To help determine an appropriate level of flow down the damaged spillway at Oroville Dam, the California Department of Water Resources (DWR) will release up to 20,000 cubic feet per second (cfs) this afternoon, then ramp down the flows and assess any further damage to the eroded spillway.  The test flow will run for two hours, perhaps as soon as late this afternoon.

The test flow is expected to further erode the lower reach of the spillway, where a cavity opened yesterday as approximately 55,000 cfs was being released from the reservoir into the Feather River downstream.  DWR shut the spillway on February 7 to investigate the erosion.

With the test flows, engineers will verify how much flow the spillway can handle.  The spillway is necessary to maintain reservoir operations, given the immediate forecast of continued rain for the next two days and also in preparation for the remaining runoff season.

In the coming days, DWR will continue to investigate ways to bolster and protect the spillway.  At the same time, as part of a contingency plan, the DWR is removing trees and debris from the corridor near the dam where water would flow in the event the emergency spillway is needed.

The emergency spillway, separate from the damaged spillway, is not gated, and water would flow naturally from the reservoir if it were to reach its capacity of 3.5 million acre-feet at 901 feet elevation.

As of this afternoon, the reservoir holds 3 million acre-feet of water. Before the test flow, approximately 14,000 cfs were being released from the reservoir through other outlets, including the Hyatt Power Plant.  The test will boost those flows temporarily to 34,000 cfs. Inflows to the reservoir are approximately 85,000 cfs.

Enough vacant space exists in the reservoir to capture the flow of the rains expected through Friday afternoon.  The dam is sound, and no imminent threat to the public exists.

DWR is coordinating closely with State and federal wildlife and dam safety officials as it responds to the spillway erosion.

Lake conditions, including lake levels, inflows, and outflows can be obtained via a recorded message at 530-534-2307.