April 12, 2024

‘Slow water’ could transform the Southwest, one little rock wall at a time

WHEN VALER CLARK and Josiah Austin moved to El Coronado cattle ranch in southern Arizona in the 1980s, the seasonal rain didn’t soak into the soil but roared through arroyos and washes, cutting them deeper into the earth. The erosion was threatening a road, so they placed a few rocks across the adjacent wash. The tiny structure worked as intended, slowing water, catching soil, and fostering the return of long-gone plants. Clark and Austin had instinctually re-created an Indigenous technique for managing water in drylands. 

Ultimately, the duo added around 20,000 small rock barriers across tributaries of the often-dry Turkey Creek, which ran through their 1,800-acre property in the Chiricahua Mountains. Within a few monsoon seasons, water seeped from the structures year-round, and the creek corridor turned green with plants. Downstream landowners were suspicious, claiming that Clark and Austin were holding on to “their” water. But when Laura Norman, a physical scientist from the US Geological Survey, measured the flow in 2013, she found that the barriers weren’t just slowing flash floods and extending supply into the dry season: They’d actually raised the stream’s flow by 28 percent. 

Today, the Southwest is staggering through a “megadrought”—possibly the worst in 1,200 years. The Colorado River, which quenches the demands of more than 40 million people in seven US states and Mexico, is seeing average flows that are 19 percent lower than in the last century. Climate change is making the region’s water woes more severe, scientists say. But drought is partly determined by the gap between supply and human demand, and right now, demand is greater than the region’s supply. What’s more, our development choices—urban sprawl, industrial forestry and agriculture, intensive cattle grazing, and the concrete infrastructure we use to try to control water—are sapping the river’s natural systems and resilience. 

Modern development tends to erase places where water slows down: wetlands, flood plains, mountain meadows, and forests. These ecosystems absorb high flows, prevent floods, and move water underground, which raises the water table. A healthy groundwater system supplies streams, wetlands, and rivers during the dry season and hydrates soil and plants, making them less likely to burn in wildfires and allowing them to release water into the atmosphere, contributing to rain. But humans have dramatically altered the water cycle by draining or filling as much as 87 percent of global wetlands over the past three centuries, interrupting the flow of two-thirds of rivers, and doubling the land area of paved cities since 1992. All told, we have transformed 75 percent of the world’s total land area for housing, agriculture, and industry.

Pile of rocks captured in wire fencing with snow on top. Called gabions, they are built to slow water.
Eight years ago, a nonprofit installed wire-wrapped rock structures called gabions in Babacomari Ranch in Arizona to detain precipitation and build up sediment. Erica Gies

Clark and Austin’s approach to land management has shown one way to reverse these negative trends, and the strategy is now spreading across the Southwest and northern Mexico. Their streambed structures, coupled with Norman’s in-depth studies on the benefits, led to the USGS co-founding the Sky Island Restoration Collaborative, a group of government agencies, nonprofits, private landowners, scientists, and restorationists in the US and Mexico who are building thousands of slow-water structures.

Called natural infrastructure in dryland streams, or NIDS, these structures include beaver dams, human versions of beaver dams, one-rock dams, check dams, log dams, leaky weirs, earthen berms, and gabions. The appropriate intervention depends on the specific site’s width and slope, nearby natural materials, and other factors. Despite the fact that several have “dam” in the name, these features do not block downstream flows like concrete hydropower dams; they just slow it down. They’re intentionally leaky to detain water, not retain it. “They’re a totally different beast,” says Norman.

She and her colleagues have documented NIDS’ effectiveness in storing carbon dioxide and mitigating flooding, water scarcity, pollution, heat, erosion, dust, wildlife loss, and food insecurity. These interventions—combined with levee setbacks to reconnect rivers with flood plains, forest and grassland restoration, and support for beavers’ comeback after they were hunted nearly to extinction—are part of the global “slow water movement” that could help boost water availability throughout the Colorado River basin.

USGS scientist Laura Norman taps snow-covered logs with foot on a ranch in Arizona
USGS researcher Laura Norman checks on a post-assisted log structure used to elevate the streambed and mitigate erosion at Babacomari Ranch. Erica Gies

At the rim of the Grand Canyon, the all-powerful nature of water is explicit: The reflective squiggle a mile below carved the natural cathedral out of rock over millions of years. Yet Euro-American culture has interpreted that force as a challenge and tried to control it. Viewed solely in terms of human need, water is either considered a threat or a commodity—the new billion-dollar Colorado River deal involving the US government and three Western states is just one example. But that’s not the only way people relate to water. Other cultures, including many Indigenous groups in North America, perceive it as a friend or relative. With that perspective, the right to water comes with the responsibility to care for it, along with the many elements and organisms—soils, rocks, microbes, insects, and more—that also have relationships with it. 

Choosing to return land to water might seem wasteful to some. But by restoring drylands to wetlands, or ciénegas in Spanish, Clark and Austin have shown how healthy slow-water systems can repair delicate desert landscapes that humans have destroyed.  

A sick land

In early March, the morning after a fierce windstorm made saguaros sway and dropped snow on the low desert, I drove south from Tucson with Norman through the tiny hamlets of Elgin and Sonoita. We left behind the saguaros and paloverde trees of the Sonoran Desert and entered the Chihuahuan Desert, studded with big tuffets of sacaton grass and grazing pronghorns. At the roughly 28,000-acre Babacomari Ranch, we walked a channel of the San Pedro watershed. Norman, clad in a black cowboy hat, hiking boots, and a thick Wrangler work jacket, was meeting up with a fellow researcher to take soil samples. The channel has several gabions and log structures, installed eight years ago by Borderlands Restoration, a nonprofit that belongs to the Sky Island Restoration Collaborative. 

Gabions are chicken wire containers filled with rocks. More engineered than other NIDS interventions, but still low profile, they are typically used in valley bottoms and anchored deep into the sides of the stream banks. The pieces of wood in the log structures are spaced 6 to 12 inches apart, pushed vertically into the streambed. They are meant to help water move underground and create “messiness” in the stream that slows water, captures sediment, and creates habitat. Both features have acted as intended: Parts of them are barely visible because trapped sediment has raised the riverbed and allowed new plants, including sacaton grass, to take root.

Credit: Norman et al. (2022)

Borderlands Restoration founder Ron Pulliam served in the Clinton administration’s Department of the Interior and taught ecology at the University of Georgia. He says major results from NIDS, such as streams flowing year-round, can take 10 to 20 years—but small improvements in erosion and vegetation can happen in just a year of two. Seeing those quick results three decades ago encouraged Clark and Austin to stick with their unconventional efforts at Turkey Creek and beyond. 

While the couple divorced several years back and sold El Coronado, Clark owns several other properties on both sides of the border. In consultation with ranchers and conservationists, she founded a nonprofit called Cuenca Los Ojos that builds NIDS and teaches these practices to other landowners and community members. Cuenca is also part of the Sky Islands group, and Clark’s daughter, Valerie Gordon, sits on the board.

This hard, dirty work is a long way from Clark’s early life in New York City. Then, in her 40s, she and Austin moved to El Coronado. The landscape “was so novel and so beautiful, it became the focus of my life,” she says. Curiosity about fire, water, plants, and lichen consumed her. “I’d never looked at ants before. I thought, There’s so much life going on here that I know nothing about.” 

USGS map of Arizona, New Mexico, and Mexico showing areas studied during Aridland Water Harvesting Study
The Aridland Water Harvesting Study covers more than two dozen ranches, cities, and federally owned properties near the US-Mexico border. USGS

That attention has served her well. “Valer has amazing powers of observation,” says Pulliam, a longtime friend and slow water ally. “She has a genius for understanding the movement of water and wildlife. She can’t explain it technically. But she has this intuitive feeling for how things work.” 

Now 83, Clark recalls her first summer at El Coronado in the 1980s. “The monsoon season hit and I was terrified, because I saw how much damage the flooding was doing in the hills. It was a lot of erosion. The vegetation was being flattened. I remember asking, ‘What do the cows eat? Rocks?’” She felt something was wrong and began studying the history of the area. She discovered that local trees were cut down in the 1800s to fuel copper production. Without them, grass boomed, so settlers brought in vast herds of cattle and sheep, who made short work of the vegetation. Mining and cotton production took a toll as well. Then when rain struck the denuded land, the water cut deep channels into the earth. 

What water wants

By placing rocks across a stream channel to slow water, Clark and Austin had intuitively re-created a technique that Indigenous peoples in the Southwest and northern Mexico had deployed for centuries to slow water, buffer against drought, and reverse desertification. 

Soon after the couple added those first structures, a group of men came to El Coronado from Mexico, looking for work. Clark showed them the little rock dam. “I said, ‘It’s wetter here, and grasses are coming in. What if we do that in the hills because they’re quite bare?’ And they said, ‘We do that at home.’” For generations, they had used a similar practice to grow corn. 

The men returned seasonally for 20 years and created some 20,000 rock structures throughout Turkey Creek’s side channels in the hills. As the low barriers caught sediment and deep-rooted grasses returned, “the mountains became sponges,” Clark recalls. “The wash became a stream, and scientists came and put fish in the stream.”

Gordon says the tenacity required to see this vision through is part of Clark’s personality. “My mother is very comfortable taking an unconventional path. She is not afraid of a challenge. And I think she also likes to do what other people don’t want to do.” 

Indigenous rock structures similar to those at El Coronado can be found throughout the Southwest. Over the last decade, Pulliam saw several on land purchased by Borderlands Restoration in Arizona, and was struck by how different the watersheds looked from others in the region that were severely washed out. “All of the little side draws in this area have almost no erosion,” he says. “If you look carefully, there are ancient rock structures at least 1,200 years old still working.”

Indigenous peoples are still creating and using slow-water structures for various purposes today. Michael Kotutwa Johnson is a member of the Hopi Tribe and has a Ph.D. in natural resources. But his most important credential, according to his University of Arizona profile, is that “he continues to practice Hopi dry farming, a practice of his people for millennia.”

The Hopi, like most Indigenous cultures, are “place-based societies,” says Johnson. Their place receives just 6 to 10 inches of precipitation a year, so they have developed methods designed to conserve soil moisture. Johnson explains some of them.

Hopi read the landscape and natural water flows, then build rock dams at the bases of mesas to divert runoff into fields. They also use rock detention structures to capture nutrient-bearing sediment to hold moisture, allowing farmers to plant different varieties of crops without fertilizers or irrigation. “Crops always need new soil with nutrients,” Johnson says. Contour farming—planting across the slope of the land at a certain angle—also slows water and wind. Another strategy includes leaving the stalks, cobs, and leaves on the ground after a corn harvest to catch snow, allowing it to melt and be absorbed into the soil. 

What if slow water interventions were deployed widely across the West? Could they heal the land-water relationship and reverse desertification? “Yes,” Norman says, without hesitation.

But there’s more to the Hopis’ resilience than a series of slow-water techniques, Johnson says. “It’s about having a relationship with the environment in a place that you’ve been living for a long, long time” and about the associated cultural belief system.

Rather than trying to maximize production, Hopi growers read the landscape to see what is possible for nature to provide that year. The timing and quantity of springtime vegetation serve as “biological indicators,” Johnson says. He notes that Hopi women select plants for certain traits and keep many varieties of seed for different annual conditions. “We’ve had 200-year droughts in our history. Our place is a testament to our resilience.”

Because traditional ecological knowledge doesn’t conform to Western science’s norms, the latter has been slow to recognize it as legitimate. Johnson counters, “When you have 3,000 years of replication, that is a science.” 

Making a convincing argument

Norman, whose expertise lies in forestry, watershed management, and remote sensing, agrees strongly with Johnson’s sentiment. But she realized that nature-inspired structures, whether built by Indigenous peoples or permaculture-minded land owners such as Clark and Austin, would not be recognized as a legitimate strategy by some unless their benefits were measured according to the Western scientific method. “My science is meant to address these misconceptions about the structures,” Norman says.

She has now dedicated a decade to leading the USGS Aridland Water Harvesting Study. Her work, with geomorphologists, biologists, botanists, and hydrologists, has proven that small stones and other natural materials placed across streams can restore and create permanent wetlands, regrow plants, store carbon dioxide, reconnect streams with flood plains, recharge groundwater, and increase stream flow. 

Norman grew up in Rhode Island, then moved west to Oregon for college and on to Arizona for graduate school. She first encountered rock detention structures when researching her Ph.D. dissertation, which used satellite data and flood modeling to make sense of environmental justice impacts from poor land management in Nogales, Mexico, and its twin city in Arizona. Erosion was releasing fine particle dust into the air, resulting in human health problems; flooding was endangering people; and heavy sediment loads were causing sewers to overflow. While working with the International Boundary and Water Commission to identify locations where structures could help address these problems, she became fascinated by the way small changes to the terrain could alter water flow and ultimately the shape and character of the land. 

Black bear swimming in water hole in Chiricahua Mountains
A black bear enjoys a cool dip in a watering hole fed by a gabion in the Chiricahua Mountains. Camera traps have caught many species visiting these slow-water features. Jan Schipper / Arizona State University

Not long after, Norman heard rumors of an oasis in the Chiricahuas. Intrigued, she visited El Coronado Ranch after a rain. The rock structures detained huge pools of water, keeping the washes running. “Seeing that with my own eyes was mind-blowing,” she says.

To measure the effects, she compared a tributary of Turkey Creek with neighboring Rock Creek, which had no rock structures. Using modified stream gauges and precipitation measurements, she found that the subtle barriers reduced peak flows from summer monsoons by half and extended base flows into fall by three to four weeks. The check dams kept more water in the system, resulting in that incredible 28 percent increase of water flowing downstream. What’s more, they captured 200 tons of soil per year, cleaning the water of sediment and supporting verdant vegetation that attracted animals. 

Norman explains why there was more water in the treated stream. In contrast to Turkey Creek’s series of wetland sponges, Rock Creek has bare bedrock. “When water runs over an impervious surface and is exposed to elements, it evaporates,” Norman says. Compacted and dry soils also repel water, or become hydrophobic—“scared of water.” But when barriers make the life-giving liquid linger, it can permeate the soil.

“A lot of practitioners and ranchers were of the opinion that they were able to create more water [with rock detention structures],” says Norman. “But to be able to document that was amazing. More water storage and more water availability for everything, to reverse that degradation cycle into a restoration cycle.”

Pulliam, who has collaborated with Norman on some of her papers, says her scientific rigor has led to wider acceptance of these practices. “Early on, even at USGS, people were skeptical. But as evidence accumulated, they began to see Laura as a really innovative scientist,” he says. “Like Valer, she persisted through a period where no one had much faith in [the structures’] efficacy.”  

In 2021, the American Water Resources Association awarded Norman a medal of excellence, saying her “research is the foundation of a burgeoning community of practice and a shift in policy implementation in the arid Southwest.”

Desert oases

Studies from atmospheric scientists have found that, in the Colorado River basin, the warmer climate is creating a thirstier atmosphere, which could evaporate more water out of the soil and plants and sometimes turn snow directly to water vapor. They predict that Colorado River flows could be 20 to 30 percent lower by 2050, meaning state negotiators of the river’s sharing agreement should be planning for even less water than they have today.

But Norman and other experts studying water cycle restoration assert that it’s not just climate change making the West drier. People have also dried out the land over the last two centuries by killing beavers, cutting forests, overgrazing grasslands, and cutting off rivers from their flood plains and wetlands with levees, channels, and diversions. What if slow water interventions, including Natural Infrastructure in Dryland Streams, were deployed widely across the West? Could they heal the land-water relationship and reverse desertification?

“Yes,” Norman says, without hesitation.

In a paper published last fall, Norman and co-authors reviewed many studies that support the claim of region-wide restoration being able to counteract desertification. One reason is that NIDS create localized humidity and cooling. In a park in Phoenix, Norman found the air is up to 3 degrees Celsius cooler around structures for two days after a rainfall. 

Another reason is that about 40 percent of rain over land, on average, is formed from evaporation from soil and transpiration from plants. With forests cut, grasslands overgrazed, soil compacted, and more wetlands and flood plains paved over, that moisture is missing from the Colorado River’s water cycle. 

To undo part of the damage, slow-water projects need to be distributed throughout water basins, not centralized. The interventions are typically small, but their impact on flood protection, water storage, and localized cooling is cumulative, much as how solar panels on many roofs can generate a lot of electricity. “The whole Colorado River basin, plugged full of structures?” says Norman. “At that scale, you’d see a regional response that might impact the climate by sequestration of carbon and by cooling of temperatures from bringing moisture back into the atmosphere.”

These changes also support wildlife, providing critical refuges for animals native to the Sky Islands, one of the most biodiverse regions in North America. Supporting an array of animals—Gila monsters, black bears, mountain lions, ocelots, bobcats, coatis, javelinas, foxes, deer—is part of Cuenca Los Ojos’ mission and what drives Clark to heal land and water. “The horny toad [or horned lizard] squirts blood out of its eyes to scare you. There are just so many delightful creatures in the region.” The fact that she thinks blood-squirting eyes are delightful epitomizes her enthusiasm for everything she encounters on the land.

Scientists, including Pulliam, have been documenting the return of wildlife. They even recorded an endangered jaguar near the rock structures at Cienega Ranch, a site in the Aridland Water Harvesting Study.  “Because there’s water, the animals come,’’ says Norman.

One critter they’re tracking is famous for building its own infrastructure in water. Beavers have returned to southern Arizona after trappers wiped them out 150 years ago. They’ve also been found on Clark’s ranches in northern Mexico. “Beavers won’t settle in desiccated areas,” Pulliam says, “but if you provide seed areas where they can get established, they can gradually improve adjacent areas.”

The upwelling of a movement

Nature-based solutions are gaining ground worldwide, including in the US—incentivized by the Biden administration’s Infrastructure and Inflation Reduction acts. But they are still often dismissed as insignificant in the challenge of buffering human communities from flood, drought, and climate change. That attitude reveals a misunderstanding of the scale of human disruption to the water cycle, and therefore, the scale needed for projects like NIDS to repair that damage.

Because the federal government influences the way so much land and water in the American West is managed, it could make a monumental difference by embracing slow-water practices, says Clark. But while some federal employees support them, so far, it’s not part of the official policy at the Forest Service, Fish and Wildlife Service, National Park Service, or Bureau of Land Management. 

Still, the federal agencies are coming around, says Pulliam. One lightbulb moment came after wildfires roared through the Chiricahuas about a decade ago. “Watersheds with rock structures had much, much less damage, and the Forest Service started noticing,” Pulliam explains, adding that the department is now giving contracts to Cuenca Los Ojos and Borderlands Restoration to build structures on its land. Overall, however, he says the US government retains a bias for modern engineering in its funding. State agencies, on the other hand, are much more open to NIDS. “They all buy in. They see it. It’s in their backyard.” 

Local Indigenous communities have shown what close attention to nature’s ways can yield. “Water is really life to us,” says Johnson, the Hopi farmer, contrasting that attitude with the dominant society’s view that water is a commodity. “People are so far removed from the relationship that we have with water that they just don’t understand the complexities, and they keep making the same mistakes over and over again.” 

Maybe we can improve our relationship with water, as individuals like Johnson, Clark, and Austin demonstrate how to heal water systems, and scientists like Norman and Pulliam document the intricacies of how they work. In response to water scarcity in the Southwest, many people think the answer is to bring in more from elsewhere via dams, aqueducts, and desalination plants. But slow-water practitioners make the most of the water that’s already there. Norman recalls a local saying, half-jokingly, “Ah, that would be great if there were some magic water that just appeared!” When she started studying ecosystems benefiting from slow-water techniques, “I was like, I think we found some, you know?

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