Background
Fourmile Creek, located on a 250‑acre property east of Ankeny, Iowa, was identified as a severely incised stream with actively eroding banks that threatened a nearby recreational trail system. The creek runs adjacent to an existing wetland mitigation bank and plays an important role in local flood management, habitat connectivity, and recreation.
Our team was contracted to design and permit a comprehensive restoration project spanning more than two miles of stream. In addition to stabilizing the channel and protecting existing infrastructure, the project also includes the establishment of a new stream mitigation bank to support long‑term ecological restoration and mitigation credit generation.
Approach
During Phase II, our team conducted baseline environmental studies, including wetland delineation, floristic quality assessment, tree inventory, detailed surveying, and stream geomorphic assessment. These findings informed a restoration design guided by the Iowa Department of Natural Resources’ River Restoration Toolbox and the U.S. Army Corps of Engineers’ Natural Channel Design Checklist.
The design process required balancing several site constraints, including addressing a third‑party permit violation, maintaining recreational access for kayaks and canoes, and preserving existing infrastructure within the corridor. The final design incorporates floodplain benches and bank reshaping to improve channel stability, along with reconnecting six historic oxbows to increase flood storage and restore natural stream processes.
To enhance habitat and resilience, cleared trees will be reused on site as toe wood protection, supplemented with targeted stone structures for bank stabilization. Additional in‑stream habitat improvements include riffles, cross vanes, and a full realignment of a severely eroded tributary.
Our team also prepared the project prospectus and mitigation banking instrument, including detailed restoration plans, performance criteria, and establishment of a conservation easement. The project is supported through a funding partnership between the Polk County Conservation Board and Sandy Creek Partners.
Results
The Fourmile Creek restoration project is designed to deliver long‑term ecological, recreational, and flood resilience benefits. Once constructed, the restored stream and floodplain system will reduce erosion, reconnect wetland features, and improve aquatic and riparian habitat across the site. The project will also support mitigation credit generation while protecting public infrastructure and enhancing recreational opportunities.
Phase II construction is scheduled for fall 2026, and our team will lead long‑term monitoring and adaptive management activities over the next decade to ensure performance standards are met and restoration goals are sustained.
Markets: Water and Wastewater
Services: Environmental and Regulatory Services, Remediation, Water and Wastewater
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