Groundwater modeling tool helps rural Colorado community make informed irrigation, water management decisions

Farmers near Meeker, in northwestern Colorado, have been diverting water from the White River to flood their fields for irrigation for more than 100 years. 

Using a series of irrigation ditches, they divert huge amounts of water directly to their crops rather than relying on more efficient sprinkler systems to get the job done. While the approach might seem wasteful, a new study led by Colorado State University researchers shows that about 75% of the water used in Meeker for flood irrigation eventually makes its way back into the river through groundwater recharge. 

The work also highlights how the community’s long-standing irrigation approach supports nearby natural wetland ecosystems that are central to wildlife habitat and recreation activity. 

The comprehensive model at the heart of the research was recently described in the Journal of Hydrology and is now being used to help inform water management decisions in the area. And while every river basin and community are different, findings from the study on the relationships between agriculture, groundwater systems and rivers are applicable to future planning for water rights and the potential for changes in climate that could impact water-storage needs. 

Professor Ryan Bailey led the published research through CSU’s Department of Civil and Environmental Engineering. He said the project started as a partnership with the White River and Douglas Creek Conservation Districts and has proven to be a small but solid test case to better understand the crucial hidden links among irrigation practices, a region’s water table and the timing of river flow as a part of the larger water cycle. 

“As we worked through this project, I realized just how dependent the White River is on this groundwater return flow that comes from flooding the fields,” he said. “Because of the extensive flood irrigation, the area is essentially saturated with water. That has elevated the water table over the years and has many implications for the region including directly impacting the timing of the river’s seasonal flows.” 

Groundwater recharge feeds White River  

Only about 25% of the water from flood irrigation systems is used to maintain crops as seen here, while the other 75% returns to the White River system in some way.

The study focuses on a 33-mile stretch of the river where water is diverted into a network of distribution ditches that then feed crop fields. The team combined data such as historic flow rates on the river as well as measurements of the water tables’ elevation in the area through review of groundwater wells. Additional information about the area’s geology — including soil types and their permeability — was also considered in the holistic model.

Bailey said about 20% of the diverted irrigation water seeps back into the aquifer through the ditch beds before it even reaches the field. The rest is either used by crops, percolates down through the soil into the aquifer, or runs off the field and into lower elevation areas before re-joining the river. All of this combines during the summer months to steadily recharge the region’s aquifer, where water is stored, eventually flowing to nearby riverbeds before re-entering the White River.

In practice, only about 25% of the water from flood irrigation is used to maintain crops, while the other 75% returns to the river system in some way. A sprinkler irrigation system, by comparison, would more efficiently support plant growth. However, the team’s model shows that approach would change the timing of the key seasonal river flows that are powered by groundwater recharge activity in the region.

Bailey said in the fall months, when the river flow should be extremely low, it is instead moderate because of the groundwater entering the river from the fields. These resulting late-season return flows are a product of irrigation that occurs during the summer and fall months. If sprinkler irrigation is instituted, he said, there might be higher river flow in the summer due to a decrease in ditch diversions, but then lower river flow in the fall and winter months due to a decrease in groundwater discharge to the White River. That could impact fish populations and downstream hydropower.

“The irrigation process keeps the water table high. That supports wetland development at the edges of the fields, along the ditches, and in the banks of the river that may not exist otherwise and creates a natural environment to store water for use later in the cycle,” Bailey said. “Our model shows how tradeoffs — such as a switch to sprinklers — would negatively impact these zones and lower the region’s water table by as much as 10 to 15 feet in some places over a five-year period.”

Bailey added that the model offers the community an opportunity to make informed choices on water management practices that will likely need to span years and may change if there was a drought or more requests for water to flow down river. He said he has created a simplified sheet for now, allowing stakeholders to work with the numbers to see how changes would impact water savings, crop yields and the downstream environment, among other variables.

Bailey said this research is broadly applicable to other communities that are looking ahead to understand how shifts in climate may change their agricultural and water management activities. He said the team is planning a similar project in the nearby Yampa River Valley and has also started talking to partners in southeast Wyoming. 

Bailey Franklin is a district wildlife manager with Colorado Parks and Wildlife in the area. He worked with the CSU team on the project and said the work illustrates how important flood irrigation practices are for maintaining springs and wetland habitats in both the upland and riparian corridor, which benefit many different species of wildlife. 

“Without flood irrigation many of these springs and wetland habitats would simply dry up, thus the indirect benefits of flood irrigation to the landscape and to wildlife habitat are often not recognized,” he said.

Ryan Bailey said service-based projects like this one that directly help Colorado residents are at the core of the university’s land-grant mission.

“I think as CSU faculty we have an obligation to help people in the state by developing accessible solutions to shared challenges like water management,” he said. “I was happy to give a little extra time in travel or attending late meetings for this project, which ultimately got support from the Colorado Water Conservation Board and the Colorado Water Center here at CSU. It was a rewarding project to be a part of.”