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Home > Protecting Our Lands & Waters > Clean Water Fund > Clean Water Research Program > Controlled Drainage

Controlled Drainage and Bioreactor - Research & Demonstration Site

Principal Investigator: Ashley Brenke
Co-Investigator: Rich Perrine
Organization: Martin Soil and Water Conservation District
Sponsor: Clean Water Fund
Award Amount: $119,396
Start Date: 5/15/2012 | End Date: 6/30/2016
Project Manager: Heidi Peterson

FINAL REPORT is available in the Minnesota Water Research Digital Library


This project analyzed the impact of conservation drainage practices on water quality. Samples were collected from subsurface tile drainage. The fields used in this study were located adjacent to Elm Creek within Martin County, Minnesota. At the time of study the creek was listed as impaired for turbidity, fecal coliform, and fish index of biological integrity. The presence of elevated nitrate levels in surface water samples collected throughout the county had also been well documented. This project evaluated the water quality effects of two conservation drainage practices including controlled drainage and woodchip bioreactors.

Project Goals

  1. Learn more about the impact of conservation drainage on crop productivity and water quality.
  2. Establish a demonstration site for controlled drainage, which will become a useful resource for field days.


Conservation drainage refers to several emerging technologies and methods that provide the benefits of conventional agricultural drainage (namely, removal of excess water from fields) while reducing nitrate and other potential pollutants carried via drainage water to nearby waterways.

Controlled Drainage

Controlled drainage uses an in-field water level control structure installed on subsurface drainage to allow the water table to be adjusted at any level between the ground surface and the drainage depth. This structure can hold water in the field and prevent excess drainage.


A bioreactor consists of a trench filled with woodchips where enhanced dinitrification can occur. The subsurface drainage water flows through inlet and outlet water level control structures, which are used to adjust the amount of time that water is held within the bioreactor and in contact with beneficial microorganisms. Organisms from the soil colonize the woodchips. Some of them break down the woodchips into smaller organic particles. Other microorganisms “eat” the carbon produced by the woodchips and transform the nitrate from the water into nitrogen gas, which exits the bioreactor into the atmosphere.

This system is commonly installed at the edge of a field and been shown to reduce the amount of nitrate transported to surface waters.



The study site is in Section 5 of Center Creek Township in Martin County. 

The project took place on an operational farm where two adjacent fields were recently tiled. The first field had a controlled drainage structure and a bioreactor. The second field had a bioreactor installed but no controlled drainage structure. Martin County Soil and Water Conservation District monitored at multiple locations, including:

  • At the controlled drainage structure (bioreactor inlet, Field 1)
  • At the bioreactor outlet
  • At the conventional drainage bioreactor inlet (Field 2)
  • At the outlet of the second bioreactor
  • Upstream and downstream monitoring on Elm Creek, which is located nearby

Water samples were collected during high flows and base flows. The controlled drainage structure and bioreactors were installed in the fall of 2012. Sampling began around March 15, 2013 and continued until the end of the growing season. From April until June, samples were taken at least every week. Automated equipment collected samples whenever runoff occurred.

Water samples were analyzed for nitrate, total phosphorus, ortho-phosphorus, total suspended solids and total suspended volatile solids.

This site provided value information about the cost, installation and maintenance of conservation drainage practices on a working farm. 


  • Established a demonstration site for controlled drainage, a useful resource for field days
  • Established an engineering plan and organized the contractors 
  • Installed tile line, bioreactors and water monitoring equipment
  • Collected water samples in calendar years 2013, 2014, 2015
  • Compiled water quality results
  • Compiled crop productivity data
  • Hosted two field days
  • Created educational materials

 MDA Contacts 

Margaret Wagner
Supervisor, Clean Water Technical Unit