Boca Dam (LBAO)
Reclamation plans to modify Boca Dam beginning in spring of 2019 and ending after fall of 2020. During spring, summer and fall of 2019, the reservoir will be operated at a lower level to assist construction.
For additional project information, please contact MP Region Safety of Dams at 916-978-5328 (TTY 800-877-8339). Information related to the construction project can be directed to Kyle Hughes at email@example.com.
Boca Dam and Reservoir are components of the Truckee Storage Project, completed in 1937 by the Bureau of Reclamation and since operated and maintained by the Washoe County Water Conservation District.
Based upon extensive engineering analysis, Reclamation has found that Boca Dam and Dike is at risk from structural failure during an earthquake due to the presence of sand and gravel within the dam's foundation. During an earthquake, the dam has the potential to slump or crack (seismic induced liquefaction) leading to overtopping or a breach, as illustrated in the below figure.
Profile of dam deformation during an earthquake
The Safety of Dams Act requires Reclamation to reduce the risk of Boca Dam structural failure within acceptable levels. Reclamation plans to modify Boca Dam by removing a sand and gravel lens on the downstream side of the dam; a downstream stability berm will be constructed to buttress the dam in the event of an earthquake as illustrated below.
Profile of modified dam
The spillway will also be seismically retrofitted and the dam crest will be 25 feet wider with a reinforced concrete road surface.
The earthen material for the stability berm will be sourced from a borrow area within the reservoir and will be hauled to the dam via Stampede Meadows Road. To allow access to the borrow area, the reservoir will be lowered to 5,581 (NAVD88) during the first year of construction in 2019. This level is 28 feet lower than the maximum water surface level. Stampede Meadows Road will remain open during construction with the use of traffic control, but the road over Boca Dam will be closed. Additional project information can be found in the below referenced document.
In accordance with the National Environmental Policy Act and the California Environmental Quality Act, Reclamation has coordinated with the Lahontan Water Board and developed an Environmental Assessment/Initial Study to describe the project and impacts. The document is available at: https://www.usbr.gov/mp/nepa/nepa_projdetails.cfm?Project_ID=27372
Aerial view of in-reservoir borrow area