Top l Gibraltar Reservoir l Devil’s Canyon l Cachuma Project l Mission Tunnel l Ground Water l Recycled Water l State Water Project l Desalination l Top
Gibraltar Reservoir
Description
Constant radius, concrete arch dam (shown below) located on the Santa Ynez River, 8 miles north of Santa Barbara; owned by City of Santa Barbara; constructed 1913-22, with an original capacity of 14,500 AF; raised to current elevation in 1949; strengthened in 1990-91; water is delivered through the Santa Ynez Mountains to Santa Barbara via Mission Tunnel. Drainage Area: 216 square miles
Maximum Normal Water Surface Elevation: 1,400' above sea level Annual Yield: Average of approximately 4,600 AFY
Current Capacity: 7,264 Acre Feet (per 1998 Bathymetric Study) Operating Criteria
Diversions are limited by the 1930 Gin Chow legal judgment and the 1989 Upper Santa Ynez River Operations Agreement (USYROA, also known as the "Pass Through Agreement") which incorporates a compromise regarding the interpretation of Gin Chow. The agreement requires the City to track the difference between spills under actual operating conditions and under a "base" scenario (a hypothetical reservoir equal to the 1986 area/capacity profile). A basic goal of the agreement is to allow the City to maximize yield from Gibraltar while preventing impacts on the Cachuma Project and other downstream interests. Two modes of operation ("mitigation" and "pass through") are defined in the agreement. "Mitigation" mode requires the City to declare a maximum annual Gibraltar diversion level of up to 8,000 AFY and to mitigate the reduction in the average long-term annual yield of the downstream Cachuma Project (if any) that is estimated to result from that level of diversion. Mitigation is by relinquishment of a portion of the City's Cachuma Project entitlement. Diversions must conform to a monthly schedule. The City is currently in the mitigation mode with a declared diversion level of 5,000 AFY requiring mitigation of 67 AFY. The "pass through" mode allows the City to take a portion of its allowable Gibraltar diversions via the Cachuma Project, to the extent that spills at Gibraltar Dam exceed the amount of spills that would have occurred under the "base" scenario. The "pass through" mode is intended to be useful as the capacity of Gibraltar is reduced by siltation. Cost Information
Costs for this source of supply are primarily "sunk" or fixed costs, including the original cost of construction, plus a cost of $9 million for strengthening in 1990-91, plus the cost of Mission Tunnel. Variable costs for Gibraltar water consist of the marginal cost of treatment at Cater Treatment Plant which is approximately $50/AF.
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