Two-Stage Drainage Ditch
University of Minnesota researchers inspect two-stage drainage ditch near Adams, Minnesota.
The Nature Conservancy announced today that it has completed the first two-stage drainage ditch in southeast Minnesota to demonstrate how they can reduce erosion, improve water quality and wildlife habitat, and lower maintenance costs.
The Conservancy’s two-stage drainage ditch is located on private property near Adams, Minnesota. Site visits can be arranged through the Conservancy’s office in Preston, Minn. Contact Rich Biske at (507) 765-2450 for more information.
Farmers have been draining their fields for generations using conventional ditches that are wide and deep, capable of conveying even very large volumes of water that occur only rarely during major rain storms. Unfortunately, the steep sides of these ditches are easily eroded, causing them to transport soil as well as water from agricultural lands. Nutrients are easily transported too, and the resulting mix of sediment and fertilizer can make for degraded waters downstream.
A two-stage ditch offers a simple remedy: vegetated “benches” that are added to each side of a ditch, mimicking the floodplains that occur naturally along streams. The benches make the sides of a ditch less steep and more stable, and the vegetation helps absorb water during periods of high flow and can filter nutrients from run-off as well.
It’s not a new design, but it’s relatively new to Minnesota. Two-stage ditches were first tried in Ohio and are now extensively used in that state and Indiana.
“It’s not just about clean water,” says Rich Biske, the Conservancy’s Southeast Minnesota conservation coordinator. “It’s also cost-effective. Because there is less erosion, farmers need to clean out their ditches half as often – possibly only once every twenty years. This is a low-tech, common-sense approach that is becoming accepted practice in other Midwestern states.”
The two-stage ditch was completed as a result of collaboration between the Conservancy and several partners. Cargill and General Mills provided funding. The Conservancy also received a Conservation Innovation Grant from the Natural Resources Conservation Service. Evaluation, engineering and monitoring expertise was provided by the University of Minnesota, the Minnesota Board of Water and Soil Resources, and the Minnesota Pollution Control Agency. The Mower County Soil and Water Conservation District helped with outreach to landowners.
“There is a lot of interest,” adds Biske. “Everyone uses drainage ditches and this is the first real change in their design in at least a hundred years.”
“The two-stage ditch is just one of the innovative ideas that we want to use in watersheds that include agricultural lands” concludes Biske. “It’s a method that keeps rivers healthy for fish and other wildlife, while helping farmers improve their bottom line. That can have a tremendous impact, all the way down the Mississippi to the Gulf of Mexico.”
The two-stage ditch will be monitored to evaluate its effectiveness.
“Two-stage ditches have the potential to reduce both the maintenance costs to farmers and the loading of sediment and nutrient from agricultural lands,” said Bruce Wilson, a professor in the University of Minnesota’s Department of Bioproducts and Biosystems Engineering.
“Research on the performance of these design has been conducted in other states,” Wilson added. “Although these results show great promise, we need to evaluate their performance under Minnesota conditions. We have generally drier summers and have longer and colder winters. 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.”
The Nature Conservancy is a leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at www.nature.org.
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