Abstract
Fishways can assist fish species to overcome obstacles for performing spawning, feeding, and overwintering migrations. Flow structures in a flat-crested weir-type fishway were experimentally studied. Variations of time-averaged velocity, turbulence intensity, and Reynolds stress with longitudinal and vertical directions and flow rates were analyzed. Also, flow patterns in the longitudinal profile were given. The experiments were carried out in a large scale fishway model in the Hydraulics Laboratory at Zhejiang University of Technology. Two typical flow rates corresponding to detection and preference velocities of fish species were considered. Five different horizontal planes for each flow rate were taken. Eleven transverse lines were arranged for each horizontal plane. Ten measuring points were laid along each transverse line. Three-dimensional velocity at each measuring point was measured by acoustic Doppler velocimeter (ADV). Longitudinal and vertical time-averaged velocity distributions, longitudinal turbulence intensity distribution on the different horizontal planes, vertical turbulent intensity distribution along flow depth, and Reynolds stress distributions on the different horizontal planes and on the different cross-sections in the pool of fishway were analyzed. The experimental results showed that distribution of longitudinal velocity was characterized by topology, which constituted an apparent vertical vortex. Weir flow exhibited skimming flow in the fishway pool. Peak-value range of longitudinal turbulent intensity existed. The amplitude of variation in Reynolds stress near the surface layer reached the maximum, which provided a certain hydraulic condition for fish that favor jumping near the surface layer. This study uncovers three-dimensional flow structures, especially for turbulence characteristics, which can contribute to improving the design of crested weir fishway and to assisting fish species to pass smoothly through fishway, being of potential application value.
Highlights
A fishway is a low-head hydraulic structure, which can assist fish species to overcome obstacles to assist in spawning, feeding, and overwintering migrations
It follows from the figure that flow profiles along each depth are characterized by topology, constituting considerable vertical vortex, the velocity in each depth are characterized by topology, constituting considerable vertical vortex, the velocity in the the center of the vortex is almost zero
It can be seen that, under flow rates Q1 = 20.79 L/s and Q2 = 30.04 L/s, there exists a certain similarity in longitudinal velocity distribution except close to the baffle, and the maximum velocity at each in longitudinal velocity distribution except close to the baffle, and the maximum velocity at each cross-section is located in theREVIEW
Summary
A fishway is a low-head hydraulic structure, which can assist fish species to overcome obstacles to assist in spawning, feeding, and overwintering migrations. A fishway effect is related to hydraulic characteristics of the pool, and depends on swimming behavior of fish species. It is of important practical significance to further study the hydraulic characteristics of fishway based on the swimming behavior of fish species, especially in the effect of turbulent structures in fishway on fish swimming behavior. Designs of almost all types of fishways are based on the dissipation principle so as to lower flow velocity for facilitating anadromous fish species. The salmon swam in the form of ski-jump among the vortices, which could reduce the axial muscle activity It means that the energy cost of a fish swimming in turbulent flow could be reduced if the fish swam appropriately. The three-dimensional instantaneous velocity at each measuring point in a fishway pool was measured by acoustic Doppler velocimeter (ADV) in a large-scale pool-weir fishway flume, and turbulent structures were analyzed in detail
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