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Owner says dam roller compacted concrete raising will be largest effort of its type in the world.

The San Diego County Water Authority board of directors last week certified the environmental impact report to raise San Vicente Dam by 117 ft.

The $568-million project, to be built on top of the existing San Vicente Dam in Lakeside, will expand the reservoir to hold an additional 52,000 acre-ft of water for use during emergencies and another 100,000 acre-ft of water to supplement imported supplies during dry periods.

“Raising San Vicente Dam will significantly enhance our water supply reliability,” said Water Authority Board Chair Fern Steiner. “As we face increased challenges to our water supplies, we not only must diversify our water supply portfolio, we must also improve our infrastructure to reliably store and deliver water to our region.”

Construction is scheduled to begin in early 2009 and to be completed in late 2012. This project will be the largest dam raise in the U.S. and the largest in the world using roller-compacted concrete, according to SDCWA spokesman John Liarakos.

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Liarakos says the raised dam will be as strong as a conventional concrete dam, but will cost less because the roller-compacted concrete construction process takes less time. The downstream side of the dam will be completely covered by roller-compacted concrete and will have a new, stair-stepped appearance.

The raising of the San Vicente Dam has two key components: emergency storage and carryover storage. The San Vicente Dam raising is the fourth phase of the Water Authority’s approximately $1.2-billion emergency storage project. The ESP will provide up to six months of water if a natural disaster such as an earthquake cuts off the region’s imported water supplies. It achieves this through 20,000 acre-ft of water storage in Lake Hodges, 18,000 acre-ft in the Olivenhain Reservoir, as well as 52,000 acre-ft in San Vicente Reservoir, providing a total of 90,000 acre-ft of water for use during emergencies.

In addition to emergency storage capacity, San Vicente will hold 100,000 acre-ft of water for carryover storage. Carryover storage allows the Water Authority to store water during wet periods for use during subsequent dry years. In total, the additional 152,000 acre-ft of water in San Vicente could meet 40% of San Diego County’s needs for a year.

The city of San Diego, which owns the San Vicente Dam and Reservoir, has begun lowering the reservoir’s water level in preparation for the project. Limited fishing and water recreation at the reservoir will be allowed through the summer. To assure public safety, the reservoir will be closed to all recreation when the water level drops below the boat launch at the reservoir’s marina. It will remain closed during dam construction. The reservoir will reopen to recreation between 2014 and 2017, when the water level reaches the boat launch at the reservoir’s new, expanded marina.

Bids for a contractor will go out when the final permitting is completed, which should be late this year, Liarakos says.