Session B8- Designing a 13-foot fish ladder and innovative eel pass on a thumbnail site next to Rhode Island’s signature historic dam Horseshoe Falls Dam fish ladder

The Wood-Pawcatuck Watershed Association has completed and continues to work on anum ber of projects to improve fish passage on the Pawcatuck and Wood Rivers in southern Rhode Island. Three current projects involve dam removals, construction of fish ladders and other channel modifications in support of fish passage along a three mile section of the river near Shannock, RI, all of which have been funded through public organizations and state/federal programs including the allocations from the ARRA. One of these three projects at the Horseshoe Falls Dam involves design of a fish ladder and eel pass sandwiched between a bridge and a historic dry stone masonry horseshoe-shaped dam. An underwater diving inspection and structural evaluation was performed to assess the existing spillway and bridge structure’s conditions and identify deficiencies. Several alternative layouts were evaluated, based on the targeted fish species and populations expected to pass and utilize upstream spawning habitat. The project is in a historic district and required coordination with three property owners to address aesthetic concerns. Renderings were developed depicting the various structural faces and elevations in relation to existing structures and to visualize potential concrete formlining options matching the composition and hue of adjacent stone structures. Through extensive coordination with the state historic preservation agency and property owners under Section 106 requirements, a final configuration and design was developed fitting the character of adjacent historic features. Evaluating alternative solar panel locations for a small pump at the eel pass ramp was particularly challenging. After several meetings to review alternatives, the project team decided to develop new technology providing an innovative autonomously-adjusting mechanical assembly to regulate inlet water flows throughout the range of the dam’s seasonal headwater evaluations. This assembly’s principles of operation, design development and status of hydraulic and live eel testing to date will be presented.
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