SAN LUIS RESERVOIR

Expansion Gets Study By Bureau

Commissioner Michael Connor, announcing the San Luis study last summer.

San Luis Reservoir’s capacity and project yield could be given modest increases but the greatest benefit of raising B.F. Sisk-San Luis Dam could be improvements to its seismic safety.
A U.S. Bureau of Reclamation appraisal report appears to find the expansion project would be possible but at a cost of at least $360 million and with the biggest winner possibly being the dam itself. A fault line runs through the reservoir, creating earthquake damage concerns.
SUPPLY AID?
The study was launched last summer and was announced – with considerable surprise – by Commissioner of Reclamation Michael Connor during a Fresno water forum with an eye to eventually helping improve water supplies to users for whom environmental and drought-caused operating constraints and supply curtailments have been the rule for years.
Forty-five year old San Luis Reservoir, an off-stream storage facility west of Los Banos, is shared by the federal Central Valley Project and State Water Project.
Along with supply issues, algae has long been a problem with very low storage, adversely affecting quality of water discharged to the Santa Clara Valley Water District, an urban user in the Bay Area. A report process launched in 2001 identified raising the dam as an alternative.
The latest report finds that dam seismic safety concerns identified in a 2006 Reclamation study could be addressed by enlarging the dam embankment and abutments and shoring up the earth-fill structure. Modifications to intake towers, a spillway and access bridge would also be required. They have been found to be technically feasible to construct.
The Bureau says capacity of the existing 2.04 million acre-foot reservoir could be increased by 130,000 acre-feet (6%) by raising the surface 10 feet and dam height 20 feet, which could yield 43,000 acre-feet of additional average Delta exports.