Oroville Dam Crisis
Winter rains of 2017 brought widespread flooding to California
Winters in northern California always bring much-needed rain, but the early part of 2017 brought more rain than many areas could handle.
In a total of 50 days of rain spanning two months, Lake Oroville received an entire year's worth of water runoff. The Oroville Dam water levels rose above 901 ft, the height at which water begins to pour over top of the emergency spillway.
Oroville Dam
The 770ft tall Oroville Dam was completed in 1968. It holds back approximately 1.1 trillion gallons of water flowing from the Feather River. Lake Oroville, the subsequent product of damming the river, is the second largest lake in California.
Oroville Dam - Image 1
Crisis Timeline
Dec 2016
Oroville Dam was well below full capacity as winter rains began to inundate Northern California.
7 February 2017
California Department of Water Resources (DWR) discovered a hole developing the main spillway of the Oroville Dam.
8 - 10 February 2017
California DWR strategically released water in cycles in an attempt to mitigate constant and severe erosion to the spillway. Fear of secondary erosion that may compromise the dam itself drove DWR's decisions.
Oroville Spillway Failure Flyover and Explanation 10 Feb 2017
11 - 12 February 2017
As rains continued to fall and runoff continued to pour into Lake Oroville, water levels exceeded the 901 ft maximum level of the emergency spillway. Water began to pour over it, creating a separate erosion and downstream flooding concern. Mandatory evacuations were enacted in anticipation of and preparation for unexpected erosion that could release even more water from Lake Oroville.
Aerial view shows emergency spillway at Lake Oroville
Emergency Spillway Failure Case Studies
The Corp of Engineers and National Guard entities, along with other government and private organizations, began mapping potential flood plains in order to assist California Office of Emergency Services in crisis planning.
In the event of complete emergency spillway erosion and subsequent failure, significant NorCal populations would be negatively affected by flood waters. Source: https://services1.arcgis.com/ZIL9uO234SBBPGL7/arcgis/rest/services/Total%20Population%20Affected/FeatureServer | https://tiles.arcgis.com/tiles/zzN1kKcv4jyJtkCg/arcgis/rest/services/Oroville_Dam_Features/MapServer
Intense water flow from a collapsed emergency spillway would most certainly destroy homes and cause extensive loss of life for populations that would not or could not evacuate. Source: https://tiles.arcgis.com/tiles/zzN1kKcv4jyJtkCg/arcgis/rest/services/Depth_of_Flooding/MapServer | https://tiles.arcgis.com/tiles/zzN1kKcv4jyJtkCg/arcgis/rest/services/Oroville_Dam_Features/MapServer
Although emergency evacuations were already underway, flood waters would continue to inundate population centers for days after an emergency spillway failure, causing difficulties for further evacuations due to resulting infrastructure damage and closures. Source: https://tiles.arcgis.com/tiles/zzN1kKcv4jyJtkCg/arcgis/rest/services/Time_Until_Inundation/MapServer | https://tiles.arcgis.com/tiles/zzN1kKcv4jyJtkCg/arcgis/rest/services/Oroville_Dam_Features/MapServer
12 - 17 February 2017
As rains slowed and the sun began to shine once again, water flowing over the emergency spillway halted. California DWR lifted mandatory evacuations and began urgent construction projects to fortify the emergency spillway.
Significant erosion occurred after the initial main spillway hole was discovered.
Though the Oroville Dam main and emergency spillways held during February 2017, we can attribute its success not to man's prevention, but to Mother Nature's mercy. Since the event, California DWR has significantly fortified Lake Oroville to prevent future flooding events.
Initial construction to fortify the Oroville dam spillways was completed in 2019, with $308 million in further upgrades approved in 2021.
