4.4.6.3 Considerations on Tsunami countermeasures and evacuation
1) Considerations on Tsunami Countermeasures
According to the final report of the Countermeasures for Earthquakes and Tsunami Based on the Lessons Learned from the 2011 Off-the-Pacific-Coast-of-Tohoku Earthquake, considerations on Tsunami countermeasures are discussed and summarized , .
First of all, as a premise, a tsunami is categorized into Level 1 (L1) and Level 2 (L2) when the scale of and measures against tsunami are considered. For the largest-scale L2 tsunami, which occurs extremely rarely but produces immense damage like the last one, every possibility, including the maximum levels, shall be considered. Consequently, comprehensive measures against tsunami shall be established that give priority to the protection of the lives of residents and that implement every possible measure for the evacuation of residents. For the L1 tsunami, which occurs comparatively frequently and where the height is low but produces serious damage, coastal protection facilities shall continue to be developed and improved from the viewpoint of protection of the property of residents and stabilization of economic activities in the local areas, in addition to the protection of human life.
A basic principle for the mitigation of damage caused by L2 tsunami is to combine tangible and intangible measures. Especially in the areas that are at risk of being hit by tsunami soon after an earthquake, the town shall be designed to ensure that residents evacuate in about five minutes. To be concrete, the following are suggested:
- designation of tsunami evacuation buildings and improvement of evacuation sites and routes to establish a system that enables smooth evacuation.
- multilevel protection by the development of coastal protection facilities with a persistent structure and a second bank utilizing road embankments to mitigate the damage from floods and secure time for evacuation and, as a result, to construct towns which are resistant to earthquakes and tsunami.
- construction of administration-related and welfare facilities in a place where the risk of flooding is low,
- organic liaison between a local disaster prevention plan and city planning to promote the development of safe towns from a long-term perspective.
- improvement of hazard maps to ensure evacuation on foot and an emphasis on the necessity for evacuation in order to improve awareness of disaster prevention in the case of tsunami.
2) Considerations on Tsunami Evacuation
A working group established by the Cabinet Office to study tsunami evacuation measures had a careful discussion and came up with the following basic ideas for tsunami evacuation .
It is important to recognize that tsunamis are a natural phenomenon, and that there is always a possibility that a tsunami will strike.
Quick evacuation is the most effective and important tsunami countermeasure. In addition, structural measures, such as the construction of coastal protection facilities, and non-structural measures, such as reliable information dissemination, should all be positioned as measures to support quick evacuation.
- In order to reduce the casualties caused by tsunamis, prompt and proactive evacuation actions by individuals are fundamental.
- It is important for residents to evacuate to a higher place as quickly as possible, assuming the maximum tsunami height in the case of an earthquake with strong or weak but long tremors. In doing so, it is important to aim for the highest and safest place possible as long as there is time to spare.
- In order to ensure that tsunami warnings, evacuation advisories, and instructions – which are important triggers for evacuation actions – reach the residents, it is necessary to enhance and strengthen the information delivery system.
- Coastal protection facilities should be built according to the local conditions to cope with relatively frequently occurring tsunami heights and to protect the community from tsunamis as much as possible. For this reason, it is necessary to make efforts for appropriate maintenance and management of coastal protection facilities so that they can fully function as coastal protection facilities, etc., as well as to promote technological development of structures that can persistently function even when conditions exceed the coastal protection facilities, etc., and to develop them.
- In order to improve the feasibility of evacuation, it is necessary to develop evacuation sites, evacuation routes, evacuation stairs, tsunami evacuation buildings, tsunami evacuation towers, and other evacuation-friendly environments in conjunction with urban development, aiming to cope with the largest class of tsunami.
- In view of the fact that it takes time to build coastal protection facilities and that measures to deal with relatively frequent tsunami heights are still insufficient, it is necessary, as a provisional measure, to secure evacuation sites as high as possible, along with evacuation routes/stairways, tsunami evacuation buildings, and tsunami evacuation towers, etc., to deal with at least relatively frequent tsunamis. It is necessary to make steady progress.
- In cities, towns, and villages that are expected to be inundated by tsunamis, it is necessary to promptly formulate specific evacuation plans in consideration of local conditions.
- It is necessary to evaluate the level of safety achieved in the region, such as the status of coastal protection facilities and the safety of evacuation sites against the largest class of tsunamis, and to inform the residents.
- In order to promote disaster prevention education that fosters the attitude to take proactive evacuation actions, disaster prevention education for children and systematic disaster prevention education through cooperation among government, schools and communities are necessary.
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