Ten years have passed since the damage caused by the huge tsunami that occurred in the 2011 Great East Japan Earthquake, and the actual situation has been elucidated and future tsunami countermeasures are being discussed. First, regarding the tsunami generation mechanism, inverse analysis is performed using not only seismic motion and geodetic data but also tsunami waveforms, and characterization of the tsunami fault model has been proposed for future evaluation. At that time, the Japan Meteorological Agency announced a tsunami warning, but there were some issues to underestimate the tsunami heights.Therefore, research such as real-time observation and improvement of prediction technology is now being energetically conducted to solve this problem. The behavior of the huge tsunami recorded in the photographs, videos, and survey data at that time and its damage were overwhelming. The multiple, complex and chained damage process related to tsunami is introduced and the classification of incentives and predisposing factors for tsunami disasters, which will be useful for future disaster countermeasures. In particular, this time, new disaster types such as topographic changes, tsunami fires, and “black tsunamis” are reported. In the future, it will be important to simulate and evaluate such tsunami-related disasters, and research is being conducted to overcome the problems of conventional methods by utilizing the data obtained in the 2011 tsunami. Immediately after the great earthquake, two levels of tsunami countermeasures and the “Tsunami Disaster Prevention Town Development Law” were proposed by the national government, and efforts are being made to reduce repeated disasters. Now, it is important to obtain a consensus on the safety level in advance so that it can be reflected in the preliminary reconstruction plan.

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The tsunami damage due to the 2011 Tohoku earthquake were summarized, and the preparedness for the Nankai Trough earthquake tsunami was discussed. In the disaster, underestimation of the assumed tsunami and tsunami warning, delay in damage evaluation, and tsunami-related phenomena (sediment transport, topographical change, drifting objects, disaster debris, evacuation behavior, etc.) caused to increase the damage. After the disaster, assumption of the maximum class tsunami has been introduced, and numerical analysis and observation system of tsunamis have been developed. They make progress to prevent underestimation of tsunami warning and to grasp the damage promptly. However, there are still some problems to be solved in tsunami warning, such as tsunami earthquake, heterogeneity of tsunami source, and its cancellation. In addition, there are some technologies that have not yet been utilized in the real field of disaster. It is necessary to continue efforts to improve disaster management capabilities.

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This research aims to examine the validity and sustainability of promoting schoolbased disaster risk reduction through collaboration with family, community, and other related individuals and organizations by taking Yokohama City Kita-Tsunashima Elementary School as an example. The school introduced the School Management Council System (known as “Community School,” CS) and has continuously engaged multiple stakeholders outside the school in the school management. The study collected related materials such as the transition of the 10th year mid-term school management policy and conducted a field survey during the joint community disaster drill at the school. As a result, the study found that CS, which is an existing system in the Japanese education sector, a valid and sustainable framework, and that Kita-Tsunashima’s superb cooperation among schools, families, and communities by exercising their strengths may be a role model for other schools and communities for the disaster risk reduction. It demonstrated the accumulation of practices applying the CS framework with disaster activities at its priority brings about sustainable neighborhood planning and disasterrelated capacity development for the members of the community as by-products of the CSbased practices.

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Due to Typhoon No. 19 in October 2019, heavy rainfall (300-500 mm) fell in large river basins from the Kanto/Koushin region to the Tohoku region. The heavy rains caused extensive flooding, which resulted in broken embankments and an widespread inundation in the river basins of each region. In addition to the loss of life, extensive damage was caused to residential and industrial areas in eastern Japan. This study investigated the present condition and damage caused by the floods by examining the current status of embankments and revetments along the Chikuma River. In particular, breakage of the Sakurazutsumi (sokutai) embankment needs to be structurally analyzed in the near future. The other side, a survey of sediments and fruit trees showed that the floods caused extensive sediment deposition. The findings showed that too many trees were planted, increasing sedimentation and preventing the drainage of floodwaters. These results are important for river management. This study considered river segment analysis and river management within the context of geology, topography and river engineering. In addition, this report applied hydraulic analysis to river management and estimated factors affecting flood damage using field surveys and government data. The goal of the study was to clarify how flood damage to embankments can be mitigated in the future.

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Around 1:30 am on September 7, 1898, heavy rain brought about by a typhoon caused a debris flow in Yato Area of Oizumi Village (Hokuto-city Yamanashi) at the southern foot of Yatsugatake. Consequently, 57 were killed, and 51 were injured. The author identified the locations of the damaged houses based on the “Storm Damage Investigation Report” compiled in the Meiji era and archived in the Imperial Household Agency, and the records of the land register stored in the Legal Affairs Bureau. It was found that most of the damaged houses had been located along an agricultural canal that flowed through the village. The author also compared the distribution of damaged houses in the disaster area with the results of debris flow simulations, which was made using the Hyper KANAKO system, and found that the local topographic features were the primary cause of the concentration of victims in a specific group of houses.

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In the event of an earthquake in the Nankai Trough, chemical substance may leak from the facilities and flow out into the Yodo River. One of the problems is the water intake trouble due to chemical substance distribution and contamination of the water in purification plants as the Tsunami runs up the river over the barrage. In this study, the chemical substance transport was analyzed by 3D density current analysis method and the influence on water intake was examined in Yodo River during a Tsunami attack. As a result, the quantity of chemical substance reaching the plant was predicted. Moreover, it was evaluated that water intake may be affected. In conclusion, Analysis by this method was proven to be necessary to predict accurately chemical substance behavior due to river run-up Tsunami.

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In 2011, Japan suffered from the tsunami that was beyond expectations due to the Tohoku Earthquake. Therefore, it is necessary to take countermeasures against tsunamis caused by various factors including landslides. In this study, the three-dimensional fluid-rigid body coupled analysis method of Yoneyama et al. was applied to a simulation of the past hydraulic model experiments on tsunamis generated by landslides in order to verify its validity. As a result, the time-series waveforms and the maximum and minimum water levels of tsunamis were consistent with those of the experiments in all cases of subaerial landslides. In the case of submarine landslides, the first wave and the second wave of the time-series waveform roughly match with those of the experiments. Moreover, the waveform shifts with the passage of time, and the time-series waveform oscillates in a short cycle.

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