Use of untested emergency spillway yet again a possibility at Oroville Dam
The Department of Water Resources said it planned to slow releases from Oroville Dam’s damaged main spillway, once again raising the possibility that the reservoir could fill to the brim and the emergency spillway would have to be used.
The department said the slowdown was necessary “to prevent erosion along the north side of the spillway from compromising nearby power line towers.” The lines run to the dam’s power plant.
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Releases were slowed to 55,000 cubic feet per second. The spillway had been releasing water at 65,000 cfs since 2:30 a.m.
Officials said the slower releases “may” keep the lake level below 901 feet, the point at which water would start running over the dam’s emergency spillway. However, officials said, “there are many variables involved, and the public should not be surprised if some water flows into the emergency spillway.”
That structure, which empties onto a forested hillside, hasn’t been used in the dam’s 48-year history.
The department wanted to avoid using the emergency system because the cascade of water would carry trees and other debris into the Feather River. However, officials have said use of the emergency spillway isn’t expected to cause flooding.
Independent experts agree no imminent threat of dam failure
The Bee sought out two independent experts, to get their take on whether the heavy releases flowing down the damaged Oroville Dam spillway pose a threat to the integrity of the dam. Both agreed with state officials, who have said that while the spillway will continue to degrade, the situation poses no immediate threat to the integrity of the earthen dam that holds back Lake Oroville.
But they also said erosion is a major concern.
At the Sacramento Bee’s request, Jeffrey Mount, former chairman of the UC Davis Department of Geology, reviewed video footage taken by helicopter Friday of the canyon that is forming at the bottom of the damaged spillway as a cascade of water rushes down.
“What it’s doing is what rivers do when they flood across bedrock. They tend to cut downward, like a knife,” Mount said. “You’re getting rapid, dramatic incision into the underlying bedrock, making essentially its … own steep, canyon.
“Your No. 1 worry,” he said, “will be that it will continue to erode in the upstream direction (toward the top of the spillway) until it destroys... the spillway gates. Then, you’re close to the abutment of the dam. But you’ve got a long way to go for that.”
Mount noted that engineers can shut off the spillway flows at any time, so it’s not likely that level of destruction would be allowed. Should the damaged main spillway shut down, engineers would be forced to rely on the dam’s untested emergency spillway, which sends water over a forested hillside when the reservoir nears its rim.
Nicholas Sitar, a professor of civil engineering at UC Berkeley, agreed that “they are still relatively far away from ‘washing away the whole dam’ scenario.
The options available to state officials are limited, and not ideal, Sitar said. Continuing releases through the damaged spillway will cause it to further erode. But use of the emergency spillway will cause that stucture to “start eroding right away,” he said.
Mount said it’s possible that officials could use the damaged main spillway for the rest of rainy season, but it would depend on several factors, including how much water is spilling down the structure, and the rate of its degradation and that of the bedrock below.
‘Do we evacuate or keep drinking?’
Thursday night, as conditions at Oroville Dam appeared to be worsening, they served extra rounds of O’Dam hefeweizen at Miners Alley Brewing Co., a turn-of-the-century brick building across the street from the Feather River levee in Oroville. The patrons exchanged thoughts on what might happen to the crippled Oroville Dam upstream.
The town of 15,500 long has depended on Lake Oroville and the Feather River for tourism, commerce and its sense of being. Over its history, the town has braved flooding when the river overtopped its levees, most recently during pounding rainstorms in 1997.
So Thursday, as people flocked downtown to see torrents of muddy water gushing uncontrolled off the dam’s damaged spillway and through the river, Miners Alley manager Robyn Vandervort didn’t know whether to celebrate or grieve.
“We just kind of huddled in a group hug,” said Vandervort, whose establishment sits in an area of bars and restaurants known as the Riverfront District. “We wondered: Do we evacuate or keep drinking?”
By Friday afternoon, with state officials saying conditions seemed less dire, the bar was back to serving other beer varieties – “Lust for Dust” and “Black Bart Chocolate Porter” – celebrating the lore of the historic town, once again still standing.
On the levee, Jeremy Willard, 43, a retail clerk who had to evacuate from his Oroville home during flooding in 1997, was relieved as he took a visual measure of the river.
His wife, Michelle Gillstrap-Willard, 36, a caregiver for local seniors, recalled how Oroville celebrates its salmon festival each September, with residents turning out for the Feather River salmon run. Other times of year, there are popular fishing derbies.
“Most of the time, the river brings a lot of joy to this town,” she said. “But when it goes a little haywire, people start to panic.”
State rigs up filtration system to protect fish at Feather River Hatchery
State fisheries officials said they’ve devised a short-term fix to the problem of murky, debris-filled water that threatens to suffocate millions of baby salmon at the Feather River Hatchery below the cracked spillway at Oroville Dam. The hatchery provides a crucial supply of fish for California’s $1.4 billion commercial and recreational salmon fishing industry.
With debris flowing into the Feather River from the fractured spillway, hatchery crews have been conducting a rescue operation, trucking more than half the 8 million salmon being reared at the hatchery to clearer water at a small annex nearby. The hope was that, by sunset Friday, some 5 million of the salmon would be in those holding ponds adjacent to Highway 99 and the Thermalito Afterbay, a small reservoir west of Oroville.
The other 3 million baby salmon will remain at the main hatchery. To keep them safe, crews have rigged a system of pumps, pipes and generators to filter water to keep two holding areas operational.
The hatchery also holds 1 million steelhead eggs. In an effort to keep them alive, crews devised a filtration system using water from a municipal fire hydrant that is passed through charcoal filters.
“Pretty amazing stuff on the fly,” said Andrew Hughan, a spokesman for the Department of Fish and Wildlife.
Oroville residents watch with wonder, frustration as Feather River rages
Husband and wife Donnie Rhodes, 40, and Cami Wolfe, 36, took their kids out to see a spectacular water show Friday afternoon.
They stood with Skyler, 3, in his stroller, and daughter Haley, 15, and watched with fascination as brownish-white water exploded in waves off of the Fish Barrier Dam just upstream of the Feather River Fish Hatchery near Oroville.
“It’s amazing, amazing!” said Wolfe, who works at a hair salon in downtown Oroville. “It looks like the ocean.”
Wolfe knew about the fractured main spillway at Oroville Dam, and the prospect the reservoir could reach the dam brim and cascade down an untested emergency spillway. She wasn’t worried about flooding, she said, but plenty of her friends were.
“Oh, my gosh. There are so many going onto Facebook saying they’re worried about the dam breaking down,” she said. “I’m not worried. But that’s a lot of water for sure."
Rhodes, a building contractor, took an optimistic view that the surging flows were actually giving the river a long-needed cleansing. “If it crests over (the spillway), that’s what a river is supposed to do. Erosion or not, it will be cleaning out the river and our creeks.”
Ivy Cross, 34, who lives above Lake Oroville in Forbes Town, loves fishing for steelhead trout in the Feather River. And she wasn’t happy to see its currents so dark and angry. Cross feared the turbid water, which forced a rescue operation Wednesday at the fish hatchery, could decimate fish populations.
“I’m a hard-core steelhead fisherman,” Cross said. “They should have had that dam in order.
Officials don’t expect flooding downstream of Oroville Dam
The Department of Water Resources expressed confidence at a noon briefing that it won’t have to resort to using the emergency spillway at Oroville Dam to relieve pressure on the structure.
Department spokesman Eric See said the damaged main spillway at Oroville Dam was releasing water at about 65,000 cubic feet per second, keeping the reservoir level just below the emergency spillway rim.
Although the Butte County Sheriff’s Department has urged residents to stay alert for evacuation orders, state officials said they doubted the region downstream of the dam would experience flooding. Even if the reservoir overtopped the emergency spillway and cascaded over the adjacent hillside, it would come down in volumes that wouldn’t cause a disaster, See said.
“We call it a high flow event – it’s not a flood event,” See said. He said the Feather River below Lake Oroville isn’t expected to flow at levels exceeding 75,000 cfs, the level seen during the extreme storms of 2006.
Unlike the main spillway, which is lined in concrete, the emergency spillway dumps water onto a open hillside. If water overtops the emergency spillway, it would drag trees, earth and other debris into the river below. Cal Fire crews have cleared a portion of the trees in the ravine beneath the emergency spillway as a contingency.
Department of Water Resources engineer Kevin Dossey said, should water in the reservoir reach the emergency spillway, the releases wouldn’t be “catastrophic.” The emergency structure measures 1,700 feet across, and water likely would flow out in a broad sheet about two feet deep, he said.
Crews were bringing in concrete to bolster the lip of the emergency spillway “just as a precaution,” he said.
He added that inflow to the lake from the Sierra watershed, which peaked at 190,000 cfs Thursday afternoon, had diminished to 130,000 by midday Friday and was expected to drop to 60,000 cfs Saturday, essentially matching the amount of water flowing out of the damaged main spillway.
‘Minor’ cracks found in Oroville Dam spillway in 2009
Inspectors at Oroville Dam found “minor” cracks in the dam’s main spillway in 2009, according to a Sacramento Bee review of state inspection reports. The reports indicate the damage was repaired the following year.
The main concrete spillway, critical to flood control at the dam, has become a focal point of the current crisis. On Tuesday, dam operators discovered a large chunk of the chute had broken off, exposing an open crater of mud and dirt. The fracture since has spread the width of the chute, splitting the spillway in two.
Department of Water Resources engineer Kevin Dossey said Friday that additional cracks had appeared in the main spillway as recently as 2013 but were repaired.
“The repairs looked smooth,” he said, adding that it remains unclear why the crater formed Tuesday.
With water hitting the concrete chute at an estimated 50 mph, “spillway erosion is a natural thing,” Dossey said.
The last major incident at Oroville Dam occurred in 2009. Workers were testing six-foot valves that move water from the reservoir into the Feather River through two tunnels in the dam’s power plant, the primary outlet outside of rainy season, when the spillway is operational. When workers opened one of the valves, the flow of water caused a suction force so great it blew out a bulkhead separating the workers from one of the tunnels. Two workers were nearly sucked in, and survived by clinging to a damaged railing.
The following year, the California Occupational Safety and Health Administration cited six violations that contributed to the July 22, 2009, accident, including five considered “serious.” OSHA found, among other things, that an “energy dispersion ring” designed to eliminate the suction force had been removed two months earlier and never replaced.
It also found that the dispersion ring was damaged in 1968 and never repaired. A UC Davis study in 1993 advised DWR that, as a result, flow through the valves should be “severely limited” for safety. OSHA levied fines totaling $141,375.
A federal inspection in 2010 concluded that Oroville Dam, the tallest in the nation, needed a comprehensive earthquake safety assessment, but no significant flaws were found in the dam itself. The inspection was conducted by consultants working for the Federal Energy Regulatory Commission, which oversees hydroelectric dams in the United States.
State dam operators reassure public there’s ‘no imminent threat’
The main spillway of Oroville Dam was a stunning sight Friday morning, a miniature version of Niagara Falls as water cascaded in unruly fashion down the damaged concrete chute. California Department of Water Resources officials, sheriff’s deputies and others watching from a quarter mile away were feeling the spray even as patches of blue appeared in the sky directly above the dam.
The water pouring down the chute ran clear, a sign that although the spillway likely continues to erode, soil and dirt aren’t getting kicked up by the raging water to the same extent that happened Thursday. “It’s hitting bedrock, which is a good sign,” said Cal Fire spokesman Scott McLean.
However, large gushes of water were being misdirected by the massive fracture that now splits the spillway in two, and streaming down the hillside just east. The resulting debris formed a kind of natural dam at the bottom of the hill, raising water levels so high in the channel below the spillway that engineers had to shut down the dam’s power plant. The plant could have released up to 15,000 cubic feet per second.
Officials said they maintain hope that Lake Oroville won’t reach the brim of the dam, activating an emergency spillway adjacent to the main spillway. The emergency spillway is unlined, and would release water onto an open hillside, scraping trees, soil and other debris into the Feather River. Cal Fire crews were attempting to remove as many trees as possible from the hillside, in case the emergency system activates.
State officials said that even if the emergency spillway overtops, they don’t think it would cause river flows to crest levees protecting downstream communities.
“Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public,” William Croyle, the acting director of the California Department of Water Resources said Friday in an written statement.
Croyle said, nonetheless, that officials are hoping to avoid the emergency scenario “because there will be sediment and debris impacts downstream.”
The emergency spillway has not been used in Oroville Dam’s 48-year history.
Lake Oroville only six feet from emergency spillway
Even as Lake Oroville rose to within six feet of its rim, state officials said they think the reservoir won’t overtop, necessitating the use of the emergency spillway.
“We’re looking good,” said Scott McLean, a California Department of Forestry and Fire Protection spokesman. He noted that flows into the lake from the Sierra watershed have been diminishing.
But he added that area residents should continue to be on alert in case the situation takes a sudden turn for the worse. “Just because the sun comes up, it doesn’t mean it’s over,” he said, as patches of blue sky poked through the clouds.
Lake Oroville water levels stood at 895 feet on Friday at 9 a.m., just six feet below the level when the dam’s emergency spillway would be reached. The lake had gained about 15 feet in the previous 24 hours, mostly before midnight, state figures show.
Since midnight, its levels rose by just under a foot every two hours. That’s a little slower than the pace Thursday, largely because releases from the lake are at 65,000 cfs, up from 10,000 cfs early Thursday.
This is not the highest Lake Oroville has been. At various times during late spring and early summer, officials have allowed the lake to rise just below the spillway, state records show. But those were during times when there was relatively small amounts of water coming into the lake.
During the New Year’s floods of 1997, lake levels rose to about 887 feet, according to state records.
The Butte County Sheriff’s Department has advised residents to be on the lookout for high flows on the Feather River, which runs through the heart of Oroville a few miles downstream of the dam. They said flows weren’t expected to exceed 75,000 cubic feet per second, less than the half of what was experienced during the 1997 flood that ravaged much of the Feather watershed.
“I’m not panicking,” Sheriff Kory Honea said at the Department of Water Resources field office late Thursday.
Oroville Dam’s emergency spillway may not be used, officials say
With a break in the weather and increased outflow from Oroville Dam’s heavily damaged spillway, state officials said Friday they no longer believe the swollen reservoir will rise to the top.
After a grim assessment late Thursday, officials said Friday morning they think they can avoid using the dam’s emergency spillway, which they’ve been working feverishly to avoid. The emergency structure feeds into an unlined ravine, and the water would propel soil, trees and other debris into the Feather River.
Scott McLean, a spokesman for Cal Fire, said the damaged main spillway was releasing water at 65,000 cubic feet per second, nearly twice as much as Thursday. The releases ramped up to 55,000 cfs about midnight and hit 65,000 at 2:30 a.m.
Also helping the situation: the amount of water flowing into Lake Oroville declined significantly overnight, from 190,000 cfs to about 140,000 by 8 a.m. State officials said the lake level had risen 10 feet overnight, to 894 feet. That’s about 7 feet below the point at which the emergency spillway would have to be used.
“At this point in time, with the amount of inflow compared to the outflow … and Mother Nature holds fast and there’s no precipitation the next several days, they’re predicting the emergency spillway will not have to be used,” McLean said.
One factor working against dam operators: The dam’s power plant, which could release up to 15,000 cfs, has been shut off. Debris kicked up by the releases from the main spillway and dumped into the river made it impossible to run the plant, McLean said.
“Right now, the turbines are off,” he said.
The prospect of higher flows coming out of the reservoir had Butte County emergency officials and others huddling with Department of Water Resources engineers and Cal Fire representatives deep into the night Thursday.
Butte County officials issued a statement late Thursday warning residents to prepare for a possible evacuation, although they also said they were told flows through the Feather River, which runs through the center of Oroville, would be less than half the flows experienced during the great flood of January 1997.