Japan built a wall nearly 400 kilometers long against tsunamis

The magnitude 9 earthquake that shook the Tohoku coast on March 11, 2011, generated a tsunami with waves between 12 and 15 meters. The levees that existed at the time, designed to contain waves up to 8 meters, failed in almost 90 percent of cases. The toll was tragic: more than 20,000 people dead or missing and entire towns devastated, including the area around the Fukushima nuclear plant.

Months later, the Japanese government launched one of the largest infrastructure projects in its history. Today, about 396 kilometers of northeast coast are protected by concrete walls and levees. The planned extensions aim to reach 430 kilometers. The highest sections reach 15.5 meters above sea level and are supported by foundations up to 25 meters deep.

The total cost of the project is estimated to be between 12 billion and 17 billion dollars, almost entirely funded by the state. It is not a single continuous wall, but a succession of segments adapted to each stretch of coast, with widened bases to gain stability against overflow.

The system includes more than 440 automatic gates located in rivers, ports, and bays. These close in less than five minutes without human intervention as soon as the sensors detect an earthquake of a certain magnitude. The declared objective is not to completely stop a tsunami like that of 2011, but to slow the water enough to gain evacuation time.

Background and first real test

Japan has a long tradition of coastal defenses. In Tarō, after the tsunamis of 1896 and 1933, a 2.4-kilometer X-shaped wall 10 meters high was built, which for years was considered a world model. In Fudai, Mayor Kotaku Wamura promoted a 15.5-meter gate in the 1970s despite strong local opposition. That work, ridiculed for decades, proved crucial for the town to suffer almost no damage in 2011.

The new network faced its first real test in 2022. A magnitude 7.4 earthquake off Fukushima simultaneously activated all 443 gates of the system. It was the first time it operated under real conditions since its construction and it succeeded.

However, not everyone celebrates the work. For many residents of the Tohoku coast, the walls up to four stories high have blocked the sea view from their homes. “It looks like the wall of a prison,” said Kazutoshi Musashi, a resident of the port of Osabe whose house is facing a 12.5-meter section.

In Kesennuma, fisherman Makoto Hatakeyama expressed his concern about the environmental impact. Environmental groups and fishing associations warn that a continuously concreted coastline can alter marine ecosystems, harm fishing activities, and also affect tourism in the area.