"This is one of only a few 2-stage ditches in the state, but we hope to see more," Biske says. So would county drainage inspector Cody Fox. "I like what I see so far," Fox says. "I think we'll have less sediment in the channel with flatter side slopes and the benches below. This should be good to go for years to come.
"There's been a lot of effort to get buffers planted at the field edge above the ditch, and that's good," Biske says. "But you can treat so much more area for nitrate reductions when you treat the tile water, too."
Betts writes from Johnston, Iowa.
Slow runoff with side inlet filters
The Mullenbach Ditch has one side inlet that's designed as a filter itself. Rather than using a large culvert that delivers surface runoff directly to the ditch, a vertical inlet was installed in a filter strip that first funnels water through a 20-foot wide bed of small rocks.
"Joel Peterson, an engineer with the Minnesota Board of Water and Soil Resources at the time, designed the filter," Biske says. "The purpose was to slow the runoff down, to hold it in the filter strip for a few hours.
So many of the water impairments we have are from flushing so much water off the land so quickly," Biske says. "If we can reduce peak flow and allow the soil to do some filtering, we can do a lot of good."
A filter system like this could apply anywhere a side inlet empties into a drainage ditch.