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Pine Mill Dam Removal and River Channel Restoration

Stone was hired by the Connecticut River Conservancy to lead the engineering and design for the removal of the Pine Mill Dam on Clark Brook in Haverhill, New Hampshire. This concrete gravity dam, built around 1928 and originally used to power a nearby grist mill, had become a source of problems. Over the years, it deteriorated, leading to foundation undermining, exacerbated flooding during heavy flows, and significant sediment accumulation. These issues not only threatened nearby structures but also obstructed aquatic life movement, particularly affecting the eastern brook trout.

The project aimed to eliminate these problems and restore ecological functionality to the river by removing the dam, thereby improving sediment transport, flow conveyance, and fish passage. Stone's approach included detailed surveys, historical data review, and advanced hydrologic modeling using the HEC-RAS and the USFS Stream Simulation Methodology. These efforts led to the identification and selection of the optimal removal strategy that minimized impacts on surrounding structures and maximized ecological benefits.

The final design incorporated a comprehensive channel restoration plan, enhancing habitat with strategically placed structures like steps, pools, and riffles, and stabilizing the banks with native vegetation and erosion-control measures. Completed in September 2019, the project has not only improved channel stability and habitat but also preserved the site’s historical significance through a dedicated marker explaining the dam’s history and ecological contributions post-removal.