Water & Drought

Oroville Dam spillway to be used Tuesday. The state says it’s ready

Oroville Dam spillway crisis: Here’s what happened in visual detail

In February 2017, the main and emergency spillways of Oroville Dam were damaged, prompting the evacuation of more than 180,000 people living downstream from the structure and Lake Oroville.
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In February 2017, the main and emergency spillways of Oroville Dam were damaged, prompting the evacuation of more than 180,000 people living downstream from the structure and Lake Oroville.

Oroville Dam’s massive flood-control spillway will be deployed Tuesday for the first time since it was rebuilt for $1.1 billion after a near-catastrophe forced the evacuation of 188,000 people in 2017.

In a brief statement Sunday, the California Department of Water Resources’ deputy director Joel Ledesma said the agency has “restored full functionality to the Oroville main spillway and is operating the reservoir to ensure public safety of those downstream. The Oroville main spillway was designed and constructed using 21st century engineering practices and under the oversight and guidance from state and federal regulators and independent experts.”

The state has been hinting for weeks that the spillway could be reused soon as a wet winter starts to give way to the spring snowmelt season in the Sierra. The lake level, deliberately kept low as repairs wound down, has risen to 853 feet, or about 50 feet from the top.

The initial releases of water down the spillway will be relatively gentle, no more than 20,000 cubic feet per second. But later this week, as more water rolls into the lake, DWR said releases could rise to as much as 60,000 cfs. Rain is forecast for the Oroville area Monday and Tuesday.

The dam was releasing water at around 50,000 cfs in February 2017 when a giant crater erupted in the main spillway. Dam operators dialed back water releases to minimize the damage, causing lake levels to rise so high that water spilled over the adjacent emergency spillway several days later for the first time since the dam opened in 1968.

DWR officials said they were certain the emergency spillway, a concrete lip perched atop a natural hillside, would handle the flows. But one day later, the hillside began seriously eroding, and the Butte County sheriff ordered the emergency evacuation of the downstream area amid fears that the spillway would fall apart and release a “wall of water” into the Feather River below.

The crisis eased when dam officials ramped up releases on the main spillway. That quickly lowered the water level in the lake and water stopped cascading over the emergency spillway. By the time the snowmelt season ended and the spillway was shut off for good weeks later, practically the entire lower half of the concrete chute and adjoining hill were gone.

DWR and its contractor, Kiewit, spent the last two years fixing both spillways. A panel of independent investigators blamed the crisis on “long-term systemic failure” dating back to the original design and construction of the two spillways. In early March the Federal Emergency Management Agency said it was refusing to reimburse California for $306 million of the $1.1 billion repair bill, citing the investigators’ report and blaming the state for years of neglect. DWR officials said they plan to appeal the decision.

To the extent that the federal government won’t cover the costs, the expenses will be borne by the ratepayers of the local and regional water agencies that store water at Oroville. These include the giant Metropolitan Water District of Southern California.

For Tuesday’s reuse of the spillway, Oro Dam Boulevard East will be open to public pedestrian and vehicle traffic unless flows from the main spillway top 30,000 cfs. The boulevard offers a view of the spillway from across the Feather River.

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