The seriousness of the weak as-constructed conditions and lack of repair durability was not recognized during numerous inspections and review processes over the half-century history of the project. Following the unexpected chute slab failure and erosion, and subsequent closure of the service spillway gates to examine the damage, difficult risk tradeoff decisions were necessary over the next few days, in the face of considerable uncertainty and differing opinions, in order to manage the incident.
In addition, erosion had transported a tremendous amount of debris into the river channel, and the resulting high tailwater was threatening to flood the powerhouse. The series of decisions which were made ultimately resulted in the reservoir rising high enough to initiate flow over the emergency spillway weir. Once the emergency spillway was allowed to overtop and the rapid erosion of the emergency spillway was apparent, the evacuation order became a necessary precaution.
There were many opportunities to intervene and prevent the initial spillway failure, but the overall system of interacting human and physical factors operated in a way that these opportunities were missed by the owner, its Federal and state regulators, and many consultants hired by the owner during the half-century history of the project.
Numerous human factors, including organizational and industry factors, contributed to the physical factors not being recognized and properly addressed, and to the decision-making during the incident:. As detailed in the forensic report referenced below, there were numerous lessons learned from this incident for the owner, its regulators, its consultants, and the dam industry in the United States.
Most broadly, the independent forensic team concluded that:. Lessons Learned A complete and thorough dam record is essential. Learn More. Case Study:. Contributor Contributed By: Irfan A. Alvi, P. Photos Overview of Oroville Dam facility prior to the February incident.
Lessons Learned. A complete and thorough dam record is essential. Concrete-lined spillways are vulnerable to significant damage and potential reservoir breach if flows are not safely contained within the conveyance structure. Dam incidents and failures can fundamentally be attributed to human factors.
The completed review supports a case for taking risk-informed actions at individual dams and for prioritizing actions for an inventory of dams. Emergency Action Plans can save lives and must be updated, understood, and practiced regularly to be effective. Two diversion tunnels were constructed for diverting water around the construction area.
Diversion 2 is now used as an outlet for the water being utilized by the underground power plant. The 35 foot diameter size of the tunnels was chosen to withstand the flows of previously recorded floods on the Feather River. After final completion of the dam in , Diversion Tunnels 1 and 2 were plugged. They excavated a system of tunnels for the powerhouse, some of which connected to Diversion Tunnel 2.
There is coordination between releasing water and producing power, where releasing water takes precedence. During normal operation, a hour supply of water is squeezed both plants during a peak hour window of the day when power production is most needed. The water is then stored in Thermalito Afterbay, a holding reservoir located beneath the Thermalito facility.
A primary purpose of the Dam was to provide flood control. As the lake fills during heavy rains or large spring snow melts, water is carefully released to prevent flooding downstream, saving both lives and costly property damage DWR, Oroville-Thermalito, The dam mainly protects Butte County and area along the Feather River from large flooding.
Floods occurred every few years, costing the residents of the area millions in damages. The dam releases an average of 2. Eighty-five percent of the water demand in the San Joaquin Region is for irrigation with twenty-nine percent of the water supply coming from imported State Water Project SWP deliveries from Lake Oroville. This imported water is crucial to prevent groundwater supplies from becoming severely depleted.
Some of the water is used for environmental concerns. The water for the Delta is used to increase the water quality by lowering the salinity levels.
Fisheries Flows The construction of the dam made the upper portion of the Feather River inaccessible to migrating salmon and steel head trout who used it for spawning grounds. To make up for the lost spawning area, the Feather River Hatchery was constructed. It can accommodate adult salmon and adult steel head.
The incubator can hold 20 million eggs and 9. Historically, the majority of the steel head and salmon spawn below the Oroville Dam. The hatchery has been very successful due to the carefully monitored flow of water. Recent operating challenges To keep the recreation areas fully functional with the low water levels due to drought.
Construction was initiated in , and despite numerous difficulties encountered during its construction, including multiple floods and a major train wreck on the rail line used to transport materials to the dam site, the embankment was topped out in and the entire project was ready for use in The dam began to generate electricity after completion of the Edward Hyatt Pump-Generating Plant, then the country's largest underground power station.
The dam has confined fish migration up the Feather River and the controlled flow of the river as a result of the Oroville Dam has affected riparian habitat. The users, using the cursor on the image, have the possibility to see the difference of the Lake Oroville in a time window of the few days. The images see the little captions acquired during the event, show the high rise in water level of the Lake and the spillway.
In the image acquired during the alert, the area damaged is more evident. Another aim of these images is to promote the opportunity to download Landsat data through the ESA portals, where images captured every day are made available in near real time to the users and the scientific community.
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