Trickle Down Theory

Monitoring the land for waterlogging and salinity factors

Colorado State University civil engineering Professor Timothy Gates, is standing in the middle of an irrigated field in Colorado's lower Arkansas River Valley. Off in the distance, he sees the classic lush and verdant landscape that for more than a century has defined this valley's rich agricultural heritage. But Gates knows this picturesque scene is deceiving. The salt-encrusted, waterlogged field in which he is standing, surrounded by stunted and wilted yellowish corn, could be the future of agriculture in this once productive river valley.

Irrigated since the 1870s, agricultural fields in portions of the Arkansas River Valley began showing signs of increased salinity and waterlogging as early as the 1920s. Irrigation-induced salinization is very common to intensively irrigated areas throughout the world. About 20 to 25 percent of the world's irrigated land, including up to 27 percent in the United States, is affected by saline high water tables. The threat to global crops is serious, with some scientists estimating worldwide productivity loss valued at $10 billion per year.

Salinity and waterlogging are coupled problems that typically show up within a few decades to a century after intensive irrigation begins in a river valley. When irrigation occurs at a rate that exceeds the natural capacity of the soil and the aquifer to drain the excess water back out toward the river, the water table starts rising. If it rises too close to the surface, the crops do not have adequate aeration to grow properly. Additionally, this water contains dissolved chemicals, some of which are salts. When evaporation drives the water up out of the water table into the atmosphere, high concentrations of the salts are left behind in the soil.

Another complicating factor is that some salts also are naturally inherent to layers in the subsurface profile. These salts are dissolved by excess irrigation flows, make their way to the river, and increase salinity concentrations in waters diverted for irrigation and other purposes further downstream.

Today, farmers in the Arkansas River Valley are seeing crop yield reductions that average about 10 percent, and in some areas are as high as 70 percent. Even those areas that on the surface seem unaffected are showing signs of increased salinity in the underlying soils and aquifer.

Gates believes the solution to the Arkansas River Valley's salinity problem can be found by documenting and studying the complex interaction of groundwater flow with salt transport, irrigation and drainage systems, and the flow of the river. He is joined in this current research effort by co-principal investigator Dr. John Labadie and Ph.D. student Phil Burkhalter in civil engineering and by other students and colleagues at Colorado State University.

Over the past three years, Gates has overseen the most intensive field data collection effort ever undertaken in the Arkansas River Valley or anywhere else. His research team has installed more than 100 monitoring wells, made thousands of groundwater and surface water measurements, conducted numerous tests of aquifer flow properties, and taken thousands of soil samples from about 100 agricultural fields in the lower valley.

This data is driving the development of computer models that will allow farmers and water and land managers to better understand the cascading network of interactions that lie at the heart of the salinity problem.

"The computer modeling allows us to use the local data to take a broad perspective and look at the multiple scales at work," says Gates. "We can see the interaction between processes that occur when a farmer irrigates his individual field, how that affects other fields in the subregion, and how that in turn affects what goes on in the entire river valley. "

As Gates and his colleagues enter the next phase of the research, that of finding viable solutions, economists, agronomists, soil scientists, sociologists, and perhaps even lawyers will play more of a key role on their team. Among the engineering interventions being considered are improvements to irrigation systems to boost efficiency and reduce recharge to the water table, lining of canals to reduce seepage, installation of horizontal subsurface drains and systems for managing drainage effluent, and alteration of river operations to lower the water level in the river. Because of the legal complexities involved with changing how water is moved, drained, and supplied in a river valley, Gates expects they will need someone very familiar with water law and appropriation issues.

Since the conditions in the Arkansas River Valley are broadly similar to those in irrigated alluvial valleys elsewhere, the U. S. Bureau of Reclamation, U.S. Geological Survey, USDA Natural Resources Conservation Service, USDA Farm Service Agency, Colorado Water Resources Research Institute, Bent County Soil Conservation District, and local irrigation canal companies are all working with Gates and his colleagues to learn more about salinity and its complex web of technical, legal, and social issues.

"It's formidable work, but it's also stimulating," says Gates. "We want to see a rural lifestyle continue to be built upon productive agriculture. We also want the overall environmental health of the Arkansas River to be enhanced. Hopefully, we can give insight and guidance that will help solve similar problems throughout the western United States and the world. "