Abstract:This paper employs historical analysis, policy text research, and practical case studies to systematically examine the historical evolution of river and lake management in China, as well as the reform and innovation measures adopted in the new era. It summarizes the experiences gained from river and lake management practices in the new era and, by applying theories such as ecosystem services, sustainable development, collaborative governance, and public participation, proposes the transformation directions and implementation pathways for river and lake management in China. Research indicates that China has always attached great importance to the development of river and lake management. Currently, guided by the new development philosophy and General Secretary Xi Jinping’s important discourses on river and lake management, China has promoted the implementation of the River and Lake Chief System, the national strategy for major rivers and the national water network, and the creation of Beautiful and Happy Rivers and Lakes. These practices have collectively shaped a set of reform experiences suited to the new era in river and lake management: adhering to the guidance of Xi Jinping’s ecological civilization thought, leveraging the advantages of the national system for accomplishing major tasks, fully utilizing the role of the River and Lake Chief System, consistently upholding the concept of systematic governance, continuously strengthening the river and lake supervision system, and vigorously enhancing the application of new technologies. In the new era, river and lake management needs to achieve five major transformations: from focusing primarily on river and lake project construction to emphasizing river and lake resource allocation, from river and lake development and utilization to ecological rejuvenation, from government-dominated management of rivers and lakes to societal participation in management, from focusing on river and lake health to the construction of Beautiful and Happy Rivers and Lakes, and from traditional river and lake management to the realization of the value of ecological products. These transformations aim to further enhance the effectiveness of river and lake management, achieve harmonious coexistence between humans and nature, and ensure the sustainable utilization of river and lake functions.

Abstract:This paper reviews the research progress on the characteristics of hydrodynamic-induced cavitation bubble collapse from both experimental and numerical simulation perspectives. In terms of experimental approaches, the advantages and disadvantages of two main methods of hydrodynamically inducing bubbles, namely electric spark and laser, are compared and analyzed. The research progress on the physical characteristics of bubble collapse is elaborated from four aspects: free field, near-wall region, far-wall region, and the interaction between bubbles and particles. In terms of numerical simulation, the development of bubble numerical simulation methods is reviewed from macroscopic, mesoscopic, microscopic and multi-scale perspectives, with a focus on the interaction mechanisms between cavitation bubbles and walls, particles, and other bubbles during the collapse process. It is pointed out that future research on hydrodynamic-induced bubbles can be carried out in directions such as improving synchronous observation techniques, innovating pressure measurement technologies, and promoting deep integration with artificial intelligence and big data technologies.

Abstract:As a typical megacity facing water quality-induced water scarcity, Shanghai suffers from limited local water resources. Although transit water resources are abundant, the security of its water supply is severely challenged by threats such as saltwater intrusion and sudden pollution incidents. Based on the natural geographic conditions and water resources zoning of Shanghai, this paper introduces the composition of the city’s water resources, the characteristics of water quantity and quality, and the current utilization status. Based on existing research, methods for analyzing and estimating local water resources, transit water resources and their corresponding exploitable quantities are summarized. The limitations of certain traditional methods when applied to highly urbanized river network regions are identified and future research directions are proposed.

Abstract:To address the mismatch between point-scale physical formulations of runoff generation and concentration and their application at the watershed scale, a prototype rainfall-runoff experiment was conducted in the Nandawa experimental catchment from 2017 to 2018. Multi-source observations, including total runoff, stratified runoff components, groundwater level, and soil moisture, were collected. Based on the representative elementary watershed (REW) theory, watershed-scale conservation equations were derived using mass conservation principles, and a distributed REW hydrological model was developed. Layered runoff simulations and validations were then performed in the nested watershed in conjunction with the Xin’anjiang model. The results show that the REW model effectively reproduces seasonal runoff dynamics, with good agreement between simulated and observed series in terms of both trend and magnitude. Errors mainly occur during extreme rainfall events. The layered runoff simulation results based on the five-subzone structure are in good agreement with the observed data, effectively capturing surface runoff, interflow, and groundwater runoff. The simulated soil moisture content is generally consistent with the measured values. The runoff simulation method based on the REW model provides a new technical pathway for hydrological process simulation and mechanism analysis in small-scale watersheds.

Abstract:Given the increasing abundance of water quality monitoring data, this study develops a variational data assimilation model for one-dimensional unsteady river water quality simulation based on the optimal control theory of partial differential equations, with the goal of improving the accuracy of river water quality simulation and prediction. Twin numerical experiments are conducted using the water quality decay coefficient, initial conditions, upstream boundary conditions, and river pollutant load processes as control variables. The results indicate that the model can extract useful information from observations, rapidly correct the control variables, and identify spatially distributed water quality decay coefficients, initial conditions, upstream boundary conditions, and river pollutant load processes, thereby enabling model predictions to approach the actual water quality dynamics of the river.

Abstract:To investigate the effects of opening time of vacuum breaking valve on transient hydraulic characteristics of a mixed-flow pump unit during the shutdown process, a full-flow geometric model of the pump unit was established. The actual vacuum breaking valve device was simplified into a ball valve model with equivalent flow area, and the coupling of ball valve opening-closing motion and impeller rotation was realized by the dynamic mesh technology. Three schemes with different valve opening times were designed, namely the advanced opening scheme, the synchronous opening scheme, and the delayed opening scheme. Three-dimensional numerical simulations of the shutdown transient process were carried out. The influence mechanism of valve opening time on hydraulic stability during the shutdown process was explored from three aspects: external performance, pressure fluctuation characteristics, and internal flow characteristics. Combined with the entropy production theory, the energy dissipation law during the shutdown process was revealed. The results show that the external performance parameters, pressure fluctuation and internal flow field evolution present similar variation tendencies under different valve opening schemes, while differences exist in temporal evolution process and variation amplitude. The opening time of the valve exerts remarkable impacts on the transient performance of the unit. Compared with the synchronous opening scheme, the advanced opening scheme reduces the peak values of torque and axial force, yet it may induce more severe initial hydraulic impact. In contrast, the delayed opening scheme delays the operating condition transition, which makes the reverse extreme values of torque and axial force increase to 1.26 times and 1.21 times those of the synchronous opening scheme, respectively, and amplifies the pressure fluctuation amplitude at the siphon crown. Moreover, the delayed opening scheme significantly increases the hydraulic energy loss in the impeller region. In summary, the synchronous opening scheme can effectively suppress hydraulic oscillation, reduce load impact and energy loss while maintaining favorable shutdown efficiency, which is the optimal strategy for stable shutdown of the pump unit.

Abstract:To gain a deeper understanding of the dynamic effects of concrete-faced rockfill dam (CFRD) on deep overburden in seismically active regions, seismic response analyses of CFRDs on deep overburden were conducted using a three-dimensional wave propagation analysis method that accounts for the dynamic interaction between the dam, overburden, and foundation, considering key factors such as valley width, overburden characteristics, and ground motion properties. The results show that edge effects near the abutments induce relatively large acceleration responses at dam crest regions in the vicinity of both abutments. The high-frequency filtering effect of the deep and soft overburden attenuates the acceleration at the dam crest in the valley section. Under strong seismic loading, the reduction in soil modulus and increase in damping further reduce the acceleration response at the dam crest in the valley dam segment. The local areas near the dam crest close to the abutments are identified as potential weak areas in terms of slope sliding stability, for which targeted reinforcement measures are recommended.

Abstract:Based on observed data from 212 hydrological stations in the Yangtze River Basin, this paper analyzes the nonlinear relationships among peak discharge, precipitation, antecedent soil saturation, and drainage area. It verifies the powerlaw relationships between peak discharge and precipitation as well as antecedent soil saturation, and quantitatively analyzes the relationship between peak discharge and the ratio of relative antecedent soil saturation to relative rainfall intensity (SPR). Specifically, the relationships between the basin mean slope and the coefficients (both the constant and the independent variable coefficients) of the linear fitting equation relating SPR to peak discharge are investigated.The results show that with the increase of drainage area, the influence of precipitation on rainstorm-induced floods weakens, while that of antecedent soil saturation strengthens. With the increase of SPR, peak discharge first increases and then decreases. The basin mean slope is positively correlated with the constant coefficient but negatively correlated with the independent variable coefficient.

Abstract:To investigate the influence of vegetation patch distribution patterns on open-channel flow characteristics, three vegetation patch coverage ratios and four patch fragmentation degrees were designed under non-submerged conditions. Numerical simulations of flow through longitudinally discontinuous rigid vegetation patches in a river channel were conducted using ANSYS Fluent. The results show that the longitudinally discontinuous distribution of vegetation patches disrupts the continuity and uniformity of flow velocity in the flow field.When the unit patch size is constant, an increase in vegetation patch coverage ratio leads to a greater velocity difference between the patch region and the mainstream region. When the vegetation patch coverage ratio is constant, an increase in patch fragmentation degree promotes the homogenization of flow velocity across the entire flow field. Flow turbulence is relatively strong in the region from the vegetation bottom to half of the water depth, and both patch coverage ratio and patch fragmentation degree are important factors affecting turbulence intensity.An increase in patch coverage ratio enhances turbulence characteristics in the mainstream region, whereas an increase in patch fragmentation degree intensifies turbulence characteristics within the patches.

Abstract:To address the challenge of balancing a large field of view and high-resolution flow field measurement in 3D scaled model tests of landslide-generated impulse waves, we developed a PIV analysis system for large-scale landslide-generated impulse waves based on a multi-lens array camera. This system integrates four key technologies: wide-angle distortion correction, irregular image corner point mapping, rapid image fusion and stitching, and PIV analysis for large-scale landslide-generated impulse wave flow fields. It enables observation and PIV analysis of the movement process of landslide-generated impulse waves in 3D scaled model tests. Taking the large-scale 3D physical model test of Wangjiashan landslide-generated impulse waves as an example, PIV analysis of the landslide-generated impulse wave flow field was conducted. The results verify the accuracy and feasibility of the PIV analysis system for large-scale landslide-generated impulse waves, providing a reference for further research on the movement process of landslide-generated impulse waves in 3D scaled model tests.

Abstract:To address the issue that current coupled surface water flow and pipe network flow models are mostly based on structured grids, making it difficult to adapt to complex coastlines and urban boundaries, a real-time bidirectional dynamic coupling model, FVCOM-SWMM, was developed based on the open-source unstructured-grid hydrodynamic model FVCOM and the pipe network hydrodynamic model SWMM. The reliability of the proposed model was verified by comparing its results with those from commercial software and physical model experiments. The simulated results of a rain-tide coincident event in a coastal urban area with tortuous coastlines and complex building layouts show that the model can be used to simulate flooding processes in urban areas with complex boundaries under storm surge conditions.

Abstract:In order to identify nano-additives that can effectively enhance drag reduction performance of thixotropic slurry used in pipe jacking construction of water diversion projects, an orthogonal test with three factors and five levels was designed to obtain an optimal slurry formulation suitable for engineering practice. On this basis, reduced-scale physical model tests were conducted to investigate the effects of different nano-additives on the slurry’s drag-reduction performance. The results show that the bentonite content has a significant influence on the slurry’s viscosity, fluid loss, and filter-cake thickness, the CMC content greatly affects fluid loss and viscosity, and the sodium carbonate content mainly increases the slurry’s pH value, while only slightly affecting viscosity and fluid loss. Consequently, the optimal formulation was determined as 10% mass fraction of bentonite, 0.3% of CMC, and 0.32% of sodium carbonate. The friction reduction efficiency of the nano-additives is generally within 0.4 to 0.6 and decreases with increasing contact pressure between the pipe and soil. After applying petroleum jelly, the pipe surface becomes smoother, and both the friction force and pipe-soil cohesion are reduced. Nano carbon powder and nano zinc oxide can reduce the pipe-soil friction coefficient, and all nano-materials can reduce pipe-soil cohesion. For practical water diversion projects, nano zinc oxide is recommended as a preferred additive.

Abstract:To address the low efficiency of conventional methods for parameter inversion of rockfill dams, a rockfill dam parameter inversion method based on a Kriging surrogate model optimization algorithm is proposed. The method first extracts a small number of initial sample points from the parameter space using the Latin hypercube sampling method to establish a relatively coarse Kriging surrogate model. New sample points are then selected according to various infill criteria to update the sample set, thereby obtaining a higher-accuracy Kriging surrogate model to perform optimization until the convergence conditions are met. During the process of gradually adding the number of sampling points, this method can ensure that the newly added sample points fall within the parameter space with the greatest potential for optimal solutions, reducing the randomness of sample point selection of traditional surrogate models and thus improving inversion analysis efficiency. The verification results from an engineering case show that the proposed method can reduce the number of finite element model calculations, improve the sampling efficiency of the surrogate model, shorten the parameter inversion time, and enhance the average calculation accuracy at inversion analysis points.

Abstract:To understand the variation patterns of water temperature in the Xiluodu Reservoir area after the impoundment and operation of the Wudongde and Baihetan reservoirs, this study analyzed the spatiotemporal variation characteristics of water temperature and the evolution process of thermal stratification in the Xiluodu Reservoir area based on in-situ water temperature observation data from 2019 to 2024 and historical hydrological data from 2014 to 2018. The analysis was conducted using mathematical statistics, comparative analysis, and the Mann-Kendall trend analysis method, incorporating thermal stratification evaluation indices. The results show that after the impoundment of the upstream cascade reservoirs, the thermal stratification stability gradually increased. Downstream water temperature exhibited a flattening trend, characterized by higher values in autumn and winter and lower values in spring and summer, and the occurrence of low water temperatures showed a lagging characteristic. Furthermore, the degree of water temperature flattening and lagging increased with the number of cascade reservoirs. The peak value of the thermal stratification stability index increased from 2.52 m^-1 to 3.71 m^-1, while the vertical temperature gradient decreased year by year after impoundment. The mean inflow water temperature decreased by 0.52°C in summer and increased by 2.64°C in winter, with the annual temperature range decreasing by 7.78%. The mean outflow water temperature decreased by 0.53°C in summer and increased by 1.93°C in winter, with the intra-annual extreme variation range decreasing by 0.6% to 11.1%. The occurrence time of the minimum water temperature at various cross-sections along the channel was delayed by 4 to 26 days compared with the pre-impoundment period.

Abstract:To investigate the influence of the bottom slope ratio of the upstream and downstream connecting sections on the hydraulic characteristics of large interchange culverts, the interchange culvert of the Binhai Hub of the Huaihe River Sea-Entry Channel (Phase II Project) was taken as the research object. A parametric study on the bottom slope ratio of the upstream and downstream connecting sections was conducted using a 1∶30 normal-section physical model and the OpenFOAM three-dimensional numerical model. The hydraulic characteristics of the culvert under different flow rate and water level conditions were analyzed in terms of flow capacity, velocity distribution, sectional energy, head loss, turbulent kinetic energy, and turbulent dissipation rate. The results show that the total head loss coefficient of the culvert exhibits a nonlinear variation pattern, first decreasing slowly and then increasing rapidly, with the increase of the bottom slope ratio of the upstream and downstream connecting sections. The total head loss coefficient varies between 0.837 and 1.464. The maximum hydraulic gradient of total head occurs at the downstream culvert inlet and its connecting section, where the head loss accounts for 55.07% to 72.67% of the total head loss, and this section is the most sensitive to changes in bottom slope. Both excessively large and excessively small bottom slope ratios are prone to inducing unfavorable velocity patterns, thereby affecting the flow capacity of the culvert. The scheme with a bottom slope ratio of 1∶7 exhibits the minimum head loss, the optimal flow pattern, and excellent and stable hydraulic performance under different flow rates, with its flow coefficient ranging from 0.868 to 0.928.

Abstract:To improve the quality of underwater excavation operations, this paper proposes a digital twin-based method for intelligent guidance and operational quality control of underwater excavation. By developing intelligent guidance hardware for the excavator and establishing the geometric relationships and kinematic equations of its components, efficient calculation of the bucket tip pose is achieved. A building information model (BIM) of the underwater excavation profile is established using Three.js and Unity 3D, and a digital twin model of the excavator is constructed by integrating real-time sensor data. Finally, based on real-time calculation of the relative distance between the bucket tip and the target excavation surface, an intelligent guidance and operational quality control strategy for excavation operations is developed, and the corresponding system is implemented. Case study results demonstrate that this method enables three-dimensional visualization of the excavation process and remote collaborative monitoring, provides intelligent guidance for operators to correct deviations, and ensures the quality of underwater excavation.

Abstract:To address operational instability issues at hydropower stations, such as frequent unit start-stops and passage through vibration zones, under fluctuating grid loads, a real-time load adjustment strategy was developed to handle grid load fluctuations of varying magnitudes. This strategy flexibly selects the combination of units participating in the adjustment through four modules: power station status updating, maintaining the number of operating units, increasing or decreasing the number of operating units, and global traversal. A load optimization allocation model aimed at minimizing water consumption was established and solved using a dynamic programming algorithm. Taking the Dongfeng Hydropower Station in the Wujiang River Basin as an example, the proposed method was validated. The results indicate that, following optimization, the cumulative number of unit start-stop cycles over three days and the number of instances of crossing the vibration zone decreased by 44.12% and 67.21%, respectively, while the total water consumption decreased by approximately 7.6×105 m³. This real-time load adjustment strategy can effectively ensure power generation demand, significantly improve the economic efficiency and stability of hydropower station operations, and thus provide reliable technical support for the real-time dispatch of hydropower stations under frequent grid load fluctuations.