Capping days of tense planning at the nation's tallest dam, officials on Saturday sent water down an emergency spillway at the Oroville Dam for the first time ever after the dam's main spillway suffered significant damage.
Reservoir operators say that if current releases from the almost full reservoir can be maintained, it is less likely the lake will rise to the point where water flows into the emergency spillway at Lake Oroville over the weekend. Erosion eventually caused a 200-foot-long, 30-foot-deep hole to form near the center of the spillway, a structure used to control the release of water.
Video on the sheriff department's Facebook page showed about 35,000 cubic feet of water per second being released down the enormous slide into the river, but officials said the additional flow would not necessarily cause flooding. "We still don't expect to use the auxiliary spillway".
The net effect is that with releases virtually halted and heavy inflows from a series of very wet winter storms continuing to pour into the reservoir, the lake is rising steadily. With the Feather River Hatchery at risk of being inundated by a large load of sediment and turbidity, DWR Crews are placing debris booms in several key areas in its Diversion Pool to protect the young hatchlings and eggs. Yet it appears the inflows are starting moderate from the levels they were at late Thursday.
Water flows through a break in the wall of the Oroville Dam spillway on Thursday.
The initial damage to the spillway occurred Tuesday, about 3,000 feet downstream from where water enters from the lake.
Officials said they expected the cavity to widen as a result - and it did.
California Department of Water Resources spokesman Doug Carlson said Friday that the estimate by a department engineer is an early, ballpark figure.
In January 1997, downstream towns were evacuated when the reservoir came within a foot of pouring down the emergency spillway into the swollen Feather River.
The DWR says that the volume of water is expected to pose no flood threat downstream and emphasized that the Oroville Dam itself remains safe and that there is no imminent threat to the public. Lake Oroville now holds approximately 3.22 million acre-feet of water and stands at an elevation of 880 feet, or 96 percent of capacity.
Associated Press writers Kristin J. Bender and Ellen Knickmeyer contributed to this story from San Francisco.