As it manages storm inflow to Lake Oroville with a main spillway damaged by erosion, the California Department of Water Resources (DWR) announced late Thursday that the reservoir’s emergency spillway likely will be used, perhaps as soon as the early hours of Saturday.
In that event, total discharges from the reservoir would be consistent with flood control releases at this time of year under these weather conditions. DWR does not expect the discharge from the reservoir to exceed the capacity of any channel downstream as the water flows through the Feather River, into the Sacramento River and on to the San Francisco Bay. Inflow to Lake Oroville was expected to peak late Thursday and begin to decline through the weekend.
Oroville Dam itself is sound and there is no imminent threat to the public, said DWR Acting Director William Croyle.
“We and our many partners are doing everything we can to minimize all risks to the public and the dam,” he said.
Thursday evening operators increased the releases down the damaged, gated spillway from 35,000 cubic feet per second to 40,000 cubic feet per second, with another 7,000 cfs passing through the dam’s hydroelectric power plant outlets. But those discharges are not enough to match an inflow of approximately 192,000 cfs from a storm that stalled over the watershed. The reservoir, at 884 feet elevation above sea level Thursday, will naturally begin to spill into the emergency spillway channel at elevation 901 feet. That point may come shortly after midnight Friday.
The emergency spillway has not been used in Oroville Dam’s 48-year history, but Lake Oroville came within a foot of spilling into it in January 1997.
The emergency spillway is a vegetated hillside near the dam, and should it be used, water would wash away large amounts of soil. In preparation for the possible use of the emergency spillway, trees and brush are being removed from the hillside to minimize any flow of debris into the river. Evacuation of fish from a downstream hatchery is underway to avoid harm to young fish and eggs from turbid water.
DWR is coordinating closely with state and federal wildlife and dam safety officials as it responds to the spillway erosion and manages reservoir operations. Those involved in contingency planning and response include the Federal Energy Regulatory Commission, the U.S. Army Corps of Engineers, Butte County Sheriff’s Office, the Governor’s Office of Emergency Services, the state’s Division of Safety of Dams, CAL FIRE and state and federal wildlife agencies.
The California Department of Water Resources and host of collaborating agencies continue to monitor the Lake Oroville spillway flows late Thursday afternoon as 35,000 cubic feet per second (cfs) of water was released over the damaged spillway. More erosion is expected, but the releases will help operators absorb the inflow of the storm waters expected Thursday evening and Friday. DWR first noticed erosion on the spillway Tuesday morning and shut off flows to investigate.
There is no imminent or expected threat to public safety or the integrity of Oroville Dam in Butte County. Photos taken 4:39 p.m. PST February 9, 2017.
Kelly M. Grow, Photographer, California Department of Water Resources