Flooding Flows on the Feather: Inside the Oroville Dam (and Paddlers Chime In!)


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At 770 feet, California’s Oroville Dam 70 miles north of Sacramento is the tallest dam in the United States, impounding Lake Oroville and controlling the flow of the Feather River. But now it’s under siege from Mother nature, with February storms damaging its spillway, hindering the safe release of floodwater and threatening its structural integrity. And paddlers are chiming in socially…

Due to the flood threat, more than 180,000 people living along the Feather River have been evacuated recently, with another story pounding it this weekend.

None other than expedition kayaker Ben Stookesberry (and others) have been watching it closely:

Stookesberry post

Wow. Right now at Oroville Dam. 100,000 cfs coming down the spillway. 12 Helicopters dropping 2 ton sacs off boulders in compromised area of emergency spillway. 10 inches plus of atmospheric river on the way.

Hastag “It’sGonnaBlow” posts Issac Levinson

Clay Wright: Cue the soundtrack …https://www.youtube.com/watch?v=WbrjRKB586s

Scott Lindgren Shit is about to get real!

Julie Stanley Oh dang… I have a friend who’s hubby said “we’re fine, not evacuating. We live on a “hill” ( in the old river bed dumbass) I told her this is one of those moments you make choices for yourself and your kids.

Steve-o Kajak yeah considering the drainage above that reservoir and the forecast data, its pretty likely to get high again. they seem pretty confident in the spillway not caving too much further uphill, Id be inclined to think the same thing… but Mother Nature has its own idea of things and theyve already proven they have no idea.

Jean Labrosse Here’s a fun numbers game: catchment above Oroville = 3222 square miles, averaged rainfall of 1 inch over that area produces approx 7.5 billion cubic feet of water, time to drain that at 100000cfs= approx 21 hours. P.s Ben Stookesberry couldn’t help noticing little Creek (Oregon gulch) that’s totally bedrock next to emergency

Don Dowling Dropping (by helicopter) plastic covered rocks into a broken hillside that is steep as hell with 100,000 cfs coming down it is only going to lead to a huge pile of rocks at the bottom of the spillway! What a waste of time and money.

What’s Up In a Nutshell (ClifNotes from Wikipedia)
There are four intended routes by which water can pass the dam, in order from greatest preference to least:

1. Through the hydro-electric generators, which allow a maximum flow rate of 16,950 cu ft/s (480 m3/s).
2. Through the river outlets or bypass valve, which has a capacity of 5,400 cu ft/s (150 m3/s). The outlet was damaged during an accident in 2009 and has not been used since.
3. Through the main (service) spillway, which regularly carries water in excess of the needs of the generators down its concrete channel. The service spillway is controlled by gates and has a capacity of 150,000 cu ft/s (4,200 m3/s).
4. Over the top of an ungated auxiliary (emergency) spillway, a 1,700-foot (520 m) long weir built several feet below the height of the main dam. Once the lake reaches an elevation of 901 ft (275 m) it will naturally flow over the weir and down the undeveloped canyon slope.

The main spillway is used to quickly release large amounts of water needed to control the height of the reservoir. Reservoir management lower the height of the reservoir before storms arrive. The practice protects the dam and reduces the peak flow downstream of the dam.
As part of its normal water management operations, engineers controlling the dam were releasing water through the main spillway.

For unknown reasons, a crater developed about halfway down the length of the spillway channel. The crater was discovered on February 7, 2017. The crater allowed water to escape the concrete channel and erode the earth underneath. As more of the foundation washed away, additional portions of the concrete spillway failed, sending large volumes of water into the earth underneath and alongside the spillway, further undermining the foundation. Engineers closed the main spillway for inspection. During two test flows on February 8–9, the length of the crater increased from 250 ft (76 m) to 300 ft (91 m). Management was then confronted with two choices: continue to use the main spillway and let it suffer further damage or let the reservoir rise and use an uncontrolled release via the auxiliary spillway.

Engineers reopened the main spillway, but the 55,000 cu ft/s (1,600 m3/s) flow was not enough to prevent the lake from rising. The water eventually crested the nearby auxiliary spillway—as per design—for the first time since the dam’s construction in 1968. At the top of the auxiliary spillway is a 30 ft (9.1 m) high concrete wall, over which the water passes before flowing down an unprotected hillside used as the spillway’s channel. When the flowing water began eroding the ground beneath the top of the auxiliary spillway, officials ordered an evacuation order, fearing a collapse would send a 30-foot (9 m) wall of water into the Feather River below and flood communities downstream.

The risk of failure of the auxillary spillway caused management to increase the flow down the main spillway to 100,000 cu ft/s (2,800 m3/s) Pictures and video of the shutoff spillway show that the crater had expanded to almost the entire width of the main spillway.

After a period of heavy rain, on February 7, 2017, during ongoing flood control release of about 50,000 cubic feet per second (1,400 m3/s), a 250-foot (76 m) crater appeared in the Oroville Dam spillway. High inflows to Lake Oroville forced dam operators to continue using the damaged spillway, causing additional damage. By February 10, the spillway hole had grown to 300 feet (91 m) wide, 500 feet (152 m) long and 45 feet (14 m) deep. Meanwhile, debris from the crater in the main spillway was carried downstream, and caused damage to the Feather River Fish Hatchery due to high turbidity.[10] State workers began evacuating fish and eggs from the hatchery in an attempt to mitigate the damage.

Two days in advance of the auxiliary dam overflowing, Peter Gleick predicted it.

Although engineers had hoped that using the damaged spillway could drain the lake enough to avoid use of the auxiliary spillway, they were forced to reduce its discharge from 65,000 cu ft/s (1,800 m3/s) to 55,000 cu ft/s (1,600 m3/s) due to potential damage to power lines. In addition, a large volume of debris eroded out of the damaged spillway clogged the channel of the Feather River below the dam, preventing release of water from the hydroelectric plant, thus putting further demand on the spillway.

The immediate harm from the damage is limited to the area downstream of the breach, eroding the hillside and choking the river with the debris. However, the medium-term danger is that the spillway can erode back up toward the gate due to being undercut by the water falling into the crater, just as natural waterfalls retreat upstream. Eventually, this would threaten the spillway gate, whose loss would cause a sudden uncontrolled flood…

Staff Post
Staff Posthttps://paddlinglife.com
Paddlers writing about all things paddling.


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