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Engineers Assess Spillway Damage at Oroville Dam
By Dan Brekke February 8, 2017 Share
Update, 6:15 p.m.: State water officials say they be forced to continue using a badly damaged spillway at Oroville Dam to prevent the lake from reaching capacity in the next few days.
Doing that would like cause further damage to spillway structure and continue eroding the surrounding area, Department of Water Resources spokesman Doug Carlson said Wednesday afternoon. But that could be preferable to allowing the lake to begin flowing over an emergency spillway on the dam.
Carlson called the alternate spillway — which would send water cascading down a long tree- and brush-covered slope containing roads and power lines, a “very last ditch measure.”
“It’s an outcome that DWR is committed to not allowing to happen,” Carlson said. Like other DWR officials, he was quick to add that the spillway damage does not pose a threat to the dam itself, one of the largest ever built in the United States.
The department conducted an experiment during the day Wednesday in which it began sending a limited amount of water — about 20,000 cubic feet per second — down the damaged concrete spillway structure. The purpose of the test, Carlson said, was to see how much additional damage was done.
“We may just let the spillway do its job” despite the damage, Carlson said. Then, after the rainy season, “we could shut off the spillway, keep it dry, put construction people in there, whatever has to be done — rocks, fill, concrete mix, whatever — and get it back to 100 percent efficiency.”
The DWR’s spillway test came as Lake Oroville, the state’s second-largest reservoir, is filling rapidly with runoff from recent storms.
In order to maintain enough space in the lake to accommodate in-rushing floodwaters, managers would normally release water down the dam’s massive concrete spillway. That was just what was happening Tuesday when bystanders alerted dam personnel that there appeared to be damage to the structure.
Releases that were being ramped up to about 60,000 cubic feet per second were abruptly halted so that Department of Water Resources crews assessed the situation.
In the meantime, a high volume of runoff into the lake has continued, raising it more than 20 feet since early Tuesday. Late Wednesday afternoon, the reservoir was just 30 feet below an emergency spillway that has never been used in the dam’s half-century of use.
“It’s quite serious,” Carlson said of the dam and reservoir’s status. “The good news is that we think we have it under control.”
Things tend to break at the worst times.
Doesn't look like a cheap fix either.