AECOM performed the feasibility studies, site investigation, engineering design and construction support for the expansion of Los Vaqueros Reservoir from 100 thousand to 160 thousand acre-feet. Contra Costa Water District’s objectives for the expansion were to provide water supplies for environmental water management, increase water supply reliability, meet demand during droughts, and address shortages due to regulatory restrictions. The original 196-foot-high embankment dam, designed by AECOM in the early 1990s, was not designed to accommodate a future raise. The project was further complicated by the need for the reservoir to remain in operation during construction. Several innovative engineering solutions were developed and incorporated into the design accomplish a 34-foot raise with construction restricted to the downstream side of the dam. Operational restrictions of the in-service reservoir and tight site constraints added significantly to the complexity of construction.


  • $110 million project (construction cost $44 million)
  • 1950 acre, 160 TAF reservoir (60 TAF increase)
  • 1 million cyds of fill, 42,000 cyds RCC
  • 18 month project was completed ahead of schedule and under budget
  • Recognized by a number of industry awards including: the Association of California Water Agencies Clair A. Hill Water Agency Award, American Council of Engineering Companies National Recognition Award, and American Society of Civil Engineers, Region 9 Engineering Excellence Honor Award.