Ioway Creek Flood Mitigation

WHKS designed flood mitigation and stream restoration measures for a 2,000-foot reach of Ioway Creek on either side of the Duff Avenue Bridge in the City of Ames. WHKS assisted the City with completion of the FEMA Flood Mitigation Assistance grant application process, securing $4.5 Million to fund improvements.

The stream corridor was modeled using 2D software to determine channel velocities and flood elevations. WHKS analyzed alternatives to open the flows under the Duff Avenue bridge and minimize impacts to the parking area in the southwest corner of a commercial development on Buckeye Avenue. The site layout for a 300′ x 12′ modular block retaining wall was constructed to accommodate slope grading. The addition of a berm diverts flows at the northeast corner of the Duff Avenue Bridge.

The selected design kept the channel as-is near the Duff Avenue Bridge, with a second stage area constructed to divert water during heavy rainfall. To restrict flows at the bridge, the end spans were designed with open velocities to prevent build up of sediment. The high velocities through the bridge prevent sediment from returning to the channel.

The City acquired two buildings to accommodate the improvements. WHKS prepared right-of-way plats for acquisition and met with property owners to coordinate right-of-way and easement needs.

Several of the trees cleared along the channel were reused as root wads to stabilize the bank. Root wads and boulder clusters also provide areas for fish habitat. Rock deflectors slow the water during flooding events and maintain normal flows to the center of the stream to reduce meandering.

Wetland delineations were conducted within the project corridor to meet permitting requirements. A seeding plan focusing on pollinators was developed in the pocket wetlands.

The project received the Honor Award (Second Place) in the Special Projects Category in the 2024 Engineering Excellence Awards Competition.