
I just received this update on the Oroville Dam spillway hole from the Department of Water Resources:
SACRAMENTO – While there is still a chance the emergency spillway at Lake Oroville may be used this weekend, reservoir operators say that if current releases from the nearly full reservoir can be maintained, it is less likely the lake will rise to the point where water flows into the emergency spillway channel.
Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public, said California Department of Water Resources Acting Director William Croyle.
"We're ready to use the emergency spillway if needed," he said. "But we're trying to avoid it because there will be sediment and debris impacts downstream."
As storm runoff into Lake Oroville began to wane late Thursday, operators boosted releases from 40,000 cubic feet per second (cfs) to 65,000 cfs. Releases from the nearly full reservoir are hampered by erosion damage to the main spillway, but DWR officials said Friday that if the 65,000 cfs discharge can be maintained, use of the emergency spillway may be avoided.
If the reservoir does rise enough to tip overflow into the emergency spillway channel, that likely would happen Saturday. In that event, DWR will give the public as much notice as possible. DWR does not expect any emergency spillway discharge from the reservoir to exceed the capacity of any channel downstream as the water flows through the Feather River, into the Sacramento River, and into the San Francisco Bay.
The emergency spillway has not been used in Oroville Dam's 48-year history, but Lake Oroville came within a foot of spilling into it in January 1997.
Reservoir operators were using the main, gated spillway at the dam on Tuesday when the lower portion of the concrete chute began to erode. DWR shut off flows temporarily to investigate but has resumed using the gated spillway channel in order to try to avoid having the lake rise to elevation 901 feet above sea level, the point at which water naturally flows over a concrete weir and down a wooded hillside. That hillside is being rapidly cleared.