Hydraulic design criteria of the modified meander C-type fishway using the combined experimental and CFD models

Abstract

Fishways' structure has been developed to mitigate the harmful effects of human-made structures such as dams and weirs on the migratory fish process as an essential part of the environmental cycle. In this study, a Modified Meander C-type Fishway (MMCF) was designed and analyzed based on a fish species movement capability. The proposed fishways' structural design follows the key features of the vertical slot fishways (VSF) structure and consists of eleven successive cylindrical pools connected through vertical slots. In the present study, physical and computational fluid dynamics were used to investigate the flow characteristics inside the cylindrical pools with designed radius (R) and vertical slots as the system's connectors. Different geometry scenarios were applied to the model, such as the slots' various dimensionless opening ratios (s/R = 0.1, 0.2, 0.3) with varying bed slope scenarios (5%, 10%, and 20%). The obtained results illustrated the dimensionless hydraulic design diagrams based on the dimensionless discharge parameter (Q⁎) as a critical parameter for designing and operating the fishways. Horizontal and vertical flow velocity distribution graphs were presented, which could be used to estimate a potential low-velocity field for each specific fish species. As a geometrical improvement scenario, the pool's average-depth parameter (d) was increased for each scenario using the designed vertical baffles adjusted at the pools' opening gate with different vertical slot's height scenarios (hb/R = 0, 0.1, 0.2). Studying the radial and tangential fluctuations of the turbulent flow inside the proposed fishway demonstrated the structure's performance to make a more stable swimming path for the fishes toward the upstream movement.