Tonegawa flooding could kill up to 6,300

Up to 6,300 people would die during massive flooding in the Tokyo area if a dyke lining the Tonegawa river were to break, according to a report released by the government's Central Disaster Management Council.

The worst-case scenario in terms of deaths would be a breach of a dyke in Koga, southern Ibaraki Prefecture, coupled with slow evacuation of residents and improperly functioning drainage facilities.

If a dyke broke in Otone, Saitama Prefecture, on the south bank of the Tonegawa river across from Koga, wide areas in the Tokyo metropolitan area would be submerged, killing as many as 2,600 people and stranding up to 1.1 million people, according to the report.

It is the first time the government has compiled a flooding-damage assessment.

Although the death toll would vary depending on the location of flooding and the ability to respond in such a disaster, the report aims at improving countermeasures against massive flooding of urban lowland areas following the 2005 Hurricane Katrina disaster that swamped New Orleans and other areas on the U.S. southeastern coast.

The council's assessment is based on the assumption that a huge disaster, which would occur once every two centuries, hit the Tokyo metropolitan area.

The scale of rainfall for the scenario was based on records from Typhoon Kathleen in 1947, which left 1,930 people dead or missing. It was the worst storm to hit the metropolitan area after World War II.

If a dyke broke in Koga, water levels would reach 5 meters or higher. There are few tall structures in the area where people could evacuate to safety.

If a dyke broke in Otone, floodwater would likely reach Tokyo's Katsushika Ward in two days, leaving a combined 900 people dead in that ward and neighboring Adachi Ward.

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