Nearly 200,000 people remained holed up in Northern California shelters Tuesday while engineers rushed to repair a crumbling overflow channel and drain the rain-flooded reservoir of the national’s tallest dam.
“We’re doing everything we can to get this dam in shape that they can return and they can live safely without fear. It’s very difficult,” California Gov. Jerry Brown told reporters Monday night, Reuters reported.
Brown sent a letter to President Trump requesting him to issue an emergency declaration, which would open up federal assistance for the affected communities.
Evacuation orders for about 188,000 people remained in effect as the risk to those living in the Feather River valley below the Lake Oroville Dam, 65 miles north of Sacramento, was being reviewed, officials said.
Residents below the dam were ordered to evacuate their homes Sunday when an emergency spillway that acts as an automatic overflow channel appeared on the brink of collapse from severe erosion.
The earth-filled dam is just upstream and east of Oroville, a town of about 16,000 people. At 770 feet high, the structure — built between 1962 and 1968 — is the tallest US dam, exceeding the Hoover Dam by more than 40 feet.
Authorities said they had prevented the immediate danger of a catastrophic failure that could send a wall of water three stories tall cascading over towns below.
The main spillway, a separate channel, also is damaged because part of its concrete lining crumbled last week. Both spillways are to the side of the dam itself, which has not been compromised, engineers said.
Environmental activists and local government officials warned more than 10 years ago about the risk of catastrophic flooding below the dam, CBS News reported.
But state and federal regulators dismissed those fears at the time, saying they believed the hillside that helps hold back hundreds of billions of gallons of water was stable and needed no concrete reinforcement.
That decision has come under scrutiny now that the hillside — or emergency spillway — has been put to its first test in the Oroville Dam’s history.
In 2005, at the beginning of the dam’s relicensing process, environmental groups asked the feds to require that the California Department of Water Resources “armor” the hillside to prevent erosion from water escaping when the reservoir was beyond capacity.
Also that year, officials in Sutter County, which the Feather River runs through dozens of miles downstream of the dam, asked federal regulators to “investigate the adequacy and structural integrity” of the hillside and how it would hold during “extreme flood releases.”
“I think that the warning that was given should have been taken with the utmost seriousness,” said Bob Wright, an attorney at Friends of the River, which raised the matter along with the Sierra Club and South Yuba River Citizens League, CBS News reported.
Bill Croyle, acting head of the Department of Water Resources, refused to comment on those concerns, saying he was unfamiliar with them and would need to research the issue.
