Hydrodynamic characteristics and cross-sectional energy dissipation mechanisms in nature-like fishways

In response to the problems existing in traditional vertical-slot fishways, such as high-velocity barriers, fixed upstream channels, single energy dissipation forms, and backflow zones that tend to cause fish disorientation, this study focuses on the staggered stone wall-type nature-like fishway. It aims to explore its advantages in hydrodynamic characteristics and the influence of design parameters on the energy dissipation rate, so as to provide guidance for optimized design. Based on local physical model tests, an analysis was conducted with vertical stratification along the water depth direction. The research results are as follows: In terms of hydrodynamic characteristics, through hierarchical and coordinated optimization of hydraulic conditions, a stable and straight upstream channel capable of supporting fish passage across the entire cross-section is formed in the surface layer; in the middle and bottom layers, under the combined action of circumfluence and pore flow, an "S"-shaped channel with low energy consumption and low curvature is formed, with a clear upstream direction. The interaction between pore water flow and circumfluent water not only eliminates the backflow zone behind the wall but also forms a low-velocity resting area, thereby effectively avoiding the risk of upstream fish disorientation caused by fixed paths and backflow phenomena in traditional vertical-slot fishways. In terms of energy dissipation rate regulation, the energy dissipation rate (η) is regulated by three factors: flow rate (Q), cross-sectional bottom width (B), and the relative relationship between stone wall height (H) and water depth (h). Specifically, η is significantly negatively correlated with Q; increasing the bottom width at low flow rates can improve frictional energy dissipation efficiency, and as the flow rate increases, the advantage in energy dissipation efficiency brought by increasing the cross-sectional bottom width decays rapidly. The influence of the wall height-water depth relationship on the energy dissipation mechanism can be divided into three stages: in the unsubmerged stone wall stage, the difference in energy dissipation rate is not significant; in the critically submerged stone wall stage, the energy dissipation rate is positively correlated with water depth; in the over-submerged stone wall stage, the dominance of weir flow leads to intensified attenuation of the energy dissipation rate. Overall, the staggered stone wall-type nature-like fishway, with its hierarchically coordinated hydrodynamic characteristics and diverse energy dissipation modes, avoids the inherent defects of traditional fishways, and the relevant research results can provide a basis for the engineering practice of nature-like fishways.