Lessons Learned from the 2011 Great East Japan Tsunami: Performance of Tsunami Countermeasures, Coastal Buildings, and Tsunami Evacuation in Japan

In 2011, Japan was hit by a tsunami that was generated by the greatest earthquake in its history. The first tsunami warning was announced 3 min after the earthquake, as is normal, but failed to estimate the actual tsunami height. Most of the structural countermeasures were not designed for the huge tsunami that was generated by the magnitude M = 9.0 earthquake; as a result, many were destroyed and did not stop the tsunami. These structures included breakwaters, seawalls, water gates, and control forests. In this paper we discuss the performance of these countermeasures, and the mechanisms by which they were damaged; we also discuss damage to residential houses, commercial and public buildings, and evacuation buildings. Some topics regarding tsunami awareness and mitigation are discussed. The failures of structural defenses are a reminder that structural (hard) measures alone were not sufficient to protect people and buildings from a major disaster such as this. These defenses might be able to reduce the impact but should be designed so that they can survive even if the tsunami flows over them. Coastal residents should also understand the function and limit of the hard measures. For this purpose, non-structural (soft) measures, for example experience and awareness, are very important for promoting rapid evacuation in the event of a tsunami. An adequate communication system for tsunami warning messages and more evacuation shelters with evacuation routes in good condition might support a safe evacuation process. The combination of both hard and soft measures is very important for reducing the loss caused by a major tsunami. This tsunami has taught us that natural disasters can occur repeatedly and that their scale is sometimes larger than expected

An application of k-e model to oscillatory boundary layers

The k-ε model of turbulence is applied to one-dimensional oscillatory turbulent boundary layer flow. Computations are performed over fine meshes extending from the bottom to the outside of the boundary layer. Effects of low Reynolds number are included in the equations of turbulent kinetic energy and turbulent energy dissipation rate. An additional production of turbulent kinetic energy due to the surface roughness is simulated by introduction of a ‘roughness viscosity’ in the production term of turbulent kinetic energy transport equation. Computed turbulent kinetic energy, Reynolds stresses and friction factors are compared with experimental data. Expressions for the friction factor, wave energy dissipation factor and phase shift are obtained

ナミ ト ナガレ ノ カンショウ ニ カンスル キソ ジッケン

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シジュウシダ ダム チョスイチ タイセキブツ キョドウ チョウサ

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ツナミ ケントウ イタク ギョウム

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