Oxbows Restored in Central Iowa
Polk County is getting a renovation in a big way — oxbows across the county are being restored thanks to a Water Quality Initiative (WQI) grant from the Iowa Department of Agriculture in partnership with the Nature Conservancy and Polk Soil and Water Conservation District.
Oxbow restoration is a relatively new conservation practice that uses the natural landscape to remove 40 to 90 percent of nitrates in the water. Oxbows can also help with flood control.
“Oxbows are essentially disconnected stream meanders,” said John Swanson, a Polk County conservationist. “Over time, these wetlands fill with sediments and get degraded. It happens naturally, but in Iowa it happens a lot more rapidly because of runoff in urban areas and erosion in agricultural areas.”
Restoration of oxbows involves excavating the area down to the same depth as the adjacent stream channel to allow the constant flow of groundwater. A small connection to the stream is also made on one end of the oxbow to store floodwater. Along with the water quality and quantity benefits these restorations create, they also provide essential habitat for wildlife, including birds and fish.
The Nature Conservancy conducted a fish assessment on the oxbows it restored almost one full year after excavation. The report showed 1,900 fish and 23 different species residing in the oxbows, proving that these restorations support water quality and biodiversity.
“The oxbows themselves serve a lot of different functions,” Swanson said. “Oxbows are natural wetlands, which is a little different than a constructed stormwater wetland. We are restoring these natural structures.”
Within Polk and Dallas County, five oxbows were restored in early 2018, thanks to partnerships with the City of Urbandale, City of Clive, Walnut Creek Watershed Management Authority and Polk Soil and Water Conservation District. There are currently oxbow restoration projects in Johnston, Des Moines, West Des Moines, Clive and Ankeny, many of which are located in city parks.
