Oxbows: What They Are And How to Restore Them

An area oxbow before restoration, in 2011 [photo courtesy of the Nature Conservancy]

Before modern agriculture, most of where we now live were wetlands, a common feature of which were twisting river bends known as “oxbows.”

Part of the consequences of the current agricultural landscape – and how it interacts with the old geographic one – is extensive nutrient runoff, which can be reduced by bringing oxbows back. Partners associated with the Boone River Nutrient Management Initiative (discussed in the Monitor’s March 6 issue) have secured funding for restoring five.

“Basically it’s where the river used to flow, but the river changed course and a channel was cut off,” said Karen Wilke, Boone River project director with the Nature Conservancy in Webster City. “We re-connect it a little bit to make a wetland that provides a year-round wildlife habitat, water filtration of pollutants, and floodwater storage.”

Quantifying a lost landscape, The Conservancy, Natural Resources Conservation Service, and other partners have identified 158 potential oxbow restoration sites in the nine sub-watersheds they’ve thus far explored of the Boone River’s total 29.  “The first step is looking at GIS aerial photos to identify those old meanders that were lost,” she said. “Then we go out and ground-truth it. “

The Conservancy and partners have acquired grants to fund restoration of five oxbows over the next two years, four through the National Fish and Wildlife Foundation and one through Coca-Cola’s Replenish program. The restoration efforts are related to the larger Boone River Watershed Nutrient Management Initiative – which held a kick-off meeting at Hagie Manufacturing Feb 28 – one of eight statewide grant-funded programs with a goal of reducing nitrogen and phosphorous runoff by 45%.

Restoration involves digging to the original riverbed, a mix of gravel and groundwater about three to five feet underground. The old bends were lost to deliberate re-channeling, indirect consequences of agriculture, and natural shifts in the river’s flow.

Five previous oxbows constructed along White Fox Creek with the help of the Conservancy and its partners can hold 3.7 million gallons of water, and have reduced the nitrates that flow through them by an average of 45 percent.

“The landowner does not need to fund anything up front,” Wilke said of the current opportunities through the grant. “The only thing they need to take care of is all the soil being excavated, and to write an agreement that they’re not going to do anything different with that land for 10 years. Typically, the oxbow restorations are in marginal lands not producing corn or soybeans.”

It costs between $10,000 and $12,000 to restore a half-acre-sized oxbow.

Those interested in more information on grant-funded restorations and oxbows in general may contact Emily Funk, coordinator for the Boone River Initiative at Prairie Creek, at 295-5156, ext 199, Emily.funk@ia.adne.net, or Wilke at 832-2916, kwilke@tnc.org.  

Read more – and see more photos – in the March 27 issue of the Monitor!