California water officials continue to defend their management of Lake Oroville as a second season of main spillway reconstruction on the reservoir’s earthen dam is set to ramp up in May.

The state Department of Water Resources has updated its operations plan for the lake for this spring and summer, arguing that the plan will maximize the 2018 construction window to ensure the rebuilt main spillway is ready for next winter.

With inflows into the lake expected to be low this summer because of a below-average snowpack, state officials say the lake’s surface will have to reach 830 feet above sea level to trigger more aggressive releases.

As of mid-April, the lake was at 808 feet. The DWR expects lake levels to fluctuate through the year as the agency accommodates various uses, including providing water for the 29 State Water Project contractors and senior water rights holders. Other uses include flood protection, environmental releases, recreation and salinity control and flow requirements in the Sacramento-San Joaquin River Delta, officials explain. The operations plan will enable the agency to “maximize our construction window,” says John Leahigh, a State Water Project principal engineer.

“The fact is that public safety is our No. 1 goal, the No. 1 driver on decisions,” DWR spokeswoman Erin Mellon told Western Farm Press. “We had a good March (for precipitation) … and seeing the lake rise is good for a lot of reasons.

“But at the end of the day while we’re reconstructing the spillway, public safety is our No. 1 priority,” she says. “It ranks above all else.”

Lake Oroville is the chief reservoir for the State Water Project, whose contractors irrigate about 750,000 acres of Central Valley farmland and serve more than 26 million customers, according to the project’s website. The dam’s near-failure amid heavy storms in February, 2017, prompted the reconstruction project, which is expected to take two years and cost $870 million.

WORK TO BEGIN

The DWR has requested approval from the Federal Energy Regulatory Commission and the state Division of Safety of Dams to close the main spillway gates on May 8 to begin the second phase of work there. The closure is “crucial if we are to meet our November target” for finishing work, says Ted Craddock, a DWR assistant deputy director.

The agency’s plans include replacing chutes that lead to the radial gates with steel-reinforced structural concrete slabs and walls and resurfacing of energy dissipaters at the base of the spillway, officials said in an April 18 conference call with reporters.

On the emergency spillway, crews were to begin work April 25 on removing rip rap that was put in temporarily last year. Crews are now adding a concrete beam to an underground cutoff wall they spent the winter building and are constructing a concrete splashpad that will cover the hillside between the emergency spillway and cutoff wall. The wall and splashpad will armor the hillside to prevent the kind of erosion that led to last year’s incident, officials say.

Over the next few weeks, the DWR will also do maintenance work on three of the six turbines at Hyatt Powerplant to maximize its capacity for releasing water from the lake while the main spillway is unavailable, the agency explains.

The agency had planned to do the work in early April but put it off as it stepped up releases in anticipation of a warm “atmospheric river” storm that accelerated snowmelt. While water managers feared the April 5-7 storm could push the lake level to 830 feet and warned downstream communities that the main spillway may be needed, the lake only rose to just over 800 feet, Mellon said.

The work continues as the agency has received a barrage of criticism from area lawmakers and an independent forensic team, both for perceived management lapses leading up to last year’s mishap and for its setting of lake levels during construction.

LAKE DRAINED

The lake was drawn down below 700 feet this winter to accommodate work on the underground cutoff wall, prompting sharp criticism from U.S. Rep. Doug LaMalfa, R-Calif., whose district includes the Oroville area. LaMalfa feared that drawing the lake down that low would leave too little for contractors this spring and summer.

LaMalfa reiterated his complaints during a Northern California Water Association meeting in Chico in March, when it had become apparent that the region’s seasonal rainfall and snowpack would be below average.

But the lake level had climbed back to 65 percent of capacity and 82 percent of its normal level as of April 18, according to the DWR. In all, there was nearly 2.3 million acre-feet of water in the lake as of April 18; the lake can hold about 3.54 million acre-feet.

Mellon says the decision to drain the lake was made with guidance from FERC and the state dam safety division “while we were literally sticking dynamite in the spillway to break it up and start the reconstruction effort.” As the winter of 2016-17 brought a record inflow to the lake, “we had to make those decisions with a lot of unknowns just to be clear about public safety,” she says.

Meanwhile, two Republican state lawmakers – Assemblyman James Gallagher of Yuba City and Sen. Jim Nielsen of Gerber – issued a statement in November calling for more transparency from the DWR as plans are developed.

FORENSIC REPORT

And in January, a forensic team commissioned to study the dam’s near-failure issued a 584-page report that largely blames a culture of complacency within the DWR that insulated the agency from access to industry knowledge and technical expertise to safeguard the dam and its mile-long spillway.

“Obviously, we took that very seriously,” Mellon says, adding that designs for the reconstruction effort reflect an effort to prevent potential physical causes of last year’s emergency from happening again.

She notes the agency’s newly appointed director, Karla Nemeth, will oversee a restructured executive team that will include a new deputy director for flood management and dam safety. Further, Gov. Jerry Brown last year ordered additional evaluations of dams whose spillways are similar to Oroville’s, she says.

Mellon adds that the agency has also taken to heart the forensic team’s criticism of the department’s “silos” and “trying to break those down.

“A lot of that is an organizational effort that is well underway,” she says. “Part of it includes the new executive team addressing how to better integrate teams within the department as well as externally.”

For Oroville, the DWR is about to kick off a comprehensive needs assessment “to see what we need to do differently in our operation of the structures,” she says.

“A lot of dam owners are doing similar efforts in their world as well,” she adds.