Hydraulic aspects of pool-weir fishways as ecologically friendly water structure

Abstract

Today, natural rivers are increasingly fragmented by human-made obstacles such as dams. Due to these structures fish populations in natural rivers rapidly diminish. In this context, fishways are a useful hydraulic structure in the creation of ecosystem for fish migration. Three dimensional mean flow and turbulence structure of pool-weir fishways were experimentally explored. During the experiments, three different notch sizes were applied while the size of the orifice was kept constant. Two acoustic Doppler velocimeters were employed throughout the velocity measurements. Three-dimensional mean velocity and normalized turbulent kinetic energy patterns in the pool were experimentally analyzed considering the swimming ability of different fish species to check whether the given design conditions provide suitable flow patterns. Based on the data, a linear relationship between the parameters “the discharge” and “the average depth in a pool” was generated. An equation was derived which gives the “energy dissipation rate per unit pool volume” in terms of the parameters “geometrical characteristics of the fishway”, “head difference between pools”, “slope”, and “acceleration due to gravity”. The discharge ratios between “flow through orifice” and “flow over notch” were expressed based on the data.