After Oroville, officials across the West review dam safety

The California dam’s spillways are ready for rain as safety officials prepare for future catastrophes.

 

Following a series of intense winter storms last February, a section of the main spillway at California’s Oroville Dam cracked and crumbled, opening a huge hole in the chute. Water pummeled the exposed dirt and rock below, eroding chasms in the hillside and the spillway, about 70 miles north of Sacramento.

As officials struggled to keep more of the spillway from disintegrating over the next few days of rainy weather, the reservoir continued to rise. Eventually, it spilled over a second, never-before-used emergency spillway, a lip of concrete that funnels water down a bare hillside, which also began to wash away. That, officials feared, could undermine the side of the reservoir itself, which would send catastrophic floodwaters careening, uncontrolled, toward the communities below.

More than 180,000 people living downstream of Oroville Dam — the tallest dam in the U.S. — were evacuated on Feb. 12. In the following days, the rainstorms eased, dam managers were able to keep water off the emergency spillway and the reservoir walls held.

  • An aerial view of Lake Oroville at 83 percent of capacity while the California Department of Water Resources released water at 35,000 cubic feet per second from the main spillway on April 21, 2017.

    Kelly M. Grow/California Department of Water Resources
  • An aerial view of the damaged Oroville Dam spillway site and the huge debris field in the diversion pool just below the spillway.

    Dale Kolke/California Department of Water Resources
  • An aerial view of the Lake Oroville spillway recovery site on November 1, 2017, after months of repairs.

    Kelly M. Grow/California Department of Water Resources

To avoid the risk of further erosion, however, both spillways needed to be patched up before this winter. By early November, following months of ‘round-the-clock work, the California Department of Water Resources announced that Oroville was ready for the rainy season, though final repairs will take another year. And the consequences of the incident could last far longer: Its sheer scale means it has the potential to affect legislation and policy, as did earlier disasters at other dams. Safety officials in California and across the West are already reassessing spillways, updating disaster plans and refining evacuation maps, hoping to prevent a repeat of Oroville — or worse.

Structural failures were the immediate cause of the Oroville catastrophe. The main spillway has successfully handled larger flows than what it saw last February. While it’s not yet clear exactly why it broke apart, some researchers say part of the blame lies in poor design and shoddy maintenance — and that those problems could have been addressed. An independent group of dam experts is investigating what went wrong, with a final report expected by the end of 2017. An interim report released in September notes that there was preexisting damage and repairs at the area that first crumbled. Weaknesses there could have allowed water to get beneath the spillway, potentially blasting apart the concrete from below.

Administrative failures — problems with inspections or regulations — may share the blame for what happened at Oroville. A patchwork of agencies meant to prevent such problems regulates dam safety in the United States. Federal agencies like the Bureau of Reclamation and the Army Corps of Engineers oversee inspection and maintenance at their own dams. Dams that belong to the state, like Oroville, or a utility company or other non-federal entity, are typically under the jurisdiction of a state agency; the Federal Energy Regulatory Commission (FERC) is also involved in dam inspections at non-federal dams with hydropower projects they license, including Oroville.

The first rain of the season falls on the main Lake Oroville spillway on November 3, 2017.
Kelly M. Grow/California Department of Water Resources

Experts say it’s too early to judge how much dam safety policies at both state and federal levels will ultimately transform because of Oroville. Some states, however, are already reviewing structures and safety procedures in the wake of the catastrophe. California’s Division of Safety of Dams is evaluating spillways at 93 dams that are similar to Oroville. And in June, the state passed legislation requiring regular updates to emergency action plans — basically, blueprints for how to deal with disasters — for dams that could cause major destruction should they fail.

Other states are also reviewing emergency plans. In Montana, officials are revamping how they create evacuation maps, says Michele Lemieux, the dam safety program manager at Montana’s Department of Natural Resources and Conservation. “(For) most of our dams, and actually most of the dams in the country, all the evacuation maps are for this catastrophic failure of the dam,” she says. Those are crucial, but it’s also important to have flood maps for a range of emergencies — including, for example, the collapse of a spillway — which might not produce as much flooding as a full dam failure. “You don’t want to get people out of the way that don’t need to be removed,” Lemieux says.

In Colorado, Oroville confirmed that dam safety officials were already on the right track, says Bill McCormick, the chief of dam safety at Colorado Division of Water Resources. There, the big test came in 2013, when widespread flooding in north-central Colorado driven by torrential rain led to the failure of about a dozen small dams. Nobody was hurt or killed as a result of the failures, “but they did get people’s attention,” McCormick says. (Several people died elsewhere during the flooding.) Another wet season in the spring of 2015 made clear the need to plan for different levels of flooding and dam releases. “Our main lesson from Oroville is that we still need to be vigilant,” he says, “but we’re doing the right things.”

Federal regulators are waiting for the results of the independent investigation into the Oroville incident before deciding on any regulatory changes. David Capka, the director of the division of dam safety and inspections at FERC, says the spillway collapse at Oroville is the biggest dam safety incident he’s seen during his career. “If there are things we need to do to improve, then we want to know it,” says Capka, who became the acting director of the division in January, just a month before the Oroville fiasco. “Nobody who was involved in that incident ever wants to go through something like that again.”

  • Heavy equipment works to remove the huge debris field in the diversion pool at the base of the damaged Oroville Dam main spillway.

    Brian Baer/California Department of Water Resources
  • A crew sprays shotcrete on the weathered rock to keep it from eroding and undermining the damaged Lake Oroville main spillway.

    Florence Low/California Department of Water Resources
  • Contractors continue concrete work around the Lake Oroville emergency spillway.

    Kelly M. Grow/California Department of Water Resources
  • Supervisors inspect exposed rock to approve the placement of roller-compacted concrete in the erosion area between the upper and lower chute of the Lake Oroville main spillway.

    Ken James/California Department of Water Resources
  • High pressure washers and vacuums prepare the lower chute of the Lake Oroville main spillway for concrete placement.

    Kelly M. Grow/California Department of Water Resources
  • Workers construct stay-forms to prepare for the last section of leveling concrete placement on the upper chute of the Lake Oroville main spillway.

    Kelly M. Grow/California Department of Water Resources
  • A worker uses a cutting torch to remove a small section of rebar to accommodate a drain pipe on a new sidewall on the upper chute of the Lake Oroville main spillway.

    Ken James/California Department of Water Resources
  • Workers place leveling concrete on the upper chute of the Lake Oroville main spillway.

    Ken James/California Department of Water Resources
  • A worker sprays water on freshly placed roller-compacted concrete in the erosion area between the upper and lower chute of the Lake Oroville main spillway.

    Ken James/California Department of Water Resources
  • Workers put finishing touches on a section of structural concrete for the transitional slab on the upper chute of the Lake Oroville main spillway

    Ken James/California Department of Water Resources
  • Workers roll up blankets used in the curing process for the structural concrete panels on the lower chute at the Lake Oroville main spillway.

    Ken James/California Department of Water Resources
  • A crew removes debris in preparation for concrete placement for the transitional slab between the roller-compacted concrete and the structural slab sections on the lower chute of the Lake Oroville main spillway. Angled rock anchors will strengthen the temporary transition slab until final construction is completed in 2018.

    Ken James/California Department of Water Resources
  • Crews continue to place leveling and structural concrete near the bottom of the lower chute at the Lake Oroville main spillway site.

    Ken James/California Department of Water Resources
  • A worker puts the finishing touches on a section of the enriched roller-compacted concrete just below the transitional slab on the upper chute of the Lake Oroville main spillway.

    Ken James/California Department of Water Resources

In California, workers are putting the finishing touches on recent spillway repairs at the dam. The main spillway isn’t used every winter; water managers only need it when there’s too much water to be released through Oroville’s other outlets. While this winter’s rain forecasts for northern California are uncertain, the region regularly experiences wild swings in precipitation. “We needed to make sure that we had systems in place for this year,” says Erin Mellon, a spokeswoman for the California Department of Water Resources.

This winter, the spillway should be able to withstand as much as the maximum flows of last February, about 100,000 cubic feet per second. (Following additional repairs next year, it should be able to handle 270,000 cubic feet per second.) Construction crews are also refurbishing the emergency spillway. Next year, officials plan to line part of the bare hillside with concrete, something environmental groups warned was necessary more than a decade ago. Between emergency repairs and long-term reconstruction, the final tab for the work at both spillways is expected to be more than $640 million, some of which will come from federal funds.

In planning for the future, managers must also grapple with the effects of climate change. “California is a good example,” says David Freyberg, a hydrologist and water resources engineer and professor at Stanford University. “As we switch from snow to rain, that really changes the game for how reservoirs are operated.”

Most large dams were built to withstand extreme weather, but the guidelines for water releases around storms need to catch up to reflect changing conditions. If they don’t, incidents like Oroville, and the enormous price-tags that come with them, could become more common.

For both officials and private citizens, what happened at Oroville was a dramatic reminder of the importance of dam safety regulations. “There is a lot of thought going on right now about what kind of (dam safety or inspection) changes might be needed,” Freyberg says. “This scared a lot of people.”

Emily Benson is an editorial fellow at High Country News. 

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