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What Two Stage Ditches Accomplish in Farm Fields

What Two Stage Ditches Accomplish in Farm Fields
Researcher says it's a tool in the tool kit to help water quality.

Two-stage ditches are just what they sound like – ditches with the normal channel, plus a second stage. The second stage turns out to be a low, level area on either side of the main channel. Basically, they are narrow flood plains, making the total area where water can collect about three times wider than with a regular, single channel ditch.

Jennifer Tank, from the University of Notre Dame, has studied the effects of two-stage ditches on water quality, following seven two-stage ditches, ranging from one to 10 years old, and located in Indiana, Ohio and Michigan.

"A two-stage ditch is definitely a tool in the tool kit," she says. "It won't solve every problem, but it will help."

Two-stage ditch: This project to build a two-stage ditch was underway at the Throckmorton Purdue farm when this photo was snapped.

The key is to have the sides, the flood plain areas, be the right height compared to the ditch channel, she says. Sometimes people construct them at too high of a level compared to the channel, and they can't do their job properly.

Her studies indicate that the ditches work to reduce sediment load reaching another water body. Water floods over the second stage of the ditch, and sediment settles out. She also found that there was no difference in this regard in one year vs. 10-year-old two-stage ditches. It's a practice that needs virtually no maintenance, she says.

She has also compared different types of grasses seeded in the flood plain sides of the ditch. She has seen no difference in removal of nutrients between seeding with native prairie grasses, which can be more difficult and expensive, and seeding with cool-season, annual grasses. As long as the flood plains are built low enough, you won't get trees growing, either, she says. The areas flood too often, usually 12 to 14 times per year, for shrubs or woody species to become established. If the sides are too high and don't flood as often, then woody species might be able to survive.

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