Emergency spillway used at Oroville Dam for first time

Officials say Feather River can handle the extra water, and the dam is intact and not in danger of failing.

With rains letting up, and inflows into lake subsiding, they believed they could keep the water level behind the dam to below 901 feet.

The DWR says that the volume of water is expected to pose no flood threat downstream and emphasized that the Oroville Dam itself remains safe and that there is no imminent threat to the public. Depending on how much the spillway is used, the concrete needs maintenance about every 10 years.

Department of Water Resources employees completely halted the water flow Tuesday after they noticed the aberration.

Water began flowing down the emergency spillway at 8 a.m. Saturday, into the Feather River. To avoid that scenario, flows through the main spillway need to be increased to 50,000 or 55,000 cubic feet per second, Croyle said.

A gaping hole - some 250 feet long and 45 feet deep - appeared Tuesday in the lower part of the main spillway, which is made of concrete and rests on dirt.

They also are clearing and reinforcing a nearby emergency spillway, moving power lines and transferring endangered hatchery fish below Oroville Dam.

The cost could approach $100 million, though department spokesman Doug Carlson said the estimate by a department engineer is an early, ballpark figure.

"The loss of hatchery-produced salmon from Feather River Hatchery would be a major blow to salmon fishermen in California", McManus said, the Sacramento Bee reported.

Meanwhile, workers at a state hatchery for California's native Chinook salmon loaded up all the baby salmon into tanker trucks Thursday afternoon to try to save them from the mud, concrete chunks and other debris coming their way from the crumbling spillway. The spillway was last repaired in 2013 and officials said they do not know why it eroded this week.

But faced with little choice, the state Department of Water Resources resumed ramping up the outflow from Lake Oroville over the damaged spillway to keep up with all the runoff from torrential rainfall in the Sierra Nevada foothills.

Officials said they expected the cavity to widen as a result - and it did.

At 770 feet high, Oroville is the tallest dam in the U.S. It was completed during the administration of Gov. Ronald Reagan and serves as the keystone for the State Water Project, which sends Northern California supplies south to the southern San Joaquin Valley and the urban Southland.

  • Annette Adams