OTOA TSUKANO

Survey and analysis of the drowning accident of three children in the Inunari River, Fukuoka Prefecture

NAOYUKI INUKAI

Regarding the water accident that occurred on July 21, 2023 in the Inunari River in the Toga River system in Miyawaka City, Fukuoka Prefecture, in which three sixth-grade girls died, we examined the cause of the accident based on a field survey conducted by the Japan Society for Water Accidents.
The accident site is: It is the confluence of the Inunari River and the Yamaguchi River. No precipitation was observed on the day of the accident and the survey day. In addition, the interview confirmed that the river conditions were similar, so it is not thought that there will be any impact on the field survey. In this river, it was difficult to understand the depth of the water due to the reflection of sunlight. In addition, the water level at the water entry site was relatively low at about 0.5 m, but gradually deepened as it approached the accident site, and the water depth exceeded 2 m. It is a terrain called "hidden reservoir".In addition, a survey of the bottom of the water was also conducted. The bottom of the water was in a state where it did not collapse even if an adult was caught firmly, but it was easy to slip because there was a short vegetation growing on the bottom of the water. The bottom of the water was collected and the angle of repose was measured. The bottom of the water was a large gravel and the angle of repose was 34°~40°, and the slope of the site was 27°~30°, according to the field survey. In this water accident, the depth of the water could not be grasped due to the reflection of sunlight, the structure was like a hidden reservoir with a rapid increase in water depth, and the vegetation on the bottom of the water made it easy to slip.
In FY2022, there were five water accidents at the confluence of rivers, each of which was characterized by the complexity of the flow and the characteristics of the confluence of the river. On August 13, 2023, a similar accident occurred at the confluence of the Mimengawa River and the Monzen River in Murakami City.
In order to prevent water accidents such as this one, it is considered effective to check the condition of the river, do not allow children to enter the water alone, limit water to below the knees, and wear life jackets.