Cedar River Flood Control Master Planning and Design

Following the devastating 2008 flood, the City of Cedar Rapids and the U.S. Army Corps of Engineers initiated a long-term program to protect the community from future flood events while restoring functionality to the Cedar River corridor. Stanley Consultants supported the effort from its earliest stages, beginning with a U.S. Army Corps of Engineers feasibility study in 2011 and continuing through development of a comprehensive flood control system master plan, program management services and multiple design packages.

The resulting program established a system designed to provide protection from a 500-year flood event while functioning within a dense, developed urban environment. Rather than relying solely on traditional flood mitigation infrastructure, the design integrates structural protection, controlled drainage systems and floodplain management to address both river flooding and urban runoff.

A central challenge was maintaining drainage performance as river levels rise. As flood stages increase, gravity systems become ineffective, requiring active control to prevent backflow and localized flooding. Stanley Consultants designed a coordinated stormwater system incorporating large-diameter conveyance infrastructure, gate wells and sluice gates to isolate the storm sewer network from the river during flood events while allowing normal discharge under typical conditions. These systems operate in conjunction with high-capacity pump stations capable of moving tens of thousands of gallons per minute when gravity flow is no longer possible. Hydraulic modeling evaluated both pumped and gravity conditions to verify performance under combined rainfall and river flooding scenarios and support safe, reliable operation.

A defining feature of the Cedar Rapids system is its extensive use of removable floodwalls, more than any other U.S. city. Rather than separating the community from the river with continuous permanent barriers, the design balances flood protection with public access and urban connectivity.

The flood control strategy also incorporates managed floodplain areas as part of the system’s performance. More than 220 acres of greenway were integrated into the river corridor, including an amphitheater that functions as part of the flood protection system, eight acres of wetlands, 15 acres of playfields and approximately 12 miles of trails. These areas provide flood storage and additional conveyance capacity during extreme events while creating recreational, ecological and community amenities that remain active year-round.

By combining structural defenses, controlled drainage infrastructure and flood-adaptive landscape elements, the project created a layered flood mitigation system that adapts to changing river conditions while reducing risk to residents, businesses and critical infrastructure throughout downtown Cedar Rapids.