[Objective] In hydraulic projects, flood-discharge structures operating under compound water inlet conditions often exhibit complex vertical-axis vortices at the inlet in which the approach flow direction differs from the mainstream river direction. Traditional vortex elimination measures perform poorly under such conditions, and severe air-entraining vortices may threaten structural safety and operational efficiency. Based on a pumped-storage power station, this study aims to clarify vortex mechanisms through physical modelling and to develop an efficient and economical vortex elimination measure that completely suppresses air-entraining vortices, thereby providing design guidance for similar projects. [Methods] A 1∶50 undistorted clear-water physical model was built under Froude similarity to ensure geometric, kinematic, and dynamic similitude. Several operating conditions (check, design, energy dissipation, and scour protection) were simulated to reproduce actual operation. Vortex characteristics were observed (air-entraining vortices up to 7.5 cm diameter) without any suppression measures. Five vortex elimination schemes were then tested: Scheme 1—conventional vertical vortex elimination beams with an optimized inlet; Schemes 2-4 —addition of 30° triangular vortex elimination plates to the beams, adjusting beam spacing and width, and reducing the inlet angle α; Scheme 5—a comprehensive optimization scheme using monolithic concrete to simplify the structure. Digital imaging and thin-walled triangular weirs were used to quantitatively analyze vortex elimination effect and flow improvement of each scheme. [Results] (1) Cause of vortices: superposition of lateral and longitudinal inflows under compound conditions markedly increased initial circulation, generating strong vortices within 30° of the inlet (100% type-F vortices at stage 3).(2) Comparison of vortex elimination performance: conventional beams (Scheme 1) merely downgraded type-F to type-D vortices without eliminating air entrainment. Adding 30° vortex elimination plates and optimizing beam spacing (Schemes 2-4) reduced vortex diameter from 7.5 cm to 0.1-0.3 cm, leaving only minor concave vortices (type B) at stage 3. Scheme 5 (preferred) completely eliminated air-entraining vortices while simplifying construction and maintaining smooth flow under all operating conditions. (3) Innovations: 30° triangular vortex elimination plates conformed to the inlet geometry, reducing the inflow angle α and suppressing initial circulation. Widening the central vertical beam enhanced vortex interception and disrupted vortex structure. Scheme 5 replaced complex components with a monolithic concrete pour, balancing effectiveness and constructability. [Conclusions] Vortex intensity under compound water inlet conditions is directly linked to the inlet angle α and initial circulation. Lateral flow amplifies complexity and hazards. Combining vortex elimination beams with 30° triangular vortex elimination plates completely eliminates air-entraining vortices, reducing vortex size by over 98% and remaining effective under all operating conditions. The optimized Scheme 5 balances vortex elimination performance with economy and offers a transferable design paradigm. The findings overcome the limitations of traditional vortex elimination measures and provide valuable guidance for high-head, multi-directional hydraulic projects.

[Objective] As an important part of the side inlet/outlet of a pumped storage power station, the length of the adjustment section directly affects the hydraulic characteristics of the inlet/outlet under bidirectional flow conditions as well as the project cost. This paper aims to investigate the effect of different adjustment section lengths on the hydraulic characteristics of side inlet/outlet, focusing on changes in head loss, velocity distribution, and discharge allocation, and to recommend an appropriate range of adjustment section lengths that meets design codes. [Methods] A three-dimensional mathematical model of the side inlet/outlet of the Lianghekou pumped storage power station was established. The Reynolds Stress Model (RSM) was adopted and validated against physical model test results. The velocity curves obtained from numerical simulation showed good agreement with the experimental measurements, confirming the applicability of the selected turbulence model to the study of inlet/outlet hydraulic characteristics. [Results] For the power generation condition (outflow), increasing the adjustment section length reduced inlet/outlet head loss, homogenized the velocity distribution at the trash rack section, and kept the discharge non-uniformity across openings within 5%. For the pumping condition (inflow), increasing the adjustment section length also reduced inlet/outlet head loss and maintained discharge non-uniformity within 10%. When the adjustment section length L relative to the diffusion section length T satisfied L≥0.3T, the bidirectional hydraulic characteristics of the inlet/outlet were favorable; when 0.1T≤L<0.3T, the bidirectional hydraulic characteristics were slightly poorer but still met code design requirements. [Conclusion] The research results provide support for the design and optimization of adjustment sections.

[Objective] Appropriately reducing the diameter of branch pipes is an effective way to lower the superimposed water hammer pressure in water conveyance systems. However, there is limited research on how replacing a single large-diameter branch pipe with multiple smaller parallel branch pipes affects the hydraulic transient process in such systems. Moreover, there is a lack of research on how to design the diameters of these parallel branches to minimize hydraulic transients while maintaining flow requirements and ensuring economic efficiency. Based on the Qitai high-head gravity-flow water conveyance project, we investigated the impact of branch pipe arrangement on hydraulic transients and proposes principles for determining branch pipe diameters. [Methods] Using numerical simulation, we compared the hydraulic transient behavior in complex pipelines with a single branch pipe versus multiple small-diameter parallel branches, and examined the impact of parallel arrangements on water hammer pressure and pressure fluctuation duration, summarized the design method for branch pipe diameters in parallel schemes, and verified the engineering applicability of the conclusions using a real-world case. [Results] When the number of parallel branch pipes increased from 2 to 5, the maximum positive pressure head in both main and branch pipes significantly decreased under various scenarios. Under the most critical condition, the maximum water hammer pressure was reduced by 10.32% in the main pipe and 48.75% in the branch pipes, respectively, compared to the single large-diameter branch layout. Simultaneous valve closures in the branches did not result in additional pressure increases in the main pipe, and water hammer waves between branches did not interfere with one another. Moreover, replacing a single large branch with multiple smaller branches effectively eliminated negative pressure heads in the branches, thus preventing negative-pressure-induced water hammer, and shortened the duration of pressure fluctuations. The maximum reductions in pressure fluctuation duration at key points in the main and branch pipes were 63.16% and 46.15%, respectively. For stable hydraulic transitions and economic feasibility, the ratio of branch to main pipe diameter at the connection point should be between 0.12<β<0.28. In the Qitai project, using two parallel branch pipes (β=0.226) increased construction costs by 33.33% compared to the single large branch solution, but reduced investment in water hammer protection by 39.10%. [Conclusions] Under the premise of safe water delivery, a water supply scheme that replaces a single large-diameter branch pipe with multiple smaller parallel branches can effectively reduce valve-closing water hammer pressure and shorten the duration of pipeline pressure fluctuations.

[Objective] The integrated operation of water diversion and power generation hubs faces challenges in maintaining hydraulic stability during emergencies, particularly under sudden load rejection conditions. This study aims to develop an adaptive emergency regulation strategy to coordinate the operation between diversion sluices and power generation units, with the objectives of minimizing flow and water level fluctuations in the main canal, reducing decision-making response time, and ensuring the operational safety and efficiency of the water conveyance system. This study addresses the critical gap in existing systems where the lack of an adaptive flow regulation mechanism between sluices and turbines leads to prolonged hydraulic transients and potential safety hazards during emergencies. [Methods] A comprehensive methodology combining theoretical analysis, numerical modeling, and prototype validation was adopted. The emergency operation principle was established based on the goal of rapidly restoring flow into the main canal. An adaptive emergency regulation strategy was then developed by integrating the hydraulic relationship between power units and diversion sluices, along with operational constraints such as unit vibration range and gate opening limitations. A one-dimensional hydrodynamic model was established for the canal system extending from the hub to the downstream check gate, simulating unsteady flow under different disturbance scenarios. The model was calibrated and validated using operational data from the prototype. A typical case involving full load rejection from both power generation units was simulated to compare the proposed adaptive strategy with conventional manual operation. Key performance indicators included water level deviation, flow variation, and response time. [Results] The simulation results demonstrated a significant improvement in hydraulic stability under the proposed adaptive emergency strategy. Compared to conventional manual operation, the adaptive approach reduced the maximum water level fluctuation in typical canal cross-sections by over 40%. The maximum flow fluctuation was reduced by 58%, indicating a markedly smoother transition during emergency load rejection. Furthermore, the adaptive strategy enabled an immediate response to emergency conditions, reducing decision-making and execution time to near real-time. The coordination mechanism between the sluice and power generation units effectively balanced flow discontinuities caused by sudden turbine shutdown, thereby limiting the propagation of disturbances along the canal. The hydraulic response under adaptive control showed faster convergence to stable conditions, significantly reducing the risks of overtopping or drying in the canal. [Conclusions] This study successfully develops and validates an adaptive emergency regulation strategy for water diversion and power generation hubs, significantly enhancing operational safety and efficiency during unexpected events. The proposed strategy introduces an innovative real-time coordination mechanism between sluice gates and power generation units, representing a substantial improvement over traditional human-operated systems that often result in delayed and suboptimal responses. The findings provide a scientific and technical foundation for automated emergency management in multi-objective hydraulic hubs. The adaptive method not only ensures rapid flow recovery and minimizes hydraulic transients but also supports the maximization of power generation benefits without compromising water supply security. This approach has broad applicability in similar large-scale water diversion projects worldwide, highlighting its significance in advancing smart water management and emergency response technologies.

[Objective] Designing the shape of bifurcated pipes has long been a focus in water diversion projects. Current research on the erosion of pipes by sediment-laden flows remains limited, and studies specifically on the erosion and wear of Y-shaped bifurcated pipes are even rarer. This study aims to investigate the erosion and wear characteristics of Y-shaped bifurcated pipes and optimize their shape. [Methods] We employed numerical simulation and physical model experiments to investigate the solid-liquid two-phase flow within Y-shaped bifurcated pipes during the standalone operation of the main pipe. The influence of an elliptical arc chamfer scheme on the hydraulic and wear characteristics of the bifurcated pipe was explored. The numerical simulation results demonstrated strong consistency with the experimental data, validating the reliability of the numerical simulation method. [Results] (1) During standalone operation of the main pipe, compared with the bifurcated pipe with a circular arc chamfer, the bifurcated pipe with an elliptical arc chamfer had a more open space and gradual variations in the flow cross-section, resulting in smoother internal flow patterns. Its head loss coefficient was smaller, reduced by 6.9% compared to the circular arc chamfer pipe. The local low-pressure distribution at the bifurcation angle significantly improved, and the minimum pressure increased by 1.47 m water head compared with the circular arc chamfer bifurcated pipe, indicating that the elliptical arc chamfer bifurcated pipe could effectively improve the low-pressure distribution and enhance the bifurcated pipe’s cavitation resistance. (2) When the main pipe operated independently, the wear on the bifurcated pipe was most severe near the inlet and outlet of the main pipe, followed by the crotch area, while the branch pipe area experienced the least wear. The particle mass flow rate had the greatest impact on the wear distribution of the bifurcated pipe, followed by the particle impact velocity. By adopting an elliptical arc chamfer, the water flow could move smoothly, and the mass flow rate of particles acting on the pipe walls was reduced, thereby mitigating wear at the main pipe outlet and the crotch area of the bifurcated pipe. The average wear at the corresponding positions was reduced by 22.26% and 21.03%, respectively, compared to the circular arc chamfer bifurcated pipe. [Conclusions] During standalone operation of the main pipe, compared with bifurcated pipes with a circular arc chamfer, bifurcated pipes with an elliptical arc chamfer demonstrate a 1.47 m water head increase in minimum pressure and significant reduction in abrasion at the main pipe outlet and the crotch area. These findings indicate that elliptical arc chamfer bifurcated pipes effectively enhance both cavitation resistance and abrasion resistance of bifurcated pipes, providing valuable references for bifurcated pipe design.

Foundation scour is one of the primary causes of hydraulic failures in river-crossing bridges. By integrating flume experiments, prototype observations, numerical simulations, and artificial intelligence methods, this study reviews research on foundation scour of river-crossing bridges over the past six decades, summarizes progress in three aspects of general scour, contraction scour, and local scour, analyzes the limitations in existing research, and proposes future research directions. In terms of physical mechanisms, most existing studies focus on bridge foundation scour under simplified boundary conditions such as straight channels, non-cohesive riverbeds, and cylindrical structures. However, cohesive sediments prevalent in natural rivers exhibit complex force interactions and high randomness, resulting in scour processes for bridge foundations that differ significantly from those in non-cohesive riverbeds. Moreover, in common natural channels such as braided, branching, confluence, and alternating wide-narrow channels, water-sediment dynamics and riverbed evolution involve numerous factors with strong uncertainties, making scour mechanisms for bridge foundations more complex than those in straight channels. Therefore, future research must focus on scour mechanisms under more boundary conditions commonly found in natural rivers to improve the theoretical framework for foundation scour of river-crossing bridges. Regarding scour prediction methods, existing research primarily relies on flume experiments and prototype observations of specific bridges. The former’s prediction accuracy is severely affected by scale effects, while the latter has limited applicability. To date, there is a lack of predictive formulas or analytical models that quantitatively consider the scale effects on bridge foundation scour. Data-driven models such as artificial neural networks and deep learning can effectively compensate for the inability of conventional prediction methods for bridge foundation scour to account for complex boundary conditions. In particular, multi-module multilayer perceptrons (multi-module MLPs) can construct hybrid neural networks incorporating physical scour mechanisms, showing great potential in addressing the challenges of predicting scour under complex boundary conditions. In numerical modeling, existing methods are often applicable to low Reynolds number conditions, with insufficient accuracy in capturing turbulence at high Reynolds numbers and absence of standardized grid size criteria. Sediment transport is frequently computed using empirical formulas, and dynamic grid technologies often suffer from low precision. Existing numerical methods exhibit inadequate coupling between turbulence models and sediment transport models. Moreover, current numerical simulations are limited to non-cohesive riverbeds, with few models applicable to cohesive riverbeds and virtually no reported models suitable for stratified riverbeds. Therefore, numerical models for bridge foundation scour require in-depth investigation to address these issues in the future, improving their applicability and reliability under complex boundary conditions. In addition, intensified human interventions—including sand mining, channel regulation, and dam construction—have triggered rapid riverbed degradation in many rivers. These degradation events often occur at scales, rates, and complexity far beyond conventional understanding of general riverbed degradation, resulting in highly destructive and abrupt changes. Future research should systematically investigate riverbed evolution under human disturbances. To build a more comprehensive understanding of foundation scour of river-crossing bridges, future studies should better integrate flume experiments, prototype monitoring, numerical modeling, theoretical analysis, artificial neural networks, and deep learning methods. This will enable systematic investigation of bridge scour under human disturbance and complex boundary conditions, thereby improving the theoretical system and developing more widely applicable and reliable scour design methods.

[Objectives] Traditional culvert designs often result in excessively high flow velocities within the channel, impeding the upstream movement of weak-swimming fish species. Installing small triangular baffles inside culverts has the potential to provide upstream passage for small fish while maintaining discharge capacity. This study aims to clarify the hydraulic effects of triangular baffles by arranging multiple small baffles along one side of a flume to simulate internal culvert structures and verify the hydraulic effects through flume experiments. [Methods] Three-dimensional velocity data were collected using an Acoustic Doppler Velocimeter (ADV) to analyze the distribution patterns of turbulent kinetic energy and Reynolds stress. The quadrant analysis method was employed to quantitatively assess the impact of the baffle system on flow velocity distribution, turbulence characteristics, and momentum transport modes. [Results] The results showed that the triangular baffles created stable low velocity zones (LVZs) along the sidewall, with longitudinal velocities ranging from -4 to 15 cm/s, and velocities at the outer edge of the baffles around 25 cm/s, below the critical swimming speed of small fish such as Rhinogobius giurinus. In the mainstream zone, the lateral profiles of longitudinal velocity were nearly identical, ranging from 25 to 30 cm/s, indicating that the small triangular baffles had minimal impact on mainstream flow and thus preserved discharge capacity, achieving synergistic optimization of hydraulic efficiency and ecological function. The proportion of the low velocity zone area remained relatively consistent along the flow path, accounting for 14.80%-18.07% of the total cross-sectional area, demonstrating the feasibility of using triangular baffles to stably expand LVZs. The baffles significantly enhanced turbulence intensity in the region near the baffle-side sidewall, generating clockwise vortices and positive horizontal Reynolds stress that play an important role in maintaining swimming stability. Although the turbulent kinetic energy and Reynolds stress in downstream LVZs were higher than those in high-speed regions without baffles, they remained below the threshold of fish swimming preferences. This moderate turbulence enhancement not only provided energy for swimming but also avoided excessive turbulence that could impair the sense of direction or balance. Momentum exchange was dominated by jetting (Q₂) and sweeping (Q₄) events, whose dominance increased with higher threshold parameter H₀ (with a contribution rate of about 60% at H₀=4). The transient vortices formed had planes parallel to the fish’s spine and body axis, reducing energy loss during upstream movement and improving swimming efficiency through vortex energy transfer. This provided a more favorable flow environment for weak-swimming fish species. [Conclusions] This study identifies the distribution patterns of mean flow and turbulence characteristics and introduces quadrant analysis into the study of culvert turbulence-fish behavior interactions. It reveals the promoting effect of small baffle structures in fish upstream migration and addresses the lack of detailed flow field and turbulence structure analyses in previous research. The findings offer a feasible hydraulic optimization paradigm and model reference for the design of eco-friendly culverts.

[Objective] To address the issue that conventional river regulation structures struggle to dynamically adapt to the highly variable characteristics of natural rivers, this study develops an innovative active flow-regulating vane system. [Methods] The system combined a vertically adjustable and rotatable vane structure with a remote intelligent control module. It allowed real-time monitoring and dynamic adjustment of flow parameters, thereby overcoming the limitations of traditional fixed structures such as spur dikes and deflector vanes. To investigate its applicability in curved river channels, the flow-regulating vanes were arranged in a 180°U-shaped bend model. The verified RNG k-ε turbulence model and VOF method were used to conduct numerical simulations of the bend’s flow field characteristics before and after the vane installation. The impact of the flow-regulating vanes on the hydrodynamic structure of the bend was analyzed. [Results] 1) Numerical results showed that when the top of the flow-regulating vanes was flush with the free water surface (at a flow rate of 7.9 L/s), the longitudinal velocity near the convex bank region increased by 21.67% compared to the original bend, while the maximum transverse velocity in the central region decreased by 70.33%, effectively weakening the transverse circulation. When the vanes were submerged to 0.3 times the water depth (at a flow rate of 15.8 L/s), the longitudinal velocity still increased by 13.64%, and the transverse velocity decreased by 37.63%. 2) Analysis of the flow field structure revealed that the vanes could split the original single clockwise vortex circulation structure within the bend into two vortices rotating in the same direction, which reduced the flow’s kinetic energy, lowered the circulation velocity, and decreased transverse sediment transport. 3) The distribution of bed shear stress showed that, after the installation of the flow-regulating vanes, the bed shear stress within the bend was uniformly distributed along the convex bank side, which helped alleviate sedimentation on the convex bank while avoiding concentrated scouring. Moreover, the suspended design of the vanes reduced flow obstruction at the bend bottom, solving the sedimentation problem caused by decreased flow velocities around traditional structures fixed to the riverbed, making it a viable option for flow regulation in hardened bend channels.

[Objective] The flow patterns of energy dissipation inside tunnels are complex, and theoretical calculations cannot meet design requirements. This research aims to: (1) verify the rationality of design parameters for energy dissipation in diversion tunnels at canal head based on hydraulic model tests; (2) propose an energy dissipation layout suitable for specific projects through model optimization to address high wave height inside the tunnel, insufficient clearance below the tunnel crown, and cavitation and erosion. [Methods] A hydraulic model test with a scale of 1∶1.5 was selected to simulate the diversion channel, pressurized tunnel, in-tunnel gate chamber, energy dissipation section, and a downstream section of free-flow tunnel. Additionally, an emergency gate shaft and the ventilation pipe behind the gate were simulated. A water tank was used as the model reservoir. The project involved three different discharge conditions, each with varying reservoir water levels, resulting in eight typical working conditions for testing. Then, based on the hydraulic model test results under different conditions, the downstream flow pressure characteristics, cavitation characteristics of the weir surface behind the operating gate, pressure characteristics of the gradually expanding stilling basin floor and sidewalls, flow connection patterns, and energy dissipation performance were obtained. Finally, the dimensions of the stilling basin section and the free-flow tunnel were improved, and wave suppression measures were optimized based on the test results. [Results] The hydraulic model test revealed shortcomings in the original energy dissipation scheme and proposed a combined layout of “stilling basin + wave suppression beam” suitable for in-tunnel energy dissipation. The test results showed: 1) the maximum wave height inside the free-flow tunnel was reduced by 67%, and the tunnel crown clearance met safe water conveyance requirements; 2) The local minimum cavitation number of the water flow at the curved section of the weir surface and the expanded section of the sidewalls behind the operating gate was about 0.37, indicating a low likelihood of cavitation erosion; 3) The root mean square of fluctuating pressure at measuring points along the stilling basin floor did not exceed 1.0×9.81 kPa, meeting structural design requirements. [Conclusion] This study proposes a combined energy dissipation method of “stilling basin + wave suppression beam” to address problems of high wave height and insufficient tunnel crown clearance in the original scheme. Compared with traditional submerged energy dissipators, the combined method significantly improves dissipation efficiency and has better energy dissipation characteristics. Hydraulic model tests verify the feasibility of the optimized scheme. The energy dissipation scheme is effective in solving the problems of large waves and insufficient tunnel crown clearance in similar projects. It is effective under multiple reservoir water levels and discharge conditions, and the wave suppression beam, as an in-tunnel energy dissipation structure, has little impact on tunnel flow capacity, demonstrating certain universality.

[Objective] When the water level difference between the upstream and downstream of a long-distance gravitational water conveyance system is small, gravity flow alone cannot ensure the required design flow rate. In such cases, the intake pumping station must be activated during high-flow conveyance periods to provide pressurized supply, forming a combined gravity and pressurized flow system. The hydraulic characteristics of such systems are more complex than those of pure gravity-driven systems. Accidental pump shutdowns can easily induce water column separation in the pipeline, leading to water hammer upon rejoining that poses a significant threat to project safety. [Methods] To address this issue, this study employed the method of characteristic curve to conduct one-dimensional numerical simulations of transient hydraulic processes for four water hammer protection schemes: (1) air valve, (2) air valve + terminal valve, (3) air valve + terminal valve + overflow pipe, and (4) air valve + air valve surge chamber. [Results] In long-distance gravity-pressurized water conveyance systems where the upstream elevation was higher than that of the downstream, accidental pump shutdowns without any protective measures would generate decompression waves that caused extreme negative pressure and water column separation inside the pipeline. The subsequent compression wave reflected from the downstream outlet reservoir would cause the separated water column to rejoin, potentially resulting in pipe rupture. Therefore, effective protective measures must be adopted to eliminate extreme negative pressure in the pipeline. When using an air valve alone for water hammer protection, the minimum pressure within the pipeline was effectively increased, but the range of protection was limited. In the air valve + terminal valve scheme, the compression wave generated by the closure of the terminal valve failed to effectively mitigate the negative pressure and may even result in excessive maximum pressure due to poor closure regulation of the terminal valve. Adding an overflow pipe to this combined scheme effectively reduced the maximum pressure in the pipeline. However, since the overflow pipe reflected part of the compression wave generated by the terminal valve closure, it had an adverse effect on negative pressure protection. [Conclusions] The air valve surge chamber, combining a surge pipe and an air valve with both water and air compensation functions, is used in combination with an air valve to form a protection scheme that effectively controls both positive and negative pressures in the pipeline. This solution achieves balance between engineering safety and cost-efficiency, making it the preferred protective measure for long-distance gravity-pressurized water conveyance systems.

[Objective] With the continuous expansion of China’s water conservancy infrastructure, hydraulic structures such as dams and sluice gates have obstructed fish migration routes and altered hydrological regimes both upstream and downstream. These changes have led to fragmentation of fish habitats, population declines, and even pushed some endemic fish species to the brink of extinction. To protect aquatic biodiversity and restore river connectivity, fishways have been widely implemented as critical passage facilities. Post-construction monitoring of fishway effectiveness is essential for verifying performance and identifying potential design improvements to enhance functionality and operational management. [Methods] This study evaluated the performance of the nature-like fishway at Sanghe River Secondary Hydropower Station through comprehensive monitoring. Hydrodynamic conditions were assessed using an Acoustic Doppler Current Profiler (ADCP) and 3D acoustic Doppler velocimeter (ADV) to measure water depth, temperature, and velocity parameters, ensuring they met fish passage requirements. Fish passage was monitored using infrared underwater video surveillance and capture methods during periodic dewatering, with data collected on species composition, abundance, size distribution, and movement patterns, providing references for domestic studies on nature-like fishway construction and fish passage monitoring. [Results] Results indicated all hydrodynamic parameters met design specifications. During monitoring, reservoir levels remained stable at 75 m, with fishway depths fluctuating between 0.03-1.22 m. Average velocities were 0.79 m/s in boulder crevices and 0.635 m/s in main channels, creating suitable migratory conditions. A total of 3 954 fish from 24 species (9 orders, 14 families) were recorded, dominated by Cypriniformes (75.99%). The most abundant species were Crossocheilus reticulatus, followed by Sikukia flavicaudata and Hampala macrolepidota, with most fish measuring 10-20 cm in length and 0-5 cm in width. Migration patterns showed distinct temporal variations: 68% of fish moved upstream, with significantly greater passage efficiency during daylight hours (06:00-18:00). Peak migration occurred in July-August, validating the design assumption of April-August being the primary migration season. [Conclusions] Measures to improve fish passage effectiveness include optimizing power generation-fishway coordination, removing debris in front of dam,dredging and maintaining fishway, and regular cleaning of monitoring equipment to improve reliability. The nature-like fishway at Sanghe River has successfully reestablished connectivity and created favorable hydrodynamic conditions for fish migration, demonstrating significant conservation value for the basin’s ichthyofauna.

Based on the mechanism experiments conducted for the spillway of the Lianghekou hydropower station, this study investigates the variation tendencies of the flow regime, dynamic pressure, air vent cavities, wind speed, and aeration concentration under three types of aeration thresholds. The applicability of formulas for calculating cavity length, gas-water ratio, and water content ratio to the studied project are analyzed, and the derived conclusions could be employed for further investigation on Lianghekou hydropower station and other similar hydraulic projects. Research findings indicate that aeration in the water flow becomes more pronounced with the increasing of spillway discharge, and several hydraulic indicators increase simultaneously, including the root mean square of time-averaged pressure and fluctuating pressure, aeration rate, cavity negative pressure, and cavity length. At a given discharge, the air concentration increases along the spillway, and the vertical distribution of aeration concentration displays successively C-shaped, S-shaped, and I-shaped patterns. According to the research findings, we recommend that Shi Qisui’s formula for cavity length, Chen Zhaohe’s formula for gas-water ratio, and Hall’s formula for water content ratio are most suitable for the estimations of the present study.

To support precise measurement and control of water volume in irrigation area, this study investigated the influence of diversion outlet on the flow pattern in front of control gate, as well as the variation laws of flow coefficient and head loss of trapezoidal control gate under different slopes and water diversion angles. We observed the flow pattern at diversion outlet and analyzed the causes, and further established the flow formula for trapezoidal control gate by using dimensional analysis method and calculated the head-losses based on 495 groups of discharge tests under different water diversion conditions. The discharge tests involved different gate openings and water heads with three slopes (m=1.5, 1.75, and 2) and five water diversion angles (θ=30°, 45°, 60°, 75°, and 90°). Results revealed that a backwater area was formed in front of the control gate. The coefficient of determination of the flow formula was R²=0.934, and the average relative error of the flow was 2.83%. Relative head loss decreased as the relative opening of the control gate increased. The results demonstrated high accuracy of the proposed flow formula for trapezoidal control gate, which offers a basis for flow measurement in trapezoidal channels in irrigation areas.

The navigation flow conditions of canal directly impact ship navigation safety. Channel regulation measures can effectively alleviate unfavorable flow conditions. In the Pinglu Canal project, after the original channel was widened and deepened, a significant bottom elevation difference emerged between the canal and the tributaries along the original river course. These tributaries, entering the confluence with a large drop, adversely affect the navigable flow conditions of the mainstream. Xinpingshui is a representative tributary with a large riverbed elevation difference and a wide intersection angle with the canal. To ensure smooth navigation in the Pinglu Canal, we conducted fixed-bed model tests to investigate the navigable flow conditions at the confluence of the Xinpingshui tributary and the main canal. Based on the test results, we proposed corresponding regulation measures. Results indicate that, on the basis of the canal construction, widening both the main and tributary channels and installing additional dissipation pools and diversion dikes at the tributary mouths significantly improve the navigational flow conditions under various flood scenarios. The findings of this study can serve as a reference for improving navigation channels in similar river reaches.

Based on measured water level and discharge data in 2018, this paper investigates the propagation of flood waves in the river reach between Three Gorges Dam and Gezhouba Dam driven by hydropeaking regulation by using a one-dimensional analytical model. During daily hydropeaking operations at both dams, the outflow exhibited significant diurnal and semi-diurnal fluctuations, ranging from 1 500 to 2 000 m³/s for Three Gorges Dam and 1 200 to 1 500 m³/s for Gezhouba Dam in average. Similarly, the water level at Huanglingmiao and Nanjinguan stations fluctuated by about 0.5-0.8 m daily. The one-dimensional analytical model accurately simulates the fluctuation of water level and discharge between the two dams. The simulation results indicate that flood waves in the river reach propagate as high-frequency standing waves with a period of 1.2 hours. The maximum amplitudes of the standing waves are approximately 2.1 cm for water level and 210 m³/s for flow discharge. The flood waves are superimposed by the hydropeaking operations of both dams, and the timing of regulation at Gezhouba Dam significantly affects flood wave propagation. Specifically, increasing the regulation time from 0.6 to 1.2 hours substantially enhances the flood wave amplitude. While bottom friction of river channel has a negligible impact on wave height, it accelerates the attenuation of flood waves during propagation.

Since the completion of the Three Gorges Dam in 2003, its flood discharge and energy dissipation structures have withstood many flood tests. To further evaluate and summarize the design and actual performance of these structures, the discharge capacity of the Three Gorges Project was comprehensively assessed during the first regular dam safety inspection. The flow capacity of the power station units was verified using data from the Huanglingmiao Hydrological Station. The measured flow data from the power station indicate that the turbine output curve accurately reflects the actual flow rates of the left bank, right bank, and underground power stations. The actual discharge capacities of deep holes and surface holes were also evaluated and compared with their respective design values and model test results. The comparison reveals that the measured discharge capacity of deep holes matches the design value, while the measured discharge capacity of surface holes is slightly higher than the design value. However, the combined discharge capacity of deep holes and surface holes is basically consistent with the design value.

This study aims to address the turbulent flow patterns and significant water surface fluctuations in the original stilling basin, which lead to the formation of repelled downstream hydraulic jumps and subsequent scouring damage to the apron slab. To mitigate these problems, a combined chute block and trapezoidal block energy dissipator is employed, and the hydraulic characteristics of this dissipator are investigated. Physical model testing and numerical simulation techniques are combined to study the energy dissipation behavior under various flow rates. The energy conversion processes within the flow are analyzed, and flow velocity reduction ratios are calculated to assess the effectiveness of the dissipator. Findings indicate that, for the chute block-trapezoidal block joint dissipator with double rows of trapezoidal blocks arranged in a staggered manner, the velocity reduction ratios at three different flow rates are 60.00%, 75.34%, and 73.75%, respectively. Compared to the original stilling basin, this arrangement reduces the length of the hydraulic jump by 11.29%, 14.17%, and 10.22% across the respective flow rates. The energy dissipation mechanism is categorized into four distinct zones: the flow contraction and diversion area, the hydraulic jump swirl area, the vortex areas on both sides, and the post-jump mainstream area. The findings provide a valuable reference for the design of joint dissipators and the optimization of stilling basins.

At present, the evaluation of fishway effectiveness primarily relies on methods such as net fishing and PIT (Passive Integrated Transponder) tracking to directly assess the quantity and efficiency of fish passage. However, these approaches have limitations, including long cycle, heavy workloads, and the inability to diagnose or identify abiotic engineering issues. Based on existing monitoring data of fishway effectiveness in China, we constructed an evaluation index system that encompasses abiotic indicators such as hydraulic condition suitability, environmental factor adaptability, and internal structure conformity, as well as biological indicators like fish passage effectiveness. Canonical correlation analysis reveals that hydraulic and structural indices, including the inlet velocity index, slot width index, and energy dissipation index, significantly influence fishway effectiveness, with respective weights of 0.23, 0.16, and 0.15. By integrating fuzzy evaluation theory, we developed a fishway effectiveness evaluation model based on abiotic indices. Case analysis demonstrates that the model’s results align with direct monitoring conclusions, indicating that the model can provide more reliable scientific and technological support for fishway operations in China.

Affected by corner centrifugal force and inertial force, stilling pool at the turning section of spillway often exhibits unfavorable flow conditions characterized by uneven water depth and flow velocity distribution. To address this complex flow issue, we conducted simulations on stilling pool at the turning section of the spillway of XBT reservoir in Xinjiang. We designed 17 simulation schemes and selected flow pattern, water depth, average flow velocity, and energy dissipation rate as evaluation indices. Results indicate that the hydraulic characteristics of the turning-section stilling pool vary in different simulation schemes. To mitigate adverse hydraulic phenomena in the stilling pool, deepening the pool depth to 6.55 m, adopting a rectangular open outlet type, and equipping 9 staggered rough strips can achieve optimal flow condition. This configuration resolves the backwater problem in the middle and rear sections and eliminated overflow along the walls. Notably, the water depth at concave bank declined by 30.22% compared to the original scheme, with a marginal water level difference of only 0.02 m between the two sides. According to calculation results of the average water depth and kinetic energy of typical section in the stilling pool, the average water depth at the outlet section decreased by 49.97% from the original scheme, while energy dissipation rate enhanced from 18.97% to 62.63%.

In order to reveal the characteristics of radial and vertical jets in the opposite wall jet, renormalization group k-ε model is adopted to simulate complex three-dimensional opposed jet. The partition structure and expansion rate of radial and vertical jets are analyzed.The influences of initial Reynolds number and nozzle distance on jet expansion rate are discussed.The results show that radial jet and vertical jet have similar regional division, however, vortices in different directions formed in the flow field have different influence ranges. The initial Reynolds number has no obvious effect on the expansion rate of the radial jet. The nozzle distance has a significant effect on the expansion rates of radial and vertical jets. The larger the nozzle distance is, the larger the expansion rates of the radial and vertical jets are. Meanwhile, the nozzle distance has a certain influence on the jet development. Near nozzle spacing shortens the time for jet to reach the maximum velocity point, and speeds up the development process.