Tuesday, February 14, 2017

More on the Oroville Dam

The Atlantic:

 A crater in the middle of the primary spillway at the Oroville Dam (California Department of Water Resources via Reuters)
This winter has seen much more snow and rain, which is good news for the parched state, but bad news for the Oroville Dam, where huge amounts of water are collecting. The lake rose 50 feet in a matter of days. Earlier in February, as operators let water over a concrete spillway to reduce the pressure, a crater appeared in the spillway. Faced with too much water in the lake, they continued to use the spillway anyway, and the damage got worse. On Friday, the crater was 45 feet deep, 300 feet wide, and 500 feet long.
There’s a backup for the concrete spillway, an auxiliary spillway that had never been used. It’s really just a hillside sloping down from the reservoir, covered in brush and trees. As the situation became more dire last week, crews starting clearing the slope for its first baptism. Managers hoped pressing the auxiliary spillway into service would give them time to patch up the concrete spillway over what’s expected to be a drier season. (That could be easier said than done: Snowpack upstream is 150 percent of normal for this time of year, meaning there’s going to be more melt headed downstream than normal.)
Initially, that seemed to do the trick: The water level in Lake Oroville was dropping, and the danger seemed to be abating. On Sunday, however, officials noticed the auxiliary spillway was starting to erode—at the same time that huge amounts of water continued to flow into the lake. The fear is that if the spillway gives out, a wall of water could push down out of Lake Oroville and toward lower ground. Workers are trying to shore up the emergency spillway with bags of rocks, including dropping them from helicopters. If it gives way, the Feather River would flood downstream, and might wash out other levees farther down the river. Meanwhile, debris from erosion also forced the  state Department of Water Resources, the dam’s operator, to shut down its power plant, which could have helped to release some additional water. And there’s rain forecast for later this week.
 Los Angeles Times:
 Crews work on a damaged section of the emergency spillway at Lake Oroville on Monday.
(Josh Edelson / AFP/ Getty Images)
In the five days from Feb. 6 to Friday, Oroville received more than 6 inches of rain, according to the National Weather Service. The surrounding mountains and foothills received up to 24 inches of rain and snow in the same time period.
The storm’s runoff sent water into the Oroville reservoir at an average rate of 115,260 cubic feet per second, data show. The lake’s water level climbed 50 feet in five days.
In addition to the crisis at Oroville Dam, several levees throughout the region have seen structural damage, adding to the flood threat, Dang said. Many reservoirs in Northern California are having to release large amounts of water, causing rivers to rise.
Portions of the Sacramento and San Joaquin rivers are at or near flood stage, he said. The Feather River, downstream from Lake Oroville, has seen flooding for several days.
Although this week’s storms are expected to be smaller, they’re “certainly impactful,” Dang said.
“The storms last week have really left Northern California in a vulnerable state right now, and any amount of rainfall isn’t helpful at this stage.”
Forecasters say there is a potential for another series of strong storms in Northern California early next week that could bring additional flooding, though they are less confident about the specifics because it is still early, Dang said.
Also from the Times:

The emergency spillway begins discharging at 901 feet, so at its peak, the lake level was more than 19 inches above that.

No comments:

Post a Comment