A $1-billion upgrade to the B.F. Sisk Dam in California’s Central Valley was launched this month as part of an effort to reduce the impact of severe seismic events on the 55-year-old earthfill structure.

The 382-ft-high, 3.5-mile-long compacted earthfill embankment dam is owned by the U.S. Bureau of Reclamation (USBR). The Safety of Dams Modification Project will require adding stability berms, increasing the height of the existing dam and other safety enhancing features.

The dam, completed in 1967, impounds San Luis Reservoir, the nation’s largest offstream reservoir, which provides supplemental irrigation water storage and municipal and industrial water for the Central Valley and for California’s State Water Project.

“这项投资于位于萨克拉曼多 - 山华金三角洲以南的B.F. Sisk大坝，将为加利福尼亚社区，农民，牧场主和野生动物避难所建立供水安全，并帮助该系统更好地适应不断变化的气候。”水与科学在新闻稿中Tanya Trujillo。

The safety modification project is the agency’s largest project under the 1978 Safety of Dams Act and is scheduled for completion in 2028.

In April, NW Construction of Bozeman, MT was awarded a $120 million contract for the first phase of work on the retrofit project. The work will address issues with foundation materials used on the dam as well as the construction of shear keys, stability berms and modifications to the spillway. A key challenge for the company will be developing, processing and transporting specified materials to the intended areas of placement from the rock quarry located more than three miles away.

“This will require extensive planning and execution to move the required amounts of materials safely and successfully to meet the schedule restrictions in the contract which are dictated by the varying reservoir levels,” says Casey Patterson, vice president and operations manager for NW Construction.

The project will take at least three construction contracts and between eight and 10 years to complete, says USBR Principal Deputy Regional Director Richard Welsh.

The project received a $100-million investment last March from the Infrastructure Investment and Jobs Act which was part of the $500 million awarded to the US Bureau of Reclamation over the next five years to support critical dam safety projects.

一系列的地震风险研究于2006年完成，发现加利福尼亚大坝的基础材料不足以抵抗严重的地震事件的影响，这使下游公众在潜在的严重地震时处于风险。大坝靠近几条断层线，包括穿过圣路易斯水库的Ortigalita断层。

The project will also involve increasing the dam height by 12 ft, reducing the likelihood of water coming over the top of the structure if the embankment were to slide or slump during a seismic event. The additional dam height will create more than 130,000 acre feet of extra water storage in San Luis Reservoir.