An experimental investigation of flow resistance and turbulent flow in brush fish pass

The flow and turbulence structure of a brush fish pass was investigated in a 1:2 physical model for Reynolds numbers of 5·46 × 10⁴–1·78 × 10⁵ and Froude numbers of 0·18–0·72. Experiments were performed with three different bed slopes (2, 4, and 6%) and four different areal bristle densities. For each bed slope and bristle density, data were collected for six different relative submergences of emergent flexible bristles. Bristle density and channel bed slope were found to play a crucial role in the experiments. From dimensional analysis and physical model measurements and calculations, the friction factor was derived for the brush fish pass. The main findings can be summarised as follows; (a) flow resistance was found to be a function of the Cauchy number of the bristles, the channel bed slope and bristle density; (b) the channel bed slope is a main parameter that controls the maximum velocity and turbulent kinetic energy (TKE) magnitudes; and (c) the spatially averaged TKE seems to be considerably lower for the same dissipated power in a brush fish pass compared with other conventional fish passes (vertical slot and natural types). Hydraulic design recommendations are given to avoid a tumbling flow regime and drag coefficient scale effects.