State engineers halted the release of water from Oroville Dam’s spillway Tuesday after a massive hole was discovered in its bottom half. Pictures showed a jagged chunk eroded out of the towering concrete structure.
With Lake Oroville kept about 20 percent empty to maintain flood-safety, the state Department of Water Resources and outside experts consulted by The Sacramento Bee said the dam isn’t likely to fail.
“There’s no imminent threat of any kind to the integrity of the dam, and no danger to the population downstream,” said Department of Water Resources spokesman Doug Carlson.
Lake Oroville, located in Butte County, is the state’s second largest reservoir. Completed in 1968, the dam is 742 feet high and is the tallest dam in the United States. It can stores 3.5 million acre-feet of water.
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 was 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 to occur, 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.
Well, they're in trouble. With only three days of storage behind the dam at current inflow rates, and with rain predicted for all three of those days, we are very likely to see water go over the emergency spillway. At that point, anything, or nothing, could happen.
Sounds to me as if inspections have been lax. That's no "crack" in the spillway, that's a huge, gaping hole, that the water will quickly enlarge if much water is sent past.
Here is a video of the water, which should slide down the spillway in a sheet, hitting the hole and spewing up a plume of water and the occasional chunk of concrete.
Here's the hole with the water shut off. Not funny. There is no way to fix that quickly.
A bird's eye view of the dam and spillway, in better, less rainy times.
Oh, no matter, Moonbeam has a new road to his rancho...
ReplyDeleteSeriously, this is important, when are the people going to wake up to the fact that we have a horribly unmaintain, infrastructure.