By Kurtis Alexander and Filipa A. Ioannou
Saturday, February 11, 2017
California’s second-largest reservoir filled with so much water Saturday, thanks to extraordinary winter storms and unexpected damage to a release channel, that officials at Oroville Dam took the unprecedented step of opening the lake’s emergency spillway.
Dam operators said the maneuver posed no risk of flooding or dam failure on the Feather River, about 75 miles north of Sacramento. But the untested move sent lake water cascading down a muddy hillside where boulders and brush in the unpaved spill route threatened to wash into the river and create hazards for fish and levees downstream.
The lake’s power plant and electrical transmission towers at the foot of the dam, the nation’s tallest at 770 feet, were also being monitored for damage.
Officials said the emergency spillway, activated at 8 a.m. Saturday, would remain in use through at least Sunday night as mountain runoff from recent storms continued to swell the lake.
“The event that we never wanted to happen, and didn’t expect to happen, has happened,” said Doug Carlson, spokesman for the California Department of Water Resources, which owns and operates the dam and reservoir. “But it has performed as we hoped it would, even though it was the first time.”
Problems for the reservoir began Tuesday when a section of the lake’s primary spillway — a concrete channel to the Feather River below that is 180 feet wide and more than 3,000 feet long — collapsed amid high-volume water releases.
The resulting craterlike hole has grown dramatically, prompting officials to ease the amount of water released out the main spillway and ultimately use the emergency channel to keep the lake from flowing over the top of the dam. The emergency spillway, which is nothing more than an open hill that drains toward the river, has not been used since the dam was built in 1968, when Ronald Reagan was governor.
Lake Oroville is a key state water-storage plant, second in carrying capacity to only Lake Shasta. It supplies water to Central Valley farms as well as several urban water agencies, including the Metropolitan Water District of Southern California and the Santa Clara Valley Water District.
The reservoir also provides flood control for downstream communities and helps regulate salinity in the Sacramento-San Joaquin River Delta.
State officials had hoped to avoid using the emergency spillway and, as late as Friday afternoon, remained optimistic that necessary releases could be handled by the main spillway. Crews, however, took the precautionary measure of clearing the emergency channel of brush, trees and other debris, which served them well when they realized Saturday morning that more water needed to be liberated from the lake.
Once Lake Oroville reaches 901 feet above sea level, which is 21 feet below the top of the dam, water begins to flow automatically into the emergency corridor.
The spillway was expected to release up to 12,000 cubic feet of water per second, a relatively small amount compared with the roughly 90,000 cubic feet of water per second that was pouring into the reservoir Saturday. But it was still enough to send a steady stream of water into a diversion pool below and ultimately into the Feather River.
California Department of Forestry and Fire Protection teams were running boats downriver, where they deployed floating traps to catch debris.
“It doesn’t sound like they’re retrieving a whole lot,” said Cal Fire Capt. Dan Olson. “What little they are getting they’re moving to the shoreline.”
Dam operators continued to release water out of the main spillway, too, despite its damage. About 55,000 cubic feet of water per second was being released Saturday afternoon, well short of the 270,000 cubic feet the channel was built to handle.
The total outflow from the lake, anticipated to be as much as 67,000 cubic feet per second, was not likely to create flooding problems, officials said.
“The rated capacity of Feather River is much bigger than that, much larger,” Carlson said. “So there is no public danger. There is no expected evacuation.”
The cost of repairing the channel rose from previous estimates Saturday, to as much as $200 million, but the fix can’t be made until winter rains end and water releases are no longer necessary. An alternative option presented by state officials is to build a new spillway at another point on the lake.
Continuing to use the impaired spillway not only risks more damage to the structure, but also was posing a threat to the Hyatt Powerplant, officials said. Concrete chunks from the spillway’s tear were piling up beneath the dam, causing water to pool up behind the debris and flow toward the utility station.
“The water in the pool creates a certain amount of back pressure,” said Eric See with the Department of Water Resources. “That can lead to damage. We definitely don’t want to damage our power plant.”
The station was shut down late Friday, and as of Saturday afternoon, no damage had been reported.
Besides being unable to generate electricity when it’s closed, the power house also is unable to serve as a third release point on the reservoir. When it’s in service, the power house discharges as much as 14,000 cubic feet of water per second downriver.
Two sets of transmission towers along the emergency spillway were also at risk of collapsing as water releases softened the ground and destabilized the soil, officials said.
Water releases earlier last week on the main spillway already have turned the Feather River’s normally clear water brown with silt and debris, a problem for fish.
At the Feather River Fish Hatchery about 4½ miles downstream, where endangered salmon are reared, the cloudiness of the water was running “off the charts,” said a spokesman for the California Department of Fish and Wildlife.
With the turbidity threatening to asphyxiate the salmon, hatchery workers had been frantically collecting fish all week and trucking them to a nearby holding pond. By Saturday afternoon, 10 million salmon had been moved, officials said.
The hatchery is very important to California salmon production, said John McManus, executive director of the Golden Gate Salmon Association.
“It provides a lot of the fish that are caught in the ocean,” McManus said. “The loss of those fish would indeed be a blow to the salmon fishery.”
The cause of the spillway rupture remained unknown Saturday.
The dam and spillway passed a routine safety review in 2015, but inspectors did not specifically examine the sloped surface of the chute, doing only a visual evaluation from above. State officials did not say why a closer inspection wasn’t performed.
Improvements had been made to the the spillway in 2013, officials said, though it was not immediately clear if the work was in the same area as the recent tear.
In 2010, dam managers were reprimanded by state safety officials for operating without a critical piece of equipment a year earlier, which caused a wall to collapse at the power plant and five employees to be nearly sucked out of the facility by a powerful vacuum.
Downstream Saturday, Oroville residents had no doubt that everything was under control at the lake.
“I’m not worried,” said Cooper Davis, 15, who was working an evening shift at the Boss Burger, where he could see the river rushing below. “But you can tell that something is wrong. The water is real milky.”
The height of the river, though, remained nothing out of the ordinary.
Many residents remembered the flows in 1997, when nearly twice as much water was being released from the dam during an unusually stormy winter. The season brought widespread flooding to the region.
This year is also on track to be an usually wet one. Seasonal precipitation in the northern Sierra measured 228 percent of average for the date, as of Saturday, while snowpack across the range was at 180 percent of normal.
The forecast is for sun over the next few days. State officials hope dry weather will help lower water levels at Lake Oroville and eliminate the need for continued emergency releases.