Oroville Dam operators prepared to reduce water releases over its main spillway Saturday as repairs continued on the troubled dam.
Despite significant rainfall Friday, the water level at Lake Oroville continued to drop overnight. The lake was sitting at just above 855 feet Saturday morning. That represented a drop of 46 feet since last Sunday, when an emergency sparked the temporary evacuation of nearly 190,000 downstream residents. It was also just 5 feet above the maximum lake level for this time of year, according to U.S. Army Corps of Engineers flood control regulations.
Water releases were dialed back Friday to 70,000 cubic feet per second on the damaged main spillway. Department of Water Resources spokesman Chris Orrock said the releases were likely to be curtailed yet again, to 60,000 cfs, sometime Saturday. Until Thursday, the spillway had been pouring water out at 100,000 cfs in order to bring the lake level down quickly.
DWR is reducing releases for two reasons. First, it needs lower water flows so it can get work crews stationed on the diversion pool, the stream directly beneath the spillway that leads into the Feather River. The pool has gotten clogged with debris from the giant crater that was discovered on the spillway Feb. 7, backing up water to the dam’s hydroelectric plant. That’s made it impossible to operate the power plant, which is capable of releasing water at 14,000 cfs.
“We continue to put additional construction crews in the diversion pool,” Orrock said.
The second reason is that, as the lake level decreases, it becomes harder to push water out of the spillway at a high rate. “We’re taking too much water out of the reservoir; it’s too low,” Orrock said.
Orrock added that a second work crew was continuing to make repairs to the eroded hillside beneath the dam’s emergency spillway. It was erosion on that hillside that sparked fears that the emergency spillway would fail last Sunday, prompting the evacuation order. The order was rescinded Tuesday but downstream residents have been told to stay ready to leave again.
DWR officials have said they’re confident the reservoir will have enough empty space to withstand a major rainstorm expected to hit the region Monday and Tuesday.