Keitaro TAKAMATSU

Understanding the Occurrence of Water Accidents in Niigata Prefecture Rivers

Naoyuki INUKAI

In Niigata Prefecture, nearly 110 water-related accidents occurred between 2000 and 2022. The purpose of this study is to understand the characteristics of river water accidents that have occurred in Niigata Prefecture, to examine the causes of these accidents, and to gain knowledge for the prevention of future river water accidents.
The total number of river water accidents in Niigata Prefecture from 2000 to 2022 was 30. The ages of the victims were 40% adults, 27% elderly, and 33% minors. The accident rates were 30% in the Uono River, 23% in the Shinano River, and 10% in the Agano River. The causes were fishing (11 cases), working (9 cases), and other (walking) (10 cases). Two types of river hazard areas were identified: fast-flowing areas and areas with unstable footing. Horizontal forces indicate that rivers with flow velocities of 2 m/s or higher are highly hazardous. The sieving test showed that the grain size and angle of repose of the Uono River are larger than those of other rivers. Finally, based on the water level and flow velocity, the rivers were classified based on the degree of danger at the time of evacuation. 
In the upper reaches, the Sanashi River was judged to have water levels and velocities that would allow safe evacuation, while the Mizunashi River and the Daigenta River were judged to be dangerous places for evacuation. In the downstream area, the Daigenta River was judged to be safe for evacuation, while the Sanashi and Mizunashi Rivers were judged to be dangerous. Since the water level and flow velocity change with the amount of water, the level of danger may change due to sudden weather deterioration or dam water releases.