Japan dam failure renews focus on California dams
Kendall Taggart
California Watch
03/17/2011
As Californians closely watch the catastrophe at Japan's nuclear plants, many engineers are also studying the failure of a dam in Japan’s northeast Fukushima prefecture. The extent of the damage is still unknown.
"One dam failure is too many," said Nicholas Sitar, a professor of civil and environmental engineering at UC Berkeley.
Experts have not yet determined what caused the dam to fail. The duration of ground shaking during the earthquake, which lasted roughly three minutes, may have contributed to the breach.
"In California we do not have the kind of tectonic setting that would produce extremely long durations," Sitar said.
The Loma Prieta earthquake in 1989, for example, only lasted 10 seconds.
Following the near-catastrophe during the 1971 San Fernando earthquake, when 80,000 people living downstream of the Lower San Fernando Dam were immediately ordered to evacuate, California revamped its seismic safety dam programs.
"California probably has the safest inventory of dams in the world. Having said that the possibility of a dam failure is not zero. There is a process called structural Darwinism. An earthquake shakes a large area and if you miss something the earthquake finds it," said Raymond Seed, a professor of civil and environmental engineering at UC Berkeley.
Many older dams in California are in need of seismic retrofitting. Several years ago, the Army Corps of Engineers learned that the 57-year-old Lake Isabella Dam in Kern County had serious problems. In addition to the danger of erosion and overflow in an extreme flood season, they learned that a fault underneath it previously thought to be inactive was actually active and could produce a strong earthquake.
A number of dams in Santa Clara County are running at diminished capacity, after restrictions were imposed by the California Division of the Safety of Dams. Seismic retrofitting of Santa Clara County’s five dams, built between the 1930s and 1950s, could cost up to $150 million.
“The problem is significant,” Don Gage, chairman of the Santa Clara Valley Water District board, told Homeland Security News Wire. “You have to understand that these dams are 80 years old. The earthquake standards back then were not what they are today. We are going to have to shift dollars in our capital improvement programs from other projects to these dams.”
Since 2001, the Calaveras Dam has operated at 30 percent of capacity due to seismic concerns. The San Francisco Public Utilities Commission approved a $4.6 billion project in January that will completely replace the existing seismically unsafe dam.
