Oroville Dam: A Case Study


General Information:

  • Lake Oroville is fed by the vast, snow packed Sierra watershed that continues to send runoff into the reservoir.

  • Oroville Dam is an earthfill embankment dam on the Feather River east of the city of Oroville, California, in the United States. At 770 feet (235 m) high, it is the tallest dam in the U.S.

  • Lake Oroville stores 3.5 million AF of water

  • Metropolitan contracts for about 1.2 MAF/Y (million acre feet per year) or roughly 50% of the State Water Project (SWP) supply. The SWP moves water from the Sacramento-San Joaquin River Delta, via the California Aqueduct where it provides approximately 30% of southern California water supply. The water diverted from the Delta is provided via transfer at Lake Oroville on the Feather River. During the dry season Oroville Dam releases additional water into the Feather, which eventually flows into the Sacramento River and the Delta.

  • There is no alternative route for water to safely bypass Oroville Dam.

Figure 1: California Water System with Lake Oroville Expansion

How the Oroville Facilities are Overseen and Regulated:

• The California Department of Water Resources (DWR) owns and operates the Oroville facilities for several uses, including flood control, water supply and recreation.

• The key Oroville facilities consist of the dam, the reservoir (lake), the operational spillway, the emergency spillway and the hydroelectric generating facilities.

• Oroville Dam, as a hydroelectric generating station, must be licensed by the Federal Energy Regulatory Commission (FERC).

• 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.

• While FERC typically has jurisdiction over flood control operations as part of its licensing authority, Congress specifically granted exclusive jurisdiction over flood control operations at the Oroville facilities to the Secretary of the Army in PL 85-500. Additionally, Congress made an appropriation toward the cost of constructing Oroville Dam and Lake Oroville. This appropriation was made contingent upon an agreement between the State of California and the Department of the Army for operation of the dam for flood control benefits.

• Oroville Dam has passed all annual and independent inspections regarding the adequacy, stability, and structural integrity of the facilities, including:

o Annual inspection by FERC

o Semi-annual inspections by DWR DSOD

o Five-year Independent Engineer inspection and review

Background on Oroville Facility Licensing Process

In 2005, DWR applied for a renewal of its operating license for the Oroville hydroelectric generating facilities. Friends of the River, Sierra Club and the South Yuba River Citizen’s League filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside. These groups alleged that the emergency spillway at Oroville should be classified as an “operational/auxiliary” spillway and should be armored with concrete, citing the potential for erosion and downstream runoff impacts. During the proceeding, FERC confirmed that the emergency spillway was properly designated and that it met all FERC engineering guidelines.

They (they environmentalists) said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”

Friends of the River, Sierra Club and the South Yuba River Citizen’s League in their motion alleged based on a 2002 Yuba County Water Agency Technical Memorandum on Lake Oroville Surcharge that “[a] loss of crest control could not only cause additional damage to project land and facilities but also cause damages and threaten lives in the protected floodplain downstream.” However, the Yuba County Water Agency Report was for the purpose of assessing flood control in Yuba County and did not evaluate the structural integrity of the Oroville emergency spillway.

A filing on May 26, 2006, by Thomas Berliner, an attorney for the State Water Contractors, and Douglas Adamson, an attorney for the Metropolitan Water District of Southern California, discounted the risk. It urged FERC to reject the request to require that the emergency spillway be armored, a job that would have cost tens, if not hundreds, of millions of dollars. “The emergency spillway was designed to safely convey the Probable Maximum Flood, and DWR has reviewed and confirmed the efficacy of the PMF hydrologic analysis for Oroville Reservoir,” the attorneys noted. Ultimately, they were successful. FERC did not require the state to upgrade the emergency spillway


According to State Water contractors (SWC), SWC and the Metropolitan Water District of Southern California (MWD) raised no issues regarding the costs of armoring the emergency spillway. In their supporting documentation to FERC, the SWC and the MWD pointed out that the FERC relicensing process was not the appropriate venue to raise flood control measures that go beyond FERC’s jurisdiction, which for Oroville does not include flood control. All these types of flood control issues at Oroville Dam are the jurisdiction of the Army Corps. 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 to for these facilities.

Figure 2: Oroville Dam Proposed and Actual

Timeline of Recent Events:

Beginning January 13, record rainfall in the Feather River watershed led DWR to make reservoir releases from Lake Oroville consistent with flood control rules set by the U.S. Army Corps of Engineers and Division of Dam Safety. Flows through the operational spillway fluctuated between 0 cubic feet per second (cfs) and 10,000 cfs through January 30. Beginning January 31, flows through the operational spillway increased to more than 10,000 cfs as runoff into the river increased.

On February 7, during routine use, reservoir releases through the operational spillway were increased from 44,500 cfs to 54,500 cfs to offset increased inflows from rainfall. At that time, DWR discovered a large amount of debris coming out of the concrete lined channel of the operational spillway. DWR stopped all releases to inspect the damage. Currently, the cause of the damage to the operational spillway is unknown. After testing, DWR began to release 20,000 cfs from the operational spillway to offset inflows into Lake Oroville, and continued to increase releases through the operational spillway.

The problems at the dam started with the main spillway, which developed a crack on February 7th, which by the 11th had eroded to the point that the bottom portion of the 3,000-foot span had largely washed away. As the main spillway continues to erode, its gates could be compromised, leaving the state with few options for releasing water from the dam. The State was able to lower levels in the reservoir by releasing huge amounts of water over the damaged main spillway. The question is whether those releases caused caused so much erosion that the main spillway becomes inoperable. On February 11th, the water elevation in Lake Oroville reached 901 feet, leading to flow over the emergency spillway.

On February 12th erosion began to progress up the right side of the emergency spillway. DWR increased the operational spillway releases to 100,000 cfs to draw down the water level, reduce flow over the emergency spillway and assess the erosion. As Lake Oroville’s level rose to the top and water couldn’t be drained fast enough down the main concrete spillway because it had partially collapsed on February 7th, millions of gallons of water began flowing over the dam’s emergency spillway for the first time in its 50-year history. With flows of only 6,000 to 12,000 cubic feet per second erosion at the emergency spillway became so severe that officials from the DWR ordered the evacuation of more than 185,000 people. The water was only a foot or two deep and less than 5% of the rate that FERC said was safe. The fear was that the erosion could undercut the 1,730-foot-long concrete lip along the top of the emergency spillway, allowing billions of gallons of water to pour down the hillside toward Oroville and other towns downstream.

To mitigate the risk of emergency spillway failure, dam officials on the night of February 12th started releasing water from Lake Oroville’s crippled main spillway at a rapid pace – about 100,000 cubic feet per second. The Central Valley Flood Protection Board said those flows in themselves should not overwhelm the Feather River levees and channels downstream, which are rated to handle up to 150,000 cfs. The massive releases caused Lake Oroville levels to drop rapidly, and by 9 p.m. on the 12th water had stopped coming over the top of the emergency spillway.

With 100,000 cubic feet per second of water flowing out of the lake, lake levels were dropping about one foot every 3 hours on the morning of February 13th, state figures show. That translates to a drop of about 120,000 acre-feet every 24 hours. At current pace, the lake will fall to about 400,000 acre-feet below its emergency spillway by the morning of the 16th. To get the lake back to the levels normally mandated for flood control, it would need to fall by about 700,000 acre-feet. Officials have more modest goals. They said the night of the 12th that they hope to drain the lake by 20 to 30 feet by the next storm. At current pace, they will hit that target.

However, on the night of the 14th rain is forecast to return to Oroville and continue to fall through the 16th. The Sacramento Valley may see a half to an inch of rain, while the foothills are predicted to receive 2-to-4 inches. Snow levels are expected to hover around the 6,500-feet elevation level on the 16th. Rain is expected to return February 17th, but precipitation amounts can not be determined yet. The good news is that more of what will fall from the sky in the mountains will be in the form of snow. Snow levels could fall to about the 4,000-feet elevation level the 19th and 20th.

As of February 14th, water levels in Lake Oroville were 13 feet below the crest of the emergency spillway. DWR has begun repairs to the erosion areas below the emergency spillway. DWR, in full 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.

Reconstruction efforts:

Despite repeated requests for information, DWR refuses to say how much has been spent during the emergency. In March, State Assemblyman James Gallagher was told by DWR: $4.7 million per day, or $100 million during the month of February. The helicopters at one point cost $100,000 a day and dredging debris ran to more than $22 million. “It was a tremendous opportunity for us … a once-in-a-lifetime opportunity,” said Jeff Lund of Lund Construction Co. in North Highlands, which helped excavate debris from the river channel beneath the damaged spillway. Lund said his firm was paid about $5 million for its work at Oroville. It is estimated that over $400 million will have been spent by the time Oroville’s facilities are restored. The single biggest contracts belong to Kiewit Corp. the construction firm that won the $275 million contract to repair the battered spillway over the next two years.

The state Department of Water Resources outlines its plans for repairs and replacement of the Oroville Dam spillway by Nov. 1st, with the undamaged top chute as the priority. The independent board overseeing the repair of the spillway recommends the DWR change its priorities and focus on the damaged bottom chute rather than the top. The board’s report said the spillway design is ready for final review, with major redesigns including heightening walls beside of the main spillway. A wall dug into the ground that would block erosion up the emergency spillway weir has been moved 350 feet downhill, and is now 600 feet below the spillway weir. That is because there is better quality rock closer to the surface in the new location, according to the report.

The Board of Consultants determined the forensic teams’ list of potential Oroville Dam spillway failures are being addressed in the new design, according to a recent published memorandum. It should be noted that the board did not note any major discrepancies in its findings compared to those of the Department of Water Resources and its contractors. The board was also recently briefed on a U.S. Army Corps of Engineers semi-quantitative risk assessment, looking into possible impacts of closing the flood control outlet before June 1st, including the likely reservoir levels in doing so and also the risks of operating the main and emergency spillways in their current condition.

A workshop titled “Potential Failure Modes Analysis,” which is required by FERC any time a structure fails or undergoes remedial work or major modification. Participants of the workshop included representatives from FERC, the Division of Safety of Dams, DWR and Kiewit, who is the contractor doing reconstruction. They worked to identify potential causes for water to be released from the reservoir uncontrolled, coming up with 22. About one-third of the next page is blacked out because according to DWR representatives it contains Critical Energy Infrastructure Information.

With respect to the reconstruction efforts, Kiewit has begun work on the main spillway. Kiewit has removed what was left of the lower 2,000 feet of the chute, except for the huge baffles at the bottom, using excavators and controlled blasting. The contractor is also removing the bottom 600 feet of the upper chute, leaving the 1,000 feet immediately below the floodgates in place. That part of the upper chute has been deemed structurally sound and will not be replaced this year, but just patched and anchored. Next year it will be removed and replaced. Preliminary foundation preparation work has begun on the lower chute, including pumping concrete into smaller gaps in the rock. Two large gaps will be filled with roller compacted concrete, and then a final layer of construction grade concrete will be poured for the floor, and walls will be added.

Other Dams:

From reservoirs, large to small, 16 dams in the State were above 90% full as of February 15th. Since October 1st, more precipitation has fallen across the key watersheds of Northern California — eight areas from Lake Tahoe to Mount Shasta that feed many of the state’s largest reservoirs — so far this winter than any time since 1922, according to state totals.

Don Pedro Reservoir, the sixth-largest in California and located near Yosemite National Park. As of the afternoon of February 15th, Don Pedro stood at an elevation of 827.4 feet, just shy of its 830-foot capacity, the Turlock Irrigation District said in a statement. The district continued to make releases to the Tuolumne River, which flows through Stanislaus County and into urban centers such as Modesto.

As of midnight Feb 13th Shasta lake stood at 96 percent of capacity and 137 percent of the historical average, according to DWR. Water officials are releasing 70,000 cfs from Shasta Dam as the lake stands just 5 feet from the top of the reservoir, per the Shasta County Sheriff's Office. "This is higher than it should be for this point in time," the sheriff's office said. "The release is necessary for space to allow future storms and to prevent uncontrolled release and flooding." The reservoir holds 4,552,000 acre-feet and added nearly 4,400,000 acre-feet in Shasta Lake, as of early on the morning of February 13th, DWR records show.

Another example is found in the Keswick Dam in Shasta County. Due to the increased releases below Keswick dam, areas of Red Bluff River Park were blocked off February 10th as water levels were expected to rise once again over the weekend causing possible flooding throughout the park, similar to the floods on the 13th. The high Sacramento River levels on the 13th, which flooded River Park, were due to the increased releases from Keswick Dam to 36,000 cfs, along with rainfall. The Sacramento River water levels have decreased since February 13th, but that may change as the Bureau of Reclamation began incrementally increasing releases from the dam late on the 16th. The bureau is expected to release 70,000 cubic feet per second by the 19th.

The Anderson Reservoir, the largest in Santa Clara County, is too full, per government regulators, so the water district is unleashing much of storm water flowing into the reservoir, as officials said it is too unsafe to collect it. Otherwise, they fear, if a major earthquake were to strike while the water level is so high, there is a chance the dam could fail. As of Friday morning, the reservoir was 86.5 percent full, according to data provided by the Santa Clara Valley Water District. Because the reservoir is over safety capacity, which was evident on the morning of the 10th by the massive amounts of rushing water. Water district officials are letting a lot of the recent rain water go — a frustrating fact following five years of drought. Anderson's outlet has been 100 percent open since Jan. 9, releasing water into Coyote Creek, at a rate of more than 400 cfs. Instead of collecting and storing the water the district is releasing all incoming water into the nearby Coyote Creek, which then flows to the San Francisco Bay, and then the Pacific Ocean.

After the recent heavy rains and showers, much of the central San Joaquin Valley and foothill areas will see about five days without rain, with new concerns focused on water releases from overfilled dams. A flood warning went out on the morning of February 11th for areas along the San Joaquin River, where the National Weather Service office in Hanford said water released from Friant Dam could cause flooding downriver. It was unclear when water would be released from Friant Dam, but the weather service reported that Friant Dam had increased the water release for Saturday morning to between 7,000 and 8,000 cubic feet per second. The weather service said Mariposa Dam and Owens Dam were overflowing and lower communities were in danger of being flooded. The flood warning there was expected to last until 6:15 p.m. the 18th, if not extended.

Since February 2nd, Lake Tahoe has risen one foot, or 39.1 billion gallons of water. As of February 11th, 2017, the lake is 3.14 feet above its natural rim with an elevation of 6,226.14 feet above sea level. To reach the maximum elevation, Lake Tahoe has just 2.86 feet to go, 1.14 to reach "full." Heavy snow content in meadows and high river levels are slowing localized drainage significantly. Unfortunately, the heaviest rain is still predicted to be on the way.


To further complicate the issue: According to NASA and European Space Agency data released on February 8, parts of the California aqueduct on the west side of the San Joaquin Valley, near Avenal, sank more than two feet between 2013 and 2016 as farmers pumped records amounts of groundwater during the state’s historic drought.

The two-foot dip “creates a chokepoint” in the aqueduct, says Jeanine Jones, interstate resources manager at the California Department of Water Resources. Department models show that the canal today can move 15 to 20 percent less water than its designed capacity. This means that cities and farms in the southern half of the state might not be able to take full advantage of big storms and atmospheric rivers this winter even though state officials have increased water delivery forecasts. Congress also passed a measure last December to maximize water pumping from the Sacramento-San Joaquin delta to fill canals.

The entire scenario is filled with irony. The California aqueduct transports water to the Central Valley and Southern California cities in order to reduce groundwater pumping that was causing a land subsidence crisis in the mid-20th century. Today, the canals themselves are at risk from the same forces.

Just months past one of the driest four-year periods in state history California is now awash in fresh water due to a relentless series of Pacific storms. The Sierra snowpack is the largest in more than two decades, nearly 80 percent above normal, while the northern Sierra Nevada is on track for its wettest year on record. Reservoirs are above average and many are nearing full capacity. The state is now actually running out of places to store extra water.

California cities and farms are expecting to receive a big water dividend from the wet winter. The shrinking of land near major canals, however, complicates the ability to transport the water. Subsidence, skews the canal’s precision engineering, which is designed to slope downward at one-half-foot per mile. Subsidence is causing water to pool in the 27-inch dip near Avenal where the land has collapsed. The area around the aqueduct affected by subsidence of more than eight to 10 inches has grown roughly four-fold since NASA’s previous report, in August 2015.

The Avenal zone is one of three subsidence hot spots that NASA and state agencies have been tracking in recent years. The hotspots are adjacent to key pieces of California’s water delivery and flood control infrastructure: the California aqueduct, the Delta-Mendota canal, and the Eastside bypass.

NASA found subsidence of up to 22 inches along the Delta-Mendota Canal, part of the federal Bureau of Reclamation’s Central Valley Project water supply system. A bowl of subsidence roughly 25 miles in diameter and 16 inches to 20 inches in depth extends across the Eastside bypass, a flood control structure used to shunt water away from the San Joaquin River during spring floods in years with deep snowpack.

The Sustainable Groundwater Management Act will presumably address the problem in the long-run. But the act’s timetable — agencies are not required to establish sustainable use until 2040 — is too slow to help now.


Recent events with the Oroville dam demonstrate the inability for California to effectively manage atmospheric rivers and isolated wet years during drought conditions. The warm precipitation from Pacific storms and atmospheric rivers cause rapid snowmelt which in turn rapidly depletes the snowpack, causing flood conditions as seen in Lake Tahoe. This depletion of the snowpack in conjunction with heavy rains overloads the reservoirs of the California water system, as seen in the cases of Oroville, Shasta, and others. The inability to effectively capitalize on these wet year supplies is evidenced by the drought conditions that continue to affect the southern regions of the State. Even though the State's two largest reservoirs, Oroville and Shasta, are at 126% and 124% capacity, 47% of the state remains in drought conditions.

The ability to distribute water in wet years is insufficient. The State Water Project has lost 15-20% of its capacity to transport water in several parts of the State due to subsidence caused by groundwater pumping. Furthermore, the SWP is limited by its total capacity of 5,746,790 acre-feet. When the SWP and the State’s reservoirs are at capacity in the Northern regions of the State, the State is limited in its ability to store and transport water and supplies are lost to flooding and the Pacific Ocean. This effect is exacerbated by the presence of atmospheric rivers which are capable of delivering massive amounts of water on a region in a short amount of time. The system in place is ineffective at capturing and distributing these supplies.

Given that 47% of the State still faces drought conditions, the loss of supplies becomes a critical issue, the bottlenecks must be addressed. With Pacific storms catalyzing snowmelt -- while the reservoirs fed by the snowpack remain full – the snowpack supplies will be lost to flooding and the ocean, reducing critical supplies during the Spring and Summer months. If drought conditions continue, this loss of supply will intensify an already taxing feedback loop; without water in the SJV farmers over-pump groundwater supplies, which causes subsidence, reducing the amount of water farmers can receive from the SWP, increasing their reliance on groundwater pumping. These bottlenecks demonstrate the unstable reliance our current water supply system has on favorable conditions – not too wet and not too dry. This range must be addressed.

The implications of these bottlenecks in our infrastructure have the potential to be severe. Public opinion holds that drought has ended due to the heavy rainfalls seen in the beginning of 2017. Due to the system’s inability of capturing snowmelt effectively, this may not be the case. Furthermore, the effect of believing we are no longer in a drought may change conservation habits as people may be lured into a false sense of supply. Thus, it is important that drought regulations remain in place, so that supplies can best be stretched in the event that these storms are an outlier in a larger drought cycle. We must also consider the rate at which the snowpack may be melting in the face of warm precipitation from Pacific storms and global warming. If the melting rate of the snowpack is too quick, the supplies provided by the snowmelt will be lost as uncaptured flood water or discharge to the ocean.

While the state’s reservoirs are built to release water slowly, officials are being forced to quicken the pace of releases when they are at capacity. Water from brimming reservoirs is guided into nearby rivers. If those rivers are full, water can seep over and under levees, or through hidden cracks, leading to erosion. Erosion could further strain the hundreds of miles of levees that line the Central Valley’s vast river networks, built to protect homes, businesses, and farms from floods. The series of storms that slammed the area in December 1996 and lasted for a week caused numerous levees to collapse. Widespread flooding that inundated 300 square miles led to extensive damage and evacuations of 120,000 people, as well as nine deaths.

As can be seen, the State faces an environmental juxtaposition, drought continues in regions in the SJV and the South, while the risk of flood looms over the Northern portions of the State. While this can be attributed to climatic conditions it should force policy-makers and stakeholders to reevaluate the ability of our State’s water system to respond to wet and dry conditions effectively. It should also be noted that floods, shortages, and limits of infrastructure effect multiple arenas, including ecological and socioeconomic systems (see Santa Barbara case study).

Finally, a strategic question should also be asked, how do we avoid Jevon’s paradox? If we use conservation to meet the demands of continual growth, then we find ourselves locked into an unsustainable cycle (see Red Queen’s Race) of creating new permanent demands, which ultimately put a stronger strain on an already overtaxed water system -- one that is dependent on a narrow range of climatic conditions that may be increasingly unlikely in a changing climate.

Potential Solutions

  • The implementation of Low Impact Development (LID) and the restoration of mountain meadows (Sierra Meadows Partnership) will improve the biotic and abiotic capture and storage rate of atmospheric rivers and storms.

  • Amending SGMA to hasten the sustainability requirement from 2040 to 2025 while enforcing the Waste and Unreasonable Use doctrine to reduce further subsidence and thereby halting the diminishment of the ability of the SWP to convey water quickly.

  • Improved landscape planning/development practices so that they hold water as a central planning requirement. Effectively overcoming Jevon’s paradox by limiting urban expansion and the creation of new permanent/unsustainable demand.

  • Focusing on redevelopment and density instead of development of new land.

  • Reinvestment in State infrastructure to reduce the threat of erosion to critical dams and levees.

  • Continued conservation methods to adapt to drought being the new normal, prolonging the life of limited supplies.

  • Water budgets.

  • Smart Controllers/Outdoor water use practices.

  • Recycled Water.

  • Water meters.

  • Continuing to enforce Executive Order B-37-16.

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