Authorities were warned that the Oroville Dam was at risk of collapse 16 years ago

Water gushed over the Oroville Dam emergency spillway. Environmental groups saw this coming
Water gushed over the Oroville Dam emergency spillway. Environmental groups saw this coming
Image: Josh F.W. Cook/Office of Assemblyman Brian Dahle via AP
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If the earthen hillside that acts as an emergency spillway for California’s Oroville Dam crumbles, the giant lake the dam contains could release a 30-foot wave over the downstream community of more than 185,000, who were ordered to evacuate their homes late Sunday (Feb 12). That’s why officials are in a race against time to release as much water as possible—100,000 cubic feet of water per second as of Monday morning, the Los Angeles Times reported—before the next rain storm hits the region and swells the lake later this week.

But this life-or-death scramble may have been avoided if state and federal officials had heeded the warnings of environmental groups who have been pleading with them to reinforce the dam’s earthen emergency spillway and improve emergency infrastructure for about 16 years.

The primary retaining wall of the Oroville Dam, often simply called the “spillway,” is made of concrete. The dam’s emergency or auxiliary spillway is a secondary retaining wall, intended to act as a second barrier between the lake and surrounding communities in the event the water breaches the primary spillway and floods over the sides. The problem is that it’s more or less simply a hillside made of packed earth, built outside of the lake’s primary retaining walls.

If flood waters are powerful enough, they can easily erode this emergency spillway made of packed earth. And if that earthen hillside crumbles, there’s nothing beyond it to prevent a massive wave from wiping out communities.

And indeed, due to recent heavy rains in California, the Oroville Dam’s emergency spillway has eroded significantly. The Sacramento Bee has a good aerial photo of the damage.

As far back as 2001, the environmental group Friends of the River assembled a report calling for “a full spillway for the emergency spillway”—or in other words a fully concrete emergency spillway where flood water could be contained—to replace the earthen hillside. They wanted officials to require the operators of Oroville Dam to commit to building a reinforced spillway before renewing their operating license.

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Then, in 2003, Friends of the River, along with several other local organizations which collectively called themselves the Yuba Feather Work Group, sent a letter to the manager of the Oroville Facilities Relicensing Program urging officials to address the problem of the earthen “spillway lip” (the same hillside that officials now fear may crumble), which they warned at the time would not hold up to a major flooding event.

“At present, the ungated spillway at Oroville Dam consists of a spillway lip only—and utilizes a hillside as the project spillway,” they wrote. “Utilizing such a spillway has the potential to cause severe damage to the downstream hillside, project facilities, and downstream environments located in the path of the flood release.”

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Finally, in 2005, the Friends of the River, along with the Sierra Club and the South Yuba Citizens League, filed a formal motion with the federal government presenting their case even more urgently. In a motion submitted to the Federal Energy Regulatory Commission, they wrote that the aging dam did not meet federal safety standards, and that a major rain event could flood the concrete spillway and proceed to erode the earthen hillside which acted as the dam’s emergency spillway, putting downstream communities at risk of flooding. The government, they wrote, must “issue a licensing order requiring the licensee to armor or otherwise reconstruct the ungated spillway.”

“Written communications on this issue from the intervenors to, or made available to, the licensee date back to August 23, 2001,” the motion reads. “Oroville spillway deficiencies, their impact on flood management operations, and the need for the licensee to address these issues have been discussed at nearly every Yuba Feather Work Group meeting for several years.”

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But the spillway was never reinforced. According to the Mercury News, the Federal Energy Regulatory Commission rejected that request “after the state Department of Water Resources, and the water agencies that would likely have had to pay the bill for the upgrades, said they were unnecessary.”

After the Mercury News resurfaced that 2005 motion, the Department of Water Resources acting director told reporters Monday that he was “not familiar with 2005 documentation or conversation” about reinforcing the emergency spillway at Lake Oroville, the LA Times reported.