Seawalls Offered Little Protection Against Tsunami’s Crushing Waves (NYT)

[somone]

http://www.nytimes.com/2011/03/14/world/asia/14seawalls.html

Seawalls Offered Little Protection Against Tsunami’s Crushing Waves
By NORIMITSU ONISHI

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.

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...

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...

[Paradoxical]

1. There is nothing humans can build that will stop a 30 foot tall tsunami.

Unless they plan on lining the coast with man-made mountains.

[aquart]

2. What would the tsunami have taken out without the seawalls?

[ProgressiveProfessor]

3. That is the better question.

Undoubtedly they helped, but how much