Mission Tunnel is used to convey water from Gibraltar Reservoir (and sometimes Devil’s Canyon Creek) to the Cater Water Treatment Plant. The tunnel itself is also a source of water for the City - groundwater seeps from the walls, ceiling, and floor into the tunnel. This 3.7 mile tunnel goes through the Santa Ynez Mountains and was constructed in 1904-1911. At the time it was the longest water tunnel in the world.
This infiltration of groundwater into Mission Tunnel has averaged approximately 1,200 AF annually, although this has fluctuated considerably over the years due to varying seasonal and yearly rainfall rates.
Tunnel infiltration augments water conveyed from Gibraltar Reservoir- flowing to Cater Water Treatment Plant via gravity. Rehabilitation work was completed in December 1994 and the tunnel is inspected annually by City Water Resources and Engineering staff.