Oroville Dam spillway preps for first test after near disaster in 2017

Months of heavy rain across Northern California—and more to come this week—have Lake Oroville reservoir in Butte County brimming and the dam’s newly repaired $1 billion spillway facing its first big trial.

In late February, the California Department of Water Resources (DWR) announced that Lake Oroville sat at an estimated 773 feet, about 40 feet below the minimum level at which the spillway might need to be used. Since then, DWR says rains have pushed the reservoir up to 845 feet, with a projected capacity of 850 feet by April 5.

“Due to storms expected in the Feather River basin, DWR is taking steps to prepare for use of the main spillway potentially as early as the first week of April,” according to a DWR press release Tuesday.

Ordinarily the release of water into a spillway at one of the state’s major reservoirs would be unremarkable.

However, all eyes will be on the Oroville Dam (the tallest dam in the U.S.) if the spillway comes into use thanks to the dam system’s dramatic near failure in 2017.

In February of that year, the main Oroville Dam spillway crumbled during similarly heavy winter rains. Due to the damage, dam personnel had to employ the second backup spillway—i.e., a nearby dirt hillside.

Erosion pushed the secondary spillway dangerously close to failure, which would have released a “three-story wall of water” on nearby communities like Oroville, Yuba City, Marysville, Gridley, and Live Oak.

Nearly 200,000 residents evacuated in anticipation of what could have been a Biblical-grade disaster that, gratefully, didn’t happen.

In 2018, a six-person team of geologists and engineers filed a damning report blaming the debacle on “a long-term systemic failure of DWR” and accosted the state agency as “significantly overconfident and complacent about the integrity of its infrastructure, including its dams.”

Since then, the San Jose Mercury News reports that the state spent $1 billion on construction and repairs at the dam, including restoring the spillway.

There’s a lot riding on the dam’s performance if the state sees fit to use the new spillway in the near future.