Earthen Dam Removal

Tannery Brook Dam Removal

Princeton Hydro was hired to remove this 30-year-old, over 20-foot-high earthen dam and make the site non-jurisdictional due to dam safety maintenance costs and property liability concerns. The dam owner had previously received costs of approximately $400,000 to repair the dam and $200,000 to $300,000 to remove the dam. 

Princeton Hydro teamed with RiverLogic Solutions to provide a design-build approach that reduced the cost of removal to $150,000. Princeton Hydro conducted field work, prepared a hydrologic and hydraulic (H&H) assessment, including assessing potential changes in flood storage and downstream impacts, completed the engineering design and project plans, and secured permitting from the appropriate local, state and federal authorities. RiverLogic Solutions provided input into the design approach and construction sequencing, and the fee proposal for the removal of the dam. 

In an effort to further understand the potential downstream impacts and complete additional due diligence, Princeton Hydro went beyond the original scope of work requested by New Hampshire Dam Safety for the H&H analysis, and extended the HydroCAD model further downstream to the first significant road crossing, and included the contributing watersheds, downstream wetland complex, bridge geometry, and additional data sources. The watershed characteristics were determined from the Digital Elevation Model (DEM) for the area, and based on aerial photo interpretation for land use. Flow was then reach-routed through the downstream wetland complex. 

As part of the routing analysis, Princeton Hydro assessed the proposed conditions of the site to evaluate whether the dam would be considered non-jurisdictional post-breaching. To be considered non-jurisdictional the dam breach had to pass the 50-year storm event with minimal impoundment. The minimal impoundment was defined by New Hampshire Dam Safety to be less than one foot during the spillway design storm (50-year event).