Dam Safety

Oroville Dam Spillway Damage in USA: Worst is yet to come

Oroville Dam, the tallest Dam in USA was found to have suffered severe damage to its spillway on Feb 7, 2017. A crater of about 180 feet width, 250 feet length and 30 feet depth was found in lower portion of the 3000 ft long spillway on Tuesday when 55000 cusecs (cubic feet of water) was flowing down the spillway.

That water release down the damaged spillway was stopped the same day. But the water level in the Oroville dam was than already over 80%, fast climbing to over 90% by the evening of Feb 9, 2017 and with inflow of 128000 cusecs on Feb 7, rising to 191000 cusecs on Feb 9, the officials of Department of Water Resources (DWR) of California decided to first test the damaged spillway by releasing 20000 cusecs twice on Feb 8, 2017. This further damaged the spillway, increasing the depth of the crater to upto 300 ft as per some reports and not only increasing the length and width, but also eroding the adjoining hills.

Still, with inflow increasing, the DWR decided to restart the releases through damaged spillway on Feb 9, 2017, first at 35000 cusecs, increasing to 42000 cusecs, with possibility of increasing it to 55000 cusecs. This apparent risk of huge additional damage to the spillway was taken to avoid the possibility of water overflowing from the top of the dam through the emergency spillway. This is considered risky since there are no gates, the water would flow over the earthen wall and the emergency spillway has never been used since commissioning of the dam in 1968. The closest they came to was 1 feet below the emergency spillway level of 901 feet in 1997. By Feb 9 evening the water level behind the dam had already crossed 887 feet, still climbing rapidly.

Damaged spillway of Oroville Dam (Media reports in USA)
Damaged spillway of Oroville Dam (Media reports in USA)

Oroville, at 770 ft height (40 ft higher than Hoover dam) with a storage capacity of 3.5 million acre feet (MAF, second largest reservoir of California state) was found to have suffered “a partial collapse” and has “A MASSIVE HOLE” in its spillway, which is the main water release mechanism of the dam. The dam was 82% full (3 pm on Tuesday, Feb 7), level was already 0.15 MAF above the prescribed level, with capacity to store just three days of inflows, currently at 128000 cusecs, and only outflows of about 5000 to 15000 cusecs from power plant. The dam in California state on Feather river was constructed in 1968.[i] An interesting site[ii] the provides how in 1965 an accident occurred during the construction of the dam, leading to death of 34 people.

Its 819 MW power station was the largest underground power station of USA when commissioned in 1968, with 819 MW capacity, part of it can function as pump storage facility, interestingly, with two off stream reservoirs. Its in the the Sacramento River, eventually reaching the Sacramento-San Joaquin Delta.[iii]

Schematic illustration of Oroville Dam (Media reports in USA)
Schematic illustration of Oroville Dam (Media reports in USA)

A media report[iv] said: “Croyle, DWR’s acting director, said it was not yet clear what caused the crater to form. Three recent inspection reports for the dam – one from 2014 and two from 2015 – noted no visible signs of deficiencies along the chute.” What this reveals is that while there were three inspections in 214-15, there have been none for the last about one and half years. Not clear why this is the case. Its not clear if the latest inspection will be questioned or questions will be raised about lack of inspection since 2015.

An official was quoted by the media[v]: “As of 6 p.m. Feb 8, the lake was (872 ft?) 29 feet below the level considered full. It had risen 17 feet since noon Tuesday (from 855 ft?). There was 3.1 MAF of water in the lake, about 89 percent of the 3.5 MAF capacity. If the department cannot utilize the spillway, and the lake gets to full capacity, water will pour over an emergency spillway at the north side of the dam, See said. The emergency spillway, which was built with the dam in 1968, has never been used and would generate considerable erosion.”

Damaged spillway of Oroville Dam (Media reports in USA)
Damaged spillway of Oroville Dam (Media reports in USA)

By Friday (Feb 10) evening, the lake level reached 891 feet, expecting it to overflow over the emergency spillway on Saturday morning. Eric See with the Department of Water Resources says the water will eventually hit bedrock. “The erosion will essentially stop or slow down greatly at that point,” explained See, “if that’s the case we could have use of the existing spillway which is what we’re hoping for.”[vi]

As of 9 a.m. Feb 10, Lake Oroville was at just over 895 feet, six feet from the top. The lake had gained about 15 feet in the previous 24 hours, mostly before midnight. Since midnight, its levels rose by just under a foot every two hours. Water releases have been increased to 65,000 cusecs, according to the Department of Water Resources[vii], later it was reduced to 55000 cusecs. The department said the slowdown was necessary[viii] “to prevent erosion along the north side of the spillway from compromising nearby power line towers.” The lines run to the dam’s power plant. This was additional complication from the use of damaged spillway, which apparently was not foreseen.

Inflow to the dam from the Sierra watershed, which peaked at 190,000 cusecs on Feb 9 afternoon, had diminished to 130,000 by midday Feb 10 and was expected to drop to 60,000 cusecs on Feb 11, essentially matching the amount of water flowing out of the damaged main spillway.

Engineers inspecting the damaged spillway of Oroville Dam (Media reports in USA)
Engineers inspecting the damaged spillway of Oroville Dam (Media reports in USA)

On Feb 10, large gushes of water flowing down the damaged spillway were being misdirected by the massive fracture that now splits the spillway in two, and streaming down the hillside just east. The resulting debris formed a kind of natural dam at the bottom of the hill, raising water levels so high in the channel below the spillway that engineers had to shut down the dam’s power plant. The plant could have released up to 15,000 cubic feet per second. This was yet another complication from the use of damaged spillway.

By Feb 11 morning, the water finally started flowing down the emergency spillway[ix].

Caring for the fish Meanwhile, over half of the 8 million of baby salmon from state hatchery in downstream river were loaded up into trucks on Feb 9, to try to save them from the mud, concrete chunks and other debris flowing from the crumbling spillway. For the fish left behind, an arrangement was done to reduce the silt in the muddy water.

Google Earth Map of Oroville Dam
Google Earth Map of Oroville Dam

Transparency in handling the emergency One of the heartening feature of this whole situation is that senior dam engineers were seen talking with media at length on all the days of this emergency at Oroville dam so far and were also happily answering all the questions that media had. The engineer informed about the 2-hour water release test on Wednesday starting 3.20 pm; the Dam already being about 87% full by Thursday evening, wet days till Friday ahead (followed by five dry days), that they still had about 60 run off days and how they want to avoid using the emergency spillway, but are ready if they have to use it. He also informed that the earliest the repair work can start is about 90 days from now.[x]

Oroville residents Gary Lease and Beth Bello were possibly the first notice the possible damage to the spillway when they were out for a morning walk on Feb 7, when they saw the water spilling erratically and shot video of it which has been widely shared. “We noticed, ‘wait a minute there’s a whole bunch of water shooting up out of the spillway,'” Lease recalled. “And we got closer and we saw little chunks of concrete flying up too. And we go ‘wow this isn’t right.’” “It’s not normal to have the water going up from midway of the spillway,” Bello added.

It was good to see DWR officials briefing media everyday on the Oroville situation (Media reports in USA)
It was good to see DWR officials briefing media everyday on the Oroville situation (Media reports in USA)

Water was being released out of the dam at nearly 60,000 cubic feet per second Tuesday morning when the chunks of concrete came loose, according to the DWR.[xi]

The official website gives detailed info about the water situation at Oroville dam.[xii] The official website has a number of documents including the environment impact reports and statements, FERC authorisation, among others.[xiii]

While the Oroville Dam issue gets worse, ANOTHER DAM related DISASTER in USA: A broken 21-mile Dam in Nevada has added to the snowmelt and rainfall, creating unprecedented floods in some parts. There is possibility of Dake Dam Reservoir also overflowing. In neighboring Utah, the rapid increase in temperature has led to fast melting of snowpack.[xiv]

Muddy water flowing down the damaged spillway of Oroville Dam (Media reports USA)
Muddy water flowing down the damaged spillway of Oroville Dam (Media reports USA)

Criticism of Dam Officials So far there has not been much media criticism about the way this emergency has been handled by the official agencies. One instance[xv] of this is noteworthy though: “Butte County District 1 supervisor Bill Connelly said the DWR should have released water much sooner. They didn’t prepare in knowing in advance that there was a snow pack way above average and it was projected that there were warm rains coming,” said Connelly, who grew up in Oroville and has been involved in the dam’s re-licensing for the last 14 years.” There seems some justification in this, since the water level at the dam was kept constant for several weeks, the penstocks were in repair even during flood season and the fish pass water release mechanism for release of 4000 cusecs do not seem to be working.

Moreover, the report says: “Recently a photograph surfaced showing crews working on a crack in the same vicinity of the spillway in 2013. The State Division of Dam Safety reported that the last inspection was performed in 2015 and was reportedly “visual” and at “some distance. This is evidence of a lack of correct maintenance that puts my citizens at risk,” said Connelly.” This raises serious questions, DWR response that “there wasn’t more evidence that more needed to be done.”


Inspectors at Oroville Dam found “minor” cracks in the dam’s main spillway in 2009, according to state inspection reports. The California Occupational Safety and Health Administration cited six violations that contributed to the July 22, 2009, accident, including five considered “serious.” OSHA found, among other things, that an “energy dispersion ring” designed to eliminate the suction force had been removed two months earlier and never replaced. It also found that the dispersion ring was damaged in 1968 and never repaired. A UC Davis study in 1993 advised DWR that, as a result, flow through the valves should be “severely limited” for safety. OSHA levied fines totaling $141,375.

The damage discovered in 2009 was repaired in 2010.

Jeffrey Mount, former chairman of the UC Davis Department of Geology[xvi], after reviewing video footage taken by helicopter on Feb 10 of the canyon that is forming at the bottom of the damaged spillway as a cascade of water rushes down said: “What it’s doing is what rivers do when they flood across bedrock. They tend to cut downward, like a knife. You’re getting rapid, dramatic incision into the underlying bedrock, making essentially its … own steep, canyon. Your No. 1 worry will be that it will continue to erode in the upstream direction (toward the top of the spillway) until it destroys… the spillway gates. Then, you’re close to the abutment of the dam. But you’ve got a long way to go for that.”

One citizen observer was though made enlightening remark: “Rhodes, a building contractor, took an optimistic view that the surging flows were actually giving the river a long-needed cleansing. “If it crests over (the spillway), that’s what a river is supposed to do. Erosion or not, it will be cleaning out the river and our creeks.”” Indeed, the river needs such flood flows at regular intervals to perform its tasks.

Graph from official DWR website showing how the water level at Oroville Dam increased in 2016-17
Graph from official DWR website showing how the water level at Oroville Dam increased in 2016-17

In conclusion: A blog on American Rivers website[xvii] warned: “Levees and dams are the opposite of resilient – they work until they fail. And when they do fail the consequences can be catastrophic – leading us to do harmful and expensive “repairs” to our rivers, further perpetuating the cycle of vulnerability and destruction… The problem with the Oroville Dam spillway is probably just the first sign that the Central Valley flood system will require hundreds of millions of dollars in repairs after the 2017 runoff season is complete. Authorities and experts claim there is no risk of dam failure, and I hope they are right. An emergency spillway immediately to the north of the existing spillway should be able to accommodate the overflow, but it has never been used in the half century since the dam was built and entails sending a large volume of water down an unarmored hill side.”

There is no way of knowing the risks involved in this venture as yet. But it would be interesting to know what lessons the society and the government in USA learn from this unprecedented event.

Himanshu Thakkar, SANDRP (ht.sandrp@gmail.com)


[i] http://www.sacbee.com/news/state/california/water-and-drought/article131348349.html, https://ww2.kqed.org/news/2017/02/07/engineers-assess-spillway-problem-at-oroville-dam/, http://www.newsmax.com/TheWire/oroville-dam-spillway-sinkhole/2017/02/09/id/772697/http://sacramento.cbslocal.com/2017/02/07/damage-reported-at-oroville-dam-spillway-after-officials-increase-water-releases/, http://www.sacbee.com/news/state/california/water-and-drought/article131348349.html,   A video from the county sheriff: https://www.facebook.com/bcsonews/videos/779534778863469/

[ii] http://djkuba.tripod.com/ODamTrainTunelWreck.html

[iii] https://en.wikipedia.org/wiki/Oroville_Dam

[iv] http://www.sacbee.com/news/state/california/water-and-drought/article131579999.html

[v] http://www.redding.com/story/news/local/2017/02/08/officials-run-test-flows-dam-damaged-storms/97670534/

[vi] http://sacramento.cbslocal.com/2017/02/09/oroville-dam-emergency-spillway-could-open-by-early-saturday/

[vii] http://www.krcrtv.com/news/local/butte/oroville-dam-less-than-7-feet-from-the-top/324494642

[viii] http://www.sacbee.com/news/state/california/water-and-drought/article131941279.html

[ix] http://www.latimes.com/local/lanow/la-me-oroville-spillway-20170211-story.html

[x] http://www.kcra.com/article/officials-release-water-from-oroville-dam-to-test-damaged-spillway/8694754

[xi] http://fox40.com/2017/02/07/photo-shows-damage-along-lake-oroville-dam-spillway/

[xii] http://cdec.water.ca.gov/cgi-progs/queryDaily?ORO

[xiii] http://www.water.ca.gov/orovillerelicensing/

[xiv] https://www.ksl.com/?sid=43126767&nid=148

[xv] http://www.krcrtv.com/news/local/butte/emergency-spillway-unecessary-for-now-2013-photo-of-damage-surfaces-supervisor-blames-dwr/325934917

[xvi] http://www.sacbee.com/news/state/california/water-and-drought/article131941279.html

[xvii] https://www.americanrivers.org/2017/02/troubles-californias-oroville-dam-wake-up-call/

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