Mitigating Streambank Erosion
Protection of a 24-inch water main under Squaw Creek that serves 18,000 residents and Iowa State University was the primary goal of this project. The water main was threatened by ongoing bank erosion resulting from a tall, unstable bank, highly erodible soils, and frequent high flows and flooding. Previous attempts to control erosion in this highly flood-prone area were unsuccessful, prompting the City of Ames to seek a sustainable, long-term solution.
During the analysis and planning phase, the project evolved due to safety concerns regarding a low-head dam located in the area. The dam created eddy currents that compounded erosion, impeded fish passage, and posed a drowning hazard. Before project completion, two kayakers survived a life-threatening situation after being sucked into the dam undertow, drawing further attention to the safety hazards of low-head dams.
Working with FEMA over a six-year period, Hazard Mitigation Grant Funding (HMGP) was secured to fund streambank stabilization and mitigate the threat posed by the dam. Streambank stabilization involved:
- Flattening both the east and west bank
- Incorporating a low-flow bench to reduce flow velocities and bank pressure
- Protecting lower banks with stone revetment
- Reinforcing upper banks with erosion control mat, native vegetation, and live stakes
Rock Arch Rapids: An Alternative to Dam Removal
While complete removal of the low-head dam was desired, a scour analysis indicated that it protects piers of the Lincoln Way bridge and another water main immediately upstream. Construction of a rock arch rapids, which is a series of steps that gradually transitions water flowing downstream from the dam to meet channel elevation, was a successful and innovative alternative to dam removal. This solution also eliminated the roller (or boil) below the dam to improve safety for recreational stream users and created a series of pools that allow fish to migrate upstream.
Completed in spring 2017, this project successfully protected city infrastructure, uplifted stream functions, and stabilized the streambank. It also improved recreational safety, restored stream connectivity, and enhanced the aquatic and riparian habitat.
Partnerships between the City of Ames, state and federal regulatory agencies, and other stakeholders drove project success, which was highlighted at the 11th Annual Iowa Water Conference.