Trouble with the spillway at Lake Oroville:
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.
...The lake, which is part of the State Water Project, feeds into the Feather River. 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.
...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.