Inverted Partial Rock Ramp Fishway: Winchell-Smith Dam Case Study

Partnering with the Farmington River Watershed Association (FRWA), and as part of an overall Farmington River Enhancement Grant from the Connecticut Department of Environmental Protection (CTDEP), Princeton Hydro was tasked with the design of fish passage improvements at two (2) dams on the Farmington River.  Located within the town limits of Farmington, Connecticut, the existing dilapidated rock fill/timber crib Winchell-Smith Dam is approximately four (4) feet high, and spans the entire 200’+ wide channel at this location, with the adjacent historic mill building, currently serving as a  restaurant.  To balance the desire for the falling water aesthetic over the dam (request of the adjacent mill restaurant owner) with the goal of providing efficient fish passage, an inverted rock ramp fishway was selected for design.  This less common rock ramp configuration required detailed hydrologic and hydraulic (H&H) modeling to ensure sufficient flow over the dam while maintaining optimal passing requirements (depths and velocities) through the rock ramp for the target fish species.  To account for the range of fish passage flow conditions experienced at the Winchell-Smith dam, the proposed fishway also required the design of a staged weir configuration to allow modification of flows directed to the fishway through the use of weir boards.       

Design of the proposed weir inlet to the fishway ramp utilized various data sets gathered during field investigation and data collection, including nearby USGS stream gages, as well as pressure transducer (stage only) gages installed both upstream and downstream of the dam.  Weir specific stage-discharge relationships were determined for multiple weir configurations, and by combining the overall stage-discharge relationships for the Farmington River above Winchell Smith Dam with the weir stage-discharge data, a correlation was obtained allowing determination of depth (and velocity) and associated recurrence interval for various fish passage flow conditions.

Beyond the case study of the Winchell-Smith design, brief discussion is included regarding regional efforts of fish passage enhancement on the Farmington River, including a significantly larger dam removal downstream of the subject dam, as well as considerations for design of inverted rock ramp fishways vs. traditional rock ramp fishways.