The Oroville dam, the highest dam in the United States, after a major break in its spillway, has reached its emergency level for the first time since it was built.
With a height of 235 meters, it was inaugurated on November 14, 1967. It is a loose material dam of more than 61 million m3, being the second longest dam in the United States of its kind. For more historical information, check out this article on the Oroville Dam.
On to the current crisis- The water level at Oroville peaked on Saturday, Feb 11, 2017 at about 902 feet, which sent water cascading over a concrete weir and into an unlined emergency spillway that had never been used. As you can see in the image below from 2014, drought has made the spillway an absent concern and since it has never been needed, it has not been on the radar for Oroville Dam officials.
On Sunday however, the earthen emergency spillway began to show signs of heavy erosion. Fearing that the damage could undermine the concrete weir that formed the lake’s shore and cause it to fail, and send a wall of water coursing into the Feather River below, officials ordered sweeping evacuations for more than 188,000 people.
The spillway is supposed to be able to regulate the controlled flow of any extraneous water from the reservoir. As the illustration shows, the water is intended to flow down a concrete path to safely join the river below the dam. A second emergency spillway is also adjacent to the concrete spillway as shown in the diagram here:
Previous to this incident, the emergency spillway had never been used. Currently, as of Feb 14, 2017, a torrent of water is now flowing down both the traditional and emergency auxiliary spillway as shown by the California Safety Administration and many local news stations. The evacuation remains in effect for almost 200,000 people. There is currently no concern about the Dam failing but the spillways are becoming very overwhelmed and flooding is expected in the area adjacent to the water pathways.
On Sunday, CBS Sacremento released raw Helicopter footage showing the dangerous spillway in dire circumstances as the water barraged the landscape and compromised the surrounding sediment.
It is unclear if any of the tactics that emergency officials are enacting are having an impact to slow the water from impacting the local area but it is certain to get worse as the forecast calls for additional rain for California later this week.
The Associated Press has reported that efforts to lower water levels by increasing flow through the concrete spillway is lowering the level of the Lake Oroville Reservoir but will it be enough to circumvent the imminent collapse of the auxiliary spillway.
This story will continue to develop and be updated as new information is released. Stay tuned and post any comments or questions below.
For more information, check out
En Espanol – Crisis Presa Oroville