More Dams Coming?

July 1, 2003

Despite their recreational and functional value, most reservoirs come at a cost. To build a reservoir, we must drown a valley. In the Bay Area, that probably entails flooding valuable wildlife habitat, such as oak woodlands, vernal pools, and riparian corridors. It is not surprising, then, that several current reservoir proposals are drawing fire from local environmental groups.

In 1988, Contra Costa voters approved funds for the construction of a reservoir in Los Vaqueros Valley. Opponents warned that the proposed 100,000-acre reservoir would be just the foot in the door for a larger reservoir project. To fend off opposition, the Contra Costa Water District (CCWD) promised to submit any future expansion plans for voter approval, and offered to build recreational trails for hikers, bikers, and equestrians; establish new wetlands; restore riparian corridors; and plant oak seedlings.

Sure enough, CCWD, in conjunction with the CALFED Bay-Delta Program (a consortium of state and federal agencies), is now looking to expand Los Vaqueros Reservoir to 500,000 acre feet. This would inundate an additional 1,980 acres of the valley, including, ironically, one to two acres of mitigation wetlands, up to 176 acres of recently planted oak seedlings, and many of the new trails.

CCWD hasn’t completed environmental studies or identified funding sources for the $1 billion-plus plan, much less developed a specific proposal. Yet CCWD is considering going to the voters this November to get approval for expansion in some form. CCWD claims the project will improve water supply and quality for Contra Costa and surrounding counties. Opponents argue that diversion of more water from the Delta—threatening already marginal populations of native fish and flooding habitat used by special-status terrestrial species—is the last thing we need. Twelve environmental and sportfishing groups are pressuring the district to postpone the vote until environmental studies are completed and full costs and funding sources are identified.

To find out more, visit the Los Vaqueros website at Friends of the River ( and the Sierra Club (Eric Wesselman at 510/622-0290, ext. 240) are working to slow down the expansion plans.

Another project making waves is the Santa Clara Valley Water District’s (SCVWD) San Luis Reservoir Low Point Improvement Project. Every year, the water level in the 2.04 million-acre-foot San Luis Reservoir drops so low that algae blooms in the upper 30 feet of the water column are drawn into the pumping plant’s intake, contaminating the water supply. At lower levels, the intakes become exposed, preventing the plant from delivering water.

Two of the alternatives being considered involve dams that would flood portions of Henry Coe State Park near Morgan Hill. Although the proposed Upper Pacheco Reservoir expansion would only flood a small portion of the large park’s east side, the proposed Los Osos Reservoir would flood 2,000 acres of parkland and its surroundings, including eight archaeological sites plus popular equestrian and bike trails. CCWD is now conducting feasibility studies; a draft environmental impact report/study should be available for public review in late 2003 or 2004. The current proposals can be viewed at The new group Advocates for Coe Park has set up a website with more information at

About the Author

Matthew Bettelheim is a freelance writer and a wildlife biologist with URS Corporation.

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