Scientists studied a stretch of the Gila River — a tributary that feeds into the Colorado River — for more than a decade. They found that even during very low flows, its floodplain can continue to support native cottonwood and willow trees.
The key, researchers say, lies in the river’s natural complexity.
During large floods, the river spreads out and carves a network of side channels across the floodplain. Those channels help store and move water underground, allowing plants to access moisture even when the main river runs low.
“Let's manage rivers to promote their health and function, and that's retaining the flows, giving them space, so when there are floods, they can spread out and do good work,” said Martha Cooper, a scientist with The Nature Conservancy and a co-author of the study.
The research draws on more than a decade of data tracking groundwater, vegetation and river flows in southwestern New Mexico. It shows that even relatively small, steady flows can sustain riparian ecosystems as long as groundwater levels don’t drop too quickly.
That’s especially important for young cottonwood and willow trees, which rely on stable groundwater as they take root.
But the study also highlights a key vulnerability.
In areas where water is diverted for agriculture, groundwater levels can fall rapidly — sometimes fast enough to threaten young plants during critical growing periods.
Even so, researchers found that some human water systems can actually help. Seepage from irrigation ditches and return flows can keep groundwater levels high enough to support vegetation in certain areas.
That points to a more nuanced picture, one where rivers and agriculture don’t have to be in conflict.
“If we can work to manage rivers to maintain their health, they'll meet our needs better in terms of moving sediment for us, moving water for us, providing habitat that supports wildlife,” Cooper said.
Because the Gila feeds into the Colorado River, the findings of the study could have implications across the Colorado River Basin and the broader Mountain West, where climate change is expected to bring more intense drought and more extreme floods.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
