Typhoon Hagibis struck Japan in October 2019, bringing severe damage in the eastern part of Japan due to heavy rain associated with it. The inundation disaster occurred in the area surrounded by Tama River, Maruko River, and Yazawa River, which lies on the border between Setagaya and Ota Wards. In the present paper, the results of the field survey on the distribution of inundation depths in this area were reported, with the description of the physical characteristics of the area and the rainfall and water levels in the Tama River basin during this event. It was found that a large part of the area was inundated, and the inundation depths were larger in the places where the ground elevation was locally lower than the surroundings with the maximum inundation depth of more than 2 m. The distribution of inundation heights indicates that the water was flowing from west to east in this area.

View full abstract

Local disaster management activities such as events are conducted in practice for attaining participation from those at the age of maturity (from 18 years old to 40’s) for promoting community-based disaster management, however, studies on this theme are limited. The aim of this paper is to identify which activities attract what kind of people at the age of maturity. Through a web-based questionnaire survey, it is found that local disaster trainings and the events are highly preferred to. Moreover, those who have high factor scores for disaster management behaviors and who conduct more kinds of disaster management behaviors prefer the trainings, while the events fascinate the mediums, men and those with small kids. Finally, the paper suggests that local disaster management events could be a step of those participants toward facilitating disaster management.

View full abstract

In huge disasters, it's difficult to take a bath in own house. In past, government and nongovernment organizations supported victims by bath-services. However, it's an urgent business to prepare adequate number of bases for bath-support in advance. In this study, we estimated the value that people can take a bath even in the damaged areas, using contingent valuation method (CVM), and compared the results with the cost to prepare supporting bases. As the result, median value of willingness to pay (WTP) was calculated as 7,334 yen, and average value was 20,292 yen. By comparing WTP with the cost for preparation of supporting base, it's expected that values generated by bath-supporting bases are comparable or superior to their cost. According to the results, a measurable validity of preparation for bath-supporting bases using public funds was suggested.

View full abstract

At the time of heavy rain, driftwood accumulates at river infrastructures and blocks a river. Driftwood accumulation results in an increase of backwater. It is well known that driftwood sinks under the water surface and the entire depth region is blocked. However, there is almost no detailed information about the porosity of wood jam and the mechanism that driftwood sinks under the water surface. In this study, two kinds of flume experiments were performed. First, driftwood accumulation experiments at a two-pier bridge were conducted. We examined the effect of the approach flow velocity, approach flow depth and specific density of driftwood on the porosity of wood jam. Then, we conducted PIV measurement to examine the effect of the downward flow on the driftwood accumulation. The experimental results revealed the critical condition for driftwood blocking.

View full abstract

Recent heavy rain disasters in Japan showed the fact that although government issued evacuation information, there were people who did not evacuate. This indicates that evacuation information based on science, which is institutionalized as a decision-making mechanism for government, is not properly utilized by public. This study conducted surveys to residents of Mabi Town, Kurashiki City, Japan, which was severely flooded due to the Western Japan heavy rain of July, 2018. The study tried to identify factors which triggered risk awareness of residents comprehensively, and examined how those factors contributed to evacuation decision-makings using “Evacuation Act Curve,” the method adapted to the “Recovery Curve” surveys. As a result, the study revealed the fact that residents were tend to evacuate based on changes in familiar environment rather than science-based information, which means that disaster information was still not considered as familiar information.

View full abstract