Environment & Science

Slideshow: Water flowing over emergency spillway at Lake Oroville

Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
California Department of Water Resources/Twitter
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
Department of California Water Resources/Twitter
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
California Department of Water Resources/Twitter
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they can avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County. Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources (DWR) Acting Director William Croyle. Photo taken February 10, 2017. Brian Baer/ California Department of Water Resources
Brian Baer
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they can avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County. Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources (DWR) Acting Director William Croyle. Photo taken February 10, 2017.
Brian Baer/ California Department of Water Resources
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they can avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County. Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources (DWR) Acting Director William Croyle. Photo taken February 10, 2017. Brian Baer/ California Department of Water Resources, FOR EDITORIAL USE ONLY
Brian Baer
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
Cloudy waters from the damage spillway at Lake Oroville and Oroville Dam forced the California Department of Fish and Wildlife to truck 4 million baby salmon from the Feather River Fish Hatchery in Oroville, Calif. to the nearby fish ponds at the Thermalito Afterbay Complex in Butte County. Photo taken February 10, 2017. Kelly M. Grow/ California Department of Water Resources
Kelly M. Grow
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they can avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County. Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources (DWR) Acting Director William Croyle. Photo taken February 10, 2017. Brian Baer/ California Department of Water Resources
Brian Baer
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they can avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County. Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources (DWR) Acting Director William Croyle. Photo taken February 10, 2017. Brian Baer/ California Department of Water Resources
Brian Baer
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources stopped the spillway flow on Thursday morning to allow engineers to evaluate the integrity of the structure after water had been released at 20,000 cubic feet per second (cfs) through the night. There is no imminent or expected treat to public safety or the integrity of Oroville Dam at the Butte County site. After conferring with State and federal dam safety entitles, DWR decided to increase the release volume to 35,000 cfs to help operators absorb the inflow of the storm waters expected today and Friday. More erosion is also expected. Photo taken February 9, 2017. Kelly M. Grow/ California Department of Water Resources
Kelly M. Grow/California Department of Water Resources
Water flowing over the Oroville Dam spillway on Saturday, Feb. 11, 2017.
The California Department of Water Resources has suspended flows from the Oroville Dam spillway after a concrete section eroded on the middle section of the spillway. There is no anticipated threat to the dam or the public. DWR engineers are assessing the options to repair the spillway and control the reservoir water level. The Butte County facility is the tallest dam in the United States at 770 feet and is a key part of the State Water Project. Photo taken February 7, 2017. Kelly M. Grow/ California Department of Water Resources
Kelly M. Grow


Water started flowing over an emergency spillway at the nation's tallest dam, on Lake Oroville, for the first time Saturday after erosion damaged the Northern California dam's main spillway.

Officials hoped to avoid using Oroville Dam's emergency spillway, fearing it could cause trees to fall and leave debris cascading into water that rushes through the Feather River, into the Sacramento River and on to the San Francisco Bay. Crews prepared for several days, clearing trees and brush.

Water began running over the emergency spillway around 8 a.m., according to California's Department of Water Resources. It was the first time the emergency spillway has been used in the reservoir's nearly 50-year history.

Water was expected to continuing flowing over the emergency spillway for 38 to 56 hours, agency spokesman Eric See said at a news conference Saturday afternoon. In addition to the emergency spillway, water is also flowing through the main spillway that was significantly damaged from erosion, he said.

"This is a very unusual event for us here in Oroville," See said.

Unexpected erosion chewed through the main spillway earlier this week, sending chunks of concrete flying and creating a 200-foot-long, 30-foot-deep hole that continues growing. Engineers don't know what caused the cave-in that is expected to keep getting bigger until it reaches bedrock.

Bill Croyle, the Department of Water Resources' acting director, said officials are continuously monitoring the erosion both on site and through cameras. "This is mother nature kind of kicking us a few times here," he said.

Croyle said the main spillway will need a "complete replacement" from the damage. Officials noted earlier this week that the cost of repairing the dam could approach $100 million, but they noted the estimate was an early, ballpark figure.

Officials have stressed Oroville Dam is sound and there is no imminent threat to the public.

State officials also had been attempting to rescue millions of hatchery-raised fish imperiled by muddy water flowing downstream alongside the damaged spillway after sections of its concrete walls collapsed earlier this week

About 150 miles northeast of San Francisco, Lake Oroville is one of California's largest man-made lakes, and the 770-foot-tall Oroville Dam is the nation's tallest. The lake is a central piece of California's government-run water delivery network, supplying water for agriculture in the Central Valley and residents and businesses in Southern California.

This story has been updated.