Matt Blank | Search USGS

USGS2022

A scaled Denil fishway for upstream passage of Arctic Grayling

Denil fishways have been used with varying success to help fish pass impediments to upstream passage such as low head dams or irrigation diversion structures. They have been tested for hydraulic and fish passage performance in laboratory and field settings, usually with only minor modifications to the fishway geometry or dimensions. We tested a reduced (0.6) scale prototype of the standard-sized Denil fishway to determine if the smaller fishway, which requires less water flow, would successfully pass Arctic Grayling ( Thymallus arcticus ). The scaling factor was informed by analyzing previously published scalable Denil fishway rating equations. A prototype was tested in an open-channel flume using 8 treatments with 3 trials per treatment and 8 fish per trial. Each treatment had a prescribed combination of headwater and tailwater depths. Overall, 93% (178/191) of the fish volitionally entered the fishway and of these 91% (162/178) passed successfully. Entrance and passage were reduced only in treatments with the highest hydraulic slopes and highest water velocities at the downstream end of the fishway (i.e. with high headwater depths and low tailwater depths). The 0.6-scaled Denil fishway is likely a good alternative to standard-sized Denil fishways to enhance upstream mobility of Arctic Grayling in small, water-limited streams.

Journal of Ecohydraulics↗

USGS2022

Attraction, entrance, and passage efficiency of Arctic Grayling, trout, and suckers at Denil fishways in the Big Hole River basin, Montana

The Big Hole River basin in southwestern Montana supports the only indigenous, self‐sustaining fluvial population of Arctic Grayling Thymallus arcticus in the conterminous United States, but the basin is fragmented by numerous low‐head irrigation diversion dams. Denil fishways at 63 diversion dams provide Arctic Grayling and other fishes opportunities for year‐round access to critical habitats; however, their efficiency has not been evaluated. We quantified attraction, entrance, and passage for hatchery‐reared Arctic Grayling, wild trout (Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta ), and wild suckers (White Sucker Catostomus commersonii and Longnose Sucker C. catostomus ) during 14 field trials conducted at six Denil fishways over a representative range of fishway slopes and hydraulic conditions using passive integrated transponder telemetry. Attraction (60.4–84.3%) and entrance (44.3–78.6%) efficiencies were variable across test conditions and reduced overall fishway efficiencies (19.1–55.8%). In contrast, upon entry, passage efficiencies were high (96.2–97.0%) for all taxa across all test conditions. Attraction of hatchery‐reared Arctic Grayling increased with upstream depth (a surrogate for fishway discharge) and attraction flow, but attraction of wild fish was less affected by these conditions. Entrance of Arctic Grayling, Brook Trout, and Brown Trout decreased with upstream depth and fishway slope, especially when plunging entrance conditions associated with shallow downstream depths were present. However, entrance of Arctic Grayling and both trout species increased with downstream depth, and submerged fishway entrances demonstrated promise for increasing entrance efficiency at fishways with high discharges and steep slopes. We demonstrate that comprehensive evaluations of fishway efficiency components can identify specific solutions that improve fishway efficiency; application of these engineering solutions at individual fishways (as needed) could improve their efficiency and further enhance aquatic connectivity for fishes in the Big Hole River basin and elsewhere.

Montana↗