The California Department of Water Resources has temporarily suspended flows over the spillway at Oroville Dam to investigate concrete erosion on the bottom half of the spillway.
On the morning of Feb. 7, DWR employees noticed an unusual flow pattern and erosion on the spillway. About 60,000 cubic feet per second of water was being released to the Feather River, with about 55,000 cfs of that going through the spillway and the remaining 5,000 cfs passed through the 645-MW Edward Hyatt pumped storage power plant within the left abutment of the dam.
Spillway flows were gradually reduced until they were entirely halted at about noon.
DWR says there is no anticipated threat to the dam or the public.
The department says about 20% of Lake Oroville remains empty and there is sufficient storage room to capture the inflow of the rain showers expected through the rest of the week.
Oroville Dam is the tallest in the U.S. at 770 feet and was completed in 1967.
DWR expected to be able to resume releases from the spillway after a thorough inspection. In the meantime, DWR increased releases from the Thermalito Afterbay just downstream of Oroville Dam to avoid a drastic reduction of flows in the Feather River downstream.