The enormous energy carried by discharged water poses a serious threat to the Piano Key Weir (PKW) and its downstream hydraulic structures. However, previous research on energy dissipation in PKWs has mainly focused downstream effects, and the research methods have been largely limited to physical model experiments. To deeply investigate the discharge capacity and hydraulic characteristics of PKW, this study established a PKW model with universally applicable geometric parameters. By combining physical model experiments and numerical simulations, the flow pattern of the PKW, the discharge at the overflow edges, and the variation in the energy dissipation were revealed for different water heads. The results showed that the discharge of the side wall constitutes the majority of the total discharge at low water heads, resulting in a relatively high overall discharge efficiency. As the water head increases, the proportion of discharge from the inlet and outlet keys increases, while the proportion from the side wall decreases. This change results in less discharge from the side wall and a consequent reduction in the overall discharge efficiency. The PKW exhibits superior energy dissipation efficiency under low water heads. However, this efficiency exhibits an inverse relationship with an increasing water head. The overall energy dissipation efficiency can reach 40% to 70%. Additionally, the collision of the water flows inside the outlet chamber and the mixing of the overflow jet play a primary role in energy dissipation. The findings of this study have significant implications for hydraulic engineering construction and PKW operational safety.

The piano key weir is a new type of labyrinth weir structure form, its advantages such as stable structure, upstream and downstream inverted overhang and small base area greatly improve the scope of application, and it has high discharge capacity and overflow efficiency, which is considered as a very effective method to solve the shortage of reservoir and dam discharge flow, and has more applications abroad. In this paper, the experimental observation of the hydraulic characteristics of the discharge from the hydraulic physics model of the piano key weir confirms its good overflow capacity, but also limits the study of its complex flow. Combined with the numerical simulation software, the three-dimensional flow field of the piano key weir is numerically simulated based on the RNG k-ɛ turbulence model and the free-surface VOF technique to analyze the changes of hydraulic characteristics such as flow patterns, flow lines and flow velocities, and to clarify the hydraulic characteristics of the spillway and the mechanism of the improved spillway capacity by combining the experimental results of the physical model. In addition, a comparative analysis of the overflow capacity and flood discharge efficiency between the piano key weir and the traditional thin-walled weir is carried out to better reflect the advantages of the piano key weir in flood discharge by using the over-discharge ratio, and to discuss the application of the piano key weir in actual diseased reservoir and dam projects.

Visual cues are critical for orientation and migration in riverine fishes, providing potential mechanisms for behavioral guidance. This study investigated how light spectrum and intensity interact to modulate phototactic responses in two schizothoracine fishes from the upper Yalong River. Results showed Schizopygopsis malacanthus preferred blue light and avoided red light, with preferences shifting with flow intensity; Schizothorax kozlovi favored green light and avoided light-red light, with minimal flow impact. We propose that engineers build fishway entrances or ideal habitat attractors that prioritize low-intensity blue light (10 lx) and medium-intensity green light (50 lx), supplemented by medium-intensity blue light (50 lx). This study provides scientific evidence and application value for restoring fish habitats, fish passages, and fisheries.