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Old LADWP water tunnel to help with Sierra water glut

A nearly century-old water tunnel that’s been idle for decades is being resurrected by the Department of Water and Power to carry water from the overflowing Los Angeles Aqueduct to store underground for future use.

As the near-record snowpack in the Eastern Sierra melts, it is sending far more water down the aqueduct than city water customers can use. Putting some into underground aquifers would allow the city to store some of that water for future use.

But, there’s a problem. The city lacked the pipes to transfer water from the aqueduct to a spreading ground in Pacoima. That’s where the $3.3 million rehabilitation of the Maclay Highline comes in. It's been battered by earthquakes, and abandoned in favor of new water conveyances, but it happens to be in the right place to fill a gap in DWP's water transport plans.

Once the work is completed later this month, the repaired water tunnel will have the capacity to deliver as much as 42 million gallons a day to recharge a drought-stressed underground aquifer.

A highline is a water conduit or tunnel that generally runs above ground. The Maclay Highline actually bores for some distance 70 feet under the foothills in Sylmar, but it’s still called a highline.

Historic water tunnel falls idle

Construction on the Maclay Highline started in 1915, soon after the completion of the 233-mile LA Aqueduct that brings melted snow from the Eastern Sierra to the city. When completed in 1923, it received aqueduct water in Magazine Canyon east of the present-day I-5.

It carried the water east through the foothills to a reservoir at the top of Maclay Avenue.  From there the water was distributed to homes and farms in the north San Fernando Valley.

The Maclay Highline sustained damage in the 1971 Sylmar Earthquake, but it was repaired. It was taken out of use in the mid '80s when the city opened a new filtration plant and routed the treated water east through other pipelines.

The idle Maclay Highline was damaged again in the 1994 Northridge Earthquake. But the DWP intended to some day repair the highline because planners figured it could be used to convey water to a series of storm drains that connect to the Pacoima spreading ground

“You never want to take a facility that still has life and function to it and just decommission it and say you’re done with it,” said Mike Grahek, who oversees the L.A. Aqueduct for DWP.

But that plan sat on the back burner for years. In 2007, the tunnel was further damaged  when a developer ripped out 1,500 feet of the highline to make room for houses that were never built.

“I think they jumped the gun and the bottom fell out of the market and they stopped,” Grahek said.

But the damage to the highline triggered a test by Grahek to see if the remaining portion could still be used. In 2008, he walked the two-mile length of the water tunnel, and in some areas where it squeezes down to only four-feet tall, he crawled it.

Grahek determined most of the Highline was in good shape. And teeming with critters who made their homes in the cool dry tunnel.

“We found evidence of possum and rats other mice and there was actually a live rattlesnake,” Grahek said.

Except for the chunk taken out by the developer, the conduit and the concrete tunnel were in good shape. DWP flowed water through it for two hours – about 40 cubic feet per second – and it worked. 

But still, as the recession set in and local governments cut costs wherever they could, the plan stayed on the shelf.

Tunnel repair work underway

But then came the big winter snows of the 2016-17 winter. A near-record amount fell on the Eastern Sierra, where the DWP collects water for the aqueduct.

DWP officials realized there would be far more water coursing down the aqueduct than they could sell to customers.

There was so much snow the city declared a snowmelt emergency to free up funds to deal with the excess.

So finally, repairing the Maclay Highline made good economic sense. And at a cost of $3.3 million, most of which is labor, the city will be able to lay away a supply of water underground for future use.

Grahek oversees a crew of about 30 DWP workers doing the repairs. They were recently working on a 45-foot section of tunnel that collapsed on a small earthquake fault sometime after Grahek’s 2008 survey.

These workers have the benefit of power tools, small tractors, and modern safety equipment, unlike the men who spent years building the tunnel a century ago.

“I just imagine in my mind how absolutely difficult it was for people to get inside these mountains and chip away the rock and install this really symmetrical concrete structure and it's still here today,” Grahek said.

The tunnel is expected to begin shipping water by the end of the month, just as the weather is cooling and water demand in Los Angeles drops off.

"Because of the huge amount of precipitation we've gotten up in our watershed, we need to continue to flow the maximum amount possible," Grahek said. "That means we'll have excess water to store, and we want to store it in the groundwater table so we can retrieve it later when we might have some drier years."

The water will flow through two miles of the Maclay Highline, then be shunted into a series of storm channels, to the Pacoima Wash and finally to the Pacoima Spreading Grounds.