SENATE NATURAL RESOURCES AND WATER COMMITTEE
SENATOR ROBERT M. HERTZBERG, CHAIR

SPECIAL ORDER OF BUSINESS:
AN UPDATE ON THE OROVILLE DAM
April 25, 2017
9:00 a.m., State Capitol Room 4203
Background Paper
Oroville Dam is an earthfill dam on the Feather River, east of the city of Oroville,
and a key feature of the State Water Project (SWP). At 770 feet high, it is the
tallest dam in the U.S. and provides water supply, power generation, and flood
control. The dam impounds Lake Oroville, the second largest man-made lake in
the state of California, and is capable of storing more than 3.5 million acre-feet.1
On February 7, 2017, during an otherwise normal flood control release of about
50,000 cubic feet per second (cfs), a large cavity developed in the Oroville Dam’s
main spillway.2 This lead to a sequence of events that included:
 Massive damage and erosion of the dam’s main spillway,
 Uncontrolled releases over and concerns of failure of the dam’s emergency
spillway, and
 Mandatory evacuations downstream of Oroville Dam.
The purpose of this hearing is to provide members an update on what happened at
the dam and the plans for going forward.
1

An acre-foot is defined as the volume of one acre of surface area to a depth of one foot. It is approximately
325,850 gallons, or approximately the amount of water used by two households annually.
2

A rate of one cubic foot per second over a period of 24 hours yields approximately two acre-feet, or just under
725 acre-feet per year.

 The purpose of this background paper is to supplement information developed by
the Department of Water Resources (DWR) regarding the incident at Oroville Dam
and to provide a context for policy questions the members may wish to explore
regarding the incident and next steps. This includes questions regarding:
 Plans for repairing and restoring the damaged spillways.
 How engineering decisions are being made regarding repair and restoration of
the damaged spillways.
 How public the documents generated by the various engineering reviews will
be.
 Any additional modifications to the dam beyond the spillways being
contemplated.
 Who is paying for the emergency actions and reconstruction/restoration
activities.
 Implications for inspections, management, and operations of other dams in
California.
OVERVIEW OF DAMS, DAM SAFETY, FLOOD CONTROL DAMS, AND OROVILLE
DAM.
California is home to over 1,400 dams, 1,251 of which are under the jurisdiction of
the Department of Water Resources’ (DWR’s) Division of Safety of Dams
(DSOD). Among other things, the division inspects each dam annually to ensure
the dam is safe, performing as intended, and is not developing problems. The dam
safety program is funded entirely from the combination of dam application fees
and annual fees. California’s dam safety inspection program is considered by
many as the best in the nation. Indeed, Lori Spragens, Executive Director of
Association of State Dam Safety Officials, was recently quoted as saying
“[California has] actually what we consider the Cadillac version of a state dam
safety program.”
California has 54 dams that are considered primary flood-control structures. The
flood operations of these dams are dictated by flood-control manuals created by the
U.S. Army Corps of Engineers (USACE). The main feature of these manuals is
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 what is known as the “rule curve.” This is a set of graphs that show maximum
elevation to which the dam operator can fill a reservoir during various times of the
year. This maximum elevation is sometimes referred to as the “top of the
conservation pool.” During real-time flood operations, the rule curve also
describes how fast water should be released given the conditions of the flood
event. DWR, which operates Oroville Dam, is required to make releases according
to the rule curves outlined in the dam’s manual. The manual is dated August 1970,
two years after the dam’s construction was completed.
Construction of Oroville Dam began in 1961 and was ready for use in 1968. Lake
Oroville and Oroville Dam are part of a complex which includes the Hyatt
Powerplant, Thermalito Diversion Dam and Powerplant, the Feather River Fish
Hatchery, Thermalito Power Canal, Thermalito Forebay, Thermalito PumpingGenerating Plant, Thermalito Afterbay, and the Lake Oroville Visitors Center.
Ordinarily, there are four ways DWR can pass water through or around Oroville
Dam:
 Through the Hyatt Powerplant, with a maximum flow rate of 16,950 cfs.
 Through a river outlet or bypass valve, which, when fully operational, has a
capacity of 4,000 cfs.
 Through the gated main spillway that has a maximum capacity of 150,000 cfs.
 Over the top of an ungated emergency spillway, a concrete, 1,730-foot long
weir, built 21’ below the height of the main dam. Once the lake reaches an
elevation of 901’, it naturally flows uncontrolled over the weir and down the
natural hillside, which is used as the spillway channel.
NOTABLE EVENTS REGARDING OROVILLE DAM PRIOR TO THE EMERGENCY
2005 Dam Relicensing. On October 17, 2005, in petition to intervene in the
Federal Energy Regulatory Commission (FERC) proceeding to relicense Oroville
Dam, Friends of the River, the Sierra Club, and the South Yuba River Citizens
League (FOR) asserted, among other things, that “the emergency spillway is not
armored and extensive erosion would take place if the emergency spillway were

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 used.” Quoting from a 2002 Technical Memorandum on Lake Oroville Surcharge,
the petition states, “The hillside between the emergency spillway and the Feather
River would be subject to severe erosion when water flows over the spillway.
Depending on the rate of flow, the erodible area … could range from 50 to 70
acres. The amount of soil, rock, and debris that would fall into the Feather River
could be very large, depending on the depth of erosion. There could be damages to
downstream structures, including the Thermalito Diversion Dam and Powerplant,
Fish Barrier Dam, and highway bridges. If there is river channel blockage below
the spillway, there could be impacts on operation of Hyatt Powerplant.” The
petitioners requested FERC to require DWR to armor the ungated spillway and to
direct DWR to work directly with the Corps and other interested parties to improve
the plan of floodwater management operations at the Project.
FERC staff, in their Draft Environmental Impact Statement for Oroville Facilities,
did not address the merits of FOR’s argument. Instead, staff found “Any dam
safety issues associated with the emergency spillway are properly addressed
through the Commission’s ongoing dam safety program, not the relicensing
process.”
2009 River Valve Accident. Oroville Dam has a low level outlet at the base of the
dam called the River Valve Outlet System (RVOS). The RVOS was designed to
serve as a bypass around Hyatt Powerplant in the event of an outage of the plant
and was also designed to serve as a low level outlet in case emergency evacuation
of Lake Oroville is required. A component of the RVOS is an energy dissipating
feature known as a “baffle ring.” In 2009 the baffle ring was removed due to its
deteriorated condition. After its removal, on July 22, 2009, several workers were
testing the RVOS when a breakaway wall failed, injuring the five workers.
DWR began work to refurbish the RVOS in 2012 and accelerated the work in 2014
to allow for limited drought operations. The system was mostly refurbished at that
time, but some work remains to restore the RVOS to its full original design
capacity of 4,000 cfs.

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 Recent Dam Inspections. The goal of DSOD is to inspect all jurisdictional dams
each fiscal year. In the case of Oroville, the size and facility elements can
necessitate multiple visits to cover all areas to be inspected.
Inspections occasionally show cracks in the spillway that are then repaired, as was
done most recently in 2013. The most recent inspection was on August 22, 2016.
TIMELINE OF EVENTS AT OROVILLE.
January 13: After a series of storms beginning in December, Oroville Reservoir
first rose above 850’ elevation, the top of the conservation pool. This triggered the
beginning of flood control releases out of the Dam.
February 7: As water releases from the flood control spillway ramp up to 54,500
cubic feet per second, in anticipation of inflows expected from rainfall, DWR
employees notice an unusual flow pattern. Spillway flows stop for investigation.
Engineers find large area of concrete erosion.
February 8: DWR begins ongoing consultation with FERC and other dam safety
agencies. DWR runs test flows down the damaged spillway, monitoring further
erosion, and prepares for possible use of emergency spillway. 24/7 emergency
interagency operations centers activate to study and implement response to flood
control spillway and related structures, with careful study of weather forecasts.
February 9: The California Department of Fish and Wildlife (CDFW) starts
evacuating fall-run Chinook salmon, spring-run Chinook salmon, and steelhead
trout from the Feather River Hatchery to a hatchery at Thermalito because of
muddy water flowing from the damaged spillway.
February 11: Inflows to Lake Oroville brings lake level above 901 feet. This
engages the emergency spillway for the first time in the history of the facility.
CDFW successfully finishes relocating 100% of the spring run Chinook (2 million
juveniles) and another 3 million juvenile fall run from the fish hatchery.

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 February 12: Erosion begins to progress faster than expected at the base of the
emergency spillway. The Butte County Sheriff Korey Honea issues mandatory
evacuation orders for the Oroville area. To ease pressure on the emergency
spillway, the flood control spillway outflow is increased to 100,000 cfs. After
several hours, inflows decrease and overflow stops at the emergency spillway.
Erosion to the emergency spillway hillside is assessed.
February 13: DWR crews begin working around the clock to repair the emergency
spillway. Evacuation orders remain in effect.
FERC requires DWR to initiate immediate design of emergency repair to minimize
further degradation of both the emergency spillway and the service spillway. In
addition, FERC requires DWR to convene an independent Board of Consultants
(BOC) to review current conditions, risk reduction measures, and proposed
remedial options, and later perform a forensic analysis to determine both the cause
of the spillway failure and whether it could occur again.
February 14: As the lake level continues to drop, the mandatory evacuation order
is modified to an evacuation warning. Crews continue working around the clock to
repair the emergency spillway. An elevation of 850’ is targeted for lake level.
February 16: Flood control spillway flows are reduced below 100,000 cfs to
facilitate the clearing of debris from below the spillway. Lake levels continue to
drop. Construction to armor the emergency spillway continues.
February 17: DWR notifies FERC of the appointment of members to the BOC,
and DWR’s request to the U.S. Society of Dams and Association of State Dam
Safety Officials will identify an independent team of experts to perform an
independent forensic review, the review to begin within three months.
February 18: Lake level drops to 854 feet. Flood control spillway flows are
reduced to 55,000 cfs. Barge construction begins in order to remove debris from
the diversion pool beneath the spillway.

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 February 21: FERC approves the membership of the BOC, requires the
appointment of the forensic team by March 15, and the beginning of the forensic
analysis as soon thereafter as feasible.
February 24: The USACE approves an emergency permit to DWR to operate
Oroville Dam project in an emergency capacity until Aug. 24. Among the
requirements of the permit, the water department must return the area to the way it
was before the emergency, and it must comply with recommendations to save
wildlife.
The National Marine Fisheries Services (NMFS) notifies FERC of concerns that
dredging and dam operations at Oroville may strand or otherwise harm important
anadromous fish, including spring run Chinook salmon, steelhead, and green
sturgeon.
February 27: Lower lake levels and a long term forecast of dry weather allow
DWR to stop releases from the main spillway. Removal the debris below the main
spillway begins in earnest, along efforts to reopen the power plant and engineering
and geological investigation and assessment of the damages spillway.
February 28: A cooperative effort by CDFW and DWR is initiated to save
thousands of fish from lowering water levels along the Feather River. Notable fish
species affected included Chinook salmon and steelhead trout.
DWR estimates the debris pile below the damaged spillway to be approximately 1
M cubic yards. By April 14, a total of 1.6 M cubic yards of debris are removed.
March 1: The first meeting of the BOC was held at DWR. The purpose was to
introduce them to the staff of DWR who will be working on the restoration design.
March 2: The BOC was taken to Oroville Dam for their first view of the extent of
the damage. Also attending were staff from FERC and DSOD.
March 5: The Hyatt Powerplant was restarted with one turbine generator moving
water at 1,720 cfs. Additional units are brought online in subsequent days.

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 March 9: All 5 operational units at the Hyatt Powerplant are up and running,
allowing for a total outflow of 8,800 cfs.
March 10: The BOC met at offices of DWR for presentations of restoration design
concepts by DWR.
The Hyatt Powerplant’s five units are discharging a total of 12,900 cfs
March 15: DWR announces appointment of a separate independent team to
conduct a forensic evaluation of the failure of the spillways. DWR contacted the
United States Society of Dams (USSD) and the Association of State Dam Safety
Officials (ASDSO) to select the forensic team.
March 17: DWR increase outflows from Lake Oroville to the Feather River to
40,000 cfs by reducing releases from the Hyatt Powerplant and then reopening the
damaged gated flood control spillway.
DWR submits to FERC the BOC’s Memorandum No. 1 for the Oroville
Emergency Recovery- Spillways, dated March 10, 2017. Among other things, the
report points to design flaws at Oroville Dam’s main spillway that might have
caused the giant crater to form in the concrete chute Feb. 7. The BOC also
questions whether the state could realistically follow through with plans to
permanently repair the structure before the next rainy season.
Acting DWR Director William Croyle later said the report “shouldn’t have been
made public.”
March 20: FERC notifies DWR that it accepts the membership of the forensic
review team, states that the forensic team should begin their work immediately,
and requests a plan and schedule for their efforts within five days.
CDFW, in cooperation with NMFS releases one million of the rescued spring-run
Chinook salmon into the Feather River.
March 22: Sheriff Honea lifts all evacuation warnings and advisories for Butte
County residents previously affected by the February 12th Oroville Dam spillway
emergency evacuations.
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 March 24: DWR provides FERC with a preliminary schedule for the forensic
review team. The preliminary schedule calls for an initial review of materials
March 23 to April 12, and site inspections April 12 and April 13.
March 27: DWR begins ramping down outflows from Lake Oroville. Flows from
the damaged spillway will be reduced eventually reach zero cfs. Flows from the
Powerplant are scheduled to resume to 13,000 cfs.
At the press briefing announcing the changes in operations, Acting Director Croyle
says, “If I have anything to say about it, we’ll have a spillway to use by November
1. Whether that’s a permanent or temporary structure is still to be determined.”
March 31: The Sacramento Bee reports, “Citing potential security risks, state and
federal officials are blocking the public’s ability to review documents that could
shed light on repair plans and safety issues at crippled Oroville Dam. In a written
statement to the Bee, spokeswoman Lauren Bisnett cited federal dam-security
regulations.”
“Within the bounds of security restrictions, DWR is committed to regularly
updating the public on the findings and recommendations of the Board of
Consultants and on the work to rebuild the Oroville spillways before the next storm
season.”
April 2: President Trump announces more than a half-billion dollars would be
coming to California to help cover the damage from the winter storms, including
$274 million for repairs to the Oroville Dam spillway.
The $274 million for the Oroville spillway, an estimate provided by the
Department of Water Resources, is for emergency response costs from Feb. 7
though the end of May. The money targets stabilizing the emergency and main
spillways, as well as debris removal and work on the downed Hyatt Powerplant.
April 6: DWR releases its repair plan, acknowledging the work won’t be finished
until 2018 and will leave the fractured spillway partially undone when the next
rainy season begins this fall. Nonetheless, Acting Director Croyle said the 3,000foot-long concrete chute, whose problems led to a near catastrophe in February,
will be functional by the time the rains arrive in November.
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 April 13: DWR announces it expects to resume use of the flood control spillway to
discharge approximately 35,000 cfs on April 14, 2017.
At the press conference, Acting Director Croyle told reporters he’s considering
releasing redacted copies of safety and progress reports at the troubled Oroville
Dam after his office had tried to keep them secret because of terrorism concerns.
April 15: DWR open bids submitted by three contractors to repair the Oroville
spillway. The low bid is $275 M, significantly higher than DWR’s Engineer’s
Estimate of $220 M.
April 17: DWR awards a contract to Kiewit Infrastructure West Co., for the repair
work on Oroville Dam’s spillways. Repairs are scheduled to begin immediately to
have the system operational by November 1, the traditional start of the winter rainy
season.
April 18: An independent analysis on the primary root causes of the failure of
Oroville’s main spillway by Robert Bea, of the Center for Catastrophic Risk
Management at UC Berkeley points to design and construction flaws dating back
to the spillway’s construction in the 1960s.
According to the Los Angeles Times, Bea said the technical problems in the
spillway should call into question the adequacy of the dam itself and the adequacy
of about 20 other California dams built in the same time period.
“Good risk management would dictate that we should look at all the dams of that
era,” quotes the Los Angeles Times. “This is not an Oroville problem. It is a state
problem and a national problem.”
ISSUES/QUESTIONS FOR CONSIDERATION
What remains to be done to secure Oroville Dam for the rest of this flood season?
How will the damage at Oroville affect flood operations for the rest of the flood
season? Next season?

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 How will we determine what all needs to be done to secure Oroville for the long
run? What is the expected timeline?
Who is currently paying for the dam emergency efforts? Who will pay for the
repairs to the damaged spillways and other associated damaged facilities/property?
What is the basis for that determination?
Who paid for the evacuation of the fish from the Feather River Fish Hatchery?
Was there any damage of the fish hatchery itself? Who will pay to repair that?
How did the emergency and response affect the Feather River ecosystem? What
river restoration projects will be required, both immediately below the dam site and
further downstream? Who will pay for that?
What types of information in BOC reports and other documents provided to FERC
lead to them being made secret? How is the Legislature to provide appropriate
oversight of the administration’s plans and actions to restore Oroville without
access to such reports and documents?
What role, if any, did the age of the flood control manual have in the decision
making during the flood incident at Oroville?
What, if any, modifications are being considered to Oroville’s operations,
management, or emergency protocols? How will those decisions be made and by
who?
In what way, if any, did the constrained capacity and apparent non-use of the dam’s
river valves constrain operations?
Why wasn’t the emergency spillway armored as suggested by FOR in 2004?
Besides work to restore the spillways at Oroville dam, are any other major capital
projects underway or under consideration at the Oroville Complex? Who pays for
those projects?

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 Most of the facilities of the SWP were built in the 1960s, with design lives of 50100 years. 50 years later, what other SWP facilities require significant capital
improvements?

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