Modifying Existing Low-Head Dams to Fish Passable Rock Rapids

In 2024, GEI modified an existing dam to a fish-passable rock rapids. The constructed rapids is 650 feet in length and drops nearly 15 feet, allowing the owner to maintain a similar minimum water surface to the former dam while also meeting regulatory fish passage requirements. Volitional fish passage for cold and warmwater species has been demonstrated on similar nature-like fishways throughout the Midwest using a series of boulders, gaps, and resting pools that emulate natural river processes. This is the first design of its kind to be constructed in Michigan, with notable differences to other previously constructed rapids in Michigan with varied fish passage success. This design is a viable alternative for dam owners and regulators where fish passage is desired, a minimum water surface elevation is required, and no additional water control is necessary. This paper shares the design and construction methods related to this project.