The damaged spillway at Oroville Dam that led to evacuations of downriver communities raises an unsettling question: Could a potentially catastrophic failure happen at other dams in California as lakes fill in a wet year?
The scenario that played out at the Northern California dam is unlikely to occur at Friant Dam near Fresno, said Duane Stroup, deputy area manager for the federal Bureau of Reclamation.
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“Oroville is an earth-filled dam. Earth-filled dams can be eroded away,” he said. By contrast, Friant Dam, built in 1942, is a concrete structure that goes down to bedrock, he said.
Concrete dams can be eroded away, “but it takes a massive amount of water,” he said. “If Noah’s flood occurred, that might be a problem.”
We don’t see a problem at Friant (Dam).
Duane Stroup, U.S. Bureau of Reclamation
Friant Dam is inspected every four years by the bureau’s safety of dams program, he said. Additionally, dam operators do an annual operations, maintenance and reliability inspection. When the lake is full or nearly so, operators inspect for potential problems more frequently.
Dam safety goes further than inspections, Stroup said: “We try to imagine ways dams would fail.”
In 1997, rain fell on top of a big snowpack and water rushed into Millerton Lake, but the dam did not overflow, he said. Still, it can’t be ruled out.
“We completed a special investigation this year of what would happen if the dam were overtopped,” he said. The conclusion: “The dam would not be compromised,” he said. “We don’t see a problem at Friant.”
To prevent downstream flooding, dam operators watch how much water is being released into the San Joaquin River, he said. The river channel capacity is about 11,000 cubic feet per second, and releases now are about 9,000 cubic feet per second, he said Monday.
We’ve activated it (emergency action plan) twice this year.
Denny Boyles, Pacific Gas & Electric Co.
In the upper San Joaquin River system, both Southern California Edison and Pacific Gas & Electric Co. have dams for hydropower.
PG&E owns the earthen dam at Crane Valley in Madera County that creates Bass Lake, spokesman Denny Boyles said.
“We just completed (in 2012) a seismic retrofit,” he said. Three hundred thousand cubic yards of rock were added for reinforcement, which raised the dam by 6 feet, he said.
PG&E watches the outflow and when it gets past 750 cubic feet per second, an emergency action plan goes into effect, he said.
“We did a full-scale exercise in October,” he said. “We’ve activated it twice this year” because there has been so much precipitation in the watershed.
PG&E also operates concrete-faced, rock-fill dams at Courtright and Wishon reservoirs, Boyles said.
Southern California Edison operates six major reservoirs – Huntington, Florence, Shaver, Edison and Redinger lakes, and Mammoth Pool – and 27 dams in its Big Creek system.
The company issued a statement Monday:
“Southern California Edison’s dam safety team is closely monitoring the Oroville incident, currently does not see any meaningful parallels to SCE’s dams, and has no immediate concerns regarding the safety of its dams or the public,” the company said.
Most of the precipitation in the Big Creek system is snow and Southern California Edison has “significant reservoir capacity available,” the company said.
The company also has comprehensive dam safety surveillance and monitoring plans, and “works closely with state and federal regulatory agencies to ensure that the procedures for monitoring the dams are in compliance with regulations,” it said.
Army Corps’ dams
The Army Corps of Engineers operates Pine Flat Dam in Fresno County, Terminus and Success dams in Tulare County, and Hidden Dam in Madera County.
The corps does annual inspections before each rainy season and a more in-depth inspection every five years, spokesman Tyler Stalker said. For Pine Flat, the five-year inspection occurred last year.
Southern California Edison’s dam safety team is closely monitoring the Oroville incident
Southern California Edison
Most dams in California are regulated by the Department of Water Resources’ Division of Safety of Dams.
The division inspects each dam yearly “to ensure the dam is safe, performing as intended, and is not developing problems,” the division said on its website.
Built in the 1960s, B.F. Sisk Dam, an earthen structure that holds San Luis Reservoir in Merced County near Los Banos, is jointly operated by the Department of Water Resources and the Bureau of Reclamation.
In recent years, the federal government has studied the dam for seismic issues using computer analysis, and in 2006 “determined that there is justification to take action to reduce risk to the downstream public,” the bureau said on its website.
A new study due this year is expected to have recommendations for possible reinforcement, which would start in 2020 and take six years to complete.