Researchers offer a new idea for ditches

By Heather Thorstensen, Associated Press

Adams, Minn. (AP) - When was the last time you saw a ditch look any different than, well, a ditch?

Water drains in, then drains out.

A new research project in rural Adams will study how tweaks in ditch design affect the amount of sediment and nutrients leaving it. Known as a two-stage drainage ditch, it's said to be the first of its kind in southeast Minnesota.

Project leaders refer to the key change as the "benches." They are 10-foot wide, flat areas on both sides of the water channel at the bottom of the ditch. These are seeded with native grasses, flowers, rye and oats. When water drains in the ditch and travels over them, the vegetation acts as a filter, using nutrients in the water to grow.

The benches make the ditch wider, plus the sides of the ditch are less steep to provide more stabilization. It's about 60 feet wide from the top of the bank on one side to the top of the other. It's hoped the gradually sloped banks cause less erosion and less maintenance costs of keeping the ditch clear.

The Nature Conservancy, a partner in this project, expects the two-stage ditch to perform similarly to those in other states. They're used in Indiana and Ohio.

Rich Biske, the conservancy's southeast Minnesota conservation coordinator, said Indiana's ditches reduced nitrogen by 20 percent and caused the water to look significantly clearer. Eventually, the project will also look into phosphorus reductions. It will take at least three years of monitoring to know how much the ditch reduces nutrients, Biske said.

The benches will help reduce water speed in times of high flow. Any overflow will spread over the flat space and slow down.

Dairy farmer Randy Smith is one of three landowners involved. His land draining to the ditch is used to grow corn and alfalfa.

The ditch takes up more room than it used to, he said, but that's not a problem if it works. The old ditch was prone to erosion. He likes that the new design should be more stable and able to hold more water.

"I think it's a great idea," he said.

Bruce Wilson, a professor in the U of M's bioproducts and biosystems engineering department, said it's important to test how the design works under Minnesota conditions.

"We will be monitoring the stability of the two-stage ditch and evaluating the removal of nutrients within our test reach. These results will be compared to traditional ditches using data collected by the Minnesota Department of Agriculture," Wilson said.

This project also incorporates new ideas. The researchers are trying out a new inlet design by making surface water flow through rocks to hopefully reduce sediment and phosphorus. They've also incorporated a trench filled with rocks, not connected to any water source, to see if this helps prevent seepage forces that could otherwise make the banks less stable.

Another tweak is they've connected some tile inlets to a small ditch on the benches. Water runs through the small ditch, giving vegetation more time to filter it before water enters the channel.

The University of Minnesota, Minnesota Board of Water and Soil Resources and the Minnesota Pollution Control Agency are involved with evaluating, engineering and monitoring the ditch. The Mower Soil and Water Conservation District helped get landowners involved.

Construction took a month and was completed the first week of November. The project cost $200,000. Funding was provided by Cargill, General Mills and a grant from the Natural Resources Conservation Service. ---

Information from: Agri News, http://www.agrinews.com/

(Copyright 2010 by The Associated Press. All Rights Reserved.)

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