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Government disregarded warnings about Oroville Dam in California

Environmental groups' warnings in 2005 about an emergency spillway have proven true: floods have led to the evacuation of nearby communities.

By Kristine Guerra The Washington Post

Tue., Feb. 14, 2017 5 min. read

Article was updated Feb. 15, 2017

In 2005, three environmental groups warned California and U.S. federal officials about what they believed was a problem with the Oroville Dam's emergency spillway, the same one that was at risk of collapsing this week after storms caused the adjacent reservoir to swell.

The groups' concern, which seemed to have fallen on deaf ears at the time: The emergency spillway is not really a spillway. Rather, it's a 520-metre-long concrete weir that empties into a dirt hillside.

That means in the event of severe flooding, water would erode that hillside and flood nearby communities in northern California's gold country, the groups said then.

That nearly happened Sunday, when a hole in the emergency spillway threatened catastrophic floods and prompted officials to evacuate nearly 200,000 residents.

Authorities lifted the evacuation order for the 188,000 residents Tuesday afternoon and although Butte County Sheriff Kory Honea said the water level at the lake behind the Oroville Dam is low enough to accommodate an expected storm this week, residents should stay prepared to leave their homes again.

Residents returning home should be prepared for "the prospect that we will issue another evacuation order," Honea said Tuesday.

Honea said the risks to the damaged spillway were significantly reduced because an inspection had found no further erosion to "compromise the overall integrity" of the spillway.

The National Weather Service's Sacramento office said Tuesday rain was expected to move through late Wednesday and Thursday morning, with 5 to 10 centimetres in the foothills and mountains. But the storm is looking colder than initially projected, meaning lower snow levels and less runoff into Sierra reservoirs than the storms last week.

The brunt of a Friday storm appeared to be headed toward southern California, with lighter rain in the north.

Emergency crews were working Tuesday to fill a hole in the emergency spillway for floodwater from the dam.

A California dam inspector said authorities may never know the exact causes of the earth and concrete blow-outs below the Lake Oroville dam. Eric Holland of the state Department of Water Resources' dam-safety division said any of a number of different problems could have caused the spillway troubles. Authorities often never discover in these cases what exactly happened, he said, because flood water has washes out everything at the scene.

In October 2005, as the Oroville Dam was going through a re-licensing process, the three groups filed a motion urging a federal regulatory agency to require state officials to armour the emergency spillway with concrete so that, in the event of extreme rain and flooding, water would not freely cascade down and erode the hillside. The upgrade would have cost millions of dollars and no one wanted to foot the bill, said Ronald Stork, senior policy advocate for Friends of the River, one of the groups that filed the motion.

"When the dam is overfull, water goes over that weir and down the hillside, taking much of the hillside with it," Stork said. "That causes huge amounts of havoc. There's roads, there's transmission lines, power lines that are potentially in the way of that water going down that auxiliary spillway."

Federal officials, however, determined that nothing was wrong and the emergency spillway, which can handle 9,910 cubic metres of water per second, "would perform as designed" and sediment resulting from erosion would be insignificant, according to a July 2006 memo from John Onderdonk, then a senior civil engineer for the Federal Energy Regulatory Commission.

"The emergency spillway meets FERC's engineering guidelines for an emergency spillway," Onderdonk wrote. "The guidelines specify that during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage."

Fast-forward 11 years. The erosion of the emergency spillway became severe, with only up to 340 cubic metre of water per second, according to the Oroville Mercury Register. That's a little more than 3 per cent of what officials said the spillway can handle.

The water level in massive Lake Oroville rose significantly after potentially record-setting rain surged through the state following a long drought. The Oroville Dam, the tallest in the country, at 235 metres, remains stable, officials said as the water level fell about a metre, to a point at which water was no longer spilling over.

But the structure of the spillways, which are designed to release water from the reservoir in a controlled fashion, have crumbled.

On Monday night, Democratic Gov. Jerry Brown requested federal assistance, noting in a letter to President Donald Trump that "officials are aggressively attempting to lower Lake Oroville's water levels, as another atmospheric river storm system is scheduled to arrive within 48 hours." The emergency, Brown wrote, is "of such severity and magnitude that continued effective response is beyond the capabilities of the state and affected local governments and supplemental federal assistance is necessary to save lives and to protect property, public health and safety, and to lessen the effects of this serious situation."

This month, a portion of the main spillway – a 915-metre-long structure lined in concrete – eroded because of the high volume of water spilling over from the reservoir, creating a craterlike hole. Officials with the California Department of Water Resources, which owns and operates the dam and reservoir, then decided to use the adjacent emergency spillway for the first time since the dam was built nearly 50 years ago.

Sheets of water began spilling over the emergency spillway and onto the hillside, carrying mud and debris into the nearby Feather River.

The emergency spillway appeared to be working as expected – until Sunday, when officials spotted a hole. That raised fears of a catastrophic flood that could wipe away Oroville, a town of 16,000 people, and prompted officials to evacuate nearly 200,000 area residents.

Stork said he believes none of that would have happened had officials listened to his and others' concerns and built a proper emergency spillway 12 years ago. The two other groups that filed the 2005 motion are the Sierra Club and the South Yuba River Citizens League.

"They told us not to worry. All was good. Everything was fine. It's all safe," Stork said. "First of all, they're not supposed to fail. That's not what we do in a first-world country. We don't do that. We certainly don't do that with the nation's tallest dam. An auxiliary spillway isn't supposed to cause lots of havoc when it's being used."

Construction would have cost at least $100 million, Stork said, and the state contractors in southern California that buy water from northern California would have been forced to pay for it. The Metropolitan Water District of Southern California, which provides water to 19 million people in Los Angeles, San Diego and other areas, and the State Water Contractors would have shouldered the cost and deemed the upgrades unnecessary, according to the Oroville Mercury Register.

"The people who are bearing the personal risk of being killed and having their homes washed away are the people of Northern California," Stork said.

Pressed during a news conference Monday about the 2005 motion, Bill Croyle, acting director of the Department of Water Resources, said he was not familiar with the conversations that happened then.

"It's the first time it's ever taken water," Croyle said of the emergency spillway. "We don't know exactly why this erosion occurred."

With files from The Associated Press

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Source: https://www.thestar.com/news/world/2017/02/14/government-disregarded-warnings-about-oroville-dam-in-california.html

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