What is drainage water management?

Drainage water management is the practice of using a water control structure in the main, submain, (or sometimes lateral) drain to raise the drainage outlet to various depths. This allows farmers to have more control over drainage. The outlet or control structure shown in the figure above is:

  • Raised after harvest until early spring to limit drainage outflow and reduce the delivery of nitrate to ditches and streams during the off-season. (Figure 1)
  • Lowered so the drain can flow freely before field operations such as planting or harvest. (Figure 2)
  • Raised again after planting and spring field operations to create a potential to store water that could be used by the crop in midsummer. (Figure 3)

Potential Yield Benefits: With proper management of the structures and timely rainfall, the potential exists to improve crop yields beyond the typical crop response to drainage. However, results from field research on the agronomic benefits of the practice are very limited and inconclusive.

Demonstrated Water Quality Benefits: Published studies have found reductions in annual nitrate load in drain flow ranging from about 15% to 75%, depending on location, climate, soil type, and cropping practice. Nitrate load is reduced by about the same percentage as drain flow is reduced, since most studies have found little change in the nitrate concentration in the drain flow.

"Golden Rule of Drainage": Only drain the amount of water necessary to insure trafficable conditions for field operations and to provide an aerated crop root zone. Any drainage in excess of this likely carries away nitrate and water that is no longer available for crop uptake. --- Attributed to Dr. W. Skaggs

Understanding Drainage Water Management

dwmQuestions and Answers About Drainage Water Management for the Midwest - Regional extension publication by 10 specialists, answering questions about yield, soil and water quality, and system management. Also available in html format.

Drainage water management: a practice for reducing nitrate loads from subsurface drainage systems - Overview from the Mississippi Basin Symposium publication including potential and limitations.


Financial Incentives


Drainage water management is eligible for financial assistance through the NRCS Environmental Quality Incentives Program, and the Conservation Security Program for those who qualify. Amounts vary by state.


Water Quality Benefits


Drainage water management reduces nitrate loads from tile drainage systems that cause hypoxia in the Gulf of Mexico. Studies generally find reductions in annual nitrate load in drain flow ranging from about 20 percent to 50 percent, depending on location, climate, soil type, and cropping practice. In regions where much of the drainage takes place during the winter (such as Illinois, Indiana, and Ohio), the reduction is likely to be greater than where most of the drainage takes place in April or later, such as in parts of Iowa and Minnesota.