10/04 50 years of effort swept away / Tsunami wiped out dikes, breakwaters that took decades to build

The Yomiuri Shimbun

Municipalities along the Sanriku coast spent decades building larger, stronger breakwaters to keep deadly tsunami out. However, many dikes and breakwaters--even the world's deepest--were simply swept away or left in ruins by the massive March 11 tsunami.

Minami-Sanrikucho, Miyagi Prefecture, had been strengthening the town's defenses against tsunami for about 50 years. The destruction caused by a tsunami in 1960 prompted the town to build coastal breakwaters and floodgates that could block a 5.5-meter-high tsunami.

In 1995--the year of the Great Hanshin Earthquake--the Minami-Sanrikucho government constructed a three-story building that housed disaster-prevention headquarters. The ferroconcrete building was equipped with improved wireless telecommunications and water level-measurement devices.

Each year on May 24, the date the 1960 tsunami hit the town after speeding across the Pacific after the Chile quake, the town government held disaster-prevention exercises. Residents were drilled on how to prepare for a tsunami--and react when one is on the way.

However, these efforts were largely toothless in the face of last month's tsunami. About 70 percent of the homes and other buildings in Minami-Sanrikucho were reduced to piles of debris. The town's breakwater floodgate was destroyed, and signs indicating water levels during a 1960 tsunami caused by an earthquake off Chile were knocked to the ground by the water.

The raging waters even reached the roof of the disaster-prevention building. Only a few of about 40 town government officials survived.

"If the town government is told to compile a disaster-prevention plan based on the latest tsunami, we don't have the resources to do that," Minami-Sanrikucho Mayor Jin Sato said. "This is an opportunity for individuals to think about disaster prevention. If a tsunami hits, the only thing to do is escape to higher ground."

The Miyagi prefectural government had strengthened disaster-prevention measures and drawn up hazard maps since 2000, when the central government announced there was an 80 percent chance of a big earthquake striking off the prefecture within 20 years. Last fiscal year, the prefectural government started considering how to prepare for a tsunami on a par with one triggered by an earthquake off the Sanriku coast in 1896. That tsunami killed nearly 22,000 people and was up to 38.2 meters high.

"We'll need to reexamine disaster-prevention measures for the future," a disaster-prevention official of the prefectural government said.

In the Taro district of Miyako, Iwate Prefecture, the March 11 tsunami swept over and smashed 10-meter-high twin dikes built to protect 2.5 kilometers of coastline.

Tsunami had destroyed the area in 1896 and 1933. The dikes that guarded the town took 44 years to build and were completed in 1978.

In 1960, completed sections of the dikes protected the district from the tsunami that came from Chile. Local residents trusted the dikes they dubbed their "great walls" would protect them.

Unfortunately, they were no match for the March 11 tsunami.

Just down the coast in Kamaishi, breakwaters that had been recognized by Guinness World Records as the world's deepest also were overwhelmed.

Despite being made from 7 million cubic meters of concrete, 63 meters deep and having walls that stood eight meters above the surface, more than half of the breakwaters that stretched into the bay off Kamaishi were left in ruins.

Only a few sections of the breakwaters now poke through the water. Residents never imagined their breakwaters would get wiped out.

"I was astonished because the breakwaters hadn't even wobbled during previous tsunami," said Yoshikatsu Nodate, 73, whose home was washed away by the tsunami.

However hard it might be, the nation will have to restart attempts to overcome huge natural disasters. The sheer scale of the March 11 tsunami will force the Iwate prefectural government to rethink its disaster-prevention measures.

The prefectural government had asked municipal governments to reexamine disaster-prevention measures based on an estimate that about 1,300 people would die if the prefecture was hit by a tsunami of the same scale as the 1896 tsunami.

The prefectural government moved designated shelters to higher ground, compiled detailed evacuation routes and redrew hazard maps. But after the March 11 tsunami shattered the assumption that these steps would be enough, some officials are unsure what more could be done.

"We believed we'd done everything possible based on very detailed assumptions, but...," a prefectural government official in charge of disaster-prevention said. "I wonder what else we could do."

(Apr. 10, 2011)