New Study Identifies Simple, Scalable River Strategy to Boost Habitat Resilience in the West

As ongoing drought and heightened water demand continue to put pressure on Western rivers, new research by The Nature Conservancy  points to a straightforward solution: give rivers more room to move and sustain low flows.

A decade‑long ecological study of the Gila River found that secondary channels, which are small side channels formed during high flows, significantly improve conditions for native plants like cottonwoods, willows and other groundwater‑dependent vegetation. From 2011 to 2021, researchers collected groundwater, vegetation and topographic data along the river and found that areas near secondary channels consistently maintained shallower groundwater, critical for native plant survival during prolonged dry periods. Secondary channels proved especially important for young native plants. Even low and steady flows kept these zones viable for seedlings because the channels helped maintain shallower groundwater, bringing moisture close enough to the surface for native vegetation to survive their most vulnerable early growth stages.

“The Gila River supports a wide expanse of native riparian forest, even during long periods of low flow,” said Ellen Soles, an affiliate at Northern Arizona University and lead author of the paper. “It’s the floodplain’s complex topography that makes that resilience possible by storing and delivering water across the landscape.”

Although some stretches affected by irrigation withdrawals saw sharper groundwater declines, seepage from diversion structures and unlined ditches helped offset losses and sustain native vegetation.

“When rivers are connected to their floodplains, with adequate space to move, large and small floods move sediments, recharge groundwater and sustain native vegetation,” said Martha Cooper, TNC's Freshwater Program Director in New Mexico. "When groundwater levels remain high, they retain flows in our rivers that help native species thrive by outcompeting non-native species."

“This study highlights the importance of long-term datasets,” said Laurel Saito, a co-author on the study and water strategy director for TNC in Nevada. “Having data over periods of floods and droughts demonstrated the importance of shallow groundwater in this system, even with diversions for human use.”

The Gila is unique among Western rivers because it still retains extraordinary flow variability, including very large floods that continue to shape its channels and floodplain.

From the 1940s through the early 1980s, the Gila River was confined by levees and heavily altered, cutting it off from much of its historic floodplain and reducing native cottonwood and willow forests. By about 1960, the active floodplain had narrowed to less than half its original width, and by the 1980s, native floodplain forest cover had dropped to roughly half of what it had been earlier in the century. After channel‑engineering work stopped in the mid‑1980s and livestock were removed from most of the floodplain in the 1990s, the river began to rebuild itself. A series of large floods in the late 1980s and 1990s re‑formed secondary channels, reconnected flows across the valley floor, and restored the shallow groundwater conditions native plants need. By the early 2000s, the active floodplain had returned to near its historic width, and a new generation of cottonwoods, willows and other native species were once again established across the area.

“This study highlights the delicate relationships between streamflow, groundwater, and riparian plants,” said Dr. David Propst, adjunct professor for the Department of Biology at University of New Mexico. “It shows how critical natural flow patterns are to replenish groundwater and sustain vibrant riparian communities, giving valuable insight into how freshwater ecosystems function in arid environments.”