Drainage Designs & Practices

SHALLOW TILE DRAINAGE is the installation of porous drainage pipe at a depth of approximately 3 feet as compared to the more conventional 4-foot depth. Shallow drainage has been shown to reduce drainage water volume and amount of nitrate in drainage water by 15 to 25%. Shallow drainage may also make more water available to crops.

CONTROLLED DRAINAGE uses control structures on drainage pipe to hold the water back to adjustable levels during the year. Controlled drainage has been shown to reduce drainage water volume and amount of nitrate in drainage water by 25 to 40%. Controlled drainage may also make more water available to crops.

WOODCHIP BIOREACTORS can be used to remove nitrate from drainage water. The bioreactor consists of a trench filled with woodchips through which the drainage water is allowed to flow. Ten feet of bioreactor per acre of drained land may be able to remove 30 to 100% of the nitrate from drainage water.

STORAGE BASINS that capture and hold runoff and drainage water can be used to reduce peak flows and improve water quality. Basins can be managed as "dry" basins that are used for cropping or can be kept "wet" with wetland type vegetation that provides wildlife habitat and water treatment.

IN-DITCH TREATMENT can be enhanced by designing drainage ditches to reduce bank erosion, trap sediment, and remove nutrients such as nitrate from drainage water.

WATER TREATMENT BASINS placed to either receive and treat water before it enters ditches or at strategic locations along ditch systems can be used to settle out sediments and treat nutrients and contaminants. Different treatment basin designs are being evaluated.

DRYLAND STORAGE areas can be used in some flatter landscapes to hold water during large runoff events and still be used for cropping or pasture during drier periods. The function of capturing the water and releasing it slowly provides the same sediment and nutrient reduction benefits as many of the other practices.

ROCK INLETS can be used instead of surface inlets in many locations, removing an obstacle in the field and reducing the amount of sediment carried by the drainage water.

MDA Contacts

Mark Dittrich
Senior Planner, Conservation Drainage
Mark.Dittrich@state.mn.us • 651-201-6482