Work on Oroville Dam Ken James/Calif. Dept. of Water Resources
Workers from Kiewit Infrastructure lift and lower a slab anchor into a hole in the roller-compacted concrete on the middle chute of the Lake Oroville main spillway in Butte County, Calif., on June 25.

Oroville releases needed to meet project deadline, officials say

State Department of Water Resources crews needed to lower Lake Oroville to create a second access point for some excavation work.

Officials from California’s water agency say the latest drawdown of Lake Oroville’s surface level was necessary for construction access so the main spillway could be mostly finished by a Nov. 1 deadline.

But the state Department of Water Resources hasn’t been releasing more water than  would be needed to meet this summer’s water deliveries to the 29 State Water Project contractors, project manager Tony Meyers says.

The DWR increased releases to about 4,500 cubic feet per second (cfs) from the Hyatt Powerplant on June 21 after construction activities on the upper chute of the main spillway revealed bedrock conditions that needed additional excavation, officials say. To do the work, crews need a second point of access to the upper chute through the radial gates.

“Delaying this work would risk not meeting the Nov. 1 milestone,” Meyers told reporters in a conference call. “We need to make sure the main spillway can handle releases from Lake Oroville during early-season storms.”

The latest drawdown is reminiscent of last summer, when the department announced plans to slowly drain the lake’s surface to below 700 feet above sea level to accommodate underground work on the emergency spillway over the winter.

That plan drew complaints from Rep. Doug LaMalfa, R-Calif., whose district includes the Lake Oroville area. LaMalfa argued drawing the lake down that low would leave too little water in storage if the winter’s precipitation was below average, which it was in some areas. While federal Central Valley Project contractors north of the Sacramento-San Joaquin River Delta received their full allocations this year, State Water Project contractors only received 35 percent of requested supplies.

But this summer’s goal was only to get the lake level down to a little above 800 feet. So far, the only complaints have come from locals concerned that some Lake Oroville boat ramps will be inaccessible in the runup to July 4, when the lake is a popular tourist destination.

But putting off the excavation until after the holiday wasn’t an option, officials say.

“We are doing a construction project that normally takes years, in months, and every day is critical,” DWR spokeswoman Erin Mellon told reporters. “That Nov. 1 deadline was set because of public safety … What we don’t want to have happen is for the storms to kick in and the lake to rise and not have a spillway that can handle releases.”

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.

Project update

The discussion about releases came as the DWR was giving an update on the Oroville project. According to a DWR news release:

  • Crews are continuing foundation cleaning and placing dental and leveling concrete to prepare for placement of structural concrete walls and slabs on the 730 feet of the upper chute.
  • Slab anchor drilling is complete on the middle chute and crews began placement of structural concrete slabs on June 26.
  • Hydro-blasting of the energy dissipaters, or dentates, at the bottom of the main spillway is complete. Mechanical demolition will continue to prepare for a new layer of structural concrete anchored with epoxy-coated steel dowels.
  • Removal and replacement is complete of the top layer of a structural concrete slab placed on the main spillway last year that did not meet DWR’s quality control standards due to a poor surface finish.

 While Nov. 1 is the target date to complete major work and placement of concrete on the main spillway, some additional work will continue past that date. This work will include dry finishing and curing of concrete, joint sealing, connecting drainage systems, backfilling side walls, and site clean-up.

On the emergency spillway, according to the release:

  • Construction of the northern half of the roller-compacted concrete splashpad is complete.
  •  Foundation preparation for the placing of roller-compacted concrete at the southern half of the splashpad site continues.

Work at the emergency spillway site will continue past Nov. 1.

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