Flow and turbulence structure in a baffle–brush fish pass

The flow and turbulence characteristics of a new baffle–brush type fish pass were investigated experimentally in a 2 m wide rectangular flume with a bed slope of 4% and Reynolds and Froude numbers in the range 5 × 10 4 –2·8 × 10 5 and 0·17–0·23, respectively. The baffle–brush fishway combines the properties of a baffle (Larinier) fish pass with the features of the brush-furnished fishway. The baffle–brush fish pass ensures continuous low- and high-velocity migration corridors for both strong (e.g. salmon) and weak swimming (e.g. river lamprey) fish, with negligible flow accelerations (i.e. quasi-uniform conditions). The turbulent kinetic energy (TKE) takes its maximum value near the centre of the baffle zone and decays towards the brush zone. The effects of the Reynolds number (Re) on the resultant velocity and TKE distributions were also investigated. For Re = 2 × 10 5 , the TKE was in the range 0·05–0·21 m 2 /s 2 with an average value of 0·11 m 2 /s 2 in the baffle section, whereas it ranged between 0·007 and 0·04 m 2 /s 2 with an average value of 0·02 m 2 /s 2 in the brush section. In the proposed fish pass there is no need to build resting pools.