- Climate Communications
Amid California dam evacuations, big risks and a costly infrastructure failure
February 12, 2017
Massive flows of water damaged the emergency spillway of California’s Oroville Dam and prompted the sudden evacuations of nearby communities on Sunday, posing a threat of severe flooding and putting at risk a critical piece of the state’s water system.
While the dam itself remained intact, erosion damage to the emergency spillway raised the potential of the structure failing and unleashing an uncontrolled torrent of floodwaters.
Trying to head off a disaster, state officials increased the flow down the dam’s main spillway on Sunday night. Their efforts to deal with the crisis could determine not only whether entire towns are inundated but also whether the state’s second-largest reservoir emerges with manageable damage or something much worse.
“It would be a massive blow to the state’s water system if they lose Oroville,” said Peter Gleick, a water researcher at the Oakland-based Pacific Institute. “The question is, will it erode away the emergency spillway? Will there be a big uncontrolled release of water? Or will they be able to draw the lake down enough to prevent that?”
He said the big worry is not that the dam itself would fail, but that a failure of the spillway could cut into the hillside and potentially release more and more water, leading to a “cascading failure.”
As of Monday morning, the level of Lake Oroville had dropped about 3.5 feet after officials doubled the flows down the Feather River. Still, downstream communities remained under evacuation orders due to the threat of flooding, and residents had no word on when they might be allowed to return.
Rich Gray, of the Placer County Sheriff's Department, monitors the Oroville Dam's main spillway from a lookout point on Feb. 14, 2017, in Oroville, Calif. Crews working around the clock atop the crippled Oroville Dam have made progress repairing the damaged spillway, state officials said. Marcio Jose Sanchez, AP
Oroville Dam is located in the foothills of the Sierra Nevada east of the Sacramento Valley. The dam, which was completed in 1968, has risen rapidly this winter as the Feather River and its tributaries have gushed down swollen after storms that brought heavy rain and snow. The storms, which came after more than five years of severe drought, have led officials to release water from various dams across Northern California.
Lake Oroville is the largest reservoir in the State Water Project, a network of canals and pumping stations that move water from Northern California to the Central Valley and Southern California. It’s one of the key reservoirs in the system that stores water for the dry spring and summer months.
Gleick said if a major flood were to occur, dealing with a water supply problem would then become “a secondary issue.”
California is prone to swings in weather between dry spells and “atmospheric river” storms that roll in from the Pacific. State officials have recently been weighing various infrastructure projects to help buttress the water system, using funding from a $7.1-billion bond measure approved by voters in 2014.
“I think we’re learning that we’d better be paying a lot more attention to our existing infrastructure. There’s a lot of debate about what should we build that’s new,” Gleick said. “Well, let’s spend some of our money on fixing and maintaining the infrastructure we have. It’s critical for our economy.”
The potential danger of a severe flood became apparent suddenly on Sunday afternoon. A day earlier, the Department of Water Resources had said in a statement that the releases from the reservoir did not “threaten the dam or downstream communities.”
William Croyle, the department’s acting director, had said on Saturday that the spillway was operating as intended and based “on our current situation, there is no threat.”
A gaping hole appeared in the dam’s main spillway last week, and then water began pouring over the emergency spillway for the first time in the reservoir’s history.
Croyle provided a preliminary damage estimate to reporters on Saturday, saying repairing the main spillway could cost between $100 million and $200 million. But the damage costs appeared to be mounting with the additional erosion damage to the emergency spillway.
“It caught everybody by surprise,” Gleick said. “Storm flows can cause an enormous amount of damage and erosion, and that’s what we’re seeing.”
On a farm downstream from the dam in Gridley, Tom Schultz said miles of levees along the swollen Feather River remained intact, largely protecting farmland even as floodwaters flowed through some of the orchards. He said he went through previous evacuations during floods in 1986 and 1997, when some levees failed.
Schultz, as president of the local levee district, stayed on his kiwi and walnut farm to help keep watch while others evacuated. Speaking by phone from his home, which is perched on a hill about 100 feet above the river and 15 miles southwest of the dam, Schultz said he was packed and ready to leave quickly if he needs to.
"We think we’re OK, but if there’s a break, I’m heading out of here, too,” Schultz said. “I’ll make good decisions and leave if it looks like it’s going to be bad.”
Regardless of how the emergency situation plays out, it will be important to follow up by analyzing how to prevent such situations in the future, said Roger Bales, an engineering professor and director of the Sierra Nevada Research Institute at the University of California, Merced. He said it will be important to analyze how the dam operating rules should be improved to release more water earlier in the year if warranted, and what sorts of new information are needed to improve forecasts.
As for the damage, he said, even a small failure of the emergency spillway will mean some expensive repairs.
“If repairs take longer than just this summer, which seems likely,” Bales said, “the reservoir may need to be operated at a lower capacity until those repairs are done.”