The Illinois Department of Natural Resources Office of Water Resources commissioned Hanson to complete a comprehensive feasibility study of public safety improvements and ecological restoration opportunities at the Sears and Steel dams on the Lower Rock River near Milan, Illinois. Originally constructed for hydroelectric power generation, these low-head dams are obsolete and present significant public safety hazards and barriers to aquatic organism passage.
Hanson evaluated five structural and non-structural alternatives through a multidisciplinary study that included stakeholder engagement, topographic and bathymetric surveys, geomorphic assessment, 1D and 2D hydraulic modeling, computational fluid dynamics (CFD) modeling, sediment investigations, ecological surveys and cultural resource evaluations. Hydraulic modeling, including detailed CFD analysis, identified the presence of dangerous hydraulic rollers across a range of flows, conditions that have contributed to multiple drowning incidents. Hanson also used inundation mapping to assess changes in water-surface elevations and river velocities associated with each alternative.
Ecological assessments identified impediments to fish passage and habitat degradation. Sediment investigations identified approximately 4.3 million cubic yards of impounded material, with gradation and environmental testing to evaluate passive sediment management if dam removal is pursued. Sediment fate analysis was performed for the dam-removal alternatives to evaluate downstream sediment movement and inform appropriate sediment containment measures.
Hanson also developed preliminary concept drawings and construction cost estimates for each alternative, with findings and recommendations documented in separate safety reports for the two dams. Public meetings and outreach efforts provided opportunities for community and stakeholder input.
