Abstract:Five water system connectivity schemes were designed to quantitatively evaluate the connectivity of the western polder area of Gaochun District in Nanjing. Based on the hydrological, hydrodynamic, and water quality models, the water environmental response characteristics under each scheme were simulated. The results show that connecting river channels (scheme 1) significantly improved the water quality of rivers such as the Caotang Xishan River, with annual average mass concentrations of ammonia nitrogen, total phosphorus and total nitrogen in the Caotang Xishan River decreasing by 0.65, 0.14, and 1.21 mg/L, respectively, indicating that river channel connection can accelerate pollutant attenuation. Connecting the Chenglonggang River and Guanxi River (scheme 2) reduced annual average mass concentrations of ammonia nitrogen, total phosphorus, and total nitrogen in the Chenglonggang River by 0.84, 0.15, and 0.90 mg/L, respectively. However, it caused a slight decline in the water quality of Gucheng Lake and rivers such as the Hengxi River, indicating that when the self-purification capacity of the water body is exceeded, the channel connection will pollute originally good-quality water bodies. Deepening river channels (scheme 3) and widening river channels (scheme 4) have a weak impact on the water environment. Increasing tributaries (scheme 5) reduced the water volume of the Qiqiao River, leading to increases in annual average mass concentrations of ammonia nitrogen, total phosphorus and total nitrogen by 0.11, 0.02, and 0.04 mg/L, respectively, thereby negatively affecting the water environment of the lake area of Gucheng Lake downstream.

Abstract:To investigate the influence laws of the width-to-depth ratio and the radius-to-width ratio on the hydrodynamic characteristics of open-channel bends, this study established a three-dimensional numerical model based on the RNG k-ε turbulence model and the volume of fluid (VOF) free surface tracking method. Numerical simulations of bend flow under four width-to-depth ratios and four radius-to-width ratios were conducted, with a focus on analyzing hydrodynamic characteristics such as water surface profiles, velocity distribution, secondary flows, and bend separation flows. The results indicate that the flow turbulence characteristics intensify as the width-to-depth ratio or radius-to-width ratio decreases. With the reduction of these ratios, flow redistribution becomes increasingly significant, circulation strength strengthens, and the probability of flow separation in bends increases. For the U-shaped bends with small width-to-depth and radius-to-width ratios simulated in this study, the critical conditions for flow separation are identified as a width-to-depth ratio of 1.5 and a radius-to-width ratio of 1.0.

Abstract:Aiming at the issue that the strong impact force of tidal bores can cause significant sediment transport and bed deposition, thereby altering regional hydrodynamic characteristics, a small-scale refined numerical flume was constructed based on the OpenFOAM two-phase flow model.The propagation evolution and hydrodynamic characteristics of vortical tidal bores on varying topography were investigated, and the effects of bore height, pre-bore water depth, and topographic height on vortical tidal bores were analyzed.The results show that topographic uplift leads to drastic changes in the velocity and vorticity of the vortical tidal bore, and the bore energy significantly attenuates through vortex breaking and viscous dissipation. Weak vortical tidal bores degenerate into undular bores in shallow water, whereas strong vortical tidal bores maintain high-frequency oscillations due to concentrated energy. An increase in bore height reduces the attenuation of propagation velocity in shallow water and increases the turbulent kinetic energy of the surface water body. An increase in pre-bore water depth weakens the turbulent kinetic energy in shallow water and reduces the bore propagation velocity. An increase in topographic height slows down the propagation velocity of the vortical tidal bore. During propagation in shallow water, the turbulent kinetic energy decay rate of strong vortical tidal bores is significantly higher than that of weak vortical tidal bores. Based on the above numerical simulation results, a modified formula for bore propagation velocity that accounts for topographic uplift is proposed, and its calculated results are in good agreement with the numerical results, validating the accuracy of the formula.

Abstract:Based on the principle that the volume of solid particles carried out of or into the stratum by muddy water equals the change in pore volume, a formula for the variation of porosity (void ratio) with time during the seepage process of muddy water is derived. Based on Darcy’s permeability coefficient formula, the relationship between the permeability coefficient and the initial porosity (initial void ratio) as well as the initial permeability coefficient is established, and a formula for the temporal variation of permeability coefficient during the muddy water seepage process is developed. According to the critical initiation condition for piping, where the seepage drag force acting on free soil particles is balanced by their effective weight, formulas for calculating the critical seepage velocity and critical hydraulic gradient for piping initiation are derived, and a numerical method based on finite element software is proposed to iteratively solve the initiation and evolution process of unsteady seepage piping. The proposed method is validated using a piping failure case in the filter layer of a medium-sized reservoir dam in Shandong Province. The results show that the method can accurately reproduce the evolution of piping failure in the filter layer. The permeability coefficient of the filter layer increases sharply within a short period after particle loss is completed, leading to a rapid increase in hydraulic gradient and triggering a chain failure, eventually resulting in the breakthrough of the clay inclined wall and the formation of a concentrated seepage channel. The calculated piping failure mode agrees well with the measured locations and development patterns of collapse pits in the field.

Abstract:To address the high-dimensional and nonlinear complex optimization problems in the optimal operation of cascade reservoirs, a two-stage multi-objective improved artificial fish swarm-particle swarm optimization (TMIAFS-PSO) algorithm was proposed. This algorithm employs segmented mapping to expand the search space of the initial population, and enhances local and global search capabilities by adjusting the adaptive step size and introducing a diversified movement strategy. Additionally, the algorithm adopts a two-stage filtering strategy to retain particles that meet the constraint conditions and incorporates an improved artificial fish swarm optimization strategy to further expand the particle search range. A case study was conducted on the cascade reservoir group consisting of Wudongde, Baihetan, Xiluodu, and Xiangjiaba in the lower reaches of the Jinsha River. The results indicate that, compared to other algorithms, the Pareto solution set of the TMIAFS-PSO algorithm exhibits better convergence and uniformity, demonstrating the superiority of this algorithm. By analyzing the water level variations of the operation schemes generated by the TMIAFS-PSO algorithm, a relatively stable optimal operation scheme for this cascade reservoir group is summarized.

Abstract:To address the multi-objective coordination problem of water supply, power generation, and ecological targets in the Huokou-Shanzai cascade reservoir system of the Aojiang River Basin, this study proposed a multi-objective non-inferior solution set optimization method based on the improved NSGA-Ⅲ algorithm. By constructing a decision-making strategy that integrates the two-layer reference point method and the boundary weighting approach, this method achieves the scientific selection of the non-inferior solution set. Based on this method, a multi-objective operation model for the cascade reservoir system in the Aojiang River Basin was established and compared with single-objective operation models. The results indicate that the multi-objective operation model effectively addresses the challenge of exponential growth in reference points under high-dimensional objectives. Compared to single-objective (power generation, water supply, or ecology) operation models, the multi-objective operation model maintains a certain level of power generation while significantly reducing the probability of water supply shortages, eliminating ecological water deficits, and substantially decreasing spillage. The multi-objective operation model effectively balances the risks among power generation, water supply, and ecological goals, demonstrating its comprehensive optimization advantages under complex constraints.

Abstract:To investigate the distribution of spatial active earth pressure on the walls of square shafts, a failure model of the sliding body in surrounding soil under different aspect ratios was established. A formula for calculating the spatial active earth pressure was derived, and the influence of physical and mechanical parameters of the retaining wall and surrounding soil on the spatial active earth pressure was analyzed. The results show that when the aspect ratio of the square shaft wall is small, the sliding body consists of an upper triangular prism and a lower wedge. When the aspect ratio is large, the sliding body is a single wedge with a trapezoidal cross-section. As the aspect ratio increases, the spatial active earth pressure at the same burial depth gradually increases. With the increase of burial depth, the earth pressure gradually transitions from a nonlinear variation to a stable state, approaching the Coulomb’s earth pressure. The critical aspect ratio of the retaining wall increases with the increase of the wall’s aspect ratio and decreases with the increase of the soil’s internal friction angle. When the aspect ratio of the retaining wall is less than 10, the difference between the spatial active earth pressure and Coulomb’s earth pressure is significant. When the aspect ratio exceeds 10, the difference is less than 10%.

Abstract:To address the problems of outdated management levels and low degree of intelligence in current waterlogged farmland areas, a digital twin-based management platform framework for waterlogged areas is proposed based on an analysis of key business requirements, taking physical waterlogged areas as units and business applications as driving forces. Using BIM+GIS, the Internet of Things (IoT) and UAV oblique photogrammetry, methods for constructing digital and visualized scenarios of waterlogged areas are developed. A three-level geospatial data foundation is established, a platform architecture consisting of sensing device layer, platform support layer, business application layer and user interaction layer is designed, and functional modules including a unified map of the waterlogged area, intelligent flood control and maintenance management are developed. A case study conducted in a waterlogged farmland area of the Sanjiang Plain shows that the proposed digital twin-based management platform realizes functions such as four pre-measures (forecasting, early warning, rehearsing, pre-planning) for flood control, farmland drainage and maintenance management, and improves the scientific and informatization levels of waterlogged area management, validating the rationality of the platform framework design and the feasibility of key technologies. This study provides a reference for the application of digital twin technology in waterlogged area management.

Abstract:To address the current problem where a large volume of water withdrawal and usage data is not collected online, leading to large statistical time intervals and untimely detection of data deviations, a real-time water resources metering data acquisition system was developed. The system employs cameras to capture real-time images of the data displayed on water withdrawal and usage meters. Through image processing and recognition, the corresponding water volume data are extracted, enabling online collection of water volume data. Based on the digital image technology, a method for locating the character area of water meters was constructed, and an adaptive template matching algorithm for water meter characters was created, improving the recognition accuracy to 97.5%. The system has been applied to the real-time acquisition of water withdrawal data from a large-scale water user in Shandong Province. A comparison with the user-reported data shows that the system has an automatic verification function, providing support for the refined management of water resources.

Abstract:Based on the risk removal and reinforcement project of the clay core wall dam of the Chetianjiang Reservoir, a numerical model of pulsating grouting for clay core wall dam was established using the basic theory of fluid-solid coupling. The influence of pulsating grouting parameters such as pulsating grouting pressure, grouting time and grouting frequency on the stress and strain of clay core wall dam under the impounding condition was simulated and analyzed, and compared with the results of field grouting test. The results show that the stress and displacement of the dam increase with the increase of pulsating grouting pressure, grouting time and grouting duration, and decrease with the extension of grouting interval. When the pulsating grouting pressure ranges from 0.5 to 1.5 MPa, most of the dam body is under pressure and the force is relatively uniform. Affected by the upstream water pressure, the horizontal displacement of the upstream dam is smaller than that of the downstream dam. When the pulsating grouting pressure ranges from 0.5 to 1.5 MPa, the grouting time ranges from 1 200 to 1 800 s, the grouting duration ranges from 7 to 9 s, and the grouting interval ranges from 3 to 5 s, it is beneficial to improve the deformation control of the dam body by the pulsating grouting under the impounding condition, so as to effectively improve the stability of the dam body during the pulsating grouting process.

Abstract:Conventional air valve models usually fix the air pocket at the air valve node and neglect boundary movement caused by pocket volume variation during air intake and discharge, which may lead to pressure calculation errors at adjacent nodes. To overcome this limitation, an improved air valve model, namely the spreading air valve model, is proposed. This model updates the air-pocket boundary position in real time according to the variation in air-pocket volume, so that the motion of the water-air interface is more consistent with the actual physical process. By coupling the gas state equation with the fluid governing equations, the dynamic and simultaneous solution of air-pocket pressure, volume and mass is realized. Validation results from a pressurized water pipeline project show that the spreading air valve model can effectively simulate the hydraulic transient process, reasonably predict water column separation and water hammer pressure variation, and significantly improve the accuracy and reliability of water hammer protection design for pipeline systems.

Abstract:In order to accurately determine the effective pore size of needle-punched nonwoven geotextiles, the wet sieving method and the low-field nuclear magnetic resonance (NMR) technology were used to carry out experimental research. The relationship curves between the cumulative percentage and the pore size were drawn, and the effective pore size value of nonwoven geotextiles was obtained and compared. The reliability of the low-field NMR measurement results was verified by combining the NMR imaging technology and Python programming pixel recognition method. The results show that the low-field NMR measurement technology with hydrogen atom as probe can accurately determine the effective pore size of nonwoven geotextiles. The combination of the NMR imaging technology and Python programming pixel recognition method can verify the accuracy of the low-field NMR technology in determining the effective pore size of nonwoven geotextiles. The low-field NMR measurement technology can avoid the shortcomings of the wet sieving method and improve the accuracy of the effective pore size measurement results.

Abstract:To analyze the spatiotemporal characteristics of the fluoride water environmental capacity in the main channels of the lower Ganjiang River network, the T-Copula function was introduced to construct an uncertainty water environmental capacity calculation framework based on the flow rate-water quality joint probability density distribution. Taking fluoride as the target pollutant, the distribution characteristics of the fluoride water environmental capacity in the main channels of the lower Ganjiang River network during different periods in 2024 were analyzed, and a sensitivity analysis was conducted based on the modified one-variable-at-a-time (OAT) method. The results indicate that all main channels possess a certain water environmental capacity throughout the year, although some channels face a potential risk of exceeding this capacity. The highest and lowest expected values of water environmental capacity were observed in the mainstream section of the lower Ganjiang River network and the northern branch’s fishery water use zone, respectively. The expected values of the water environmental capacity in the river network during different periods exhibit a certain fluctuating pattern. The seasonal variation in river flow is identified as the key driving factor causing the dynamic changes in the fluoride water environmental capacity in the lower river network.

Abstract:To evaluate the disturbance caused by the tail reach project of the Ganjiang River on the river’s aquatic ecosystem, a two-year monitoring program was conducted on benthic macroinvertebrates within the main stem and its four downstream branches (the Main, North, Middle, and South branches). A total of 32 species belonging to 23 genera across 3 phyla were recorded. The ecological status was assessed using the benthic index of biotic integrity (B-IBI). The results indicated that the benthic community in the tail reach of the Ganjiang River was dominated by filter-feeding and pollution-tolerant mollusks. In terms of spatial distribution, the Main Branch and the slow-flowing areas upstream of the dam exhibited stable community structures and higher biodiversity. Conversely, the community compositions of the Middle, North, and South branches were relatively simple, characterized by lower biotic integrity. After the operation of the project, the Main Branch maintained the highest biotic integrity, demonstrating robust resistance to disturbance. Monitoring sites in the main stem, as well as the North and South branches, reached undisturbed or slightly disturbed status according to the B-IBI. However, the Middle Branch experienced significant shifts in community structure, indicating that its aquatic ecosystem was heavily disturbed by the project.