The dam is built on "Jurassic age greenschist facies meta volcanic rocks of the Smartville Ophiolite complex," which is vastly inferior to better monolithic bedrock because it contains "heterogenous, highly fractured and sheared metamorphic rocks." This may prove to be a poor choice for a gigantic earthen dam to rest on because "this complex fracture network represents planes of weakness along which the bedrock is susceptible to erosion and possibly catastrophic failure."
The groups’ concern, which seems to have fallen on deaf ears at the time, was that the emergency spillway is not really a spillway. Rather, it’s a 1,700-foot-long concrete weir that empties into a dirt hillside.
Construction would have cost at least $100 million, Stork said, and the state contractors in Southern California that buy water from Northern California would have been forced to pay for it. The Metropolitan Water District of Southern California, which provides water to 19 million people in Los Angeles, San Diego and other areas, and the State Water Contractors would have shouldered the cost and deemed the upgrades unnecessary, according to the Oroville Mercury Register.
Late Tuesday, President Donald Trump approved federal emergency aid for California as a result of the potential failure of Oroville Dam's emergency spillway, and separately to help recovery efforts in areas affected by January storms. Oroville Dam is the nation's tallest earthen dam.
Rock is prepped to be used on the Lake Oroville Dam after an evacuation was ordered for communities downstream from the dam, in Oroville, California, U.S. February 13, 2017. Oroville Dam area residents cleared to return home
5 Hours Ago | 01:54
State officials say they may slow down the spigot at the troubled Oroville Dam, even as they face approaching storms.
"This next storm won't pose a risk to the emergency spillway or the work we're doing," William Croyle, acting director of the California Department of Water Resources said at a noon press briefing in Oroville, California.
He explained that the planned ramp-down of water releases from the primary spillway is a result of both progress in lowering the dam levels and also as a precautionary move because "we don't want to tear our flood-control structure up any more than it has."
Forecasters are confident that the first two storm systems will not cause huge inflows into Lake Oroville. They are less confident about the third system, which is due sometime Tuesday. That storm could be bigger and warmer, meaning more rain and snowmelt streaming into the swollen reservoir.
“The third wave is looking like our problem child,” said Michelle Mead, a warning-coordination meteorologist at the National Weather Service in Sacramento.
-- Oroville Dam: Crews work into the night to bolster eroded spillway as next storm approaches, Sac Bee, Feb 15
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