE) ISBN 978-1-880653-68-5; ISBN 1-880653-68-0(Set); ISSN 1098-6189 (Set) Lessons Lear ned from Recent Stor m Surge Disaster s and Estimation of Extreme Tidal Levels for Coastal Defense Per for mance by Using Stochastic Typhoon Model Hiroyasu Kawai, Shigeo Takahashi, Tetsuya Hiraishi Marine Environment and Engineering Department, Port and Airport Research Institute, Yokosuka, Kanagawa, Japan Noriaki Hashimoto Faculty of Engineering, Kyushu University, Nishi-ku, Fukuoka, Japan Kuniaki Matsuura Metropolitan Regional Office, Japan Weather Association, Toshima-ku, Tokyo, Japan century, and improved it for future climate with a simple assumption. ABSTRACT By using these models, the tidal level with a return period of 10 to 1,000 years was estimated in Seto Inland Sea, Japan. A basic frame of This paper reviews some storm surge disasters that recently occurred in performance evaluation of storm surge defense facilities was proposed Japan, Korea, and the United States due to an intensive typhoon or with three design tidal levels. hurricane. In these disasters an unexpected high tidal level inundated coastal areas on low-lying ground. The possibility that storm tidal level exceeds the design one of storm surge defense facilities should be in- RECENT STORM SURGE DISASTERS vestigated. This paper, therefore, estimates extreme storm tidal levels in Seto Inland Sea, Japan by using a stochastic typhoon model and dis- History of Storm Surge Disasters and Countermeasure in Japan cusses on a basic frame of performance evaluation of the facilities. Each year several typhoons affect Japan and some of them trigger KEY WORDS: Storm surge disaster; typhoon; hurricane; low-lying coastal disaster. The Typhoon Vera in 1959 among them generated a 3.5 m storm surge at Nagoya on the Coast of Ise Bay while the astro- land area; design tidal level; stochastic typhoon model; coastal defense nomical tide level was higher than the mean sea level. High waves on facility. the storm tide level breached shabby dike and inundated a wide low- lying land area below sea level. Much timber in Nagoya Port entered INTRODUCTION the area and destroyed many wooden buildings. The majority of a loss of approximately 5,000 lives over Japan was due to the storm surge In Japan, storm surge defense facilities have been constructed since the flooding. It is the worst storm surge disaster in the history of Japan. storm surge flooding with nearly 5,000 victims due to Typhoon Vera in 1959, yet coastal disaster repeated in 1999 and 2004 with a loss of lives After the disaster the Japanese Government constructed many concrete (e.g. Kawai et al. 2000; Takahashi et al. 2002). In Korea, Typhoon storm surge defense facilities such as storm surge breakwater, dike, and Maemi in 2003 triggered the most tremendous coastal disaster since seawall on the coast of the bays with significant storm surges. The de- Typhoon Sarah in 1959 (e.g. Choi, 2004; Kawai et al. 2005). Also in sign tidal level is generally determined among the following criteria. the United States the storm surge due to Hurricane Katrina in 2005 (1) The mean spring high tide level plus the maximum storm surge breached floodwall in New Orleans (e.g. Takahashi et al. 2006) and measured at a tide station or computed with a standard typhoon took more than 1,800 lives. In these disasters the tidal level exceeded (2) The highest tidal level measured at a tide station defense facilities and consequently their rearward areas were flooded. Hence, the first criterion is adopted for major bays with an enormous The possibility of a higher tidal level than the present design one should population and expensive properties such as Tokyo Bay, Ise Bay, and be investigated and a scenario of the worst disaster is necessary for Osaka Bay. The government chose a typhoon with an intensity of Ty- future disaster mitigation. This paper reviews these disasters and les- phoon Vera for a standard typhoon and simulated the worst storm surge sons learned from them, with the results of our field investigation. in the bays. For instance, Fig. 1 shows the typhoon tracks for Osaka Bay. The design storm surge at the innermost of Tokyo, Ise, and Osaka In Japan, the design tidal level for storm surge defense facilities is de- Bay is 3.0, 3.5, and 3.0 m respectively. Since the design tidal level is termined with a standard typhoon having an intensity of Typhoon Vera. determined deterministically as above-mentioned, its return period is Yet its probabilistic meaning is still unknown because the duration of still unknown. The second criterion is adopted for the central region of tide observation is insufficient for accurate extreme-value analysis on Seto Inland Sea including the coast of Takamatsu City. tidal levels. A stochastic typhoon model, simulating typhoon parame- ters with the Monte Carlo Method, seems one of the useful tools to Recent Storm Surge Disasters in J apan breakthrough the difficulty. This study, therefore, developed a stochas- tic typhoon model based on typhoon statistics around Japan over a half In spite of the defense facilities, storm surge and wave disaster occurred 1792.