New anti-tsunami walls

April 15, 2015

Self-elevating sea walls able to counter tsunami hundreds of meters wide

http://ajw.asahi.com/article/0311disaster/quake_tsunami/AJ201504150067

By AYAKO TSUKIDATE/ Staff Writer

NAGOYA--Researchers say coastal barriers that use the force of waves to elevate automatically, and so spread the impact of tsunami or storm surges, proved effective in simulated tests and could offer an alternative to erecting massive sea walls.

Researchers at Nagoya University performed the experiment in laboratory conditions on April 7 with assistance from Hitachi Zosen Corp. and a number of organizations.

They found that the barriers can handle a tsunami measuring several hundred meters across.

When placed atop conventional sea walls, the so-called flap gates provide additional height and a buffer but do not mar the scenery as long as they remain flat.

Researchers created a scale model of a comprehensive coastal barrier because structures in the past were only capable of dealing with waves of up to around 10 meters across. This limited their use to openings in sea walls and other small spaces.

"This mechanism raises a sea wall just in the nick of time," said Norimi Mizutani, a professor of civil engineering at the Nagoya University Graduate School of Engineering. "So this is the answer that local residents have been looking for because it preserves the scenery but counters tsunami at the same time."

Many municipalities have been under pressure to erect higher sea walls since the magnitude-9.0 Great East Japan Earthquake of March 11, 2011, triggered towering tsunami that devastated coastal areas of the Tohoku region.

However, gaining the consent of residents has been a challenge due to concerns that such massive structures will wreck the landscape.

When water rises and pushes up against the flap gate, the buoyant force raises the structure to form a wall, thus blocking the inundation.

A model with eight panels connected with a metal cable and one-fourth the size of the envisioned design was used for the test.