Designing a Nature-like Fishway at Long Pond Dam

The Long Pond Dam currently serves as a barrier to migratory fish along Whitford Brook, a tributary to the Mystic River. Whitford Brook has seen significant declines in fish populations, in part due to dams along the river corridor that prevent fish from accessing upstream spawning habitat. Diadromous fish, including Alewife, Blueback Herring, American Shad, American Eel, and Sea Lamprey rely on access to upstream spawning habitat to complete their life cycle. For Long Pond specifically, CT DEEP Fisheries estimated that fish passage restoration could provide an annual run of more than 250,000 alewives. In conjunction with other recent improvements along Whitford Brook, facilitating fish passage at this location would create a 6.6-mile stretch of connected river corridor from the confluence of Whitford Brook with the Mystic River upstream to the top of Lantern Hill Pond.

A nature-like fishway was identified as the targeted means of providing fish passage by Save the Sound as the configuration of the outlet structure and embankment were well suited to that approach (relative to a technical fishway) and because dam removal was not considered a viable option due to the recreational and habitat (spawning) value of the impoundment.

Princeton Hydro’s scope included: evaluation of existing data including past H&H studies and engineering evaluations/inspections of the dam; site investigations including geomorphic assessment and wetland delineation; topographic, utility, and boundary surveys; development of a concept design; H&H analysis; geotechnical investigations; fish passage design; development of an engineering package (plans, technical specifications, construction cost estimate) and applications for regulatory approvals; and finalization of design documents based on regulatory feedback.

The primary challenge presented by this project was that the dam in its existing configuration was not in compliance with CT DEEP dam safety standards and that improvements/modifications to the dam to bring it into compliance were being handled by others. Further, site constraints dictated that installation of a nature-like fishway would require replacement of the dam’s outlet structure, which would increase the scope and complexity of the project beyond that originally envisioned.

While Princeton Hydro’s design of the nature-like fishway is largely complete, construction can not move forward until finalized plans for bringing the dam into compliance are completed by others and integrated with the proposed fish passage design. Princeton Hydro continues to coordinate with Save the Sound and other project partners to assure that future site improvements will work seamlessly with the proposed fish passage improvements.