Metropolitan Water District Bores Under Mountain

September 28, 2010

A 450-foot tunnel-boring machine emerged from under the San Bernardino Mountains in Southern California at Devil Canyon recently, creating a nearly 4-mile tunnel as part of a large-diameter regional water line that will help improve the quality and reliability of imported water serving nearly 19 million Southern Californians.

The breakthrough completes the massive mechanical mole's nearly five-year passage through dirt, rocks and granite up to 1,500 feet beneath the mountain range as part of Metropolitan Water District's Inland Feeder project.

“For those of us who have followed this project since it first appeared on the drawing board 20 years ago, this is truly a thrilling moment,” said Metropolitan Board Chairman Timothy F. Brick. “This is a landmark achievement for the Inland Feeder, a vital link in securing a more reliable, higher-quality water supply for Southern Californians.”

The 3.8-mile Arrowhead West Tunnel is the last of three needed for the 44-mile Inland Feeder, a high-capacity, gravity-fed water delivery system stretching from the foothills of the San Bernardino Mountains to Metropolitan's Colorado River Aqueduct in the Riverside County community of San Jacinto. Mining on the other two project tunnels – the 4.3-mile Arrowhead East Tunnel and 8-mile Badlands Tunnel – was completed last May and in July 2001, respectively.

When completed in 2010, the Inland Feeder will provide Metropolitan the flexibility to deliver water when available from Northern California during wet periods – primarily during the winter when it rains.

The feeder also will improve the quality of Southern California's water supply by allowing more uniform blending of water from Northern California with Colorado River supplies, which have a higher mineral content.

First envisioned in the late 1980s, the $1.2-billion Inland Feeder will deliver water to be stored in surface reservoirs, such as Metropolitan's Diamond Valley Lake near Hemet in southwest Riverside County, and groundwater basins for later use.

Metropolitan General Manager Jeff Kightlinger said the project will help Southern California cope with future weather pattern uncertainties, which may bring more rain and less snowpack to Northern California, and longer periods of drought to Southern California.