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Drainage on demand

DWM holds promise to expand across the U.S.


October 29, 2014
By Treena Hein

Topics
A DWM system allows for controlled drainage. An increase in the use of an innovative drainage system called “drainage water management” is being promoted by the U.S. Department of Agriculture’s Natural Resources Conservation Service in Illinois and other states in the region

An increase in the use of an innovative drainage system called “drainage water management” is being promoted by the U.S. Department of Agriculture’s Natural Resources Conservation Service in Illinois and other states in the region, as it provides significant benefits for both farmers and the environment.

Drainage water management (DWM) allows farmers to control the amount of water that’s drained from the top few feet of the field’s surface. A box-like structure is attached to existing drainage pipe near the field outlet, with a number of large thick bars that can be inserted or removed to control water flow. It is similar to controlled drainage systems being used in Ontario, which employ a round structure and vertically movable panels.

The DWM system provides a myriad of monetary and environmental benefits, from boosting crop yields to improving water quality of nearby watersheds through preventing nutrient run-off. “Farming is a risky business, subject to all kinds of influences like weather and global economics that are out of the producer’s control,” notes Dr. Ruth Book, an Illinois NRCS state conservation engineer. “With DWM, the farmer can decide when to drain the field and when not to. Think about how helpful this could be in a drought year, for example. If the producer knows that the summer is going to be hot and dry, he or she could hold back some of the water from the spring rains.”

DWM can be installed with both new and existing tile drainage, but the field should have a slope of less than one percent. If that sounds restrictive, consider that in the state of Illinois alone, DWM is suitable for use in nearly 10 million acres of fields. There are now 14 counties in Illinois that are targeted for DWM demonstration projects. Many installations have already occurred through technical and financial support from the Natural Resources Conservation Service (NRCS), and more are in the works.

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This year, NRCS sponsored a special DWM project in the 37 square-mile watershed around the town of Tovey in collaboration with the Christian County Soil and Water Conservation District. Book says the predominantly flat, tile-drained cropland in that area of Illinois is very suitable for DWM. “The partnership goal is to help producers implement DWM and related practices on at least 20 percent of the cropland in the watershed over the next five years, or approximately 750 acres per year,” she explains. “The expectation is that this achievement will demonstrate a measurable improvement in surface water quality entering nearby Sangchris Lake.”  

It goes beyond the lake, however. Fertilizer use in Illinois crops is a major contributor to the nitrogen load in the Mississippi River Basin. About 90 percent of the nitrate-N that’s discharged via the Mississippi River is due to agriculture, Book notes. Research has shown a definite correlation between tile drainage and high nitrate levels in surface water, and although there seems to be an apparent conflict between needing to drain fields for crop production and the need to reduce nitrates entering surface water, Book says DWM is a way to accomplish both. “During fallow periods, the water table is raised, creating conditions that are very similar to what the field was like before the drainage system was installed,” she says. “Also, the water table can be raised during the cropping season to retain water that would have otherwise drained away, potentially supplying water to the capillary root zone of the crop, but also reducing nutrient loading.” The effectiveness of DWM in reducing runoff is directly related to the volume of drainage water that is retained in the field, so operators are encouraged to keep the system closed, draining the field only when necessary to grow crops and do field work.  

Contractors, training and next steps
Book praises the Illinois Land Improvement Contractors Association as “a great partner” in the effort to spread DWM use. “Drainage contractors not only help us sell drainage water management and other conservation practices related to drainage, but they also are out there on the front line, actually installing,” she says. “Most drainage contractors already have the equipment they need to install drainage water management. Implementation is quite simple, usually involving just the addition of a water control structure at strategic places in the drainage system.”  

Flat fields can often be managed with a single water control structure, but Book says it’s possible to stair-step the DWM system to accommodate changes in elevation. She explains that when the field has more slope, it’s helpful to lay out the drainage system so farmers can manage the water table with the minimum number of structures. “We’ve had many drainage contractors attend training sponsored by the Agricultural Drainage Management Coalition and NRCS,” she explains, “where they learn how the drain system layout can be changed to facilitate DWM.”  

Illinois is part of the 10-state focus area in the NRCS Agricultural Water Management effort to spread the installation of DWM, but it’s the state with the longest history of DWM use and the one with the most suitable acres. Following in Illinois’ footsteps, some of the other nine states are offering financial assistance and considering the development of special regional DWM projects.

In a few years, Book believes Illinois District Conservationist Tony Hammond will be able to report a dramatic increase in the adoption of DWM in Christian County. “Tony and the staff at the U.S. Department of Agriculture field office in Taylorville have been publicizing the great things DWM can offer, and he’s beginning to show some results. Now that we have our conservation professionals trained on the practice, I think we’ll be seeing much more implementation of DWM all over the state.” With all the benefits provided by the system – and the strong support being offered – DWM is poised to become the standard on flat farmland in the U.S. and beyond.