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 completed site investigation, sediment probing, geomorphic assessment, engineering design plans, and secured permitting from the appropriate local, state, and federal authorities. RiverLogic Solutions provided input into the design approach, construction sequencing, and construction cost estimate. 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 completed a detailed hydrologic analysis to model flow 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-breach by passing the 50-year storm event with less than one foot of impounded depth.

In addition to meeting Dam Safety requirements, Princeton Hydro obtained a Wetlands Permit and Non-Site Specific Permit, as well as a USACE NH Programmatic General Permit from the NHDES Wetlands Bureau. Princeton Hydro completed a Phase 1 Due Diligence Assessment and additional design calculations to gain approvals from the Water Quality Planning Section and Environmental Health Program. Finally, Princeton Hydro also coordinated with the Town of Boscawen on a public information meeting as per New Hampshire state law (RSA 482-13). Re-naturalization of the former impoundment, now a beautiful brook meandering through a wide meadow, progressed quickly, and within weeks, vegetation re-established. The channel was allowed to naturally reform within its historic thalweg, evident by the alignment and re-exposure of large wood and rootwads.