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)
Showing posts with label breakwaters. Show all posts
Showing posts with label breakwaters. Show all posts
Sunday, April 10, 2011
10/04 Expert: Residences should be moved to higher ground
Yasushi Kaneko / Yomiuri Shimbun Staff Writer
The government should consider moving residents living in low-lying costal areas to higher ground, according to a specialist in coastal engineering.
Waseda University Prof. Tomoya Shibayama has inspected the areas affected by the tsunami caused by the March 11 earthquake via helicopter. "More than half of the breakwater in Kamaishi, Iwate Prefecture, was destroyed by the tsunami, and the one in Ofunato was no longer visible," he said.
Towns on the Sanriku coast have long experience with tsunami, including notable tsunami caused by domestic earthquakes in 1896 and 1933, as well as one following a quake in Chile in 1960. According to Shibayama, these tsunami measured about four meters at the tallest at Onagawacho, Miyagi Prefecture.
The March 11 tsunami in the town, however, was more than four times this height, he said, and came with force of dozens of tons per square meter, similar in strength to the 2004 Indian Ocean tsunami that killed more than 230,000 people.
Tsunami after the March 11 earthquake were much bigger than those anticipated in disaster action plans made by towns on the Sanriku coast, effectively rendering their protective measures meaningless, Shibayama said. "It's clear now that breakwaters and seawalls don't do much to protect residential areas from tsunami," he said.
To preserve regional communities, local governments should consider revising their land-use programs and move low-lying residential areas near the sea to higher ground, Shibayama said.
The village of Ultogia, Samoa, was hit by the 2009 tsunami and about a month later, neighborhoods near the sea began moving to higher ground. "In Japan, the central and prefectural government should take the initiative [and implement similar policies] because of the difficulty of coordinating the rights [of the affected parties]," he said.
The central and local governments also need to increase the tsunami size their disaster action plans are predicated on and revise evacuation plans based on even larger tsunami, he said.
The central government's tsunami guidelines stipulate that citizens should seek refuge on the third floor or higher of buildings built of reinforced concrete. However, according to officials of Minami-Sanrikucho, Miyagi Prefecture, people on the roof of a four-story building said the tsunami reached their knees, about 15.5 meters above the ground.
"Residents need to evacuate to areas about 18 meters high, equivalent to a building's sixth floor," Shibayama said.
(Apr. 10, 2011)
The government should consider moving residents living in low-lying costal areas to higher ground, according to a specialist in coastal engineering.
Waseda University Prof. Tomoya Shibayama has inspected the areas affected by the tsunami caused by the March 11 earthquake via helicopter. "More than half of the breakwater in Kamaishi, Iwate Prefecture, was destroyed by the tsunami, and the one in Ofunato was no longer visible," he said.
Towns on the Sanriku coast have long experience with tsunami, including notable tsunami caused by domestic earthquakes in 1896 and 1933, as well as one following a quake in Chile in 1960. According to Shibayama, these tsunami measured about four meters at the tallest at Onagawacho, Miyagi Prefecture.
The March 11 tsunami in the town, however, was more than four times this height, he said, and came with force of dozens of tons per square meter, similar in strength to the 2004 Indian Ocean tsunami that killed more than 230,000 people.
Tsunami after the March 11 earthquake were much bigger than those anticipated in disaster action plans made by towns on the Sanriku coast, effectively rendering their protective measures meaningless, Shibayama said. "It's clear now that breakwaters and seawalls don't do much to protect residential areas from tsunami," he said.
To preserve regional communities, local governments should consider revising their land-use programs and move low-lying residential areas near the sea to higher ground, Shibayama said.
The village of Ultogia, Samoa, was hit by the 2009 tsunami and about a month later, neighborhoods near the sea began moving to higher ground. "In Japan, the central and prefectural government should take the initiative [and implement similar policies] because of the difficulty of coordinating the rights [of the affected parties]," he said.
The central and local governments also need to increase the tsunami size their disaster action plans are predicated on and revise evacuation plans based on even larger tsunami, he said.
The central government's tsunami guidelines stipulate that citizens should seek refuge on the third floor or higher of buildings built of reinforced concrete. However, according to officials of Minami-Sanrikucho, Miyagi Prefecture, people on the roof of a four-story building said the tsunami reached their knees, about 15.5 meters above the ground.
"Residents need to evacuate to areas about 18 meters high, equivalent to a building's sixth floor," Shibayama said.
(Apr. 10, 2011)
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