Modernized procedures at California’s Oroville Dam could improve flood safety, report finds
Modernized changes to long-held operating procedures at the dams walling Lake Oroville and New Bullards Bar Reservoir in Northern California could improve flood safety for communities along the Feather and Yuba rivers.
That’s the finding several agencies reached in a new report exploring the effects of using improved monitoring, weather and runoff projections to determine when and how to release water from the reservoirs.
“California’s reservoirs play a critical role in safeguarding our communities from floods and maintaining our state’s water supply, especially as we continue to see more extreme weather events in the form of larger, wetter, and more frequent storms and longer, more severe periods of drought,” said Michael Anderson, a Department of Water Resources climatologist, in a Thursday news release.
The Forecast-Informed Reservoir Operations report, a collaboration of several local and state agencies, found that timing water releases in advance of atmospheric rivers — using forecasts to predict storms’ strength and duration — could mitigate the risk of flooding downstream while improving water storage, according to the news release.
The report also accounted for the effect of an additional spillway at New Bullards Bar Dam. Yuba Water Agency, which operates the dam, has had the spillway designed and is seeking state and federal funds to pay for it, with 2027 targeted for construction.
The New Bullards Bar Dam walls off the north Yuba River while the Oroville Dam regulates the Feather River. Those two rivers converge near Marysville and Yuba City, dozens of miles downstream of each dam, connecting the use of each of their respective dams to one another.
Researchers used historical forecasts, reservoir storage and river flow data in determining that better forecasting and release timing, paired with the addition of the new spillway, could reduce the flood risk from prolonged storms, such as the ones in 1986 and 1997 that struck Yuba County.
The report focused on flood control but also found that water supply management could benefit from the changes.
“This is a critical step towards making more floodwaters available for groundwater recharge when we see extremely wet storms,” said Karla Nemeth, Department of Water Resources director, in the news release.
The new plan “drives tighter coordination between reservoir operators and water districts downstream, creating opportunities to use reservoir releases to build up our groundwater reserves for dry years,” she added.
Similar forecast-informed planning has been implemented at Lake Mendocino in the Russian River watershed and will soon integrate into Prado Dam in the Santa Ana watershed, according to the news release. The plan for the Feather and Yuba rivers differs in its scale and complexity, as well as its primary goal of reducing flood risk, as opposed to prioritizing water management.
Flood protection
Oroville Dam in particular stirs reminders of the importance of flood protection along the Feather and Yuba rivers.
More than 180,000 residents were evacuated from Butte, Sutter and Yuba counties in February 2017 when concerns mounted that the dam’s spillway would fail, sending a torrent of water downstream. That would-be crisis was averted, but the scare added to a history of flooding disasters that have plagued those communities.
New Bullards Bar Dam holds similar importance to the Yuba River.
Building an atmospheric river control spillway at New Bullards Bar Dam would target reducing peak flows downstream and relieving stress on the levee system during heavy atmospheric river events, said John James, Yuba Water’s director of resource planning, in the news release.
“With both FIRO and the ARC Spillway, we’re essentially gaining the amount of flood storage that would historically only be created through building additional infrastructure,” James said. “In this case, we’re enhancing existing infrastructure and using the latest in science and technology to modernize flood operations and improve public safety.”
The new spillway would have gates lower than the dam’s existing spillway, allowing water to be released while the reservoir is at lower levels, such as before a large storm passes through. Meanwhile, the current spillway capacity and infrastructure at Oroville Dam, operated by the Department of Water Resources, meet the needs outlined in the recent report, according to the release.
Water management
The Department of Water Resources and Yuba Water Agency during the rainy season both draw down their reservoirs to create flood storage space within certain requirements designated by the water control manual each has with the U.S. Army Corps of Engineers.
With more predictive timing and accuracy of incoming storms, under the new plan, each dam could release water earlier in the season, creating space in reservoirs to capture more runoff, potentially increasing overall water supply.
The broader process of updating the federal water control manuals that the dams abide by is ongoing. The plan coordinating the dams walling the Feather and Yuba rivers is separate but works in conjunction with the federal manual.
The joint planning between the dams was supported by the engineers corps and “is an important step toward formalizing our district’s use of improved weather forecasts for strategic water management decisions at New Bullards Bar and Oroville reservoirs,” said Jenny Fromm, the Army Corps Sacramento District’s chief of water management, in the news release.
Public meetings addressing the water control manual changes are expected to take place this year.
