An experimental study of turbulent structures in combined fishway of overflow weir and vertical slot

Three-dimensional instantaneous flow velocity was measured by an Acoustic Doppler Velocimetry(ADV) in a combined fishway with an overflow notched weir, and a vertical slot with an identical layout. Turbelent structures, such as time-averaged velocity, turbulence intensity, Reynolds stress, correlation function, and turbulence scales in the fishway pool were analyzed based on the jet mechanics and statistical theory of turbulence. The experimental results showed that flow patterns in the combined fishway pool of the overflow weir and the vertical slot, exhibited complex three-dimensional turbulent structures. The effects of the overflow weir on turbulence intensity and Reynolds stress were more considerable, relative to the vertical slot, especially in the pool surface layer. But correlation of the eddy structures in the weir flow region was better than that in the wall jet region, due to vertical slot. Also there were larger eddy structures in the weir flow region, whereas the eddy size in the wall jet region was smaller. Compared with the single fishway, turbulent structures in the combined fishway were more complicated. These studied results can provide an important guide for optimizing fishway design and rehabilitating fish habitat.