Since Dec. 1 Lake Oroville’s storage has increased approximately 178 feet and gained 1.66 million acre-feet of water. While the Department of Water Resources (DWR) continues to monitor lake levels, DWR is also very closely monitoring weather forecasts and mountain snow levels.

The spillway at Oroville Dam is seen in this aerial photograph taken via drone in Butte County. Photo taken May 4, 2021.

With ongoing wet weather and in anticipation of increased runoff inflows into the reservoir, DWR will increase outflows through the Hyatt Powerplant on Wednesday. The main spillway at Lake Oroville may also be used as early as Friday for additional water releases.

The specific date will depend upon the size and timing of the next series of storms and flood control requirements set by the U.S. Army Corps of Engineers (USACE).

Although a relatively small spill is anticipated at Lake Oroville, the new spillway is fully operational and capable of handling much higher releases if needed. In 2018, DWR rebuilt the spillway to the highest engineering and safety standards, with the spillway concrete thickness averaging 7.5 feet and a significantly improved drainage system.

In addition, DWR installed an array of monitoring instruments in the new spillway. These include new piezometers beneath the spillway to monitor seepage, real-time automated surveys of the spillway walls, and numerous surveillance cameras. The new spillway was used in April 2019 up to a flow of 25,000 cfs.

DWR will continue to optimize water storage in Lake Oroville to support environmental and water delivery needs in the summer, while allowing for carryover storage into next year.