A scaled Denil fishway for upstream passage of Arctic Grayling

Abstract

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.

Keywords:

• Denil
• fishway
• fish passage
• Arctic Grayling

Acknowledgements

We thank Bob Muth, Sharri Lunde, Jason Ilgen, Matt Toner, Cal Fraser and the rest of the BFTC staff for their support; Sean Clearwater, Ralph Johnson and Bill Clinton for allowing us to use MSU Architecture department lab equipment for Denil construction; and Lynn DiGenerro at the U.S. Geological Survey Montana Cooperative Fishery Research Unit for administering the funding for this project.

Author notes

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

This study was performed under the auspices of Montana State University protocol 1350.00 guided by the Animal Subjects in Research and the Institutional Animal Care and Use Committee (IACUC).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was funded and supported by the U.S. Geological Survey Science Support Partnership (SSP) Program (Project ID, 19-R6-04) the USFWS Region 6 Fish Passage Program (Denver, CO) and the USFWS Bozeman Fish Technology Center (Bozeman, MT).