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All That Snow Looks Great, But When It Melts, Watch Out LA

Los Angeles Aqueduct (Sharon McNary/KPCC)
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The Los Angeles Department of Water and Power announced its latest snowpack measurement in the Eastern Sierra Monday and it's at an encouraging 171% of what's considered normal (compared to the state reading of 153%).

It's a mark that matters because much of L.A.'s water supply comes from the snow that falls on the Eastern Sierra mountains, which is is ferried south via the Los Angeles Aqueduct when it melts.

But a surplus snowpack can actually present a different kind of challenge for Los Angeles water managers, who are getting ready to grapple with a bumper supply of water.


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Think of the L.A. Aqueduct as a giant, 233-mile-long funnel capable of holding about 365,000 acre feet of water. That's about 70% of L.A.'s overall water demand.

It's not clear how much water this year's snowpack will produce, but the record snowpack in 2017 produced about one million acre feet of water. That's too much for a funnel only about one-third that size. That means that water managers have to figure out where to put the excess water as it melts off the mountains.

And the problem becomes potentially worse if a warm streak hits and melts the snow fast, said Anselmo Collins, who manages water operations for the L.A. Department of Water and Power.

The aqueduct could be overwhelmed, leading to flooding of roads and bridges in Inyo and Mono counties, along Highway 395.

Excess water could also flood and damage some $2 billion worth of dust control equipment and water control berms installed on the Owens Dry Lake Bed. The aqueduct takes water that would normally flow into the Owens Lake so all that equipment is important for preserving air quality in the region.


That 2017 surplus of water? Mayor Eric Garcetti actually declared a state of emergencyto deal with it the historic 241% of normal at the time of his declaration, the most snow recorded since the Aqueduct was constructed in 1913. Later in the season the snowpack measured 204%, still twice as much as normal. The city spent $27 million to cope with the excess water.

A similar water emergency declaration won't be needed this year, Collins said. However they will duplicate some of the tactics of 2017 to deal with excess water.

For starters, DWP will route some of the water to spreading grounds in Mono and Inyo counties.

And some of the water will be used to recharge the water table in Los Angeles.

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In 2017 the utility restored an old water tunnel called the Maclay High Line to move water from the end of the aqueduct near the I-5 in Sylmar to a flood control channel that feeds a water spreading ground in Pacoima. The tunnel has an interesting history, but had been taken out of service years ago.


Yes, bills will go down a bit.

More water in the aqueduct means DWP doesn't have to buy as much imported water from the Metropolitan Water District. MWD has its own aqueducts that bring water from Northern California and the Colorado River.

During our drought years, purchased water from MWD has made up more than half the city water supply. But in this water-rich year, 70 percent of the city's water will come from the aqueduct. That leaves only about 30% of L.A.'s city water supply coming from Metropolitan's imported supply plus groundwater, recycled water and conservation, DWP spokeswoman Ellen Cheng said.

Less MWD water means a lower DWP bill. How much lower? The part of the bill that reflects purchased water will be about 25% lower, Cheng said.

DWP's board had already set the upcoming July through December rates with the added runoff in mind, so customers will get some benefit.

Correction: A previous version of this story incorrectly described the sources of non-aqueduct water that would be used in Los Angeles in the coming year.

This story is part of Elemental: Covering Sustainability, a multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.