Oroville Dam Spillway Failure: 5 Fast Facts You Need to Know

The Butte County Sheriff’s Department evacuated of residents in Oroville, California on February 12. Those who live downstream or in low levels by the Oroville Dam were ordered to evacuate Sunday night due to the emergency spillway’s potential for failure. The Associated Press reported that at least 188,000 people have evacuated the area because of the incident.

In a press conference late Sunday night, the Department of Water Resources in California updated the situation and said that it appears to be under control.

Officials said the water level of Lake Oroville has been reduced and the water flow over the emergency spillway stopped at 8:45 p.m. Pacific.

An earlier press conference was held by the department Sunday and it posted on its Facebook page that an evacuation center has been set up at the Silver Dollar Fairgrounds in nearby Chico.

Because of the potential danger to inmates and staff, the Butte County Juvenile Hall was reportedly completely evacuated and residents who live on the valley floor in neighboring Yuba County were also ordered to be evacuated. In addition, inmates at the Butte County Jail were evacuated.

At the first press conference, Sheriff Kory Honea said the flow of Oroville Dam’s “auxiliary spillway” has decreased, and erosion hasn’t progressed as quickly as first feared. He said that a plan is currently being developed to fill the hole and repair the spillway. That plan, as the Department of Water Resources in California said, is to use helicopters to fill the hole with rocks.

Here’s what you need to know about the dam and the evacuation of Oroville:

1. The Failure Is Due to a Hole In the Emergency Spillway

The evacuation of the city and “imminent” failure of the dam’s emergency spillway is due to a flood control release of about 50,000 cubic feet of water per second. During the standard process of releasing the water on February 7, much damage was found in the dam and a large crater formed. Workers continued to use the damaged spillway to move the water because the water level at Lake Oroville was high. But the emergency spillway was prepared to be used for the first time in the dam’s history.

Three days later, an even bigger hole was found by officials, the San Francisco Chronicle reported. The hole had grown to about 45-feet deep, 300-feet wide and 500-feet long.

Because of the extensive damage, the workers activated the emergency spillway. At first thought, there was no threat to the safety of nearby residents, but an overflow of the spillway started and water spewed out onto the nearby hills.

2. The Dam Is One of The Largest In the World

Oroville Dam is one of the 20 largest dams in the world and is the largest earth-filled dam in the United States. It’s also the tallest dam in the U.S., standing 770-feet tall.

At its full capacity, the Oroville Dam measures 3,537,577-acre feet and has a drainage area of 3,607 square miles.

3. Oroville Has a Population of Over 15,000 People


According to the U.S. Census Bureau, the city of Oroville has a population estimate of 16,260 as of July 1, 2016. During the 2010 census, the city reported a population of 15,546. Oroville is located north of Sacramento near Plumas National Forest.

4. The Dam Opened in 1968

Proposals to construct a dam in Oroville started as early as 1951, but it was strongly opposed by voters. However, major flooding during the decade in Oroville and around it saw an emergency flood-control bill be drafted so that funds can be raised for the construction.

That construction started in May 1957 and it didn’t officially open until 1968.

5. The Dam Assists In Irrigation Water for the San Joaquin Valley

Since its construction, the Oroville Dam has helped its surrounding areas immensely.

It’s allocated the flow of the Feather River from the Sacramento-San Joquin Delta in the California Aqueduct, a system of canals and pipelines that transports water from the Sierra Nevada Mountains. The aqueduct is over 400-miles long and provides a large amount of water for irrigation use in the San Joaquin Valley and also water supplies on the Southern California coast.

This post will be updated.

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