OROVILLE, Calif. — A California congressman is questioning the degree to which state officials want to draw down Lake Oroville this winter, but the officials say it’s necessary to accommodate continued work on the dam.
Rep. Doug LaMalfa, R-Calif., whose district includes the Oroville area, argues it would be unnecessary for officials to drain the lake to as low as 640 feet of elevation by Dec. 31, as one Department of Water Resources scenario outlines.
Draining the lake that low would only leave 850,000 acre-feet in the lake with only about 100 days left in the winter to fill it, he contends. The spillway gates aren’t touched by water until it reaches 813 feet, which is 2.35 million acre-feet of water, he said.
“Construction won’t be affected by lake water if it’s a dry winter, and if it’s wet, they won’t be doing much anyway,” said LaMalfa, a rice farmer from nearby Richvale, Calif.
DWR spokeswoman Erin Mellon said the plan to lower the lake’s surface is based on federal “guidance” and weighs the need for adequate storage space if a big storm comes early with other uses of the lake.
“If weather hits there is enough space” for rain and runoff without interfering with construction, Mellon said.
State water officials want to bring the lake’s surface down to 700 feet elevation to enable crews to work past Nov. 1, which was their self-imposed deadline for getting the dam’s spillways ready for next winter’s rain and runoff. Officials insist the project hasn’t fallen behind schedule.
With guidance from the Federal Energy Regulatory Commission, the agency has established a projection schedule to draw down the reservoir’s elevation to enable late-season work and to provide some wiggle room if it starts raining.
The schedule calls for the lake to be taken down to 670 feet on Nov. 1 if inflows are low and 700 feet if they are high. By the end of December, the plan calls for a surface elevation of 640 feet to 680 feet.
Among the anticipated winter projects is construction of an underground cutoff wall for the emergency spillway, which has a targeted completion date of late December or early January.
While it’s “highly unlikely” the emergency spillway will be needed by November, lowering the surface “will allow us to keep a safe level” of the lake, said Jeanne Kuttel, a DWR chief engineer.
LaMalfa notes that the lake’s lowest elevation last year was 725 feet, in December. If it’s dropped to 640 feet this winter, that would be 600,000 fewer acre-feet stored in the lake, he argues.
Asked if it’s possible the DWR could stop at 700 feet rather than draining the lake further, Mellon said it “all depends on downstream requirements. We are going to meet all our requirements this year.”
Their remarks came during an Aug. 9 update on the $275.4 million effort to repair and rebuild the nation’s tallest dam, whose spillways nearly failed in February.
Lake Oroville is the main reservoir for the State Water Project, which irrigates more than 600,000 acres of Central Valley farmland and serves 20 million urban customers in the San Francisco Bay area and Southern California.
As of Aug. 10, the lake was holding 2.5 million acre-feet, or 56 percent of capacity and 79 percent of normal for the date, according to the DWR’s California Data Exchange Center.
Since 1968, Lake Oroville’s Oct. 31 surface elevation has averaged about 812 feet, though it has dipped below 700 feet on five occasions during dry years, according to a spreadsheet provided by the DWR. Last year’s Oct. 31 surface elevation was about 737 feet, up from 665 feet a year earlier.