USA’s tallest, Oroville Dam on Feather river in California suffered severe spillway damage, as discovered on Feb 7, 2017. As we wrote in our blog “Oroville Dam Spillway Damage in USA: Worst is yet to come”[i] on Feb 12, 2017, worse was yet to come, but the author did not imagine the threat would materialize so soon. Here we try to capture the key events since that blog.
Water started overflowing the emergency spillway on Saturday, Feb 11, 2017. On Sunday, Feb 12, evacuation orders were issued for about 188 000 people living along the river downstream from Oroville Dam.
The California Department of Water Resources said on Twitter at about 4:30 p.m. PST (0030 GMT on Feb 13, 2017)[ii] that the emergency or auxiliary spillway next to the dam was “predicted to fail within the next hour.”
Evacuation orders for nearly 200,000 people living below the tallest dam in the United States remained in place early on Feb 13 after residents were told to flee. Authorities issued the evacuation order on Sunday, saying that a crumbling emergency spillway on Lake Oroville Dam in north California could give way and unleash floodwaters onto rural communities along the Feather River. They said evacuation orders remained in place for some 188,000 people in Oroville, Yuba County, Butte County, Marysville and nearby communities. Earlier California Governor Jerry Brown asked the Federal Emergency Management Agency on Feb 10 to declare the area a major disaster.
The acting Water Resources director Bill Croyle stressed “Once you have damage to a structure like that it’s catastrophic”. However, he added: “the integrity of the dam is not impacted” by the damaged spillway. It seemed like he was played a bit with semantics, since spillway is very much an integral part of the dam.
“The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville,” the California Department of Water Resources said on Feb 12[iii]. “Those potential flows could exceed the capacity of downstream channels.”
Peter Gleick of Oakland Institute said[iv], “the big worry is not that the dam itself would fail, but that a failure of the spillway could cut into the hillside and potentially release more and more water, leading to a “cascading failure.””
The California state water resources department said crews using helicopters would drop rocks to fill a huge gouge.
DWR said on Feb 11 that the cost to repair the primary spillway was estimated to be as much as $200 million. With the significant damage to the emergency spillway, the price tag on repairs could go much higher.
According to official website[v], the highest level of dam was reached on Feb 12 at 3 am, at 902.59 ft, about 1.59 ft over the level of emergency spillway. At that stage, storage behind the dam was 3.58 Million Acre Feet. Possibly taking extra risk, the water flow from the damaged concrete spillway was increased to 100 000 cusecs on Sunday.[vi] Around 4:30 p.m., the Department of Water Resources warned in a Facebook post that the emergency spillway would fail within the hour. But a decision to increase the flow of water through the damaged concrete spillway appears to have prevented an imminent failure.[vii]
Sheriff Honea said on Feb 13 that no decision had been made as to when people would be allowed back into their homes, as the authorities were still assessing the risks.[viii] The UK Daily Mail on Feb 15, 2017 provided some of the most breath-taking photos.[ix]
Finally on Feb 15, CNN reported[x] that the evacuated residents were allowed to return, but were asked to remain alert about the situation.
By Feb 18, the water level had come down to 855 ft, 46 feet below the emergency spillway overflow level of 901 ft, the outflow was at 70 000 cusecs since Feb 17, likely to be reduced to 60 000 cusecs. Till Feb 16, the outflow was 100 000 cusecs. The outflow was reduced to help crew to clean up the debris collected downstream of the concrete spillway as the collected debris was backing up the water level to the powerhouse, not allowing the powerhouse to function. Moreover, with reduced level, it was becoming more and more difficult to continue to push water out of the damaged concrete spillway. Another crew was repairing the hillside downstream of the emergency spillway.[xi]
The damaged main concrete spillway continued to face more erosion and damage under continued onslaught of fast moving water, but officials said that was expected and that it was stable.[xii] The extent could be seen from some new revealing photos.[xiii]
California Department of Water Resources crews at the Oroville Spillway was facing another challenge: a massive 150 000 cubic yards (about 8000 truck loads of) mound of concrete and debris that formed in the area below the primary spillway.[xiv]
State officials said on March 2 that approximately 110,000 cubic yards of debris have been removed, and the water in the channel has dropped substantially. The hydropower plant could be made operational on March 3, which can than help release upto 14000 cusecs of water, the water release from the damaged spillway can be reduced to that extent. The hydropower plant stopped functioning due to build up of debris increasing the water level near the plant.[xv]
On Feb 27, water release from the damaged spillway was completely stopped to clear the debris that was stopping the operation of the hydropower plant. However, this sudden stoppage had its own damaging implications, as we see below.
On March 3, the first of the six units of hydropower project was restarted, and it was hoped that the rest of the units would also start operating soon so that the spillways don’t have to be used rest of the spillway season this year.[xvi]
By Monday, March 6, 2017, crews had removed some 427,000 cubic yards of rocks and debris from below the spillway.
New round of damages on Feb 27, 2017 On Monday, Feb 27, 2017, farmers along the Feather river experienced a new round of damages when water flow was suddenly stopped from damaged spillway on Sunday, Feb 26, 2017, from 50000 cusecs to zero. “For miles along the channel, huge chunks of the river’s banks collapsed into the water, toppling wild cottonwood, oak and black walnut trees. Filter said neighboring farmers lost irrigation pumps into the river. Roots from some of Filter’s orchards are now dangerously close to the gaping wounds in the river bank… Filter, the Live Oak farmer, said he appreciates the unprecedented and dangerous situation the state is in. But looking out Monday over the mangled river bank and the downed trees – some of them oaks nearly a century old – he said he wishes the state would have shut down water flows from the main spillway more gradually. He worries bigger chunks of the riverbank will collapse in the next round of storms, bringing down some of his valuable trees with them.[xvii] David Petley has explained this further in this blog on March 7, 2017.[xviii] State officials were yet to accept the damaging impacts of their action of suddenly stopping flow.
Key Facts[xix] The California Department of Water Resources owns and operates the Oroville facilities for a number of uses, including flood control, water supply and recreation. The key Oroville facilities consist of the dam, the lake, the operational spillway, the emergency spillway, and the hydroelectric generating facilities.
U.S. Army Corps of Engineers (Army Corps) and DWR Division of Safety of Dams (DSOD) share regulatory oversight authority over flood control operations at the Oroville facilities.
On February 7, reservoir releases through the operational spillway were increased from 44,500 cfs to 54,500 cfs, reaching that level for the first time in the season. Soon damage to the spillway was discovered. It is not clear when were water releases of this magnitude made earlier.
DWR, in compliance and at the request of FERC oversight authority, is organizing an independent board of consultants, experts in fields including structural engineering and spillway hydraulics, to assess conditions and recommend further actions and facility repairs.
A settlement of the FERC license was reached allowing the Oroville hydroelectric generating facilities to continue hydropower operations until 2008. Each year since 2008, FERC has granted a one-year license extension for these facilities.
Ill Designed Emergency spillway puts the dam engineers in the dock “Solid rock. All this is rock,” Bill Croyle, acting director of the Department of Water Resources, said with an air of confidence at the Feb. 11 briefing, while indicating the emergency spillway.[xx] The flows over the concrete lip of the unpaved spillway that started on Feb 11 were tiny compared with what it was designed to handle. At the peak of the spill, about 18 inches of water was sheeting out of the reservoir, spreading over the top of the hill and forming a stream as it followed a ravine down to the Feather River. The 1,700-foot long lip, known as a weir, was supposed to handle up to a 16-foot flow over its top.
Some 27 hours after the flow over emergency spillway started, state officials told Butte County Sheriff Kory Honea that erosion was chewing away at the base of the spillway’s concrete lip. It was on the verge of collapse, threatening to send a towering wall of flood water surging through downstream communities, endangering tens of thousands of people. Honea ordered a mass evacuation of about 2 lakh people.
The erosion slowed and dam managers succeeded in getting enough water out of the reservoir to stop the emergency spill late Feb. 12. California narrowly averted what could have been one of the worst dam disasters in state history. Interviews and records suggest that the near-catastrophe grew out of fundamental problems with the original design of the emergency spillway that were never corrected despite questions about its adequacy.
The “solid” bedrock that Croyle thought would stand up to the force of the spill was soft and easily eroded. The long concrete lip of the spillway was not anchored into the rock. Critical power lines were strung across the spillway, which consists of nothing more than an earthen hillside covered with trees and brush. “There is no way to rationalize running water down a hillslope with deep soils and a forest on it and weak bedrock,” said Jeffrey Mount, a UC Davis emeritus professor of geology and expert on California water. Federal and state officials said the cause of the spillway’s near-failure was under investigation.
Outdated flood manual of Oroville Dam Ann Willis, a researcher at the UC Davis Center for Watershed Sciences, is among the critics who say the the manuals are too rigidly tied to outdated weather models. At Oroville, the manual dated August 1970 cites weather patterns prior to the 1950s, and data doesn’t account for the catastrophic floods of 1986 and 1997. Plus, the manuals are designed around weather patterns that include capturing water from spring snowmelt, an annual occurrence expected to shift, in both timing and amount, with continued climate change.
Joe Forbis, chief of water management at the Corps’ Sacramento office acknowledged his agency would prefer to have updated manuals. But, he said, it’s difficult because the updates require complex engineering and environmental studies. Funding would have to be approved by Congress.
Jay Lund, director of the Center for Watershed Sciences at UC Davis, said he expects the malfunctions now crippling Oroville Dam will prompt a review of operations and likely an update of its operating manual as part of any retrofit. It also may focus attention on other aging flood infrastructure in the state.[xxi]
One of the fall out was that the California governor asked for USD 450 million for flood control.[xxii]
Many unanswered questions The way this whole episode had unfolded raises many questions, some of which we asked in our previous blog, some above. Here are some more.
Media reported[xxiii] that three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government in 2005, as part of Oroville Dam’s relicensing process, urging federal officials to bolster the dam’s emergency spillway. The groups warned that the dam did not meet modern safety standards.
The environmental groups asked federal regulators to require the state to armor the hillside that forms the emergency spillway. The dam’s operating rules called for use of the spillway as part of flood-control operations, they argued, so the slope needed to be armored to prevent damaging — and potentially dangerous — erosion.
In filings with the agency that oversees the dam — the Federal Energy Regulatory Commission — the groups cited a 2002 technical memo prepared for the Yuba County Water Agency that concluded emergency spills would cause extensive erosion on the hillside, potentially destroying high-voltage transmission towers and a road. Soil, rocks and debris would clog the Feather River. The Federal Energy Regulatory Commission rejected their 2005 request.
In 2005, officials with Sutter County, which the Feather River runs through several dozen miles downstream of the dam, asked federal regulators to “investigate the adequacy and structural integrity” of the hillside and how it would hold during “extreme flood releases.”
“I think that the warning that was given should have been taken with the utmost seriousness,” said Bob Wright, an attorney at Friends of the River, which raised the issue along with the Sierra Club and South Yuba River Citizens League.
Bill Croyle, acting head of the Department of Water Resources, refused to comment on the 2005 concerns, saying he was not familiar with them and would need to research the matter.[xxiv]
The impending disaster came as no surprise to officials in Butte and Plumas counties. The rural counties, which surround Lake Oroville, had challenged the state’s environmental review of dam operations in a 2008 lawsuit, arguing the state “recklessly failed” to properly account for climate change in its long-term dam management plan. In 2012 Yolo County Superior Court Judge Daniel P. Maguire upheld DWR’s environmental review. In 2012 Judge ruled in favor of the state when he wrote in his statement of decision that an environmental review “need not (and should not) speculate about the future.”
The counties appealed to California’s 3rdDistrict Court of Appeal, where the case has been sitting ever since.
On February 13, the day after the Butte County sheriff issued the evacuation orders, FERC ordered California to convene a five-member board to assess how to reduce the risk of flooding and analyze what went wrong.[xxv]
Even before the evacuation was announced, one blog[xxvi] had raised some questions: “So, I am merely raising the question: if engineers were reluctant to predict the current topping of the emergency spillway — a relatively benign event that was rather easily predicted — how much confidence can we have that the damage to the main spillway won’t compromise the dam? I think engineers are going to have to be a little more forthcoming about whether such a failure — which threatens thousands of people immediately downstream — is indeed possible in the coming weeks and months as the massive mountain snowpack melts and continues to fill the lake — and continues to erode the spillways.”
A Dam contractor asked: “When will we, at last mandate proper maintenance and inspection of these high hazard and medium hazard dams? Why are we willing to suffer a loss of hundreds of millions of dollars to save a couple of dollars on proper and responsible dam safety and repairs? Whatever you may hear, this is a significant event which could be horrible in its scope and its magnitude. Let us pray that it does not breach, and let us hope that, at last people are sufficiently concerned to act.”
Joseph Countryman (a civil engineer with 20 years of experience with the Army Corps of Engineers overseeing reservoirs in California, Utah and Nevada) said[xxvii]: “I have never seen a concrete lined spillway all of a sudden show up with a hole in the middle of it. Never seen that. It’s even hard to contemplate how that happened. And then after that, they sent a little bit of water over the emergency spillway and were getting erosion there. So it just seemed like one catastrophe after another”.
“Most of the dams in the United States are over 50 years old, when we didn’t understand floods as well as we do now. So we have a number of dams in the U.S. that have spillways that aren’t large enough for the floods that they should be designed for,” said John France, vice president and technical expert on dams for the engineering consulting firm AECOM.[xxviii] He said the problems at Oroville should raise alarms across the country.
One expected US to make all kinds of information public in pro active way, but media reported that the government refused to make the inundation maps public for various flood scenarios, even under freedom of information act. This is strange and difficult to understand:[xxix] “The Record Searchlight asked for the release of the documents from the city of Redding under the California Public Records Act and from the bureau, which operates Keswick and Shasta dams, under the Freedom of Information Act.”
On Feb 13, Dave Petley asked in his blog[xxx], “It is clear that the flow has exceeded the emergency spillway and has flowed over unprotected ground adjacent to it, which inevitably was vulnerable to erosion. To me this seems quite extraordinary – how did the design allow that to occur – but that is a question for another day.” Next day, in another blog[xxxi], Petley wrote: “The most serious problem appears to be a gully towards the bottom of the image, but there is also substantial amounts of erosion occurring on the other side too. The danger is of course that these gullies will suffer headward erosion until they undermine the spillway lip. whereupon collapse may occur. One challenge is that the quality of the rock does not appear to be high, which accounts for the rapid erosion in both cases.”
Some republicans saw in this disaster an opportunity to push for more hydropower projects.[xxxii]
Climate Change? Officials claimed that Northern California received about 225 percent of normal rainfall since Oct. 1. The Guardian reported[xxxiii], “Northern California is in the midst of its wettest rainy season on record – twice as wet as the 20th century average, and 35% wetter than the previous record year.” But to say from this that “It proved to be almost too much for America’s tallest dam to handle” is clearly incorrect. The dam could have easily handled the wet season if the regular spillway was not damaged and could have continued to carry the 150 000 cusecs outflow it was designed to carry. However, the warning from the Guardian that more such crisis are in store for us in changing climate is entirely correct: “Dams in the United States were built 50 years ago, on average. Since then, the Earth’s surface temperature has warmed about 0.75°C, and there’s now more than 5% more water vapor in the atmosphere as a result, which intensifies storms. With hotter temperatures, more precipitation falls as rain and less as snow, and California’s Sierra snowpack also melts earlier in the year.”
In Conclusion Many of the questions raised here about this episode may be answered in days to come. There is a lot to learn in this episode for California, USA and rest of the world. In India, with already huge stock of old stock of dams, and our far from confidence inspiring legal or institutional situation in dealing with such events, we have a lot to to learn quickly. Climate change makes learning necessary lessons even more urgent. It is doubtful though if any of that would happen easily.
Himanshu Thakkar, SANDRP (email@example.com)
[xxvi] http://www.drroyspencer.com/2017/02/is-failure-of-the-oroville-dam-possible/ there are other blogs raising questions, see for example: http://motls.blogspot.in/2017/02/oroville-dam-risks-may-be-underreported.html
[xxix] http://www.redding.com/story/news/2017/02/16/bureau-says-sacramento-river-flood-maps-secret/98024166/, http://www.redding.com/story/news/local/2017/02/18/newspaper-seeks-release-flood-maps/98065788/