Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Assessing the efficacy of flow restrictor plates in denil fishways for upstream passage of arctic grayling (#84)

Tyler Blue 1 , Katey Plymesser 1 , Matt Blank 1 2 , Kevin Kappenman 3 , Joel Cahoon 1
  1. Civil Engineering, Montana State University, Bozeman, Montana, United States
  2. Western Transportation Institute, Bozeman, Montana, United States
  3. United States Fish and WIldlife Services, Bozeman, Montana, United States

Habitat connectivity is imperative in the preservation of access to habitat, food, and refuge for fish and other aquatic species.  The Arctic grayling (Thymallus Arcticus) is a population of fish that has seen the impact that cutting off upstream habitat has on the life cycle of a species.  A species once abundant in the rivers and lakes of Michigan and Montana, the Arctic grayling is now a species of concern in Montana.  To help preserve Arctic grayling, approximately 60 Denil fishways have been installed on irrigation diversion structures throughout the Big Hole River watershed.  The Denil fishway requires high flow levels in the ladder to facilitate grayling passage and irrigators need this water during low flow seasons to meet their water needs. In an attempt to meet the need of Arctic grayling and irrigators, a study was conducted to test the efficacy of flow-control weirs (“flow-restrictor plates”) installed at the upstream end of the Denil fishway to decrease the required flowrate needed to pass Arctic grayling.  This study investigated three distinct restrictor plate designs in addition to a control (no plate installed).  Each treatment received the same five depth treatments in order to best compare flow restriction, passage efficiency, and several other hydraulic and ecologic factors.  Upon the completion of the data collection phase, analysis was done to assess the efficacy of these plates.  The end goal was to develop a statistical model that could predict passage efficiency in a Denil fishway for a given plate based on a set of other variables.  Ultimately, it was found that the sole predictor of passage efficiency was flow rate and that any addition of a device that restricts flow rate will decrease passage for Arctic grayling.