Seawalls Offered Little Protection Against Tsunami’s Crushing Waves
Published: March 13, 2011
JAKARTA, Indonesia — At least 40 percent of Japan’s 22,000-mile coastline is lined with concrete seawalls, breakwaters or other structures meant to protect the country against high waves, typhoons or even tsunamis. They are as much a part of Japan’s coastal scenery as beaches or fishing boats, especially in areas where the government estimates the possibility of a major earthquake occurring in the next three decades at more than 90 percent, like the northern stretch that was devastated by Friday’s earthquake and tsunami.
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Along with developing quake-resistant buildings, the coastal infrastructure represents postwar Japan’s major initiative against earthquakes and tsunamis. But while experts have praised Japan’s rigorous building codes and quake-resistant buildings for limiting the number of casualties from Friday’s earthquake, the devastation in coastal areas and a final death toll predicted to exceed 10,000 could push Japan to redesign its seawalls — or reconsider its heavy reliance on them altogether.
The risks of dependence on seawalls were most evident in the crisis at the Daiichi and Daini nuclear power plants, both located along the coast close to the earthquake zone. The tsunami that followed the quake washed over walls that were supposed to protect the plants, disabling the diesel generators crucial to maintaining power for the reactors’ cooling systems during shutdown.
Cooling system malfunctions caused overheating and partial fuel meltdowns at two reactors at the Daiichi plant, becoming Japan’s worst nuclear accident.
Peter Yanev, one of the world’s best-known consultants on designing nuclear plants to withstand earthquakes, said the seawalls at the Japanese plants probably could not handle tsunami waves of the height that struck them. And the diesel generators were situated in a low spot on the assumption that the walls were high enough to protect against any likely tsunami.
That turned out to be a fatal miscalculation. The tsunami walls either should have been built higher, or the generators should have been placed on higher ground to withstand potential flooding, he said. Increasing the height of tsunami walls, he said, is the obvious answer in the immediate term.
“The cost is peanuts compared to what is happening,” Mr. Yanev said.
Some critics have long argued that the construction of seawalls was a mistaken, hubristic effort to control nature as well as the kind of wasteful public works project that successive Japanese governments used to reward politically connected companies in flush times and to try to kick-start a stagnant economy. Supporters, though, have said the seawalls increased the odds of survival in a quake-prone country, where a mountainous interior has historically pushed people to live along its coastline.
A fuller picture of how seawalls protected or failed to protect areas beyond the nuclear plants will not emerge for at least a few more days. But reports from affected areas indicate that waves simply washed over seawalls, some of which collapsed. Even in the two cities with seawalls built specifically to withstand tsunamis, Ofunato and Kamaishi, the tsunami crashed over before moving a few miles inland, carrying houses and cars with it.
In Kamaishi, 14-foot waves surmounted the seawall — the world’s largest, erected a few years ago in the city’s harbor at a depth of 209 feet, a length of 1.2 miles and a cost of $1.5 billion — and eventually submerged the city center.
“This is going to force us to rethink our strategy,” said Yoshiaki Kawata, 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.”
Mr. Kawata said that antitsunami seawalls were “costly public works projects” that Japan could no longer afford. “The seawalls did reduce the force of the tsunami, but it was so big that it didn’t translate into a reduction in damage,” he said, adding that resources would be better spent on increasing evacuation education and drills.