1 year later: Oroville Spillway crisis and evacuation timeline

On February 12, 2017, the City of Oroville was evacuated due to an imminent threat of the emergency spillway failing. In total, almost 200,000 people were evacuated through Butte, Sutter, and Yuba County. These key dates shed some light on what happened leading up to and shortly after the evacuation and the spillway incident.

Oct. 1, 2016-Jan. 31, 2017: The California water year starts in October and was quickly on track to become one of the wettest in recent years. The heavy rain ended the California 5-year drought and became the second wettest year since 1983 in terms of runoff. According to the Department of Water Resources, large swaths of the Northstate received between 200-300 percent of average rainfall. This meant that reservoirs like the one sitting behind the Oroville Dam quickly grew to capacity.

Feb. 1 - Feb 6.: DWR ramps up water release over the primary spillway at a rate of 30,000 cubic feet per second (cfs).

Feb. 7: A large hole formed along on the primary spillway, which halted releases of water. According to the DWR, as water was released from the primary spillway in anticipation of more rain, employees at the dam noticed that something was wrong. They stopped flows at the spillway to investigate and that is when engineers found large areas of concrete erosion.

Feb. 8: As investigators and engineers examined the damaged spillway, flows were reduced to less than 10,000 cfs, while at the same time heavy rain is battering the region, meaning an inflow of 120,000 cfs into the lake. Between Feb. 6 and Feb. 10, 12.8 inches of rain fell into the Feather River basin.

Feb. 9 - Feb. 10: Inflows peaked at over 190,000 cfs while outflows remained relatively low, between 55,000 and 65,000 cfs. Due to the additional rainfall, the Butte County Office of Education urged public schools in Oroville to close Friday after concerns of possible flooding in the area.

Feb 11: Inflow into the lake brings lake levels above 901-feet, which means that water went over the emergency spillway for the first time in the history of the dam.

Feb 12: At 4:10 p.m. a message went out to all media outlets issuing an immediate evacuation as ordered by Butte County Sheriff Kory Honea. "Failure of the auxiliary spillway structure will result in an uncontrolled release of flood waters from Lake Oroville," read part of the message. The DWR explained that erosion began faster than expected at the base of the emergency spillway, creating a cause for concern. The main spillway outflow was increased to 100,000 cfs. An estimated 180,000 people in total were evacuated downstream by orders of Sheriff's in Yuba and Sutter County. Several hours later, inflows decrease and outflows at the emergency spillway stop.

Feb 13-14: The evacuation order remained in place through the 13th as the DWR assessed the damage, left outflows at 100,000 and worked to repair the emergency spillway. On Feb 14, Sheriff Honea reduced the evacuation orders to evacuation warnings as the lake level dropped below 885-feet, 16-feet below the crest of the emergency spillway.

Additional Background

In 2005, DWR applied for a renewal of its operating license for the Oroville hydroelectric generating facilities. During the relicensing process, Friends of the River, Sierra Club, and the South Yuba River Citizen's League filed a motion to intervene in the relicensing. These groups alleged that the emergency spillway in 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 designed and that it met all FERC engineering guidelines.

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.

In their supporting documentation to FERC, the State Water Contractors (SWC) and Metropolitan Water District of Southern California (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. SWC and MWD raised no issues regarding the costs of armoring the emergency spillway.

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.

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