The presence of dams has direct negative effects on populations of migrating fish and their riverine habitat as well as impacts on the ecosystem services they provide. Fishways, provide upstream and downstream passage that is safe and timely, comprising specifically of “physical structures, facilities, or devices necessary to maintain all life stages of such fish, and project operations and measures related to such structures, facilities, or devices which are necessary to ensure the effectiveness of such structures, facilities or devices for such fish” (National Energy Policy Act 1992). Fishways, sloped channels or elevators that connect the tailrace to the head of the dam, are one type of mitigation strategy; however there is a need for evaluating their effectiveness as populations of migrating fish continue to decline. This study is a two part investigation of the Auxiliary Water System (AWS), a pivotal technology in guiding fish into the fishway entrances. To effectively attract fish to the fishway, contributions from the AWS are essential; however, the hydraulic complexities associated with AWS inside the entrance channel may be causing negative behavioral responses to safe and timely fish passage.
The content of the research presented in this paper is twofold. First it provides a review of the state of AWS in the field through a review of criteria manuals and the building of the Fishway Systems at Hydropower (FiSH) database. The database hosts predominantly fishways from the Northeast. The results indicate most AWS designs are gravity fed floor diffusers followed by gravity fed wall diffusers.
Second, the study provides primary insight on the behavioral response of American shad to wall diffusers in the fishway entrance. During the spring of 2019, research was conducted on a full-scale wall diffuser using actively migrating American shad to evaluate the behavioral responses in a controlled flume environment. The experiment held constant flow conditions in the entrance channel immediately upstream of the diffuser. Flow through the AWS remained constant, while the diffuser velocity varied from 0.5 to 1.0 fps. Hydraulic data on the diffuser was gathered from a 1:8 scale physical model. The data analysis draws spatial and temporal correlations between the hydraulic parameters of the system, namely velocity, and the tracked fish movement through the study area. The data analysis from the behavioral and hydraulic experiments indicates better passage and preferable hydraulics for the 0.5 fps velocity treatment. The evaluation of this widely used technology further informs decisions regarding improvement and implementation of fishway technology.