tagryn's musings

This is the sea wall in Taro (Tarou), Japan. It is about 10 meters (30 feet tall). It was constructed after the 1933 Sanriku earthquake when a tsunami destroyed the village. It was regarded as one of the most robust anti-tsunami accomplishments in the world.

Unfortunately, even it was not high enough against this tsunami, and may have actually made things worse:

The 10-metre high walls — more than a kilometre long — gave tiny Taro the feel of a fortified village, impregnable against all comers. But not every one felt so sure. When fisherman Tatsuo Haroki felt the force of Friday’s earthquake, he knew there wasn’t a seawall on earth that was going to save him. He was right: he estimates the waves triggered by the quake that landed on top of Taro were between “12 and 15 metres high.” They just sailed over Taro’s ramparts, he says, and pulverized the village into a mess of matchsticks and a whirling whirlpool that turned Taro into slurry.
[...] In Taro, once the water cleared the seawall and hit the village, it stayed and raged there, having trapped the entire village inside a kind of ‘bowl’ formed by the seawall itself and the mountains behind the village. In fact, it could be said that it contributed to trapping victims and drowning many inside the perimeter’s powerful waters.

Video report on the aftermath in Taro here.
Second report:


There looks to be a major reconsideration of the value of seawalls as tsunami barriers in the wake of the catastrophe. "This is going to force us to rethink our strategy," Yoshiaki Kawata told the New York Times. He is a specialist on disaster management at Kansai University in Osaka and the director of a disaster prevention center in Kobe. "This kind of hardware just isn't effective," he added.

Rikuzentakata. Minami Sanriku. Kesennuma. The list is long. And Taro, as well. There was no mercy, no solace. It came. It killed. It destroyed, pure and true to its nature.
The Tarou sea wall is now...without honor. It failed in its only reason for creation, now destined to serve as a monument to the folly of static defense.

POSTSCRIPT 3-19-11: To be fair, I wasn't sure how a seawall would perform against a large tsunami. Obviously, a 30' seawall going against a 7'-10' tsunami should stop it, while the same wall facing a 100' monster won't make much difference, but it was the middle ground - where the tsunami was larger, but only by a few feet or more - that was murky. I had hopes the walls would effectively "cut the feet out" from under the wave, permitting some spillage over but largely taking out most of the power of the tsunami. However, after watching the video of the '04 Indonesian tsunami, it was clear that many tsunami are not a single big wave, but a series of surges that arrive in quick succession before withdrawing until the next set. In that case blocking one part of the surge would just cause the water to pile up and allow the next surge to build on top of it in a kind of step-and-ladder effect. Unfortunately, it looks like the latter may be closer to what really happens.

UPDATE 6/17/11: Counterpoint, one village where the anti-tsunami barriers worked as intended. Google Maps satellite imagery

UPDATE 2/20/12: Google Streetview has rolled their camera truck through many of the hit areas, including Tarou, Fudai, and Ryoishi, giving ground-level views of the aftermath and cleanup. Taro is especially heartwrenching: the barrier is still there, but there's nothing left behind it to protect anymore except concrete building foundations. In Ryoishi, you can see where a whole section of high concrete barrier was just blasted aside by the force of the wave. Fudai is better: everything from the shore to the barrier is scraped clean, but the barrier did stop the tsunami. Kesennuma is interesting: on one bank it looks absolutely devastated, but on the other side things look perfectly normal. Minamisanriku has wide swaths of nothing but empty ground, also.
I recommend using Streetview in combination with Google Earth for easier scrolling, but Google Maps will work as well.