Colorado River Aqueduct - The San Jacinto Tunnel

The San Jacinto Tunnel

The San Jacinto tunnel is considered the key link in Colorado River Aqueduct system. The 13 mi (21 km) long,16 ft (4.9 m) diameter tunnel runs underneath the San Jacinto Mountains between Cabazon and Gilman Springs. The $23 million project started on April 8, 1933. Tunnel crews dug from four directions; the two main portals and two shafts.

On July 1, 1934, one of the tunnel crews narrowly escaped the tunnel as ground water had burst in and began filling up the tunnel and shafts at a rate of nearly 8,000 US gallons per minute (0.50 m3/s). MWD chief engineer F.E Weymouth had noted in his 1930 report on the tunnel routes that the Parker route “involves less risk than any of the other proposed lines.” The continued intrusion of water was too much for the original contractors working on the project to handle, and in February 1935 the MWD terminated the contract and took over the job. More pumps were brought in and a portion of the tunnel was re-routed. Three crews of 34 men, working eight hour shifts worked on the tunnel.

The MWD continued to encounter tunnel seepage. The amount varied but never dropped below 540 US gallons per minute (0.034 m3/s), and sometimes topped 30,000 US gallons per minute (1.9 m3/s). By 1935 the seepage had started to become a concern around the San Jacinto Valley as springs, creeks and streams had begun to dry up. On October 21, 1935 the Riverside County Board of Supervisors passes a resolution calling on the MWD to prevent water from entering the tunnel or from flowing away from the place it was encountered. The MWD responded by stating that water entering the tunnel during digging is nearly unavoidable, and that lining of the tunnels near the end of construction should prevent further inflow. Lawsuits were filed against MWD by nearby landowners and most of these were settled out of court, with MWD paying out over $350,000 between 1936 and 1944.