A Cascading Failure

Feb. 16, 2017

More than a decade ago, federal and state officials and some of California’s largest water agencies dismissed concerns that the spillway at Oroville Dam could erode during heavy winter rains. But on February 12, more than 185,000 people were evacuated from areas downstream of the dam, because of concern over its structural weakness.

Oroville Lake is located in the foothills of the Sierra Nevada, east of the Sacramento Valley. As storms delivered extreme precipitation this winter, lake levels rose rapidly. Since the dam’s construction in 1968, the emergency spillway had never been used. The concrete structure, called a weir, was designed to convey outflow to reduce pressure on the Oroville Dam when it reached extreme levels.

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In early February, when faced with too much water in the lake, state officials decided to release water through the spillway. Water flowed over at a rate of 29 million gallons a minute, eroding the dirt and concrete below. A crater reportedly 45-feet deep, 300-feet wide, and 500-feet long appeared below the spillway, undermining its integrity.

“The dam is solid,” Bill Croyle, acting director for the California state Department of Water Resources told USA Today. “The control structure has been damaged.”

However, as The Mercury News reported, three environmental organizations—the Friends of the River, the South Yuba Citizens League, and the Sierra Club—had warned federal officials in 2005 that the emergency spillway was not able to handle extreme flooding. At that point, state officials balked at the cost of paving the emergency spillway and federal officials deferred improvements.

In addition, officials said that the emergency spillway was designed to handle 350,000 cubic feet per second and the concerns were overblown. On Sunday, with reported 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 Federal Energy Regulatory Committee said was safe—erosion at the emergency spillway became so severe that officials from the State Department of Water Resources ordered the evacuation of area residents. State water officials were able to release additional outflow from Lake Oroville’s main spillway and the erosion on the emergency weir slowed.

CityLab reports that nationwide, the federal government has invested relatively little in dams and levees. The 2009 stimulus bill provided $290 million for flood-prevention projects and another $490 million for repairing infrastructure projects, including dams, on reservations. This seems an insignificant amount considering that repairs to the Orville Dam alone are estimated to cost between $100 million and $200 million.

But there appears to be increased momentum for investment. In December, former President Obama authorized hundreds of million dollars for water infrastructure projects by way of the Water Infrastructure Improvements for the Nation Act and while on the campaign trail, President Trump proposed offering $137 billion in federal tax credits to private firms that back transportation projects.

We wonder: Could crises such as this one catalyze infrastructure repair efforts and inspire increased spending?
About the Author

Laura Sanchez

Laura Sanchez is the editor of Distributed Energy and Water Efficiency magazines.