CS18A - Concurrent Session 18A: Hamilton Dam Removal - Innovative Design and Collaboration to Achieve a Wide Variety of Objectives

Abstract Description: The recently announced Flint State Park in downtown Flint, Michigan is a major project for revitalizing the city’s riverfront. Riverbank park improvements, greenway connectivity, and in‐river naturalization are all major components of this effort to turn this area into a public amenity. Within the city, naturalization of the river will improve habitat and access along nearly 2 miles of channel, address anthropogenic impairments from damming, channelization, dredging, and urban development, and improve access and recreational opportunities. The lynchpin of the naturalization was removal of the Hamilton Dam, which in addition to local benefits, opened nearly 25 miles of streams to lake sturgeon and walleye passage for the first time in over a century.

Built in 1920 as part of the water supply system, Hamilton Dam fell into disrepair after decommissioning, eventually being listed as a high-hazard structure. Work in 2018 removed the superstructure and control gates and stabilized the structure to remove it from the list; however, the remaining weir was a substantial barrier to fish passage and a hazard to river users with a hydraulic height of seven feet. Final removal included demolition of the weir, foundation, and stilling basin, coupled with construction of a series of riffle structures to transition the water elevation differential up- and downstream of the dam. Post-removal conditions had to provide fish passage, improve instream habitat, and accommodate boat travel while tying into an existing contaminated sediment remediation structure, reduce flood risk to existing structures, and support planned park improvements.

Meeting multiple, and sometimes conflicting, objectives required innovative use of both natural channel design elements and standard civil engineering approaches. Dam demolition design was driven by dam stability, contaminant release risk, bed and bank shear stress, flood stage, and sediment transport. Ecological design focused on instream habitat, passage requirements of target fish species, and geomorphic condition of unmodified reaches of the Flint River. Constructed riffles were designed based on Flint River reference reaches, with structure cross-sections and profiles optimized by 1-dimensional hydraulic modeling to meet no-rise and meeting upstream constraints. Fish passage structures were designed using 2-dimensional modeling to confirm critical flow velocity and depth met target species biological criteria. Regular coordination with stakeholders, permitting agencies, and the public were also critical for success. Construction was completed in autumn 2024, and upcoming geomorphic and biological monitoring in collaboration with University of Michigan Flint will demonstrate its efficacy in coming years.