Why Has the Thai Flood Lasted So Long?

NASA Photo Comparing Thai Floods of 2008 and 2011
NASA Image comparing the flood zones of Oct. 25, 2011 (top) and Nov. 11, 2008 (bottom). Bangkok and the Chao Phraya River are marked to the south.

Why Has the Thai Flood Lasted So Long?
Yomiuri Shimbun: タイ大洪水、なぜ長期化?
Mashi Arai reporting from Bangkok October 27, 2011

The submerged land area in Thailand is still expanding, and the flooding is becoming a long term problem, because the amount of rain is unprecedented and the affected area has gentle terrain.

According to the Thai Weather Bureau, this year’s rainy season (May to October) there was 50% more precipitation than usual in the area of the Chao Phraya River, which connects the north and south of the country. It was the most rain in 60 years.

According to Mr. Akira Terakawa’s analysis of the river environment for the Ministry of Land, Infrastructure, Transport, and Tourism, the industrial parks which host several Japanese businesses in the Ayutthaya Region and surrounding environs, now in the center of the flood zone, were designed to handle one big rainfall every ten years; this year’s mass precipitation was unexpected.

As opposed to Japan, whose steep terrain causes water to flow away quickly, Thailand has gentle terrain and slow-flowing rivers.

This weekend, a high tide is expected in the Gulf of Thailand, which will make it more difficult for river water to approach the sea.

If floodwater were to breach Bangkok for the first time, it would arrive in a calm flow, not a quick push.

Once the water arrived, however, removing it would take time. Rangsit University Associate Professor of Civil Engineering Seri Supharatid predicts that “if there were full-scale flooding in Bangkok, it would take more than a month to remove the water.”

Original/原稿:
タイ大洪水、なぜ長期化?

NASAが公開した、タイ中部の洪水被害の拡大を示す画像=NASA提供

 【バンコク=新居益】タイで大洪水による冠水が広がり被害が長期化しているのは、例年以上に多い降水量と、なだらかな地形のためだ。

 タイ政府当局によると、今年は5~10月の雨期に、国を南北に貫くチャオプラヤ川の上流地域で、平年より約5割多い雨が降った。過去60年で最多の雨量といわれている。

 タイで洪水を調査している寺川陽・国土交通省河川環境評価分析官によると、多数の日系企業が入居する中流域のアユタヤ県などの工業団地は、10年に1度の大雨に耐えられるよう設計されており、今年の大雨は想定外だった。

 地形が険しく川の流れも速い日本とは異なり、タイの国土はなだらかな地形で、川の水は元々、緩やかに流れている。

 今週末には、タイ湾で大潮を迎え潮位が高くなるため、川の水は海に向かって流れにくくなる。

 首都バンコクで本格的に冠水が始まっても、急流が一気に押し寄せるのではなく、穏やかな水の流れとなりそうだ。

 ただ、いったん水があふれ出したら、引くまでに時間がかかる。ランシット大学のセリー・スパラティッド准教授(土木工学)は「バンコクが本格的に冠水すれば、水がなくなるまで1か月以上かかる」と推測する。
(2011年10月27日09時58分 読売新聞)

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