13.2.17

THE WATER CANNOT OVERTOP THE LEVEE.

The troubles Californians are having with the rain-swollen Lake Oroville, held back by a monstrous earthen dam, remind me of lessons I thought hydraulic engineers had learned years ago.   You'd think a clogged spillway and water overtopping the South Fork Dam and ripping the dam apart, with great loss of life in Johnstown, would be sufficient caution for owners of contemporary water projects to maintain the proper state of good repair.

Apparently not.
More than a decade ago, federal and state officials and some of California’s largest water agencies rejected concerns that the massive earthen spillway at Oroville Dam — at risk of collapse Sunday night and prompting the evacuation of 185,000 people — could erode during heavy winter rains and cause a catastrophe.

Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.

The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
There's an animated display at the Johnstown Flood Museum that demonstrates, without the loss of life, what loss of crest control looks like.

The regulators said no to the upgrades.
Federal officials at the time said that the emergency spillway was designed to handle 350,000 cubic feet per second and the concerns were overblown.

“It is important to recognize that during a rare event with the emergency spillway flowing at its design capacity, spillway operations would not affect reservoir control or endanger the dam,” wrote John Onderdonk, a senior civil engineer with FERC, in the Federal Energy Regulatory Commission’s San Francisco Office, in a July 27, 2006, memo to his managers.

“The emergency spillway meets FERC’s engineering guidelines for an emergency spillway,” he added. “The guidelines specify that during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage.”
Oops.
This weekend, as Lake Oroville’s level rose to the top and water couldn’t be drained fast enough down the main concrete spillway because it had partially collapsed on Tuesday, millions of gallons of water began flowing over the dam’s emergency spillway for the first time in its 50-year history.

On Sunday, with flows of only 6,000 to 12,000 cubic feet per second — water only a foot or two deep and less than 5 percent of the rate that FERC said was safe — erosion at the emergency spillway became so severe that officials from the State Department of Water Resources ordered the evacuation of more than 185,000 people. The fear was that the erosion could undercut the 1,730-foot-long concrete lip along the top of the emergency spillway, allowing billions of gallons of water to pour down the hillside toward Oroville and other towns downstream.

Such an uncontrolled release from California’s second-largest reservoir while it was completely full could become one of the worst dam disasters in U.S. history.
Let's hope that the inevitable investigations don't take place against the backdrop of a West Coast Johnstown.
“When I think about the fact that the (auxiliary) spillway at Oroville did not even have concrete lining on it, I’m just really surprised,” said Rep. Doris Matsui, a Democrat from Sacramento. “I would think that would be the first thing you could do.”

“Some hard questions have to be answered about why this facility was apparently neglected in a way that left it vulnerable to these problems,” said Rep. Jared Huffman of San Rafael, the top Democrat on the House subcommittee with oversight over dams. “Clearly there were warning signs, there were people saying, ‘we need to fix this.’ ”
The concrete channel of the primary spillway broke account a sinkhole;  that will give geologists some research opportunities, perhaps involving the dynamics of a heavy mass of water behind the dam or seismic activity in the area.  Unlike the South Fork Dam, which was an abandoned component of Pennsylvania's Main Line of Public Works, later purchased by a club of wealthy Pittsburghers and not cared for, the Oroville Dam is a major component of California's water and hydroelectric power networks.

Neglect the maintenance of a state of good repair at your peril.

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