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

The effects of fishway entrance design on the passage time of adult American shad (#36)

Kevin Mulligan 1 , Alex Haro 1
  1. United States Geological Survey, Turners Falls, MA, United States

A common problem among fishways is attraction and entry.  Competing flows and complex hydraulics in and around the fishway can at times hinder passage and result in significant migration delays.  The purpose of this study was to evaluate how flow conditions at a fishway entrance and the structural design of the entrance can affect entry.  In most instances, a fishway entrance consists of a fully submerged hydraulic control (e.g. gate) located at the downstream end of an open channel that guides fish to the main body of the fishway (e.g. lift, pool-and-weir).  Changes to this hydraulic control design can influence the hydraulics (e.g. entrance jet velocity, flow pattern) and thus attraction and entry performance.  To address these issues, a study was performed in 2016 and 2017 with upstream-migrating, adult American shad (Alosa sapidissima) which documented the performance of a variety of hydraulic controls under a limited number of conditions.  Submergence depth (i.e. the height difference between the tailwater elevation and the gate crest) and river temperature were shown to be the main drivers in performance.  Gate type was also significant, where the novel reversed overshot gate performed the best followed closely by the standard overshot gate.  The vertical gate, by far the most common among fishways, performed much worse than the other two gate types.  Additional trials in 2018 evaluated the effect of different water surface elevation drops across the gate for American shad and blueback herring (Alosa aestivalis).  The results of these studies provide guidance to state and federal resource agencies and the hydropower industry on methods to improve fishway attraction and entry rates.