Knowledge Notes, Cluster 1: Structural Measures
Japan’s Tohoku region built 300 kilometers of coastal defense over the course of 50 years. National and local governments invested a total of $10 billion to build coastal structures and breakwaters in major ports. During the Great East Japanese Earthquake, the defensive structures along the coast suffered unprecedented damage: 190 of the 300 kilometers of coastal structures collapsed under the tsunami. In some areas they did serve to delay the arrival of the waves, buying extra minutes for people to evacuate.
Because many tsunami gates designed to reduce flooding along rivers were toppled, the Government of Japan launched a structural assessment to better understand the causes of failure. The assessment concluded that construction standards and stability performance under worst-case scenarios should be further investigated. Structures should be able to withstand waves that exceed their design height, reducing the force of the water before they collapse and thereby mitigating damages.
Thanks to Japan’s strict and rigorously enforced building codes, earthquake-related losses from the March 2011 disaster were limited, with most of the deaths and economic damage being caused by the ensuing tsunami. A multilayered approach to DRM is needed, employing both structural and nonstructural measures. Defensive infrastructure alone is not enough to cope with infrequent disasters of high impact. Nonstructural measures also need to be established, including early-warning systems, rigorous planning and regulation, prompt evacuation of residents, and a variety of institutional and financial measures, such as insurance, rehabilitation funds, and emergency teams.
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