According to a report by the National Police Agency, 162 cases of water accident occurred for children under 16 years old in 2016. 31 cases were death by drowning. 20 deaths occurred in rivers. 14 deaths occurred not while swimming but playing with water. This implies that drowning frequently occurs in shallow water. One preventive measure is to wear a life jacket, but life jacket use is far from common in Japan.
To show the importance of wearing a life jacket even in shallow water, we conducted an experiment measuring the pushing force applied to a child’s body using a child-sized dummy in a flow-velocity-variable pool. Water speed ranged from 0.5 m/s to 2.2 m/s and the water depth ranged from 10 cm to 60 cm. We measured the pushing force when the dummy was placed in both a standing and seated position at the same water depths.
The pushing force applied to the body increased as the water depth increased and it also increased as water speed increased. For example, the maximum pushing force at a speed of 2.2 m/s was 4.1 kgf in a depth of 30 cm and 14.3 kgf in a depth 60 cm. The pushing force in the seated position was 2.1 to 4.9 times larger than that in the standing position.
We found that the pushing force by streams of water increases as water depth and speed increase, meaning that the force significantly increases when children fall down or move from a standing position to a seated position, even in shallow rivers.