Diver Swept out to Sea

Video of diver being swept away (in Japanese)

Lake Hamanako, in Shizuoka Prefecture, Japan, is well known for its high number of boating and swimming accidents. On July 27th, at the point where the lake empties into the sea, the nation’s first live drift experiment was held, using both dummies and human beings. Japan has a very complex aquatic environment, where fresh and salt water come into frequent contact. Even in this land of brackish water, Lake Hamanako has more than its share of accidents. The experiment is intended to contribute to the prevention of maritime accidents.

Dummy at mouth of Lake Hamanako

The experiment was conducted by the Japan Hydrographic Association with the support of The Nippon Foundation. At a little past two in the afternoon, a diver wearing a life jacket leapt from a boat moored in the lake. In no time at all, he was swept away from the boat. He moved so quickly that it appeared almost as if the boat had started its engines and driven away. Within 15 minutes he was swept 1.2 kilometers away to the ocean. Another diver with fins on his feet attempted to swim against the current, but made absolutely no progress.

Diver being swept out to sea

The speed of the current at the mouth of the lake ranges from 1.5 to 2 meters per second. This is about the speed of an Olympic swimmer, and at the mouth of the lake where fresh water meets salt, the waves are particularly large and unpredictable. The boat from which the video was taken was strongly buffeted by the waves, and the diver who was swept to the sea commented that he was in the ocean before he knew it.

Professor Aoki Shinichi

According to coastal engineering professor Aoki Shinichi of Toyohashi University of Technology, who was present at the experiment, Lake Hamanako has both a large tidal flow and a narrow entrance, making its currents particularly fast and dangerous. According to the Japan Hydrographic Association, from 1997 to 2007 the lake saw 22 accidents involving small craft, swimmers or fishermen. The number is particularly high when compared with similar lakes in northern Japan, which experienced only 2 or 3 accidents in the same time.

Photo taken by the diver who took part in the experiment

In addition to measuring the speed of the complex currents, the experiment included videos of dummies, people and markers dropped in the water at various points. The same experiment will be conducted again in August in Hokkaido in Northern Japan and a report covering the results of both experiments will be distributed to water safety personnel and institutions throughout the country.

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