Low pre-3/11 tsunami embankments leave 1,300 km of coastline vulnerable


Tsunami embankments are too low on some 1,300 km of coastline in 16 prefectures, according to projections before the Great East Japan Earthquake on March 11, 2011, the Board of Audit reported in a recent survey.

That means one-fourth of the prefectures’ total coastline remains vulnerable to tsunami estimates that were made before the 9.0-magnitude earthquake on 3/11. Nine of the 16 prefectures face the Sea of Japan.

In addition, about 1,500 km of the total coastline either lack embankments or they are of undetermined height.

According to the survey, embankments need to be built on 5,511 km of coastline to protect houses and other structures in the 16 prefectures. At present, only about 2,690 km of the coastline, roughly half the total, are protected by embankments higher than estimated pre-3/11 tsunami heights.

The biggest stretch of vulnerable coastline, at 364 km, was in Hokkaido, accounting for 26.7 percent of all embankments in the prefecture.

On the other hand, more than half of the embankments in Ishikawa Prefecture, covering some 224 km of coastline, were lower than tsunami estimates, while Wakayama Prefecture, facing the Pacific, had 124 km, and Niigata Prefecture 172 km.

The monstrous 3/11 tsunami overwhelmed seawalls and other coastal defenses in Tohoku.