The Fourmile Creek Stormwater Wetland in Des Moines is a man-made system engineered to filter pollutants and excess nutrients from urban and agricultural runoff before it reaches Fourmile Creek. By slowing water flow and detaining excess volume, the wetland helps reduce flooding and improve water quality. Its design includes a sediment forebay, shallow meandering channels, and a deeper pool, all working together to support pollutant settling and plant absorption. 

This project originated from several factors: Fourmile Creek has long faced stormwater challenges as it crosses the metro area, and statewide nutrient-reduction initiatives encouraged the use of wetlands to help mitigate runoff. The site itself was located in a floodplain where multiple homes had been bought out and demolished due to persistent flooding, leaving behind an abandoned neighborhood, vacant field, and areas where dumping had become an issue. As part of the effort, the former roadway was also converted into a recreational trail to connect with the existing trail system. 

Ultimately, the project accomplished three major goals: 

– Created a nutrient-reducing stormwater wetland to treat runoff from the adjacent neighborhood before entering Fourmile Creek. 
– Transformed an abandoned neighborhood and vacant field into a restored natural prairie ecosystem. 
– Converted an unused roadway into a recreational trail, expanding community connectivity. 

Polk County Conservation led the effort with the goal of treating stormwater nutrients, restoring natural prairie habitat, and enhancing outdoor recreation opportunities for the community. Our team provided design and construction oversight in close collaboration with our Transportation team, which handled the trail components and construction. 

While the project progressed over the span of a couple of years, one of the main design challenges came from intercepting an existing storm system buried unusually deep. This required extensive excavation to create the wetland, and the resulting material had to be strategically reused to build up the new trail system, helping reduce hauling costs. 

In addition to improving water quality, habitat, and recreation, this project helped launch a long-term relationship with Polk County Conservation, who are now among our largest clients in Iowa—leading to several ongoing collaborations across the region.