The landscape of 53,000-acre Walnut Creek Watershed flows from the farm fields to the west into growing residential neighborhoods and business districts of the Des Moines Metro. The watershed touches eight communities and two counties, eventually draining into the Raccoon River less than one mile from the Des Moines Water Works intake for a public water supply serving nearly one-half million users. Because of these impacts, Walnut Creek has become a priority watershed for local jurisdictions to reduce flooding impacts and improve water quality.
In 2017, The Nature Conservancy partnered with Polk Soil & Water Conservation District to identify and fundraise oxbow wetland restorations in the Walnut Creek Watershed. Traditionally these oxbows are restored on the agricultural landscape, but as work began to identify sites along Walnut Creek several opportunities were found within natural areas in both Urbandale and Clive. After coordinating with local parks and community development staff, six oxbows were eventually identified and restored in late 2017.
An oxbow is a meander of a stream that has been cut off from the present flow of water. Over time oxbows fill in with sediment and loose the habitat and water quality benefits they once provided.
Restoring oxbow wetlands provide multiple benefits including improving water quality, reducing flooding, and improving wildlife habitat. Several oxbows in Iowa have been researched to quantify these benefits. Some of the findings include:
The restoration process for these oxbows is rather simple. During periods of dry weather, typically summer or fall, construction crews excavate out soil that has been deposited into the wetlands over time. Excavation continues until the historic riverbed depth is reached, typically finding a layer of gravel and reconnection to groundwater. This connection to groundwater is key to providing a regular source of oxygen, allowing fish to survive during low water. Once excavation is complete, banks are sloped back and revegeted.
This oxbow restoration was made possible by a collaborative effort between the City of Urbandale/Clive, The Nature Conservancy, Iowa Department of Agriculture and Land Stewardship, Natural Resources Conservation Service, and Polk Soil & Water Conservation District.