In a region latticed with pipelines and canals, the consequences of dry conditions in one basin are exported to neighboring watersheds.

The Buena Vista Pumping Plant, in southern Kern County, lifts water in the California Aqueduct. Part of the State Water Project, the aqueduct spans hundreds of miles, transferring water from northern watersheds to farms and cities in the south. Photo © J. Carl Ganter/Circle of Blue

By Brett Walton, Circle of Blue — June 16, 2022

  • The American West has been plumbed into a series of “mega-watersheds.”
  • Because basins are connected by pipelines and canals, drought in one region affects distant watersheds.
  • A big Southern California water agency plans to draw more water from the Colorado River this year because of inadequate moisture in the Sierra Nevada.

On a map that might grace the walls of a high school classroom, the watersheds of the American West are distinct geographical features, hemmed in by foreboding plateaus and towering mountain ridges.

Look closer and those natural boundaries are less rigid. A sprawling network of pipelines and canals pierce mountains and cross deserts, linking many of the mighty rivers and smaller streams of the West. These “mega-watersheds” have redrawn the map, helping cities and farms to grow large and productive, but also becoming political flashpoints with steep environmental costs.

“It is absolutely one interconnected system,” said Bill Hasencamp of the Metropolitan Water District of Southern California, a wholesale water provider.

Hasencamp was speaking from a Southern California perspective, a region that is a pivot point since it draws water from basins hundreds of miles away in Northern California and the Colorado River. As the manager of Colorado River resources, Hasencamp has one eye on Met’s 19-million person home territory while the other peers eastward across the Mojave Desert at the shrinking lakes Mead and Powell, which also supply his agency.

Not every river in the West is linked and few regions are as networked as Southern California. But there are enough connections that the water supply consequences of the drying American West are not felt in isolation. They are exported to neighboring watersheds.

Start in Northern California. The Trinity River Diversion, a federal project, connects the Klamath River basin to the Sacramento River watershed. The Sacramento River flows south until meeting the San Joaquin River in the West Coast’s largest estuary. Water from the two rivers is pumped, via state and federal canals, to counties south of the Sacramento-San Joaquin Delta.

Once Northern California water arrives in Southern California, it mingles with water from the Colorado River, which is imported through the 242-mile Colorado River Aqueduct.

Upstream on the Colorado River, there are more links. Tributary streams in Colorado are diverted through the San Juan-Chama Project into New Mexico, where the water enters the Rio Grande system and supplies Albuquerque and Santa Fe. The Central Utah Project pulls Colorado River water into the orbit of the fast-growing Wasatch Front, which is not in the basin.

In the headwaters state of Colorado, 11 major interbasin transfers unite rivers on both sides of the Rockies. The Moffat and Adams tunnels cut through the Continental Divide, a feat of engineering that brings Colorado River water into the South Platte River basin, where it is gulped by Denver and other Front Range cities.

The Moffat tunnel, built in 1936, moves Colorado River basin water across the Rockies, for use in homes and business in Denver. Photo © Brett Walton / Circle of Blue

Smaller projects also crisscross the landscape. San Francisco reaches into the Tuolumne River. Los Angeles taps the Owens River. The Potter Valley Project diverts water from Northern California’s Eel River into the Russian River, which flows through Sonoma wine country.

Water managers like Hasencamp enjoy having a range of sources to draw upon. If one area is dry, they can turn to another watershed. “It’s just one egg in a big basket,” Hasencamp said.

Problems develop when several of those eggs turn out to be rotten at the same time. The weather in sparsely populated northern counties in California affects water supplies not only in Southern California, but also for cities, farms, and ecosystems throughout the Colorado River’s mega-watershed.

Hasencamp illustrated the consequences of the spillover effect with some numbers. Met draws water from Northern California via the State Water Project and water from the Colorado River via the Colorado River Aqueduct. Met isn’t expecting much water from the State Water Project in 2022, so it will lean more heavily on the Colorado, tapping “credits” stored in the lake.

“If you look at this year, because it’s been so dry in Northern California, we’re going to move about 1.15 million acre-feet through the Colorado River Aqueduct,” Hasencamp said. An acre-foot can supply about three households in the area for a year. This year’s anticipated water delivery from the Colorado is more than double what it was in the recent past. “Just three years ago in 2019, when it was really wet in Northern California, we only diverted [from the Colorado River] in the neighborhood of 500,000 acre feet.”

In short, when Northern California is dry, Hasencamp’s agency draws more water from the Colorado River, placing additional pressure on Lake Mead, which is at its lowest point since it was filled in the 1930s. Hasencamp reckons that 500,000 acre-feet, at this point, is about 8 feet of elevation in Lake Mead. Every foot matters these days, when the enfeebled reservoir is just 28 percent full — low enough that mandatory water cuts are in place in Arizona and Nevada.

These complex hydraulic systems can be viewed from several angles, said Felicia Marcus, a visiting fellow at Stanford University’s Water in the West program.

“In some ways, it’s the miracle of modern engineering, without which modern California simply wouldn’t be possible,” said Marcus, a former chair of the state’s water regulatory agency. “On the other hand, it has consequences. The issues there are both environmental and political or social.”

For all the water supply flexibility they provide, these diversions are not risk-free. They have depleted water for native fish. Many of them — from the Owens River in California to the West Slope of Colorado — contend with legacies of acrimony and mistrust, feelings that arose decades ago due to the political imbalance between rural areas where water was extracted and urban areas that benefitted.

New Mexico in the ‘Crosshairs’

Southern California is the prime example of the mega-watershed concept. But it is not the only one.

New Mexico straddles two major watersheds: the Rio Grande and the Colorado. Thanks to an interbasin transfer, Albuquerque receives water from both.

“We’re in sort of the crosshairs,” said John Stomp, who was the chief operating officer for the Albuquerque Bernalillo County Water Utility Authority for 10 years before he retired in 2020. “So we’re obviously concerned and looking at both conditions all the time.”

The link between the basins is the San Juan-Chama Project. A federal diversion completed in 1971, the project channels water from San Juan River tributaries in the Colorado River basin and delivers it to the Rio Chama, which flows into the Rio Grande. The amount of water the project provides to the Rio Grande varies each year. Diversions take place only when flows in the three tributaries exceed minimum requirements that change each month.

San Juan-Chama water helps to reduce Albuquerque’s reliance on local groundwater. The city discovered in the 1980s that it was over-extracting its aquifer. The imported water also provides much needed dry season flows in the Rio Grande to assist endangered species like the silvery minnow, a fish, and the southwestern willow flycatcher, a bird that nests in riverside trees.

Similar to their counterparts in Southern California, Albuquerque water managers speak in the language of tradeoffs.

“We’re using Colorado River water to substitute for Rio Grande water, so if Colorado River water is not available, then we have to get an equal amount of groundwater, which puts more of a strain on the Rio Grande system,” Stomp said.

More strain is a common refrain in these dry times in the Southwest. It is not, however, always the outcome. The spillover effect could work in the opposite direction, toward less stress.

Hasencamp mentioned one possibility. More water conservation and use of recycled water in Southern California relieves pressure on the Colorado River and Sacramento-San Joaquin Delta.

Met is working with partner agencies in Arizona and Nevada to further that cause. The Southern Nevada Water Authority, Central Arizona Project, and Arizona Department of Water Resources allocated several million dollars for planning studies related to a regional water recycling facility to be located in the Los Angeles metro region.

A deeper relationship might emerge from that partnership. The out-of-state agencies could contribute to the construction and operation cost of the $3.4 billion facility in exchange for some of the 168,000 acre-feet of water it would produce. The exchange would mean that Met leaves more water in Lake Mead. The states already store water for each other, but such a swap would be a path-breaking agreement.

“Those decisions haven’t been made yet, though,” Hasencamp cautioned. “But those are the types of creative partnerships that I think we’re going to need in the future.”