For years, flooding was an unwelcome reality for the City of Sumner, Iowa. Repeated storm events challenged residents, infrastructure, and public safety, culminating in a devastating 2017 storm that dropped approximately 10 inches of rain in just 24 hours. Roads became impassable, power was disrupted, and the community was left confronting the growing reality that its existing stormwater system could no longer keep pace with increasingly intense rainfall events.

Recognizing that piecemeal repairs would not solve the problem, the City partnered with MSA to take a comprehensive look at the watershed and stormwater system. Through detailed hydrologic analysis, watershed modeling, and evaluation of multiple design alternatives, the team identified a long-term solution that would not simply move water faster but strategically manage it before it reached vulnerable neighborhoods.

The resulting effort became a multi-phase flood mitigation program designed to protect the community from future flood events while positioning Sumner for long-term resilience. The first phase included construction of detention basins capable of capturing and storing stormwater before it entered the city. Together, the basins provide approximately 95 acre-feet of storage and reduced peak flows entering the community from roughly 750 cubic feet per second to about 120 cubic feet per second during major storm events. Beyond flood protection, the basins also improve water quality by capturing sediment and slowing runoff.

Building on that foundation, the Walnut Street Stormwater Improvements project completed the critical conveyance infrastructure needed to move stormwater safely through the community and to the Little Wapsipinicon River. The project included approximately 2,600 feet of stormwater conveyance improvements, including large-diameter reinforced concrete pipe, box culverts, drainage channel enhancements, and related infrastructure improvements. A new sanitary sewer lift station was also incorporated into the design, resolving a long-standing conflict between stormwater and sanitary sewer systems while helping reduce inflow and infiltration during storm events.

Like many municipal infrastructure projects, the work was not without challenges. The project team navigated constrained urban work areas, utility conflicts, extended wet conditions, river surcharges, and even a high-pressure gas main strike during construction. Success required close coordination among the City, contractor, utility providers, funding agencies, and residents. Through proactive communication and adaptive project management, construction was completed with zero lost-time injuries, while maintaining access for residents, businesses, and community institutions throughout the process.

Environmental stewardship was equally important. The project incorporated habitat-friendly culvert designs, wetland seeding within drainage corridors, and careful coordination with regulatory agencies to protect natural resources and wildlife. These enhancements ensured the project delivered benefits beyond flood reduction, creating a more resilient and environmentally responsible system for future generations.

What makes the Walnut Street Stormwater Improvements project particularly noteworthy is not just the infrastructure itself, but the vision behind it. The City committed to nearly a decade of planning, design, funding coordination, and phased implementation to transform a recurring problem into a long-term community asset. By combining watershed-scale planning, local investment, and FEMA Hazard Mitigation Grant Program funding, Sumner successfully delivered a solution that protects homes, businesses, and public infrastructure from future flooding while improving overall system performance.

Today, the Walnut Street Stormwater Improvements project stands as a model for how communities can leverage engineering innovation, strategic funding, and long-range planning to address complex flooding challenges. For municipalities facing similar concerns, the project demonstrates that resilient infrastructure is about more than managing stormwater. It is about protecting people, safeguarding investments, and building confidence in a community’s future.

This project was chosen to receive a 2026 Project of the Year Award in the Environment category, $2.5M-$5M division, by the American Public Works Association Iowa Chapter.