Update, 2:45 p.m. Tuesday: The evacuation order affecting some 180,000 residents along the course of the Feather River below Oroville Dam has been reduced to a warning, allowing residents to return to their homes, Butte County Sheriff Kory Honea said during a press conference.

“Taking into account the current level of risk, the predicted strength of the next round of inclement weather and the capacity of the lake to accommodate increased inflow associated with those storms, we have concluded that it is safe to reduce the immediate evacuation order currently in place to an evacuation warning,” Honea said.

The Department of Water Resources indicated during the conference that the inflow of water to the reservoir continues to drop and that about 100,000 cubic feet of water per second is being released.

“We’re continuing to make significant gains in removing water from the reservoir,” acting DWR chief Bill Croyle said.

DWR officials said the goal is to get the level of the reservoir down to flood control storage, which is about 850 feet.

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Update, 8:15 a.m. Tuesday: Large-scale releases of water continue at Oroville Dam, and the level of the giant reservoir there has dropped to about 12 feet below the emergency spillway structure that engineers believed was on the verge of failure on Sunday.

The Department of Water Resources and other agencies are continuing to assess the condition of the slope below the dam, parts of which were scoured down to rock by the force of water rushing over the emergency release structure over the weekend.

The crisis was triggered a week ago, when serious damage to the dam's main spillway was detected just as runoff began cascading into the nearly full lake after a series of wet, warm storms.

Gov. Jerry Brown has issued an emergency declaration to help speed up state agencies' response to the Oroville crisis. On Monday, he told reporters at a Sacramento-area media briefing with emergency officials that he's confident the Trump administration will respond promptly to the state's requests for aid.

Responding to questions about whether the Department of Water Resources should have done more to reinforce the emergency spillway system -- as suggested by environmental groups during a 2005 relicensing process -- Brown said:

"Every time you have one of these disasters, people perk up and start looking at analogous situations and things that you might not have paid as much attention to. But we live in a world of risk – the earthquake shook the Bay Bridge, and then we the state and all the different governors had to put up a new bridge."

Tuesday morning, 180,000 people remain evacuated along the course of the Feather River in the east-central Sacramento Valley. At a media briefing Monday, Butte County Sheriff Kory Honea said the evacuation order, issued hurriedly on Sunday, would be in place until agencies handling the situation at the dam say the danger of a catastrophic emergency spillway failure is past.

A series of storms expected to begin rolling across Northern California on Wednesday night are expected to trigger a new rise in Lake Oroville -- the reason dam managers are continuing to try to lower the lake as fast as the damaged main spillway will allow.

Update, 1:20 p.m. Monday: Here are four big takeaways from the Department of Water Resources (with other local officials) noontime briefing on the situation at Oroville Dam:

First: The evacuation order that forced 180,000 people from their homes on Sunday will remain in place for now. Butte County Sheriff Kory Honea, whose jurisdiction includes the dam and the communities immediately downstream, said he is depending on the advice of "subject-matter experts" from the DWR and other agencies before people are allowed to return home.

Second: The desperate effort to lower Lake Oroville's level after an imminent failure of the dam's emergency spillway continues. With water pounding down the severely damaged main spillway at nearly 100,000 cubic feet per second -- that's about 750,000 gallons, for those of us who don't measure water in cubic feet -- the giant reservoir is falling at about 4 inches per hour and is now about 5 feet from the top of the emergency spillway.

Third: Dam and water managers are preparing for the resumption of winter storms over the Feather River watershed above Lake Oroville. The DWR's 10-day precipitation forecast, based on analysis of weather models, suggests that the next round of storms will be much colder and drop less than half the precipitation than the very warm weather systems that helped trigger the Oroville crisis.

Fourth: The DWR and other state and federal agencies are going to face very tough questioning about whether something should have been done years ago to shore up the emergency spillway structure and adjacent hillside. Those questions will be prompted by a story by KQED Science Managing Editor and San Jose Mercury News reporter Paul Rogers, who details concerns raised about the soundness of the emergency spillway system back in 2005.

Update, 11:15 a.m. Monday: Water levels continue to drop this morning at the nation's tallest dam, reducing the risk of a catastrophic spillway collapse and easing community fears. However, officials say they do not yet have enough information to lift an evacuation order that displaced nearly 200,000 people Sunday night.

Officials from the California Department of Water Resources are in the process of inspecting an erosion scar on the spillway at the dam on Lake Oroville. After a series of storms this month, the water level rose significantly at the lake and the high water forced the use of the dam's emergency spillway, or overflow, for the first time in the dam's nearly 50-year history on Saturday.

With more rain expected Wednesday and Thursday, officials are trying to fix the damage and hoping to reduce the dam's water level by 50 feet ahead of the coming storms. According to the California Department of Water Resources, the lake level was about 5 feet lower this morning (and dropping) than at its high point last night. It continues to drop about 3 to 4 inches per hour.

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The sudden evacuation order on Sunday caused confusion and chaos, as more than 500 people showed up at a Red Cross evacuation center in Chico. The shelter ran out of blankets and cots, and a tractor-trailer with 1,000 more cots was stuck in the gridlock of traffic fleeing the potential flooding Sunday night, said Red Cross shelter manager Pam Deditch. The Beale Air Force Base also took in about 375 residents, according to the L.A. Times.

A California Highway Patrol spokesman said two planes would help with traffic control and possible search-and-rescue missions this morning. At least 250 California law enforcement officers are posted near the dam and along evacuation routes to manage the exodus and ensure evacuated towns don't become targets for looting or other criminal activity. And the California National Guard also notified all of its 23,000 soldiers and airmen to be ready to deploy, the first time an alert for the entire California National Guard had been issued since the 1992 riots in Los Angeles. FEMA has also said it is setting up an incident command center with the California Office of Emergency Services.

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While fears have eased slightly, a lot is still unknown.

"We need to continue to lower the lake levels, and we need to give the Department of Water Resources time to fully evaluate the situation so we can make the decision to whether or not it is safe to repopulate the area," said Butte County Sheriff Kory Honea.

Acting Director of the Department of Water Resources Bill Croyle said officials will be able to assess the damage to the emergency spillway now that the lake level has come down. Unexpected erosion chewed through the main spillway during heavy rain earlier this week, sending chunks of concrete flying and creating a 200-foot-long, 30-foot-deep hole. Engineers do not yet know what caused the cave-in, but Chris Orrock, a Department of Water Resources spokesman, said it appears the dam's main spillway has stopped crumbling, even though it is still being used for water releases.

A gallery from DWR of the erosion earlier this week:

[gallery type="rectangular" size="medium" ids="11307354,11307355,11307356,11307357,11307358,11307359,11307360,11307361,11307362,11307363,11307364,11307365"]

The Associated Press contributed reporting to this story.

Update: Sunday, Feb. 12, 10:45 p.m.: The level of Lake Oroville has dropped enough to prevent water from cascading over the emergency spillway, stopping the erosion that threatens the structure, water officials said late Sunday.

Butte County Sheriff Kory Honea said this doesn't mean the area is out of danger, however, and he doesn't yet know when he might have enough information to lift the evacuation order.

"We need to give the Department of Water Resources (DWR) time to thoroughly evaluate [the spillway], in order to make decisions about whether or not it is safe to repopulate areas," Honea said. "I recognize how tough this situation is on people, but as you've heard tonight, we needed to do that to ensure the public safety. And that's the thing we'll focus on going forth."

Gov. Jerry Brown issued an emergency proclamation late Sunday, freeing up personnel and equipment to help with everything from evacuations to flood control to patrolling evacuated areas. The California Highway Patrol, Cal Fire and the National Guard have deployed helicopters, planes, fire engines and high water trucks -- or have them standing by -- and have mobilized hundreds of law enforcement and other personnel, including swift water rescue teams.

DWR on Sunday nearly doubled the flow over the primary concrete spillway, from 55,000 to 100,000 cubic feet per second. That brought the level of the lake down below the lip of the emergency spillway by mid-evening, easing the threat of collapse. But water officials now want to lower the lake another 50 feet, to make room for storms due later this week.

The agency's acting director, Bill Croyle, said officials were able to get up in helicopters to inspect the spillway visually Sunday night, but need to be out on the ground tomorrow at first light to look at the erosion scar. Croyle said the goal is to ensure the emergency spillway not only doesn't fail, but is able to be used the rest of the winter rainy season, if necessary.

"This erosion scar happened for a reason, so we want to understand that," Croyle said, adding that the department has not yet dropped any bags of rocks into the erosion scar, or taken any other corrective measures to repair it

Officials said evacuation orders affect 76,000 residents in Yuba City, 65,000 in Yuba County, 35,000 in Butte County and 12,000 people in Marysville. The California Highway Patrol is urging evacuees to take Highway 99 or State Route 70 north to escape the area.

Original Story, Sunday Feb. 12:

State water officials say the "auxiliary" spillway at Oroville Dam could fail at any time and they ordered emergency evacuations late this afternoon for thousands of people from Oroville to Gridley.

"We didn't have the luxury of waiting to see if all was OK," said Butte County Sheriff Kory Honea, explaining that when he ordered the evacuations, officials believed the spillway might collapse within hours. "We needed to get people moving and save lives in case the worst-case scenario came to fruition."

The California Department of Water Resources urged residents of Oroville to head north, toward Chico. Residents elsewhere downstream should follow the orders of their local law enforcement, the department said. Officials have set up an evacuation shelter at the Silver Dollar Fairgrounds in Chico.

The spillway is still holding, despite a hole that is eroding at its lower edge, due to the pressure of water cascading over the lip of the spillway. Earlier Sunday, water officials estimated the hole was eroding inward at a fast enough rate to cause a collapse sometime in the early evening, but at a press conference shortly after 6 p.m., officials said the hole was eroding more slowly than they'd expected.

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Sheriff Hornea said the plan is to use helicopters to drop bags of rocks into the crevice and prevent further erosion. Cal Fire incident commander Kevin Lawson said the agency has helicopters and engines standing ready to be deployed and is mobilizing hand crews on both sides of the river to assist with any flooding.

Water officials said they are relieving pressure on the spillway by increasing water flows down the primary concrete spillway, and that they have not seen any further damage Sunday to the concrete, due to the additional water. The primary spillway developed a massive cavity last week, which has expanded as water flows increased.

The auxiliary spillway is separate from the main dam structure. It's essentially an ungated 1,700-foot-wide notch in the rim of the reservoir, which began overflowing Saturday morning, days after the dam's concrete-lined main spillway began to crumble. Below an initial concrete lip, water courses over bare earth all the way to the Feather River below, scouring the incline of earth, rocks and trees.

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Despite earlier reports that the lake level was dropping on Saturday, erosion on the auxiliary spillway has increased beyond expectations. Oroville Dam contains California's second-largest reservoir, and is currently holding back more than 3.5 million acre-feet of water.

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