As Lake Oroville nears capacity, DWR says no need to fear spill overs

Visitors to Oroville Dam may also notice minor amounts of water flowing from drains built into the emergency spillway. Both conditions are normal and expected given the emergency spillway design.

OROVILLE — With Lake Oroville creeping toward capacity, concerns over emergency spillage loom.

The California Department of Water Resources, however, said this won’t happen because of controlled outflows and monitoring. DWR Spokesperson Raquel Borray said the dam is being watched closely.

“DWR’s Water Operations unit closely monitors weather forecasts and runoff into Lake Oroville and adjusts releases as needed to provide continued flood control protection to the city of Oroville and downstream communities,” Borrayo said. “As Oroville Dam and the spillway continue to operate as intended, DWR will maintain releases using the Hyatt Powerplant and main gated spillway.”

As of Tuesday, Borrayo said, total releases into the Feather River come out to 10,000 cubic feet per second with the majority — 9,350 cfs — going through the Thermalito Afterbay Outlet and the remaining 650 cfs pouring through the low-flow channel. She added that DWR is making adjustments as they are necessary.

Though the lake isn’t necessarily overflowing, Borrayo said weather events such as gusts could cause water to spill.

“Of note, with Lake Oroville at full capacity, windy periods are likely to cause waves to splash onto and over the crest of the emergency spillway,” Borrayo said. “This will result in minor surface wetting of the downstream side of the emergency spillway crest and the very upper sections of the splash pad. Visitors to Oroville Dam may also notice minor amounts of water flowing from drains built into the emergency spillway. Both conditions are normal and expected given the emergency spillway design. The dam and emergency spillway continue to operate as intended.”

At 4 p.m. Tuesday, the lake’s level was gauged at 899.19 feet, amounting to 3,524,785 acre-feet of storage. At that same time, inflows were monitored at 10,686 cfs.

In 2017, the main spillway broke and the lake overflowed into the emergency spillway causing extensive damage both to the spillway itself as well as areas downstream. At the time, evacuations were in place and residents downriver from the lake were urged to leave the area.

Since then, both the main and emergency spillways have been rebuilt. A large “splash pad” was added to the emergency spillway, which is a concrete weir. The main spillway has gates that open to allow up to 270,000 cfs into the Feather River through the Diversion Pool and Thermalito Afterbay and Forebay.

“Water releases over the emergency spillway are uncontrolled releases and would only occur during an emergency in which Oroville Dam and the spillway are unable to operate as intended,” Borrayo said. “There are no plans to increase storage levels at Lake Oroville that would necessitate releases over the emergency spillway.”