Efforts to lower Lake Oroville and prevent erosion below emergency spillway continue

The crisis of catastrophic flooding was temporarily averted at the Oroville Dam just 74 miles north of Sacramento, as California state water officials rushed to shore up severely eroded areas surrounding the dam's main spillway and emergency spillway Monday.

The massive erosion and water damage Sunday had threatened to compromise the reservoir's 30-foot concrete rim that keeps the reservoir water contained at the top of the emergency spillway.

"The dam itself is sound. The dam...is doing its job," said Bill Croyle, Acting Director of California's Department of Water Resources, at a news conference Monday.

"There's no water spilling over the emergency spillway at this time. That's an important thing," said Butte County Sheriff Kory Honea, who emphasized that the mass evacuation of an estimated 188,000 residents remains in place.

Fears remain that if erosion continues creeping upslope and causes a failure of the emergency spillway's concrete rim, a 30-foot wall of water could descend into the Feather river and towns far downstream.

Trucks dumped boulders onto eroded spots Monday that need shoring up. Overhead, two helicopters dropped more boulders in white bundles onto the damaged spillway.

Governor Jerry Brown and California Senators Dianne Feinstein and Kamala Harris requested federal aid from President Trump Monday.

"I'm sure that California and Washington will work in a constructive way," Governor Brown said.

Time is short, with the next storm expected to arrive Thursday.

"Our objective is to lower the lake level by 50 feet in order to prepare for future inflow of water," said Sheriff Honea.

That is no easy task, according to hydrologist Peter Gleick, chief scientist at the Pacific Institute think tank.

"Fifty feet is a lot of water. They're talking about one million acre feet of water," said Gleick, "In order to draw down the water 50 feet, they're going to have to run a lot of water down the main spillway. And the main spillway we know is also damaged."

Also a danger, that continues through spring, is that any warm rainfall risks melting the Sierra snowpack. That would greatly increase runoff into Lake Oroville, and could raise the water level to a dangerous point.

"If a tremendous amount of water is released, we're going to see flooding down the Feather, down the Yuba, down the Sacramento all the way to the delta. And the delta is already stressed because it's been an incredibly wet winter. There's already pressure on levees in the delta and I think we could see cascading failures," said Gleick, noting that would be the worst case scenario.

He added that over the years, houses and industries have been built close to the rivers and levees, increasing the potential damage if water overwhelms or tops the protective levee walls.

Officials with the Department of Water Resources said Monday night they do not believe the current water discharge will harm downstream channels.