Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Montana Fishery Project

Efficacy of the Nature-like Fish Bypass Channel at Huntley Diversion Dam, Yellowstone River, Montana

September 2018 - March 2022


Participating Agencies

  • Montana Fish, Wildlife and Parks: MTNRDP

The Huntley Diversion Dam was constructed in 1934 at river kilometer 566 on the Yellowstone River 15 km downstream from Billings, Montana, to supply agricultural irrigation and municipal water. The 3.2-m high rockfill and concrete structure can divert up to 730 cfs of water. Limited upstream movement past the dam was possible by strong-swimming fish species (white sucker, carp, goldeye, brown trout, shorthead redhorse, longnose sucker, flathead chub), but such passage was probably accomplished via the natural side channel on the north side of the island on the north side of the dam; the side channel flows primarily during high runoff discharges. Moreover, no upstream or downstream passage of marked individuals of most species present was observed. In addition, the dam appeared to limit the upstream distribution of a genetically distinct population of sauger; sauger formerly occurred in the Yellowstone River and its Clark Fork tributary upstream of Huntley Dam. Lack of access by this popular sportfish to habitats upstream of the dam may limit recreational opportunities as well as viability of this unique population. Huntley Dam was repaired and modified following flooding in 1996 and 1997. Concurrently, a nature-like fish bypass channel was constructed around the north end of the dam on the island to enhance fish movements around the dam. Unfortunately, the length of the completed channel was much shorter than originally planned. It failed to provide passage, probably because of excessive gradient and water velocities. The bypass channel was reconfigured to more appropriate design specifications in 2015, but its hydraulics and efficacy for fish passage have not been evaluated. Nature-like fish bypasses are designed to resemble natural streams or side channels. Their gradient is lower than that of typical fish ladders and their sinuosity and inherent substrate roughness provide diverse water velocities, especially along their margins, thereby ostensibly facilitating passage by a variety of species and sizes. Nature-like bypasses are still rare (though more popular in Europe than in North America) and only a few evaluations of them have been conducted. None of these evaluations were conducted in situations even remotely resembling the reconfigured Huntley bypass channel. As with all fishways, attraction is critical for nature-like bypasses; fish have to both find the entrance and decide to enter it before attempting to navigate it. Adequate flows are key to attraction, but insufficient evaluations exist to provide thresholds and design criteria, especially for diverse fish assemblages such as that of the Yellowstone River. Upon entry, a fish must traverse the passage successfully and also exit it; again, hydraulics must be appropriate. Failure can occur at any of these stages and assessment thereof is an important component of an evaluation if it is to identify causes of passage problems and possible remedies. Influential factors affecting bypass efficiency (depending on species and size) can include discharge, velocity, gradient, channel length, temperature, and turbidity. We propose to conduct an evaluation of the reconfigured Huntley fish bypass in 2019 and 2020 by estimating fish passage rates through the bypass and measuring and modeling the hydraulics of the bypass channel to determine its passability by various species under different river stages. Our specific objectives are to: 1) determine approach, attraction, and passage efficiencies (%) of important and abundant fish species through the bypass, 2) determine the locations of any passage bottlenecks within and near (i.e., immediately above and below) the bypass channel, 3) determine fish passage durations through the bypass, 4) determine the seasonal and daily timing of fish passage, 5) characterize the topography, bathymetry, and hydraulics of the bypass and its inlet and outlet to characterize its connectivity with the Yellowstone River, and 6) model the hydraulics of the bypass to identify excessive velocities, attraction flows, and other factors affecting fish passage over the range of flow rates that characterize the river’s hydrograph. Completion of these objectives will provide an evaluation of how well the fish bypass works, ascertain the causes of any deficiencies, and identify corrective measures if needed.