The Influence of Local Hydrodynamics on Fish Movement in Fluvial Infrastructure

Abstract

River systems across the developed world have been dammed for a variety of reasons, including power generation, recreation, and flood control. While providing benefits, there are a wide array of negative environmental effects associated with this infrastructure, including disconnecting migratory fish habitat, rendering certain fluvial populations unable to complete their life cycle. To reduce this impact, it is necessary to pass fishes across dams. However, it is not desirable to pass all fishes; in the case of invasive species, dams act as beneficial barriers to prevent wider proliferation in watersheds. Thus, conservation goals require increasing passage rates for some fishes while reducing passage rates of others. This dissertation focuses on ways to leverage the local hydrodynamics associated with fish passage infrastructure to achieve passage goals. Fishes primarily pass dams using fishways, adjacent structures designed specifically for this purpose. Many of these designs impart intense turbulence into the flow, and the turbulent fluctuations can prevent fishes from successfully passing; for fishes that can pass, heightened stress has negative impacts at times such as loss of fertility or increased mortality rates. Altering these flows to be more amenable to successful passage is therefore of interest. Chapter 2 of this dissertation provides a framework for applying turbulence theory to fishway design for estimation and remediation of strain rate and eddy size, two flow metrics shown to be harmful to early-life stage fishes. This framework offers a simple way to consider the turbulent hydraulic conditions prior to construction of new, or retrofit of existing, fishways. Another challenge to habitat restoration efforts is a deficiency in meaningful environmental turbulence data, due to a lack of instrumentation able to directly measure turbulence metrics in-situ. Chapter 3 details and provides proof-of-concept for a novel field instrument utilizing Particle Image Velocimetry (PIV) to address this instrumentation gap. Fishway efficiency largely depends on the turbulence present; to assess a common fishway design, Chapter 4 maps the hydrodynamics within Denil fishways, the detailed flows in which have never been quantified experimentally. Using a physical model of a Denil fishway and PIV, flow patterns at several slopes and flowrates are measured to examine how the flow changes with different design grades. This study found there are two primary flow phenomena that hinder passage: with increasing slope, low-speed refuges are lost, and areas of heightened vorticity with high potential to destabilize fishes develop directly in the swimming path. Detailing environmental hydrodynamics may be additionally used to block passage and improve trapping of invasive species. Chapter 5 explores improving sea lamprey (an invasive parasitic fish in the Laurentian Great Lakes) trap entrance rates through mapping the hydrodynamics surrounding and within two common trap types, mesh face and solid face. These flows were measured in flumes in both a controlled hydraulics laboratory and at Hammond Bay Biological Station (HBBS). These measurements are paired with sea lamprey observation conducted at HBBS in response to these flows, to develop an understanding of both what turbulent conditions are experienced at these traps, and how sea lampreys respond to them. This study found the solid face trap to be attractive at close range, but performed poorly due to presenting hydraulic obstacles to sea lampreys attempting entrance. The mesh face trap at high flows was the most successful design with the highest entry rates.