Ioway Creek Flood Mitigation

Ioway Creek Flood Mitigation

AMES, IOWA

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 Ames, Iowa. 

The stream corridor was modeled using 2D software to determine channel velocities and flood elevations. This process included scenarios to reduce flooding in particular areas as well as scenarios that provided the largest impact to the community. WHKS assisted the City with completion of the FEMA Flood Mitigation Assistance grant application process, securing over $4.5M in FEMA funding for the improvements.

WHKS analyzed alternatives to open the flows under the Duff Avenue bridge and minimize impacts to the parking area in the southwest corner of the commercial development on Buckeye Avenue. The site layout for a modular block retaining wall was constructed to accommodate slope grading. The 300 foot long, 12-foot tall wall allows the flows to continue without significant reduction in velocity, which will reduce the deposition of sediment under the bridge. The addition of a berm at the northeast corner of the site 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 being constructed for water to divert to during heavy rainfall. The flood elevation in this area was reduced up to 2 feet relative to the 100-year flood event. To restrict flows at the bridge, the end spans were designed with open velocities to prevent the buildup of sediment. The high velocities through the bridge prevent the sediment from returning to the channel.

Trees were cleared along the channel for unrestricted flow along several areas of the channel. Several of the trees were reused as root wads installed into the streambank to stabilize the bank. The root wads as well as boulder clusters provide areas for fish habitat. Rock deflectors are used to 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.

WHKS prepared and submitted permitting applications including USACE-404, Iowa DNR-Floodplain, and Iowa DNR-Sovereign Lands. The project included coordination with the US Fish and Wildlife Service regarding potential impacts of the improvements to threatened and endangered species.

SERVICES PROVIDED:

  • Floodplain and hydraulic modeling
  • Flood mitigation design
  • Retaining wall design
  • Survey
  • Grant application assistance

IMPROVING LIVES, BUILDING COMMUNITIES

The project improves creek capacity and resilience in large storm events and increases protection to the area development using stabilization techniques.