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Concurrent Sessions A: Design of Nature-Like Fishways for Fish Passage; Bypass Channels and Rock Ramps

The nature-like fishway has attracted attention as a fish passage solution that allows a dam to remain in place while providing passage to a wider variety of fish species and life stages as compared to traditional technical fishway options. Nature-like fishways provide additional instream habitat and are more riverine in appearance than technical fishways, allowing the fishway to be incorporated into attractive park-like settings. By providing more diverse fish passage, better instream habitat, and improved aesthetics over technical fishways, the nature-like fishway is an appealing option for the establishment of fish passage at dams with a low likelihood of removal. Although bypass channels, a type of nature-like fishway, have gained acceptance in Europe, they are still a relatively new idea in the United States. The aim of this discussion will be to further introduce the nature-like fishway and to present a design protocol based on projects here in the United States. For a nature-like fishway to be passable, the velocity, cover, and depth of flow must be scaled to the swimming and biological characteristics of one or more fish species. A design protocol, drawing upon examples of nature-like fishways constructed by Milone & MacBroom, Inc. (MMI), is presented. These examples include a fishway at the Grangebel Park Dam, a long, low structure located at the upstream limit of tidewater on the Peconic River. The dam consists of an earth embankment, a principal (north) spillway, and an auxiliary (south) spillway with a raceway channel. An Alaskan Steep Pass type of fishladder was seasonally placed in the north spillway channel. The Town of Riverhead, New York and the watershed association identified the south spillway as a location for a more permanent, attractive, lower maintenance facility for the passage of alewife and American eel. During its three years of operation, the nature-like fishway has proven to be very successful. This design protocol will also include a nature-like fishway that is under design on the Swan River in Brookhaven, NY and one that will be under construction on the Naugatuck River in Seymour, CT.