24 hours later, no problems reported with Oroville Dam’s emergency spillway

Water continued pouring out of Oroville Dam’s emergency spillway Sunday morning, although state officials said the flows were manageable and downstream problems were minimal. A dry spell has helped considerably, reducing the amount of water flowing into swollen Lake Oroville.

One day after water started trickling over the concrete lip of the emergency spillway for the first time in the dam’s 48-year history, the flows accelerated to 12,600 cubic feet per second at 1 a.m. Sunday and then began subsiding. A few hours later, the flows were down to 12,100 cfs, said Chris Orrock, a spokesman for the state Department of Water Resources.

DWR officials had been reluctant to let water run down the emergency spillway because the flows are uncontrolled and cascade into a heavily wooded ravine, raising fears of huge amounts of debris being deposited into the Feather River. But Orrock said DWR crews stationed downstream to catch trees and other materials have encountered only “minimal” debris.

Engineers have said they expect the flows from the emergency spillway to stop sometime Monday evening.

Orrock added that the dam’s main spillway, which suffered an enormous gash Tuesday, appears to have stopped crumbling despite continued pounding from water releases at roughly 55,000 cfs. “There's been no additional erosion that they can see,” he said.

“It seems overall the situation has stabilized,” Orrock said.

California’s second largest reservoir was plunged into crisis when the gash opened up in the dam’s main concrete spillway, forcing a temporary shutdown just as a dam operators were releasing water to make room for a huge rainstorm. Engineers resumed releasing water down the damaged spillway Wednesday, hoping to keep the lake from filling to the brim and bringing the never-before-used emergency spillway into the picture.

Despite those efforts, the reservoir started lapping over the emergency spillway at 8 a.m. Saturday.

Bill Croyle, the acting director of DWR, told reporters Saturday that repairing the damaged spillway could cost $100 million to $200 million. He added that officials are watching weather forecasts closely. A new storm is expected to roll in Thursday, although it’s supposed to be colder than last week’s and therefore wouldn’t bring a sudden rush of water into the reservoir.

On Sunday, crews operating heavy machinery were working to construct a new road so workers could clear the channel near the main spillway. Once that happens, a power plant at the base of the dam can restart and release more water from the reservoir. The plant had been shut down Friday because all the concrete and other debris streaming into the river from the broken spillway had raised water levels to the point that the turbines couldn’t run.

This story was originally published February 12, 2017 at 11:10 AM with the headline "24 hours later, no problems reported with Oroville Dam’s emergency spillway."