Boulder arrangement on a rocky ramp fishway based on the swimming behavior of fish

A rocky ramp fishway is one of the Nature like fishway, comprises a long sloping channel and boulders on a slope (Katopodis et al., 2001). The turbulence and backwater around the boulders creates refuges of decreased local flow where fish can rest. However, recent studies have shown that turbulent flow may influence fish migration (Smith et al., 2006). This paper is focused on boulder arrangement and height of boulder on rocky ramp fishway. The swimming performance of char (Salvelinus richardson) and freshwater sculpin (Cottus pollux) around boulders on experimental channel were observed using ultra-high-speed cameras, and the appropriate arrangement of boulders for each species was considered. In total, 27 hydraulic conditions were assessed considering variable distributions, shapes, heights of the boulders as well as variable flow depths by observing swimming behavior for each condition. Laboratory measurement shows that sculpin, which are bottom fish, require a density, and several linear arrangements of boulders to allow migration. As increasing the vertical low-velocity area, which is created behind high boulders does not always result in a good outcome for sculpin. However, this solution is not suitable for char; therefore, a diverse arrangement of boulders is required on individual rocky ramp fishways to allow the movement and migration of multiple species. We propose to add cloister in the fishway for free migration of weak swimmer.