DWR: Oroville releases will slow down, Lake continues to rise
Water releases out of eroded Oroville Dam Spillway increase
Water releases out of eroded Oroville Dam Spillway increase
Water releases out of eroded Oroville Dam Spillway increase
Lake Oroville is at 99% capacity as of 5 p.m. Friday with only 3.5 feet left to fill, according to the California Department of Water Resources.
DWR announced about 5:50 p.m. Friday that reservoir operators plan to make a slight reduction of releases from the damaged spillway to prevent more erosion along the north side of the spillway.
Get the latest reports, photos and videos here.
Officials will slow the releases down the gated spillway from 65,000 cfs to 55,000 cfs, the department said.
DWR does not anticipate the emergency spillway to be used, but tells the public they should not be surprised if it does.
If the emergency spillway is used, it would be the first in the Oroville dam's 48-year history.
DWR insists there will be no threat to the integrity of the dam or flooding downstream on the Feather River.
DWR announced about 12 p.m. Friday that it does not anticipate needing to use the emergency spillway at Lake Oroville as water flows into the reservoir have decreased and outflows by way of the normal erosion-damaged spillway have been increased.
A team of project geologists, engineers and dam experts assessed the situation and conducted a test of the damaged Oroville Dam Spillway and decided it was the best option to release water through that as the lake was filling up.
"They knew there would still be some erosion, but it was still a usable structure and they could continue to use the spillway," DWR spokesperson Eric See said in a Friday news conference.
Kevin Dossey, senior engineer with DWR, said spillway erosion is common and repairs have been made in recent years.
"There was some patches needed. We made repairs and everything checked out as far as it looked like it would hold, be able to pass water again," he said.
When asked whether DWR is at fault for the break in the spillway, Dossey said it's clear something unexpected happened earlier this week.
"Obviously something has happened that we did not expect to happen. I don't think anybody who was in the inspection team or the repair team would say that more should have been done because there wasn't any evidence that more needed to be done," Dossey said.
He also explained that the dam gets yearly inspections from both state and federal inspectors.
According to the July 2015 inspection report, "The FCO structure appeared to be satisfactory with no visible concrete or structural deficiencies."
However, the report also indicates the inspection was done visually and inspectors did not walk the spillway.
"The discharge channel was not walked this time; however, a visual inspection from some distance indicated no visible signs of concrete deficiencies," the report states.
On Thursday evening, water officials announced that it was looking more likely that they would need to use the emergency spillway, but with inflows decreasing and outflows increasing, they pulled back on that. However, they are still preparing the area in case the emergency spillway would need to be used.
HOW MUCH WATER IS GOING IN AND OUT OF LAKE OROVILLE?
Water officials upped the outflows on the eroding spillway to 65,000 cfs Friday morning. The power plant, where additional water was being let out, was shut down due to elevated levels in the diversion pool, DWR officials said.
However, more than double that amount is coming into the the reservoir -- 116,000 cfs -- as of 4 p.m. Friday, down from 150,00 cfs earlier in the morning. The inflows to Lake Oroville have decreased by about 45,000 cfs since Thursday night, and all forecasts indicate that the inflows will continue to lessen heading into the weekend.
Get bird's eye view of initial erosion on Oroville Dam Spillway
As of 2 p.m. Friday, the reservoir stood at 98.5 percent full, just five feet shy of being reaching full capacity.
WHAT'S THE DEAL WITH THE EMERGENCY SPILLWAY
The emergency spillway, located to the north of the controlled spillway, has never been used in the lake's 48-year history. It would send water down a hillside to uncontrolled land.
The only way the emergency spillway would be used is if the lake reaches full capacity at 901 feet elevation or 3.5 million acre-feet.
Crews worked Thursday and Friday to clear trees and vegetation from the area below the emergency spillway in an effort to reduce the amount of debris that would flow down into the Feather River.
This spillway is designed to protect the integrity of the dam.
"You will never have a situation where any water would go over the top of Oroville Dam," See said. "You never want to have overtopping of your dam because on an earthen dam, like Oroville Dam, because you can have erosion on the backside, which is very bad."
ARE THERE FLOOD OR DAM FAILURE CONCERNS?
Water officials continue to reiterate that despite the damaged spillway, there is no threat to the public or the Oroville Dam.
"This problem is with the spillway, it is not with Oroville Dam," See said. "There's no erosion going on with Oroville Dam. Oroville Dam is completely in tact and is not in jeopardy in any way from this event."
The hole that is eroding is about two-thirds down the spillway, and most of the erosion is expanding down the hill, not up toward the lake or dam, DWR officials said Thursday.
As for flooding, even if the water was to start spilling down the emergency spillway, there is no concern for communities downstream along the Feather River.
The water flows down Feather River are still much less than what the region saw in 2006, and it would not create any flooding issues for towns like Oroville, See said.
HOW DID THIS ALL START?
A maintenance employee was working Tuesday morning near the Oroville Dam Spillway when he noticed an anomaly in how the water was being sent down after water officials opened the spillway to maintain a mandated buffer in the lake in case of a flood event.
Water officials shut off the water streaming down the spillway and noticed a hole, which was initially reported to be about 180 feet wide by 250 feet long by 40 feet deep, the DWR said.
However, as the rain persisted in Northern California, the inflows to Lake Oroville increased and the reservoir was rapidly rising.
Officials conducted a test on Wednesday to see how much water the spillway could handle and began releasing about 20,000 cfs for several hours, leading to further erosion and chunks of concrete peeling off the chute.
Part of right-side wall were lose and the hole was made significantly bigger. By Thursday afternoon, water could be seen spewing all along the bottom of the dam as officials decided to increase the outflows to prevent the lake from filling up.