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County officials ordered the evacuation of approximately 188,000 residents surrounding the Lake Oroville dam in Northern California after erosion was found in the primary and emergency spillways. This crisis was precipitated by record setting rain this year, with Northern California receiving 228% more than “normal rainfall for this time of year.” The dam has held, but the primary spillway, which prevents overflow during high water levels is damaged due to erosion. This has produced a hole “250 feet long, 170 feet wide and about 40 to 50 feet deep.” The emergency spillway, which has never been used before, has also been damaged by erosion. This prompted mandatory evacuations orders by Butte County Sheriff Kory Honea, due to the risk of “30-foot water walls” from a potential collapse of the spillways.

The Oroville Dam prior to damage (Wikimedia Commons)

This dam is critical to California; Lake Oroville has “3.5 million acre-feet of water and 167 miles of shoreline,” and the Oroville dam is the nations’ tallest at 770 feet tall. The lake is a central source for California’s water delivery system, supplying areas from the Sierra Nevada agricultural regions in Central California to residential areas in Southern California.

California has sent 100 highway patrol officers to the region, along with three helicopters and two aircraft, in an effort to help solve the dam crisis. 1,200 California National Guard units and the military police, have been placed on alert. About 100,000 cubic feet per second of water has been drained from the lake through the main spill way, in order to reduce pressure on the emergency spillway and drain the lake. Boulders have also been dropped on the hillside in an effort plug the hole. The dam crisis is currently stable, but danger exists due to the risk that the damaged infrastructure could be stressed by storms later in the week. In order to prepare for impending rain, crews are trying to repair dam controls, and “lower lake levels 50 feet.”

Sources and Further Reading:

  1. BREAKING: No word when evacuation order for 188,000 will be lifted as Oroville threat remains – Sacramento Bee
  2. 188,000 under evacuation orders amid impending failure of Oroville Dam’s spillway in Norcal – ABC7
  3. Evacuations ordered over concerns at California dam system – CNN
  4. 188,000 evacuated, emergency declared as California’s massive Oroville Dam threatens floods – Washington Post
  5. Thousands evacuate as Oroville Dam spillway expected to fail – ABC7
  6. A race against the weather to avoid disaster at California’s Oroville Dam – CNN