The San Diego County Water Authority’s San Vicente Dam Raise project, the largest water storage project in the region’s history, has reached another important construction phase. Placement of roller-compacted concrete (RCC) is under way to build a new, 650-foot-long, 40-foot-high auxiliary “saddle” dam.
The $450 million project includes the tallest dam raise in the United States and will more than double the reservoir’s current capacity to 242,000 acre-feet. (An acre-foot is about 326,000 gallons, or enough to supply two average single-family households of four people for a year.) The additional storage capacity is greater than any existing reservoir in the county and will be used to help meet regional water needs during emergencies or dry years. The San Vicente Dam and Reservoir, located in Lakeside, are owned by the city of San Diego.
The saddle dam fills in a low point in the hills around the reservoir to help contain the reservoir’s new, higher water level. Construction crews have completed the saddle dam to about half its final height. Concrete placement to raise the main dam 117 feet will begin this fall and is expected to be complete in 2013.
“We are making good progress and the project is proceeding on budget and within its expected timeframe,” said Bill Rose, director of engineering for the Water Authority.
Crews already have constructed aggregate mining and crushing equipment and an on-site concrete batch plant at the project site. The batch plant measures and combines the exact proportions of aggregate, cement, flyash and water required for the custom mix of roller-compacted concrete (RCC) needed for the dam raise. Producing aggregate and concrete on site will eliminate approximately 100,000 truck trips through the nearby community during RCC placement.
RCC is just as strong as conventional concrete, but contains less water and can be placed more quickly. The concrete is rolled out and compacted in layers, one on top of another, without interruption. Crews will work 24 hours a day, seven days a week during the approximately six to eight months of the concrete placement activity on the main dam.
The California Department of Water Resources, Division of Safety of Dams, has approved the RCC mix design for the project. The dam safety agency’s approval gives the Water Authority the go-ahead to begin raising the existing San Vicente Dam.
The project is one of the final components of the Water Authority’s $1.5 billion Emergency Storage Project and broader $3.8 billion Capital Improvement Program. The Emergency Storage Project is a system of water conveyance and storage facilities that will ensure San Diego County will have up to a six-month supply of locally stored water and can move that water around the region in case of a natural disaster or other interruption to imported water deliveries. The enlarged reservoir will provide 52,100 additional acre-feet of emergency storage, and 100,000 acre-feet of carryover storage – water that is stored during wet years to be used to help manage supplies during subsequent dry years.
San Vicente Reservoir is closed to all recreation during construction. Once the dam raise is complete and the reservoir is refilled, a new, expanded marina will reopen for boating and fishing.