A Concrete Lining

A 35-Mi. Stretch of the Coachella Canal Gets a Needed Upgrade

By Greg Aragon

The last unpaved miles of the 122-mi.-long Coachella Canal are being replaced by a new concrete-lined canal. The new $90 million waterway is projected to save about 26,000 acre ft (about 8.5 billion gallons) of Colorado River water that is currently lost annually due to canal seepage.

The state-funded project, designed and engineered by Montgomery Watson Harza, along with Bookman Edmonston, both of Sacramento, should be completed by the end of December, when water is expected to be transferred to the new canal.

Earthwork is about 99 percent complete on the 35-mi. section and crews are now mainly working on fencing, landscaping and environmental work.

One of the most unique aspects of the job is that it is being built right next to the old canal, in the same, roughly 200-ft.-wide right-of-way.

"The two canals, from centerline to centerline, are only about 50 ft. apart," said Dan Charlton, senior irrigation engineer for Coachella Valley Water District (CVWD), owners of the canal. "So we had to be very careful [of seepage] because there is no lining on the bottom of the existing canal."

He said that to make sure that water from the old channel didn't leak into the new one, the bottom of the new canal was built on higher ground.

Wayne Dahl, project manager and engineer of record for Bookman Edmonston, said building a new "parallel canal" next to the old one was not the water district's first plan.

"Originally the [old] canal was going to be lined in place with pipelined bypasses going around," he added. "But the risky part was that the bypasses had to go across [mountain] washes and there was no way to protect them."

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Because of this, he said a parallel canal was built. "Even though there can be three or four years where the washes never flow, rain would have been a disaster," Dahl added.

He said the new canal "absolutely mirrors" the old one.

To protect the new canal from rainwater runoff, crews are building 25 new siphon stations. These bridge-like structures, which range from 200 ft. to 800 ft. long, direct the canal underneath the ground in places where the washes travel above.

Dahl said another reason the engineering team decided upon the parallel method was that it turned out to cost about $30 million less than lining the canal in place.

The lining project is located between the Salton Sea and the Chocolate Mountains, about 50 miles from the Mexican Border near Highway 111. Construction began in October of 2004, in the town Niland and is moving north toward Mecca, at the western end of the Salton Sea.

To get the channel laid will all that concrete, crews relied on a well-organized "paving train" rolling down the bed at a rate of about 2,000 ft. per day. The train consists of a trimming machine, followed by the paver, a joint jumbo machine, a finishing machine and lastly, a curing machine.

When an unusually hot summer hit the California desert area in June, the project team switched to laying the concrete at night.

Crews are also currently installing a 29-mi.-long, 8-ft.-high wildlife fence to keep out deer and bighorn sheep, as well as digging 36 ponds for the animals to drink from.

When the Coachella Canal was completed in 1949, only its northernmost 37 miles were lined with concrete.

In 1980, the CVWD decided to replace the southernmost 49 mi. of the earthen canal with a parallel, concrete-lined waterway, an act which saved more than 130,000 acre ft. of water annually. This is the section where the canal branches off of the All-American Canal in Imperial County.

The remaining 35 mi. of still-earthen canal, which are currently being replaced, flow above soil with a high concentration of clay, which yields less seepage. But as Colorado River water becomes more precious, the CVWD decided to finish the job and build a new concrete canal.

To do this, it had to prepare 160,000 yds. of concrete and move 5.6 million cu.-yds. of earth.

"Getting all the dirt moved is a big challenge," said Shawn Otheim, project manager for Alamo-based R&L Brosamer, the general contractor. "It's not a typical situation. You have an existing canal on one side of you, and on the other side the spoils from when they dug the existing canal, so there are a lot of holes and hills. And it matters where you put every grain of dirt."