In the right places, flood irrigation might be doing more good than harm
By Emily Downing
Every spring, Chris Williams looks forward to seeing the terns alight on the meadows of the southern Wyoming ranch that he manages. It’s a fleeting sight—the birds are there for one day and then they’re gone, off to breeding grounds further north. However brief, the terns’ stopover on the ZN Ranch is an essential part of their migratory journey, as it is for the dozens of other species Williams sees every year.
“We provide this edge of green right in the middle of the sagebrush, which is important for a lot of animals,” Williams says. “Our irrigation isn’t just about waterfowl and wading birds, but it’s that edge habitat that supports deer, elk, antelope, sage grouse—all of it.”
The ZN Ranch, like most other ranching operations in the Upper North Platte watershed, relies on a system of dirt ditches dug by hand in the 1880s to sustain that edge of green. In the spring, when tributary creeks are running high, the ditches divert water and spread it over the floodplain to grow lush grass that will be cut for hay. In the face of a drying western climate, ranching operations that use flood irrigation to grow food for livestock have come under fire for taking too much water out of streams and rivers. But new research is showing that flood irrigation in certain places does so much more than grow hay—it might just be the glue holding western ecosystems together.
As the West’s water resources are stretched thin, policymakers and the public are calling for increased irrigation efficiency on agricultural land to reduce one of the highest demands on water in the West. The reasoning goes that flood irrigation—where water is spread out over a field and left to slowly saturate the soil—is inefficient because much of the water that’s diverted is “lost” to seepage and evaporation, rather than directly supporting growing plants. Conversion to center-pivot sprinklers, lined canals, and other irrigation methods intends to minimize these losses while ensuring as much water as possible goes to crop production. As a result, federal programs that fund irrigation infrastructure upgrades are prioritizing the conversion to drip or pivot sprinkler irrigation systems.
But this calculated way of thinking about crop production doesn’t account for the interconnected pathways that water follows as it moves through a healthy watershed, supporting aquifers, fisheries, and wildlife along the way. Specifically, flood irrigation that happens along historic river floodplains can provide a slew of benefits beyond agricultural yields.
Before rivers became highly regulated and channelized, floodplain meadows served as sponges, soaking up the spring runoff that topped the creek’s banks. Beaver dams and other diversions slowed the fast-moving snowmelt, spreading it over low-lying meadows and saturating everything. The flooding formed temporary wetlands that provided habitat for migratory waterbirds and food for big game animals. Later in the season, when river flows were low, water that wasn’t absorbed by the plants growing along the floodplain returned to the waterway’s main channel, helping keep it flowing and functional.
Today, the dirt ditches used by Williams and his neighbors along the banks of Pass Creek mimic these natural flooding cycles, sustaining ribbons of green that provide outsized value for wildlife and human communities. A 2024 study published in Agriculture, Ecosystems, and Environment found that although flood-irrigated floodplain meadows are only 2.5 percent of the Intermountain West’s irrigated footprint, they provide 58 percent of the region’s temporary wetlands (shallow wetlands that exist for fewer than two months each year) and 20 percent of seasonal wetlands (wetlands that remain wet between two and six months each year).
Both wetland types are needed by waterbirds and waterfowl at different stages of their lifecycle, from nesting and breeding to fueling up during migration. Patrick Donnelly, a spatial ecologist for the Intermountain West Joint Venture and the US Fish and Wildlife Service who led the research, says that without flood irrigation practices, many of these wetlands would vanish, creating massive habitat gaps for migratory birds. (Disclosure: the author is employed by Intermountain West Joint Venture.)
“These sites are often invaluable because they’re putting water in the right place at the right time of year to provide the right kind of habitat for the birds moving through the area,” Donnelly says. “When they dry up, due to infrastructure conversion or maybe even the loss of the agricultural operation to development, the flyway becomes increasingly fragile.”
Emerging research also suggests that flood irrigation can provide other benefits by saturating soils and feeding groundwater supplies, although there is still much to learn about how surface and groundwater are connected. Frontiers in Environmental Science recently published one such study on the Henry’s Fork River in Eastern Idaho, an important fishery at the headwaters of the Snake River.
Christina Morrisett, the lead author of the research, says that from 1978 to 2000, many agricultural producers along the Henry’s Fork converted from flood irrigation to pivot infrastructure. As expected, surface water diversion from the river decreased by 23 percent over those years, meaning operators were taking less water out of the river. However, return flows to the river also decreased significantly. That’s because when irrigators change to a system that sprinkles or drips small amounts of water onto crops, it waters the crops and nothing else. “You’re probably not putting anything back into the system,” says Morrisett. The end result was that there was less water in the river after the conversion than there had been before.
In contrast, Williams points out that the irrigation water he uses is recycled multiple times as it moves downstream. After helping plants grow, the “excess” water from flood irrigation infiltrates the earth and can make its way back to the river, creek, or aquifer and continue downstream for future uses. “My upstream neighbors turn it out and put it on their fields and then it goes back into the creek and I’ll pick it up and irrigate with it again and again,” he says. “That water will get used four or five times before getting back to the creek.”
Morrisett says that’s one reason why operations located higher up in watersheds might be the most important places to maintain traditional flood irrigation practices. There, irrigated meadows in the floodplain can soak up and slowly release water for wildlife and downstream users across the growing season. “Water flows downstream, so whatever isn’t used high up can be recycled by someone else,” she says.
As communities of the West make difficult decisions about water, science that pinpoints where irrigation provides multiple ecosystem services will be increasingly helpful. Further research into how water moves through watersheds and affects groundwater supplies and aquifers—and how human actions influence both of those things—will also be important.
In the meantime, supporting farmers and ranchers like Williams who use flood irrigation high in the watershed is an easy way to bolster resilience and preserve critical habitat in the West. Funding federal and state programs that enable producers to continue doing what they’re already doing, on a relatively small percentage of private land, will have outsized impacts on preserving watershed function—and key habitat—in the places where it counts. That way, the terns (and the sandhill cranes, the warblers, the mule deer, the pronghorn, and the elk) have somewhere to return to next spring, and all the springs in the future.
Emily Downing is the Water 4 Communications Specialist for the Intermountain West Joint Venture, a regional public-private partnership that conserves habitat for the benefit of priority bird species, other wildlife, and people. Her role involves producing media that tells the story of emergent wetland habitats on public and private lands in the Intermountain West. In her free time, she is outside with her husband and dogs exploring the mountains and sagebrush around their home in Polaris, Montana.
Header image: A field in Utah’s Upper Bear River Watershed is flood-irrigated to produce grass hay. Flood irrigation in historic floodplains higher in watersheds can create a sponge effect that slowly releases water back into the waterway over the course of a growing season. (Intermountain West Joint Venture)
