Design, hydraulic evaluation, and passage efficiency of a roughened channel rock ramp fishway for white sucker and longnose dace

Abstract

Effective fish passage structures are essential for maintaining connectivity in aquatic ecosystems, improving climate resilience, and supporting native fish populations. Rock ramp fishways have become popular due to their nature-like design and ability to accommodate a wide range of species. However, additional research is needed to develop species-specific design criteria for flow rate, slope, length, and boulder configuration. This study evaluated the design, hydraulic performance, and passage efficiency of a roughened-channel rock ramp fishway constructed and tested in the open-channel flume at the Bozeman Fish Technology Center. Nine hydraulic conditions were examined by combining two slopes (3% and 5%) with five flow rates (0.0315, 0.0631, 0.0946, 0.1262, and 0.1893 m 3/s). Detailed depth and velocity measurements were collected to characterize the hydraulics at each treatment. Velocity contour plots were created to visualize the hydraulic conditions, providing insight into potential swim paths, resting refugia, and velocity barriers. Volitional swim trials were conducted with white sucker (Catostomus commersonii) and longnose dace (Rhinichthys cataractae), with fish movements tracked using four stationary PIT antennas. Each treatment was repeated three times for a total of 28 trials using 84 white sucker and 168 longnose dace. Participation rates were high for both species across all trials, but passage results revealed clear differences in swimming behavior and capabilities. White suckers exhibited consistently high passage success (97%) across all hydraulic conditions. In contrast, longnose dace showed high passage success at lower flows (83-100%) but success decreased sharply with increasing flow rate, particularly at the 5% slope. Travel-time analysis indicated that longnose dace rested in velocity refugia between bursts of swimming while suckers ascended the ramp in a single sustained effort. Logistic regression showed that flow rate, slope, and fish length were key predictors of longnose dace passage, and probability of passage curves were developed to estimate longnose dace passage across the test conditions. Passage models were not developed for white sucker because they achieved high passage at all test conditions. Overall, this study contributes valuable insight on the design, hydraulics, and biological performance of a roughened channel rock ramp. These results highlight the importance of considering slope, flow rate, and species-specific swimming abilities in rock ramp design and applications.