Preserving history while restoring a river’s natural systems

Dams constructed on Rhode Island streams and rivers up through the early 20th century brought waterpower for new industry but also created barriers to the fish runs that supported valuable ocean fisheries. Adaptations to the iconic Horseshoe Falls dam in Shannock Village, RI are helping restore critical ecosystems and bringing the natural migratory fish and eel populations back to the Pawcatuck River.

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Challenge

The people who live in Shannock Village love their community – its intimacy, its heritage, and its character. At its heart is Horseshoe Falls. As important as this spot is to the village, the dam that creates the iconic falls is one of several blamed for the dramatically reduced yields of Long Island Sound fisheries. With Atlantic salmon, American shad, river herring, and American eel populations at record lows, important migration passages need to be restored while preserving the historic qualities of the village center.

Collaboration

In addition to the intricacies inherent in reestablishing eel and fish runs, designing a structure for a constrained footprint, and working near a fragile historic stone masonry spillway, coordination with three property owners to address aesthetic concerns was required. To account for these distinct influences, numerous in-house services had to coordinate their efforts including geotechnical, structural, mechanical and civil engineering, hydraulic modeling, and landscape architecture, which included repair/restoration of the historic structures. We partnered with other firms for wetland assessment and surveying.

Practice Areas Involved

Design

To balance restoration of river life with preservation of the dam and its surroundings, a mix of persistence and respect was required. Following diving inspections and detailed hydrologic and hydraulic analysis of water flow, several alternative designs were evaluated. While a Denil-style fish ladder solved for the fishway, eel passage presented a unique challenge. Due to aesthetic, maintenance and layout constraints, the typical water flow solution, a solar-powered water pump, was not feasible. With support from the Wood Pawcatuck Watershed Association and project agencies including NOAA, RIDEM, USFWS, and USGS, a custom-designed water flow control assembly that uses a self-regulating floating baffle was fabricated, piloted, lab tested, and integrated into the fish ladder.

Impact

The Horseshoe Dam project is one of three along the Pawcatuck River with the goal of reestablishing lost migratory fish routes. Since installation, there
have been observations of eels passing through the eel pass assembly, which is a huge validation for this first-of-a-kind approach. The fish ladder has
been operational since the 2012 spring passage season, allowing fish to pass upstream for the first time since the dam was originally built
circa 1730. will continue stocking fish and monitoring passage to restore populations to this part of the river
and upstream spawning areas. The USFWS and Rhode Island’s Division of Fish and Game will continue stocking fish and monitoring
passage to restore populations to this part of the river and upstream spawning areas.