New field drainage systems designed to reduce flow of sediment, nitrates

WILLMAR -- New methods of draining water from farm fields are being implemented in Kandiyohi County in an attempt to reduce sediment and pollutants from getting into lakes and streams.

Biofilter near Willmar Senior High School
This biofilter was installed last year near the Willmar Senior High School. Water from a county tile system is intercepted and allowed to seep through a bed of wood chips in the biofilter to remove nitrates before the water is returned to the drainage system. (Submitted photo)

WILLMAR -- New methods of draining water from farm fields are being implemented in Kandiyohi County in an attempt to reduce sediment and pollutants from getting into lakes and streams.

The alternatives include biofilters, rock inlets, drop inlets and stream barbs.

The goal, said Kandiyohi County Drainage Inspector Loren Engelby, is to keep sediment and nutrients out of the water and "in the fields where they're needed."

Traditional farm drainage systems, like the ones used in the late 1800s when tiling of wet fields began in the state, are still being used, said Engelby. In that basic system, water is channeled through a network of underground tiles and then fed into a drainage ditch system, often carrying dirt and fertilizer with it as it empties into rivers and lakes

But Engelby, who manages about 850 miles of publicly owned drainage ditches and tiles in the county, said the county's management style is to "focus on water quality."


And with more rules and regulations likely coming in the future, he said "we need to take responsibility for these water quality issues in the ag community" and continue to make improvements.

As a result, he's been researching and using new techniques that still get the job done in the fields and reduce environmental damage downstream.

One of the newest methods that has Eneglby excited is an underground bioreactor that allows water to slowly filter through a bed of wood chips.

Research indicates these biofilters have the potential of removing 90 percent of nitrates from tile line water, said Engelby.

He installed the first one last year on a county ditch system south of the Willmar Senior High School.

During construction, about 30 cubic yards of woodchips were placed in a 7-foot-deep hole that measured 10 by 30 feet.

Water from the county tile is intercepted, allowed to seep through the woodchips where bacteria breaks down the nutrients and then discharged back into the tile system.

Engelby said he'll monitor the water quality to determine if nitrates are indeed being removed.


"I hope they work because I'd like them to catch on and do more of them," he said.

The Hawk Creek Watershed District paid for half of the $3,000 cost of the bioreactor, he said, and money from the county's water plan fund is paying for lab testing of the water.

Some of the other new controls he's implementing include alternative inlets where water goes from fields and into a tile or ditch system, including using a bed of stones near the inlet to filter out sediment.

A metal cage around a drop-inlet can prevent field trash, like corn stalks, from entering and clogging up the tile lines.

Open drainage ditches are also vulnerable to erosion.

Engelby has worked with contractors to place large rocks along the banks to create "stream barbs" that divert the current away from the sides of the ditch and into the middle of the stream.

Improvements to public drainage systems are paid for by the benefitting landowners. The percentage of the total cost they pay is based on the percentage of benefits their acres receive from the drainage system.

Kandiyohi County is currently in the process of re-determining benefits on eight drainage systems near Willmar, a process triggered by the city's wastewater runoff going to a different ditch system.


Once that analysis is done this summer, Engelby said the county will select another six to eight ditch systems to analyze for a re-determination of benefits until all the ditches have been viewed and benefits established.

Because most ditches haven't had benefit adjustments for 80 to 100 years, he said it's time to re-evaluate the ditch systems to make sure property owners are paying their fair share.

Besides the public drainage system, Engelby said there are five to 10 times more privately owned miles of drainage tiles in the county. Private landowners who are interested in using some of the new techniques can contact Engelby for information on research, installation and cost-sharing.

Although landowners have to pay for improvements on their private property, Engelby said area watershed districts do provide cost-sharing options.


Carolyn Lange is a features writer at the West Central Tribune. She can be reached at or 320-894-9750
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