Water & Drought

Why Oroville Dam’s woes could cut into California water supplies

New look at Oroville Dam spillway after reopening

New video shows water coming down Oroville Dam's main spillway on March 21, 2017. The dam’s main spillway fractured Feb. 7, 2017, prompting a temporary shutdown of the structure as a big storm rolled in. On Wednesday, more than a month after a nea
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New video shows water coming down Oroville Dam's main spillway on March 21, 2017. The dam’s main spillway fractured Feb. 7, 2017, prompting a temporary shutdown of the structure as a big storm rolled in. On Wednesday, more than a month after a nea

The fractured spillway at Oroville Dam has forced the state to spend tens of millions of dollars on emergency repairs, with millions more to come.

Here’s another potential cost: a slice of California’s water supply.

Dam operators are expected to run Lake Oroville, the state’s second largest reservoir, at lower-than-usual water levels this summer as they wrestle with the complicated and lengthy task of fixing the dam’s broken spillway. Despite one of the rainiest winters on record, that will mean less water held in storage – and less available for delivery later this year to Southern California, Silicon Valley and portions of the San Joaquin Valley.

“If they can’t continue to fill the reservoir and they have to hold it down while they’re in the process of making repairs to the spillway ... they’ll have less water available to release for export,” said Curtis Creel of the Kern County Water Agency, an agricultural irrigation supplier that’s one of the Oroville’s major customers.

Creel said he thinks the lake could be held considerably lower, sacrificing several hundred thousand acre-feet of water that would otherwise be available for crops. The state Department of Water Resources, which runs Oroville, said it hasn’t determined yet how low it plans to run the lake this summer but acknowledged that risk factors at the dam will likely figure into its calculations.

State water customers, hoping for a hydrological bonanza after five-plus years of drought, are now bracing for some measure of disappointment. They said they believe dam operators will release some water out of the reservoir earlier than usual for safety’s sake. Because the state’s main downstream reservoir in Merced County is already full, that means much of that Oroville water will wind up in the ocean instead of getting delivered during California’s sweltering summer and fall to the agricultural and municipal water districts that take deliveries from Oroville and pay for its upkeep.

“Given what’s happened with the lake, they’re going to be extra cautious this year,” said Deven Upadhyay, the head of water resource management at the Metropolitan Water District of Southern California. Metropolitan’s 19 million customers rely on Oroville for about a third of their water supply.

One factor hindering water supplies is the length of time it will take to fix the spillway. A panel of independent consultants hired by DWR has concluded that it will probably be impossible to fix the spillway completely this year because of design flaws and the severity of the damage that’s occurred. With an ample snowpack ready to melt, some elected officials have urged DWR to be extra careful this year about water levels at the reservoir.

“There needs to be more of a buffer there at Oroville Dam, especially now that we don’t have...a fully functional spillway,” said Assemblyman James Gallagher, R-Yuba City.

The spillway fracture, which occurred during a heavy rainstorm, caused lake levels to rise so high that water flowed over the nearby emergency spillway for the first time ever. Fears that the emergency spillway might fail prompted a two-day evacuation of 188,000 downstream residents in February, and state officials have been diligent about keeping lake levels in check ever since.

Oroville’s water customers agree that running the dam safely is a must, even if that cuts into their shipments. They said they should have adequate supplies anyway. The rainy winter has improved water conditions throughout California enough that Gov. Jerry Brown might lift his drought emergency declaration next week.

Nevertheless, these customers said they want as much water as possible this year so they can store it in their own reservoirs in case 2018 turns out dry.

“There’s tremendous value in having water in storage,” Upadhyay said. “We don’t know what (2018) is going to bring.”

Lake Oroville is the linchpin of the State Water Project, the elaborate water delivery system built in the 1960s by Gov. Pat Brown, father of the current governor. A total of 27 municipal and agricultural districts rely on water piped from Oroville for at least a portion of their supply.

Until the spillway cracked Feb. 7, this was shaping up as a banner year for shipments from Oroville. In January, DWR reported that contractors like Metropolitan and Kern would get 60 percent of their requested allocations this year.

As the rains continued, contractors had been counting on the allocations to jump to as high as 80 percent, the best since 2011. Indeed, they thought DWR would have announced an increase by now. Instead, they’ve been told the agency is holding off on any announcements.

The waiting is particularly galling to farmers. “For agriculture, where folks are making decisions on what they’ll be able to irrigate or not irrigate, locking this down earlier is important,” said Creel in Kern County. “Are we concerned about the water supply? Absolutely. Frustrated about it? Yes.”

DWR officials said this year’s allocation won’t fall below the 60 percent already promised. But updated allocation figures will have to wait at least two more weeks.

“The department will be reassessing the allocation in mid-April based on runoff forecasts resulting from the April 1 snow surveys,” DWR spokesman Ted Thomas said. “Any risks associated with management of Lake Oroville levels will be factored into that assessment.”

Oroville must be kept at least one fifth empty during winter, under U.S. Army Corps of Engineers rules. Water levels are allowed to rise starting in early April; the lake could be nearly full by the second week of May. That would leave more than 3.5 million acre-feet in the reservoir through summer, providing ample supplies for contractors.

The spillway fracture changes that equation.

DWR has made a concerted effort in recent weeks to reduce lake levels. The reservoir is about 25 feet lower than it was this time last year. Dam operators on Monday shut off the spillway for about two weeks, in part to dredge debris from the Feather River at the base of the spillway and make repairs to the dam’s hydroelectric plant. DWR expects to use the spillway once or twice more this spring, although it will also rely on the hydro plant to release water.

In Silicon Valley, water contractors have been told informally that the reservoir will be kept relatively low this year, said Cindy Kao, a top official at Santa Clara Valley Water District. Santa Clara will have enough water to get through 2017, but Kao said she’s concerned about the possibility that spillway repairs will drag on into next year.

“Oroville will likely be operated more conservatively until they’ve made enough progress in repairs on damage to the spillway,” Kao said. “It’s a concern for the longer term.”

Dale Kasler: 916-321-1066, @dakasler

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