Gibraltar Dam and reservoir are located on the Santa Ynez River in Santa Barbara County, about 9 miles north of the City and upstream from Lake Cachuma. The City owns and operates the dam and reservoir pursuant to a Notice of Appropriation posted on October 11, 1904. Stored water is diverted through Mission Tunnel to the Cater Water Treatment Plant. The dam is a constant radius, concrete arch dam constructed in 1920 with an original capacity of 14,500 AF; it was raised to current elevation in 1949 and strengthened in 1991. Gibraltar Reservoir is the source of about 40 percent of the City of Santa Barbara’s water supply during a normal water year. Loss of storage capacity due to siltation has been an issue since the dam was constructed, often exacerbated by wildfires in the Gibraltar watershed. To monitor changes in capacity, and pursuant to the requirements of the Upper Santa Ynez River Operations Agreement, the City commissions a bathymetric survey of Gibraltar Reservoir at one to three year intervals.