The Walnut Street Bridge was the third project in a coordinated effort to replace aging downtown river crossings in Des Moines, IA. The bridge’s transformation builds on the success of the Grand Avenue and Locust Street bridge replacements while delivering a safer and more accessible structure designed to serve the community for generations. The project included the complete removal and replacement of the bridge, bridge approach pavement, and adjacent pedestrian facilities, creating a modern crossing that balances transportation needs, river performance, and riverfront aesthetics.
The Walnut Street Bridge over the Des Moines River, before and after reconstruction.
The original Walnut Street Bridge was built in 1911 and had undergone reconstruction as recently as the 1960s. After another half-century of use, changing transportation demands, accessibility requirements, and long-term maintenance considerations presented an opportunity to reimagine how the bridge could better support the evolving downtown corridor. Like the other bridge projects along the Des Moines River, the goal was to enhance safety for motorists while maintaining connectivity to existing bicycle and pedestrian facilities, the river walk, and parking spaces. Shuck-Britson, Snyder & Associates’ integrated structural engineering team provided bridge, roadway, and pedestrian facility design services to bring that vision to life.
Upgraded Waterway, Hydraulics & Flood Management
Some of the most significant project improvements can be found beneath the bridge itself. Drilled pier foundations were utilized to accommodate the relatively shallow depth and hard bedrock. The replacement structure was designed to improve the river’s hydraulic performance and increase resiliency during high-water events. By reducing the number of piers within the channel and incorporating a sleeker pier design, the bridge allows water to flow more efficiently. The raised roadway profile improves waterway capacity and crossflow, helping water move through the corridor more effectively during flood events. These enhancements also reduce scour potential around the foundations, improving the bridge’s long-term durability and performance while supporting the city’s broader flood management objectives.
The new bridge abutments were designed to accommodate the presence of the existing US Army Corps levies along both sides of the Des Moines River. The original massive arch abutments were left in place to minimize disruption to the levies. New abutment piles were cored through the original bridge abutments and provide independent support to the new bridge abutments. This design feature significantly reduced removals, excavation, construction costs, and permitting.
Enhanced Traffic Flow & Multimodal Accommodations
Above the river, the bridge has been transformed into a multimodal corridor that prioritizes safety and convenience for all users. The updated bridge provides dedicated bike lanes, 10-foot-wide sidewalks, and 76 parking spaces, all within the original bridge width. These features strengthen connectivity between downtown destinations and surrounding neighborhoods while encouraging a more pedestrian- and bicycle-friendly environment.
The improvements extend beyond the bridge itself. Approach pavement on both ends of the crossing was redesigned to provide clearer vehicle guidance by removing excess pavement and converting it into green space to enhance pedestrian facilities. This attractive streetscape also helps motorists navigate the corridor more effectively.
Accessibility for All Users
Pedestrian accommodations meet ADA standards and include 10-ft sidewalks and two at-grade crossings on the East and West ends of the bridge.
Accessibility was another major focus of the project. New pedestrian facilities were designed to meet current ADA standards and provide a seamless experience for users of all abilities. Two at-grade crossings located at the east and west ends of the bridge improve pedestrian access and connectivity, while materials and finishes were selected to create a cohesive appearance that complements the surrounding riverwalk and downtown infrastructure.
A Modern, Aesthetic Revitalization
In addition to its functional improvements, the Walnut Street Bridge introduces a contemporary aesthetic that reflects the ongoing revitalization of the Des Moines riverfront. The bridge features an open-railing design that provides clear, unobstructed views of the Des Moines River and surrounding cityscape. Architectural lighting further enhances the bridge’s presence, adding visual interest after dark and contributing to the welcoming character of the downtown waterfront.
A Structure Fit for the Evolving Corridor
The before-and-after transformation of the Walnut Street Bridge demonstrates the impact thoughtful engineering and bridge design can have on a community. What was once an aging river crossing is now a resilient, multimodal gateway with a service life exceeding 75 years and minimal maintenance required for 25 to 30 years. The replacement improves traffic flow, enhances pedestrian and bicycle mobility, strengthens flood performance, and elevates the overall user experience. As the final piece in a series of downtown bridge replacements, the Walnut Street Bridge helps create a cohesive riverfront corridor, supporting Des Moines’ continued growth while strengthening connections between people, places, and the river that runs through the heart of the city.
