
A 250-foot long cavity opened in the Oroville Dam spillway yesterday as approximately 55,000 cubic feet per second was being released from Lake Oroville into the Feather River downstream.
DWR shut the spillway to investigate the rupture on February 7. The discovery of the giant hole caused a halt and reduction in water deliveries downriver.
The rupture takes place at a time when Governor Jerry Brown is promoting the construction of two massive Delta Tunnels and new water storage. Project critics say that the state should instead focus on maintaining and improving existing water system infrastructure, such as properly maintaining the spillway at Oroville, rather than focusing on environmentally destructive and enormously expensive tunnels and dams.
To help determine an appropriate level of flow down the damaged spillway, the California Department of Water Resources plans to release up to 20,000 cubic feet per second this afternoon, then ramp down the flows and assess any further damage to the eroded spillway, a news release DWR reported.
The test flow will run for two hours, perhaps as soon as late this afternoon, according to Ted Thomas, spokesman for the Department of Water Resources. 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.
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, said Thomas.
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, he said.
DWR said 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.