Oroville Dam spillway damage causes massive evacuation

OROVILLE, CALIFORNIA — More than 180,000 people living around Oroville, California were ordered by authorities to evacuate on Sunday after a hole in the auxiliary spillway in the Oroville Dam threatened to flood the surrounding area.

The Oroville Dam is the tallest dam in the United States at a height of 770 feet, according to Vox.

Lake Oroville is the second-largest reservoir in California and is capable of holding 3.5 million acre-feet of water, the Sacramento Bee reported.

The problems started when officials began to make room in the reservoir for flood protection by releasing water down the dam’s main concrete spillway, a 3,000 foot chute that channels flows into the Feather River, according to the Sacramento Bee.

A huge gash was discovered on the bottom half of the chute on Feb. 7, according to the Sacramento Bee.

Fearing further erosion to the main concrete spillway, officials restricted to outflow of water down the chute.

Stormwater and runoff from the Sierra mountains caused Lake Oroville to rise to a point where water began flowing over the auxiliary spillway next to the damaged main concrete spillway.

The auxiliary spillway is not lined with concrete and controlled by release gates like the main spillway. Water that reaches its lip, a 1,700 foot span of concrete, pours down a wooded hillside uncontrolled, the Sacramento Bee reported.

On Feb. 12, officials noticed a deep gash forming in the hillside below the concrete lip.

Authorities are now worried that the erosion could cause the upper 30 feet of the auxiliary spillway to collapse, which would release the top 30 feet of water in the reservoir and flood much of Butte and Sutter counties, according to the Sacramento Bee.

On Sunday night, officials increased the outflows down the main concrete spillway to 100,000 cubic feet per second.

Levels in the reservoir have since fallen down enough that water is no longer pouring over the auxiliary spillway, Vox reported.

Authorities are now rushing to repair the damaged auxiliary spillway. Helicopters and dump trucks are are dropping rocks into the hole created by the erosion.

Forecasts are calling for storms to hit the area on Wednesday and possibly into Thursday as well.

Officials will continue to discharge as as much water as possible ahead of the storms without adding too much pressure to the damaged infrastructure, the Washington Post reported.