A road is flooded with seawater in a coastal area of Ishinomaki, Miyagi Prefecture, on June 17. (Mainichi)
Fears of flooding and mudslides have arisen in coastal areas of northeastern Japan whose terrain sank during March 11’s magnitude 9.0 earthquake as this year’s rainy season looms.
Some areas have already been exposed to flooding during high tide, and it is feared that heavy rainfall could increase the danger. At the same time, soil in many areas remains unstable, raising fears of mudslides during heavy rain.
The Sendai District Meteorological Observatory predicts that the Tohoku region will enter the rainy season soon and residents remain uneasy. A survey by the Geospatial Information Authority of Japan found that about 56 square kilometers of land in three prefectures in northeastern Japan lay below sea level after the earthquake — 3.4 times more land than before.
On June 20, authorities in the Miyagi Prefecture city of Ishinomaki, which sank as much as 1.2 meters in the quake, released a “risk map” on the municipal government’s website showing areas in danger of flooding in three basins in the facility.
The map indicates that up to 1,500 hectares of land could be flooded if 100 millimeters of rain fell on the city over a 24-hour period. A total of eight shelters lie within this area. The municipal government will use 12 pump trucks to control flooding, including seven borrowed from other municipalities.
Immediately after the quake, as many as 2,260 households in Ishinomaki were exposed to flooding at high tide. The city decided to build banks and place sandbags to keep the water out, and has half-completed the measures. With the use of pumps, the number of flooded households was reduced to about 1,260.
At the home of one 35-year-old resident of the city, seawater came only as far as her doorstep, but she remains concerned about the rainy season ahead.
“I don’t know what could happen during the rainy season,” she said.
Local authorities are taking action to address the situation. In the Iwate Prefecture city of Rikuzentakata, which was wiped out by the tsunami following the March 11 quake, seawater came as far as the area near National Route 45, some 300 meters from the shore. The Ministry of Land, Infrastructure, Transport and Tourism accordingly constructed a one-meter-high wall along the road as an emergency measure.
The Ministry’s Tohoku Regional Bureau also revised its flood prediction and warning standards for 16 rivers in Miyagi Prefecture ahead of the rainy season, lowering the water level at which evacuations are recommended. It has also set up water measurement sensors at 21 locations, and from the end of June, it will e-mail flood warnings to residents who register in advance.
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(Mainichi Japan) June 21, 2011