[env-trinity] Spillway crumbles as California reservoirs max out capacity

[Tom Stokely]

You can go to the Chronicle and SacBee links to see the photos- impressive and scary!
http://www.sfchronicle.com/bayarea/article/Spillway-crumbles-as-California-reservoirs-max-10915788.php#photo-12332274

Spillway crumbles as California reservoirs max out capacity
By Kurtis Alexander, San Francisco ChronicleFebruary 7, 2017 Updated: February 7, 2017 10:38pm   
   - 
    
   - 5
   
   - 
    
   - 
    
   - 
    
   - 
    
   - 
    
   - 

IMAGE 3 OF 7A hole was torn in the spillway of the Oroville Dam while releasing approximately 60,000 cubic-feet-second of water in advance of more rain on February 7, 2017 in Oroville, California.California’s recovery from drought has been so remarkably quick that reservoirs on the verge of record lows just a year ago are now too full to handle more rain, prompting dam operators across the state to unleash surpluses of water not seen in years.The northern Sierra’s Feather River swelled with so much mountain runoff Tuesday that state officials considered shutting the road beneath Lake Oroville, California’s second largest reservoir, to allow dangerously swift waters to pour out the foot of the dam.“I’ve been told that when it’s spilling that much, there’s so much moisture in the air that car engines conk out,” said Doug Carlson, a spokesman for the California Department of Water Resources. “This really shows how much rain we’ve had.”After he spoke, a real emergency broke out, and the agency had to temporarily close the spillway. So much water was gushing down it — 55,000 cubic feet per second — that the concrete surface eroded, like a city street with a sinkhole.After spotting the “unusual flow pattern” and assessing the situation, officials said Lake Oroville — still 20 percent empty — could handle any rain that fell the rest of the week. To keep the Feather River running smoothly, the state bumped up releases from a smaller reservoir just downstream.The story was similar all over, from Shasta Lake on the Sacramento River to Hetch Hetchy Reservoir at Yosemite to the Russian River’s Lake Sonoma near Healdsburg. Five years of water shortages have given way to maxed-out storage. And beneath each reservoir is the unfamiliar but welcome sight of whitewater gushing out spillways and into the rivers below.Water releases in and of themselves are no sure sign that the drought is over. Dam managers commonly discharge water during wet periods to prevent reservoirs from breaching, with some reservoirs, particularly small ones, filling and emptying several times during the winter.But the sheer scale of this year’s surplus is good news.Many cities and towns have lifted drought-time water restrictions as local storage sites have filled, while state officials overseeing big reservoirs in the Sierra have told customers to expect at least as much water this year as last — and quite possibly more. Federal water managers, who also operate big reservoirs in California, are expected to project their deliveries later this month.Surface water supplies typically account for two-thirds of California’s water supply.“This year we have a lot of runoff, a lot of rain and a lot of snow in the mountains,” said Louis Moore, spokesman for the U.S. Bureau of Reclamation, noting that water management has rapidly shifted from trying to capture every bit of water in the reservoirs over the past five years to draining water in order to accommodate inflows.At federally run Shasta Lake, California’s largest reservoir, more than 1.25 million acre-feet of water had to be liberated in January, enough to supply more than 2 million households for a year. The release was the most for any January going back at least a decade, according to federal data.Precipitation that falls in the Sierra usually takes about three to five days to travel down hillsides into creeks and rivers and into reservoirs.The floodgates that opened this week were in response to the weekend storms, which brought more snow to the mountains and more rain to the Bay Area. Weather conditions only intensified Tuesday, with steady downpours, high winds, flooded rivers, downed trees and mudslides wreaking havoc across much of California.The closely watched Northern Sierra Eight Station Precipitation Index on Tuesday measured 60.4 inches since Oct. 1, surpassing last year’s 12-month total. Snowpack was 182 percent of average.
MORE ON STORM
   
   - Mudslide shuts down Hwy. 17 in Santa Cruz Mountains
   - Mudslide demolishes San Rafael home, ‘like a weird movie’
   - Heavy rain, intense winds cause mayhem in Bay Area
   - Storm prompts Bay Area school closures
   - Nearly 80 flights at SFO canceled due to bad weather
Wet weather is expected to continue through Friday, and with it more water releases.State and federal water managers anticipate that even the San Luis Reservoir west of Los Banos near Pacheco Pass will fill this year. The lake in Merced County relies on water pumped from the San Joaquin-Sacramento River Delta, where outflows have been severely restricted during the drought to protect fragile wetlands and wildlife.Farmers, who have seen water supplies cut short in recent years and have been advocating for the creation of more storage, say this winter illustrates the potential benefit of new reservoirs.The surplus releases, by one estimate, would have put 585,000 acre-feet of water in a proposed reservoir off the Sacramento River.“Every so often we get a year like this where we can catch a tremendous amount of water,” said Mike Wade, executive director of the California Farm Water Coalition. “That’s what we think the state should be investing in.”Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander at sfchronicle.com Twitter: http://twitter.com/kurtisalexanderhttp://www.sacbee.com/news/state/california/water-and-drought/article131348349.html





FEBRUARY 7, 2017 4:59 PMEngineers to begin inspections at damaged Oroville Dam

1 of 2Engineers found a major crack in the concrete spillway at Oroville Dam early Tuesday, forcing a temporary shutdown of the spillway. www.twitter.com/J_GallagherAD3BY DALE KASLER AND RYAN SABALOWdkasler at sacbee.com
State engineers were expected to conduct their first inspections Wednesday morning of the damaged spillway at Oroville Dam, about 24 hours after a 250-foot-long pothole was discovered in the massive structure, forcing a halt in water releases.Officials with the Department of Water Resources continued to maintain the dam itself is safe and doesn’t pose a threat to downstream populations, a view echoed by outside experts consulted by The Sacramento Bee.Doug Carlson, a spokesman for the department, said engineers would get “their first eyeball look at the problem” and try to devise a solution.
A likely short-term remedy is to resume water releases from the spillway, even if it means creating further erosion in the chute, the agency said. “These are things we can repair,” said Eric See, the agency’s environmental program manager, in a briefing with reporters late Tuesday.The alternative, which is considered less preferrable, is to let Lake Oroville continue rising until water begins cascading in an uncontrolled fashion over the nearby emergency spillway at the north end of the dam. That would create significant land erosion problems, officials said, although the water would flow into an unpopulated area.With the main spillway shut off, the reservoir –the second largest in California – had taken on about 150,000 acre-feet of water in about 12 hours. The lake level was about 60 feet below the lip of the dam. The reservoir remained about 15 percent empty.Engineers halted releases from the main spillway after a hole was found in the bottom half of the 6,00-foot-long concrete chute. Pictures showed a jagged chunk eroded out of the towering concrete structure. The cause of the problem wasn’t yet determined.“It’s not a public safety risk,” See said. “Dam failure is not in any way a potential threat.”Jay Lund, director of the UC Davis Center for Watershed Sciences said, “I wouldn’t evacuate yet. I think they’re a ways from that.”But Lund and others said the problem is going to make it much more difficult to manage high flows from a critical piece of the state’s flood-control network, with two more months left in California’s rainy season.
Watch incredible water releases from Oroville Dam - 15,000 cubic feet per secondA cubic foot is the volume of a cube whose sides are all 1-foot long. Well, 15,000 cubic feet per second of water gushed down the Oroville Dam spillway on Tuesday, Jan. 31, 2017, as see in this video from Sacramento Valley Water as more storms are expecteSacramento Valley WaterThe lake, which is part of the State Water Project, feeds into the Feather River. Lake Oroville, in Butte County, is the state’s second-largest reservoir. Completed in 1968, the 742-foot dam is the tallest in the United States. It can store 3.5 million acre-feet of water.The last major flood in Northern California, in January 1997, did most of its damage on the Feather River. Since then, significant upgrades have been made to the area’s levees, and Marysville Mayor Ricky Samayoa said he has confidence in the levees that ring the city.“That last storm showed us how strong our levees are,” he said.On Tuesday, after the problem was discovered, Department of Water Resources engineers gradually reduced the flows before shutting off the releases altogether.At that point, Carlson said engineers started releasing water through a power plant at the dam. But the plant released only about 5,000 cubic feet of water per second Tuesday. While that’s expected to be increased to 15,000 cfs on Wednesday, that would still be a fraction of the volume of water flowing into the lake – about 128,000 cfs at midday Tuesday. Until the spillway was damaged, the lake was releasing more than 40,000 cfs, according to state data.At current rates, the agency said the lake has enough room to absorb three days of inflow.The agency said it expected to resume releases from the spillway “at a rate deemed safe,” after a more thorough inspection was performed.While resuming releases would worsen the damage to the eroded area, Carlson, the department spokesman, said that’s preferable to letting the water continue to fill the reservoir.David Gutierrez, a retired Department of Water Resources dam-safety expert, said water would pour out of an emergency spillway if the lake were allowed to fill past the brim of the dam.The emergency spillway, which has never been used, is designed for the scenario of the “biggest flood that any overgenerous engineer could ever dream of coming through that system with a full reservoir,” said Lund of UC Davis. The flows would be unregulated, meaning the state wouldn’t have any control over how much water pours down the emergency spillway, Lund said.What’s more, while the top of that secondary spillway is concrete, the main structure is unlined and releasing water could cause erosion, Gutierrez said.Joe Countryman, a retired engineer at the U.S. Army Corps of Engineers, agreed that the overall structure of the dam doesn’t appear to be at risk. But releasing more water down the cracked spillway could cause serious harm and create “major dollar damage,” said Countryman, a member of the Central Valley Flood Protection Board.The department is also increasing releases from Thermalito Afterbay, a small downstream reservoir, in order to avoid a “drastic reduction” of flows into the Feather River.That’s important, Lund said, because levees below the dam could fail if flows are suddenly shut off.“You could cause some slumping and failure in the levees in the next few days,” Lund said. “And then you have a bigger (storm) event coming in the next few days from now … so not only have you got this problem with the spillway, but you’ve also weakened the channel conveyance downstream.”Dale Kasler: 916-321-1066, @dakasler

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www2.dcn.org/pipermail/env-trinity/attachments/20170208/577c6c32/attachment.html>