Tag Archives: California Oroville Dam

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New Bill Would Toughen Calif. Dam Inspections

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DWR Photo: Lake Oroville on Jan. 19, 2018 with lake levels at 707 feet.

A year after the spillway collapse at the Oroville Dam, leading to evacuations of almost 200,000 residents and a beat-the-clock patching job to avoid a break in the tallest dam in the United States, new legislation to strengthen inspections of dams awaits approval of California Gov. Jerry Brown.

The bill would require annual inspections for high hazard dams, raise inspection standards and require consultation with independent experts every 10 years, according to ABC News.

As reported by Risk Management Magazine, problems at the Oroville Dam began when the dam’s main sluice was damaged after a winter season of record rain and snowfall, following five years of drought. Torrential rainfall caused water levels to rise so quickly that large amounts needed to be released to prevent the dam from rupturing and sending a wall of water to the communities below.

A recent report of the root-cause of the spillway failure by the Independent Forensic Team (IFC), which includes members of the Association of State Dam Safety Officials and the United States Society of Dams, notes that:

There was no single root cause of the Oroville Dam spillway incident, nor was there a simple chain of events that led to the failure of the service spillway chute slab, the subsequent overtopping of the emergency spillway crest structure, and the necessity of the evacuation order. Rather, the incident was caused by a complex interaction of relatively common physical, human, organizational, and industry factors, starting with the design of the project and continuing until the incident. The physical factors can be placed into two general categories:

  • Inherent vulnerabilities in the spillway designs and as-constructed conditions, and subsequent chute slab deterioration

  • Poor spillway foundation conditions in some locations

The IFC report concludes that all dam owners in the state need to “reassess current procedures” in light of its findings.

According to the IFC:

“The fact that this incident happened to the owner of the tallest dam in the United States, under regulation of a federal agency, with repeated evaluation by reputable outside consultants, in a state with the leading dam safety regulatory program, is a wake-up call for everyone involved in dam safety. Challenging current assumptions on what constitutes ‘best practice’ in our industry is overdue.”

Initial response to the spillway failure included erosion mitigation for both spillways during the incident, sediment removal and installation of temporary transmission lines at a cost of $160 million, According to the DWR. Phase-two includes removal of the original 730 feet of the upper chute, replacing it with structural concrete.

Weather Threatens Oroville Dam Emergency Efforts

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As measures are taken to repair a damaged spillway at the Oroville Dam in Northern California, weather forecasters are calling for rain later this week. Almost 200,000 people were evacuated from their homes below the dam, the largest in the country, on Feb. 12 as erosion of the dam’s emergency spillway threatened to flood the towns below.

While the situation was said to have stabilized on Sunday morning, conditions worsened and evacuation orders were issued. Roads in the area quickly backed up as a result, according to reports.

The dam’s main spillway was damaged after a winter season of record rains and snows following years of drought in the state.

Photo: California Department of Water Resources

California Representative John Garamendi told MSNBC that the evacuation was essential. “Fortunately when they were able to open the main spillway gates. That began to lower the reservoir level, because the water coming into the reservoir was about half of what they were able to expel down the main spillway, so it’s stabilized.”

The next issue, he said, is whether the spillway can be patched up “sufficiently to weather the storms that are clearly ahead of us.” Garamendi added that the months of March and April are the heavy storm season in the state.

Sheriff Kory Honea of Butte County said at a press conference that the Department of Water Resources (DWR) reported that the dam’s erosion is not advancing as rapidly as they thought. He said a plan is in place to plug the hole in the spillway by dropping large bags of rocks by helicopter. The DWR said that another measure being taken to relieve pressure on the spillway has been to raise the rate of discharge water from 55,000 cubic feet per second to 100,000 cfs, which it said has been working.

Helicopters transport large bags of rocks from the Oroville Dam parking lot, to the erosion site at the Oroville Dam auxiliary spillway in California, to help fight further erosion, February 13, 2017. Oroville is in Butte County. Florence Low / California Department of Water Resources

The New York Times reported that Northern California is close to 225% above normal rainfall levels since Oct. 1. According to the Times:

Repeated rounds of rain have pounded the area in recent weeks, rapidly raising the water level at Lake Oroville, the second-largest reservoir in California and a linchpin of the state’s water system. On Tuesday, a gaping hole opened in the main spillway that is used to release extra water. Early Saturday, an adjacent emergency spillway was also put into use, the first time water flowed over it since the dam was finished in 1968, department officials said.

State officials have said the 770-foot Oroville Dam itself, the nation’s tallest, is sound.

The problems with Oroville Dam are not a surprise to some. In 2005, during a relicensing process for the dam, three environmental groups warned the DWR of potential dangers with the emergency spillway, which is not a concrete spillway, but a concrete lip with a dirt hillside below. The concern was that the hillside could be easily eroded in the case of an emergency.

The Washington Post reported:

The upgrade would have cost millions of dollars and no one wanted to foot the bill, said Ronald Stork, senior policy advocate for Friends of the River, one of the groups that filed the motion.

“When the dam is overfull, water goes over that weir and down the hillside, taking much of the hillside with it,” Stork told The Washington Post. “That causes huge amounts of havoc. There’s roads, there’s transmission lines, power lines that are potentially in the way of that water going down that auxiliary spillway.”

Federal officials, however, determined that nothing was wrong and the emergency spillway, which can handle 350,000 cubic feet of water per second, “would perform as designed” and sediment resulting from erosion would be insignificant, according to a July 2006 memo from John Onderdonk, then a senior civil engineer for the Federal Energy Regulatory Commission.

Garamendi said that “What happened with the widening of the sinkhole was the result of someone overlooking the problems, including the fact that there was no concrete apron on the spillway.”

He also noted that while there will most likely be federal dollars to help rebuild the dam, “This is just one really startling, quite tragic and potentially catastrophic example of what’s happened to the infrastructure across America. We’ve seen bridges collapse in Minnesota, we’ve seen them on I-5 in Washington State and now this reservoir, which is the linchpin of California’s water system.”