[Objective] Floodplains and polders in the middle and lower reaches of the Yangtze River are an important part of the Yangtze River flood control system, which plays a key role in expanding the flood storage capacity of the river and ensuring the flood control safety in key areas. However, difficulties in decision-making on activation and timing of operation have become prominent issues in their operational management, making them a weak link in the basin’s flood control system. This study aims to establish a scientific and systematic classification index system for the use of floodplains and polders, in order to refine scheduling and coordinate the overall basin flood control safety with socio-economic development within floodplains and polder areas. [Methods] This study took the floodplains and polders in the middle and lower reaches of the Yangtze River as the research object, and innovatively constructed a hierarchical classification index system consisting of three dimensions: flood control capacity, planning attributes, and socio-economic impact. The index system included eight specific indicators, covering aspects such as levee height deficiency, relationship with urban master planning, relationship with floodplain operation planning, permanent population, key protected areas, cultivated land area, and GDP. Based on the principle of sectional classification, the middle and lower reaches of the Yangtze River were divided into six river sections: Jingjiang, Chenglingji, Wuhan, Hukou, Hukou-Datong, and downstream of Datong. Differentiated weights were assigned to the upstream and downstream sections of Datong. By constructing a decision matrix and combining standardization of qualitative indicators based on classification with linear normalization of quantitative indicators, the comprehensive scores of floodplains and polders were obtained and divided into four categories (from Class I to Class IV), clarifying their order of activation. [Results] A total of 243 floodplains and polders (excluding those that had been completely decommissioned) along the main stream of the middle and lower reaches of the Yangtze River were evaluated. The classification results showed that there were seven Class I floodplains and polders with a total flood storage capacity of 20 million m3 and relatively low population and GDP; Class II had the largest number, with 154 floodplains and polders providing a total flood storage capacity of 3.81 billion m3; Class III included 65 floodplains and polders, featuring the largest flood storage capacity (4.87 billion m3) and the highest population (about 450 000 people); and Class IV comprised 17 floodplains and polders, with a total GDP of 10.83 billion CNY. Correlation analysis indicated that “levee height deficiency” had the greatest impact on classification (correlation coefficient =-0.7), followed by “permanent population” and “GDP” (both=-0.6), while “cultivated land area” had the least influence. Taking the Chenglingji section as an example, the classification results were highly consistent with the actual flood control requirements and the socio-economic characteristics of the area. Further verification through a 1954-type flood regulation simulation showed that, compared with the baseline scheme, the classified regulation scheme reduced excess flood volume by approximately 0.55 billion m3 in the vicinity of Chenglingji, and significantly improved the overall flood control effectiveness. [Conclusion] The classification index system for the use of floodplains and polders proposed in this study has strong scientific and practical value. Its innovation lies in the systematic integration of planning attributes, socio-economic impacts, and flood control capacity, achieving a conceptual shift from a “single flood-control orientation” to a “flood control-development coordination” approach. The proposed index system provides a scientific basis for the “sectional control and hierarchical scheduling” of floodplains and polders in the middle and lower reaches of the Yangtze River. It supports the optimization of flood regulation schemes and real-time decision-making during flood control consultations, offering important practical significance for improving the overall flood regulation and scheduling capacity of the Yangtze River Basin.
[Objective] Developing new quality productive forces of water conservancy is an inevitable direction for promoting high-quality development of the water conservancy sector at present, and how to cultivate such forces according to local conditions has become a key issue faced by both the theoretical community and practical departments. Although related studies have continued to expand, there remain shortcomings in the water conservancy field, including insufficient systematic attention to differences in water resource endowment and an inadequate understanding of the formation mechanisms of new quality productive forces of water conservancy. Therefore, it is urgently necessary to carry out normative research focusing on the theoretical logic and practical pathways of development tailored to local conditions. [Methods] This study was based on resource endowment theory, comparative advantage theory, and new structural economics, and constructed an analytical framework for developing new quality productive forces of water conservancy according to local conditions. Starting from water factor endowments and functional attributes, the key roles of innovative allocation of water-related factors, upgrading of water-related industries, and the water-related science and technology talent system were systematically examined in promoting the development of new quality productive forces of water conservancy. Furthermore, by integrating regional water resource characteristics, the study identified five core dimensions—water science and technology, resource allocation, ecological value, industrial upgrading, and disaster prevention and control—and established a system of regionally differentiated development pathways. [Results] The results showed that developing new quality productive forces of water conservancy according to local conditions was a dynamic evolutionary process that started from water factor endowments and regional differences, progressed through the formation of comparative advantages and coordinated regional division of labor, and ultimately led to a spiral improvement of comprehensive capabilities. This development relied on three key driving forces: innovative allocation of water-related factors, which promoted the overall optimization of water engineering systems, water ecological patterns, and water resource utilization structures; in-depth development and transformational upgrading of water-related industries expanded the water economic value chain and strengthened the industrial foundation of the water conservancy modernization system; and improvements in the water-related scientific and technological innovation and talent cultivation system provided sustained momentum for the modernization of water conservancy. The study further identified five major manifestations of new quality productive forces of water conservancy from the perspective of the multiple values of water factors: water science and technology reflected innovation in governance capacity, resource allocation reflected improvements in water resource efficiency, ecological value reflected ecosystem improvement and enhanced services, industrial upgrading reflected industrial structure reshaping and value chain extension, and disaster prevention and control reflected enhanced regional water security resilience. These dimensions were interrelated and jointly constituted a diversified structural system of new quality productive forces of water conservancy. [Conclusion] Based on the characteristics of water factor endowments in different regions, this study proposes five representative types of differentiated development pathways. The northwestern arid regions are suited to adopt a “technology-based water compensation” pathway, improving water resource utilization efficiency through technological innovation. North China is suited to follow an “institutional adjustment” pathway, alleviating the contradiction between water supply and demand through institutional provision. Southwest China is suited to adopt an “ecological transformation” pathway, converting rich water ecological advantages into development momentum. The southeastern coastal regions are suitable for an “integrated water economy” pathway, strengthening the linkage between the water economy and regional industries. Typical high-risk regions need to adopt a “resilience enhancement” pathway, reinforcing flood control, disaster reduction, and comprehensive risk governance. These pathways reflect the heterogeneity of the formation mechanisms of new quality productive forces of water conservancy across regions and demonstrate the central role of the principle of adapting measures to local conditions in the modernization of water conservancy. Overall, developing new quality productive forces of water conservancy according to local conditions must be based on differences in water factor endowments and regional functions, forming an advantage-oriented and endogenous driving system, and achieving coordinated improvement in water science and technology, resource allocation, ecological value, industrial development, and disaster resilience. The results and pathway system of this study provide important theoretical foundations and practical guidance for regions to construct differentiated water conservancy development models.
[Objective] This study aims to analyze regional differences in agricultural and industrial water use efficiency in the Yangtze River Basin and their key influencing factors, reveal the spatial differentiation patterns of water use efficiency within the river basin, and provide scientific guidance for formulating differentiated and precise water resource management policies. [Methods] Three provinces (municipalities) from the upper, middle, and lower reaches of the Yangtze River were selected as sample regions. Authoritative data from sources such as the China Water Resources Bulletin, the Water Resources Bulletin of the Yangtze River Basin and Southwest Rivers, and the Statistical Bulletin on National Economic and Social Development from 2014 to 2023 were collected. Core water use efficiency indicators included: effective utilization coefficient of farmland irrigation water, actual irrigation water use per mu of farmland, and water use per 10 000 yuan of industrial added value. Using methods such as descriptive statistics and comparative analysis, the temporal changes and spatial differences in water use efficiency for the entire river basin and between regions were systematically evaluated. Additionally, combined with data on topography, per capita GDP, precipitation, and industrial structure of the sample provinces (municipalities), key factors affecting water use efficiency were qualitatively analyzed and quantitatively identified. [Results] (1) Temporal changes showed that in the past decade, both agricultural and industrial water use efficiency in the Yangtze River Basin gradually improved, but both indicators remained consistently below the national average level, indicating that the overall water-saving potential of the river basin still needed to be tapped. (2) Spatial differences were significant. Agricultural water use efficiency (characterized by the effective utilization coefficient of irrigation water) followed the order of downstream area > midstream area > upstream area. Per capita GDP and topography were key factors affecting coefficient changes. In general, regions with higher economic development level and flatter terrain exhibited higher agricultural water use efficiency. Industrial water use efficiency (characterized by water use per 10 000 yuan of industrial added value) followed the order of upstream area > midstream area > downstream area, with the rationality of industrial structure being its key influencing factor. The downstream area, due to the concentration of high water-consuming industries and a relatively large proportion of water use for direct-current thermal (nuclear) power, had relatively low industrial water use efficiency. (3) Actual irrigation water use per mu of farmland was affected by multiple factors such as cropping structure, climate variability, and irrigation methods. This resulted in poor cross-regional comparability, making it unsuitable as a reliable indicator for evaluating spatial differences in agricultural water use efficiency. [Conclusion] Economic development level, irrigation infrastructure conditions, and the rationality of industrial structure are key factors affecting agricultural and industrial water use efficiency in the Yangtze River Basin. In the upstream area, complex terrain, outdated irrigation facilities, and insufficient financial and technical support lead to significant irrigation water losses during water conveyance and use, resulting in relatively low agricultural water use efficiency. In the downstream area, although water-saving management measures are relatively well developed, the large proportion of high water-consuming industries in the industrial structure results in relatively low industrial water use efficiency. Based on these findings, to improve the overall water use efficiency of the river basin, differentiated and precise zonal management strategies should be implemented. In the upstream area, priority should be given to modernizing irrigation infrastructure and promoting advanced technologies. In the downstream area, efforts should focus on strengthening industrial structure optimization and formulating stricter water-saving standards and incentive-constraint mechanisms for high water-consuming industries. Future research could focus on smaller spatial scales and enhance the quantitative analysis of influencing factors to support the precise implementation of water-saving measures.
[Objective] To improve the accuracy of groundwater level time series prediction and explore the application effects of 17 decomposition techniques—EMD, EEMD, CEEMD, ICEEMD, LMD, RLMD, ITD, ESMD, WT, WPT, EWT, VMD, SSA, TVF-EMD, FDM, SGMD, and SVMD—in the decomposition of groundwater level time series data, a love evolution algorithm (LEA) - fast learning network (FLN) prediction model based on these 17 decomposition techniques is proposed. [Methods] Firstly, 17 decomposition techniques including EMD were used to decompose the groundwater level time series data, and several decomposition components were obtained. Secondly, based on the training set of each decomposition component, a fitness function was constructed, and LEA was used to optimize the fitness function to obtain the optimal FLN input layer weight and hidden layer threshold for FLN. Seventeen models, including EMD-LEV-FLN, were established to predict and reconstruct each decomposition component. Finally, the daily water level time series prediction of the Caoba groundwater monitoring well in Yunnan Province from 2019 to 2023 was used as an example to verify each model. [Results] (1) WPT-LEV-FLN, EWT-LEV-FLN, FDM-LEV-FLN, TVF-EMD-LEV-FLN models achieved the highest prediction accuracy, with average absolute percentage error (MAPE), average absolute error (MAE), and root mean square error (RMSE) ranging 0.000%-0.001%, 0.002-0.020 m, and 0.002-0.032 m, respectively. The determination coefficients (R2) were all 1.000 0. The SSA-LEV-FLN, WT-LEV-FLN, and VMD-LEV-FLN models came in second place, with predicted MAPE, MAE, RMSE, and R2 ranging 0.003%-0.007%, 0.041-0.087 m, 0.063-0.131 m, and 0.999 5-0.999 9, respectively. Other models had relatively poor prediction accuracy, with predicted MAPE, MAE, RMSE, and R2 ranging 0.017%-0.033%, 0.221-0.417 m, 0.385-0.705 m, and 0.985 3-0.995 6, respectively. Among them, WPT-LEV-FLN model had high prediction accuracy and small computational scale, demonstrating the greatest practical value and significance. (2) WPT, EWT, FDM, and TVF-EMD showed the best decomposition performance, among which WPT not only had good decomposition performance, but also produced fewer decomposition components, making it the most advantageous. SSA, WT, and VMD showed relatively good decomposition performance, and increasing the number of decomposition components could further improve the decomposition effectiveness. The other models performed relatively poorly, among which SGMD and SVMD had the least decomposition components and the greatest potential. [Conclusion] This study compares the application performance of 17 current mainstream time series decomposition techniques for processing groundwater level time series decomposition and proposes 17 prediction models, providing reference and guidance for the selection of time series decomposition methods and research on groundwater time series prediction.
[Objective] Zoobenthos are the intermediate link in the food chain of river ecosystems, and promoting the restoration of healthy zoobenthos communities through the construction of suitable habitats is critical for river ecological restoration. Based on the living habits of zoobenthos, habitat modules suitable for the colonization of various zoobenthos species are designed and applied in experiments within the ecological restoration project of Fenghuang Creek to investigate the effectiveness of ecological restoration. [Methods] Prior to project implementation, zoobenthos samples were collected once from the river channel. One year after the completion of the project, when the river ecosystem was restored, zoobenthos samples within the modules were collected, with three sampling sites set up for this study. In addition, zoobenthos were collected from a river minimally affected by human activities to serve as a natural reference state. Collected zoobenthos samples were identified and counted, and ecological indicators were analyzed. A total of ten ecological indicators were analyzed to assess the restoration of zoobenthos communities. These indicators included: individual density and biomass density reflecting biomass characteristics; total number of taxa, number of sensitive taxa, and number of EPT taxa reflecting species richness; Shannon-Wiener diversity index, richness index, and evenness index reflecting community diversity; and biotic index (BI) and biological monitoring working party score (BMWP) reflecting environmental sensitivity. [Results] Among the biomass-related indicators, no significant change in individual density of zoobenthos was observed before and after the restoration project, and the values remained below 40% of those in the natural state. Biomass density, however, varied considerably among sampling sites after project implementation, with two sites exceeding twice and four times the values observed in the natural state, respectively. Regarding species richness-related indicators, the total number of taxa reached 60% of the natural state before project implementation. After the project, it increased slightly, ranging from 66.7% to 73.3% of the natural state, indicating a relatively small difference from the natural condition. Although the numbers of sensitive taxa and EPT taxa significantly increased after the project, they remained far below the natural state, with sensitive taxa at 30.0%-40.0% and EPT taxa at only 14.3% of the natural state. For species diversity-related indicators, slight increases were observed after project implementation compared with pre-project levels, and the gaps from the natural state were small, with some indicators even surpassing those of the natural state. Although indicators related to environmental sensitivity were improved after project implementation, they remained far below the natural state, with BI values at 41.5%-44.3% and BMWP scores at 55.7% of the natural state. [Conclusion] Following project implementation, the health of zoobenthos communities in the river shows a relatively pronounced restoration, but there remains a considerable gap compared with the natural state, mainly reflected in indicators closely associated with sensitive taxa—namely, the number of sensitive taxa, number of EPT taxa, BI value, and BMWP score. This can be attributed to the fact that the structure of zoobenthos communities is influenced not only by the river habitats but also by the types of surrounding terrestrial ecosystems. The reference site in this study is minimally affected by human activities, where the natural ecosystem is well preserved and suitable for the survival and reproduction of adult aquatic insects from sensitive taxa, resulting in a relatively rich assemblage of sensitive taxa. In contrast, the river under restoration is surrounded by villages and farmland, where terrestrial habitats and communities are relatively homogeneous, and the river ecosystem is frequently disturbed. Therefore, these conditions limit the development of sensitive zoobenthos taxa to a certain extent and make it difficult for community health to approach the natural state. Based on the analytical indicators used in this study, individual density, biomass density, Shannon-Wiener diversity index, richness index, and evenness index are relatively insensitive and fail to accurately reflect the differences before and after implementation or between post-implementation and natural state. In contrast, indicators related to sensitive taxa exhibit strong sensitivity and applicability in assessing zoobenthos community restoration and are recommended for use in similar studies or projects.
[Objective] The middle route of the South-to-North Water Diversion Project faces risks of sudden water pollution due to hazardous material transport over cross-canal bridges and inflow of external floodwaters during the flood season. To support the treatment of water pollution emergencies, a unified hydrodynamic and water quality model for the canal system, including structures such as control gates, offtakes, inverted siphons, and escape gates, was developed. [Methods] The St. Venant equations were solved to simulate hydrodynamic characteristics of the water flow. Based on a cross-sectional control volume, a one-dimensional water quality model was established, with the continuity equation representing the pollutant mass conservation equation. The model was developed using FORTRAN90, enabling online pre-simulation of sudden water pollution diffusion and multi-gate joint control operations. [Results and Conclusion] Simulation results show that closing the diversion and increasing the discharge of the water discharge gate can significantly improve the pollutant emission efficiency, while the closing speed of control gates determines the pollution control effectiveness. This study provides technical support for the prevention and control of sudden water pollution incidents in the middle route of the South-to-North Water Diversion Project.
[Objective] The Four Lakes (Changhu Lake, Sanhu Lake, Bailu Lake, and Honghu Lake) Basin, located in the hinterland of the Jianghan Plain in the middle reaches of the Yangtze River, is an essential agricultural production area and an ecologically sensitive wetland area in Hubei Province. To reveal the spatiotemporal distribution characteristics of nutrients and their pollution sources in the water bodies of the Four Lakes Basin after ecological restoration, this study systematically analyzes the variation patterns of water quality and the main driving factors based on measured monitoring data, aiming to provide a scientific basis for watershed water environment management and ecological restoration effectiveness assessment. [Methods] Based on field survey data from wet, normal, and dry seasons during 2022-2023, a total of 12 sampling sites were set up in the Four Lakes Basin, covering the upstream, midstream, and downstream areas, as well as mainstream and tributaries. Nine water quality indicators were measured, including water temperature (WT), dissolved oxygen (DO), turbidity (TUR), permanganate index (CODMn), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonium nitrogen ( -N), total phosphorus (TP), and total nitrogen (TN). The water quality was comprehensively evaluated using the water quality index (WQI) method. Correlation analysis and principal component analysis (PCA) were combined to identify the main pollution factors and sources. The characteristics of water quality evolution were systematically revealed from temporal, spatial, and pollution source aspects through data statistics, significance tests, and graphical visualization performed using software such as Excel, SPSS, and CANOCO. [Results] Water quality indicators in the Four Lakes Basin exhibited significant differences both temporally and spatially. Temporally, WT, -N, TP, and CODMn were the highest during the flood season, while DO and TN showed opposite trends. TUR peaked during the normal season. Spatially, the concentrations of TUR, CODMn, COD, and BOD5 in the downstream water bodies were significantly higher than those in the midstream and upstream. The -N concentration was the highest in the midstream, while the TP and TN concentrations were the lowest in the upstream. Overall, the concentrations of various nutrient indicators demonstrated a pattern of “mainstream > tributaries”. The WQI values ranged from 15.61 to 32.88, indicating that the overall water quality in the Four Lakes Basin was at a “poor” to “very poor” level. Its temporal variation followed the order: normal season > dry season > wet season, and its spatial variation was characterized by upstream > midstream > downstream, and tributaries > mainstream. Correlation analysis showed that WT, DO, COD, -N, TP, and TN were the main factors affecting WQI, among which N -N, TP, and TN were significantly negatively correlated with WQI (P<0.05). PCA results indicated that pollutants during wet season were dominated by nutrients, primarily originating from external inputs such as agricultural fertilization, livestock and poultry farming, and domestic sewage. Pollution during normal season was mainly organic matter, largely from domestic sewage and industrial wastewater discharge. Pollution during dry season was influenced by both external input and internal release, with sediment resuspension and decomposition of plant and animal residues being important internal pollution sources. Overall, although the water quality in the Four Lakes Basin improved slightly after the implementation of ecological restoration, significant seasonal and regional pollution characteristics remained. [Conclusion] In summary, the water quality in the Four Lakes Basin exhibits significant temporal differences across the flood, normal, and dry seasons, while spatially, the upstream areas are superior to the midstream and downstream areas, and the tributaries are superior to the mainstream.. Although ecological restoration projects have been effective, the overall water quality of the basin remains at a moderate to severe pollution level. Agricultural fertilization, livestock and poultry breeding wastewater, domestic sewage, and industrial discharge are the main exogenous pollution sources, while the release of water body sediments and the decomposition of organic residues are the main endogenous pollution pathways. The innovation of this study lies in systematically revealing the spatiotemporal distribution pattern and pollution causes of nutrients in the Four Lakes Basin under the background of ecological restoration for the first time. This study also constructs a multi-level analytical framework of “WQI comprehensive evaluation-correlation analysis-PCA”, which can effectively identify key pollution factors and dominant sources, thereby providing scientific support for assessing the performance of watershed ecological restoration and implementing targeted management in the basin. The findings indicate that agricultural non-point source pollution control and sediment remediation should be further strengthened, and an integrated management system combining exogenous reduction and endogenous treatment should be established to promote the sustained improvement of the water environment and long-term restoration of ecological functions in the Four Lakes Basin.
[Objective] This study aims to explore the role of river riparian zones in southern China as sources or sinks of greenhouse gases during winter. Traditional studies often focus on individual greenhouse gases, lacking simultaneous observation and comprehensive assessment of multiple greenhouse gases such as CO2, CH4, and N2O. Therefore, the core objectives of this study are: (1) to quantify the winter fluxes of CO2, CH4, and N2O under three common riparian herbaceous plants (Ophiopogon japonicus, Allium tuberosum, and Cynodon dactylon) and in bare soil control plots; (2) to comprehensively assess the contribution of different vegetation types to the net winter greenhouse effect in riparian zones based on the global warming potential (GWP) model; (3) to identify the key environmental drivers affecting greenhouse gas fluxes; and (4) to provide a scientific basis for vegetation selection and ecological management in southern riparian zones from the practical perspective of promoting “carbon neutrality”. [Methods] This study took the riparian zone of the Xiongxi River, a typical river in southern China, as the study area. Three widely distributed and representative herbaceous plant communities, along with bare soil as control areas, were selected. Throughout the winter, on one sunny day in the middle of each month, high-precision LI-7810 and LI-7820 trace gas analyzers were used for in-situ simultaneous observations to obtain flux data for the three greenhouse gases. Meanwhile, key environmental parameters such as air temperature, soil temperature, and soil moisture were synchronously recorded. To integrate the overall impact of the three greenhouse gases on global warming, the global warming potential model was adopted. On a 100-year time scale, with CO2 as the reference, all fluxes were uniformly converted into CO2 equivalents, thereby obtaining the daily comprehensive GWP for each study area. Data analysis was conducted using statistical methods including one-way analysis of variance (ANOVA), Pearson correlation analysis, and regression analysis. [Results] Herbaceous plants significantly reduced the net carbon emissions in riparian zones during winter. After comprehensive assessment of CO2, CH4, and N2O, significant differences were found in winter GWP values across different areas. The average GWP in the Cynodon dactylon area, Ophiopogon japonicus area, Allium tuberosum area, and bare area was 3 817.77±249.24, 3 963.31± 265.66, 6 876.89±536.17,8 653.71±756.08 mg/(m2∙d), respectively. Although all areas functioned as net carbon sources during winter, the GWP was effectively reduced in the three herbaceous plant-covered areas compared to bare land. This result, for the first time, quantified the mitigation effect of herbaceous plants on the greenhouse effect of riparian zones under a winter, multi-gas comprehensive assessment framework. The impact of different vegetation types on greenhouse gas composition was species-specific. In-depth analysis of each gas component showed that CO2 emission fluxes in all vegetated areas were significantly lower than in bare land. CH4 fluxes mostly exhibited weak absorption, with the lowest average in bare areas and the highest in Ophiopogon japonicus areas. Regarding N2O flux, bare areas showed the highest average, while the Cynodon dactylon areas had the lowest. Observations also indicated a distinct diurnal variation in riparian GWP, with higher values at noon and lower values in the morning and evening. Pearson correlation analysis revealed that soil temperature was the key environmental factor driving this diurnal pattern, showing a highly significant positive correlation with the GWP value. This finding clarified the central role of temperature in regulating the carbon emission process of riparian zones in winter. [Conclusion] (1) This study overcomes the limitations of traditional single-gas studies, systematically revealing for the first time in southern China’s winter riparian environment that common herbaceous plants significantly and differentially influence regional net greenhouse effects by altering CO2, CH4, and N2O emission profiles. It confirms that vegetation cover in winter also has a certain emission-reduction function.(2) From the perspective of the synergy between riparian ecological engineering management and carbon neutrality goals, vegetation selection is crucial. Among the three plants examined in this study, Cynodon dactylon proves to be the optimal choice in winter due to its lowest GWP, whereas Allium tuberosum, though visually appealing, has the highest GWP and is therefore not recommended for planting from an emission-reduction perspective.(3) Soil temperature is the key environmental factor controlling the diurnal variation of winter greenhouse gas fluxes in riparian zones. This implies that under future global warming, rising winter temperatures may significantly enhance the carbon emission intensity of such ecosystems and should be fully considered in carbon cycle models.
[Objective] Clarifying dynamic changes of vegetation activities and time lag in response to hydrothermal conditions in Tianjin can provide a scientific basis for regional ecological environment management and sustainable development. Previous studies have investigated urban vegetation dynamic differentiation based on different data sources and time scales, while spatiotemporal patterns of vegetation over long time series, as well as the direction and extent of vegetation response to changes in hydrothermal conditions, still remain uncertain. Most current studies lack specific quantification of the lag duration of climate change. [Methods] This paper took the MODIS13 dataset, air temperature, and precipitation dataset of Tianjin from 2000 to 2022 as research objects. Based on the MatLab platform, methods such as the Hurst index, Theil-Sen trend analysis, Mann-Kendall test, geographic information system (GIS) spatial analysis, and time-lagged partial correlation analysis were adopted to investigate the characteristics of vegetation dynamics and their response to hydrothermal effects in Tianjin over the past 23 years. Additionally, this study analyzed vegetation evolution characteristics and their response to climate change, providing references for understanding ecological environment response under climate change. [Results] The results showed that: (1) annual average NDVI in Tianjin was 0.782, showing an overall trend of first increasing and then decreasing. Areas with high vegetation cover were mainly distributed in northern Jizhou District, northern Baodi District, and Ninghe District. The intra-annual fluctuation trend showed a certain positive correlation with changes in temperature and precipitation. (2) The mean Hurst index for the entire city was 0.493, with 45.225% of the areas having a Hurst index >0.5. Overall, vegetation in Tianjin showed a trend of past degradation but future improvement. Areas with continuous NDVI degradation were mainly distributed in Xiqing District, Ninghe District, and Dongli District. (3) 10.943% and 61.408% of the areas in Tianjin had time-lag effects on temperature and precipitation, respectively. The average lag time of vegetation response to temperature across the city was 2.737 months. The vegetation response to precipitation had a time lag of 1 to 3 months, with an average lag time of 1.016 months. Overall, vegetation was more sensitive to precipitation, and the average lag time of vegetation response to precipitation in the city was shorter than that to air temperature. (4) The responses of different vegetation types to air temperature and precipitation varied. Broad-leaved forests had the shortest response time to precipitation, while herbaceous cover had the longest response time. Sparse vegetation had the fastest response to air temperature, and broad-leaved forests had the slowest response. [Conclusion] From 2000 to 2022, the overall vegetation cover level in Tianjin was good, with NDVI showing a trend of first increasing and then decreasing, indicating past degradation but future improvement. The correlation between precipitation and vegetation is higher, and the lag time of air temperature is longer. Vegetation in Tianjin exhibits lag response characteristics to both air temperature and precipitation, and lag time varies among different vegetation types.
[Objective] Lateral inflow of pump station can easily cause flow separation and backflow as the water body in the forebay changes direction, which deteriorates the flow pattern in the forebay and seriously threatens the efficient and stable operation of pump station units. [Methods] In this study, the computational fluid dynamics (CFD) method was used to calculate the flow field of the inflow building of Dazhaihe pump station, and the effectiveness of the numerical calculation method was verified by physical model tests. Quantitative and qualitative comparative analyses were conducted to evaluate the flow field characteristics of the forebay and the open inflow basin under five flow field regulation measures, including flow-guiding grille, flow-straightening sills, and different types of guide walls. [Results] (1) Based on the RNG k-ε turbulence model, the inflow conditions of lateral inflow forebay and inflow basin of the pump station in the initial design scheme were analyzed, and the effectiveness of numerical calculation method for the flow field in the pump station forebay was validated through hydraulic physical model tests. (2) The combination of arc and linear guide walls achieved optimal flow regulation effect. This measure facilitated the redistribution of flow velocity, reduced the non-uniformity of flow distribution across inflow basins, and stabilized lateral inflow. The area proportion of high-velocity zones at characteristic cross-sections was relatively small, and the average velocity along the horizontal centerline of this cross-section was slightly higher than theoretical cross-sectional average velocity. The velocity distribution within the inflow basin became more reasonable with reduced variability, significantly improving the overall flow field. (3) By comprehensively comparing five evaluation indicators—axial velocity distribution uniformity at the inlet of bell-mouth pipes in submersible pumps, the range of axial velocity distribution uniformity, velocity-weighted average angle, characteristic values of vorticity, and head loss coefficients between characteristic cross-sections—the combined application of arc and linear guide walls achieved optimal inflow conditions in the inflow basins of all units. Compared with the initial design scheme, the axial velocity distribution uniformity at the inlet surfaces of bell-mouth pipes in submersible pumps increased by 14.8% on average, and the velocity-weighted average angle increased by an average of 9.2°. Additionally, the range of axial velocity distribution uniformity between units was the smallest, and no vortex ropes were observed at the inlets of bell-mouth pipes in any unit. [Conclusions] The combined regulation measure using curved and linear guide walls is proven effective in mitigating the impact of adverse flow patterns on pump station units, providing reliable guidance for improving flow conditions in similar lateral inflow pump stations. For practical engineering applications, factors such as project timelines and construction complexity should be considered. The findings of this study offer feasible technical support and recommendations for the design and operation of future similar pump stations and hydraulic structures. Current research primarily focuses on flow field optimization of the lateral inflow forebay at the preliminary design stage, and further on-site testing of pump stations is required to evaluate the actual regulatory effects of the optimized schemes.
[Objective] Topographic and shoreline changes caused by human activities such as tidal flat reclamation, channel deepening by dredging, and seabed sand mining further interfere with tidal wave propagation in estuarine and coastal areas. These changes have significant impacts on key environmental and engineering issues, including channel maintenance and management, the safety and stability of coastal hydraulic structures, the transport patterns of sediment and pollutants, and saltwater intrusion. Previous studies on tidal asymmetry in the Pearl River Estuary have mostly focused on tidal asymmetry itself; however, tidal current asymmetry induced by topographic and shoreline changes exerts a greater influence on material transport. To systematically evaluate the disturbance mechanisms of such human activities on the tidal dynamic system, this study investigates the tidal current asymmetry in the Lingding Bay area caused by topographic and shoreline changes using the skewness method. [Methods] A high-resolution hydrodynamic numerical model covering the river network, estuary, and adjacent sea areas of the Pearl River Delta was established based on Delft3D-Flow Flexible Mesh. The model was rigorously calibrated and validated using observed water levels and current velocity data from multiple stations. The simulated results agreed well with the observations, indicating that the model had reliable predictive capability. On this basis, sensitivity experiments with different shoreline and topographic configurations were conducted. Using the T-Tide harmonic analysis tool, the variations in amplitude and phase of the main astronomical tidal constituents O1, K1, M2, and S2 and the shallow-water constituents M4 and MS4 between the 1970s and the 2010s were analyzed and summarized. The skewness method was adopted to calculate the flow velocity asymmetry (FVA) and flow duration asymmetry (FDA), to reveal the spatial distribution patterns of FVA and FDA in different decades, and to explore the contributions of major tidal constituent combinations to FVA and FDA. [Results and Conclusion] (1) The tidal dynamics in the Lingding Bay area exhibited a distinct tidal current asymmetry. Shoreline extension caused by reclamation and topographic incision resulting from channel dredging led to a general increase in the amplitudes of major shallow-water constituents and a northward shift of tidal wave phases, while the phase difference between the bay mouth and bay head decreased. These changes collectively weakened the ebb dominance and shortened the ebb duration, thereby enhancing the overall tidal current asymmetry in this region. (2) For different types of tidal current asymmetry, FVA was mainly controlled by topographic changes, with the combinations of K1/O1/M2 tidal constituents and the residual current term playing a dominant role. The FVA generally exhibited ebb dominance, favoring seaward sediment transport. The skewness values of FVA within Lingding Bay still showed a spatially decreasing trend along the bay. (3) In contrast, FDA was more sensitive to shoreline changes. Its variation was mainly controlled by the combinations of tidal constituents such as M2/M4 and M2/S2/MS4. Topographic and shoreline changes induced by human activities further enhanced the contribution of these tidal constituent combinations to FDA. Overall, the FDA exhibited a shorter ebb duration, with its asymmetry increasing from the bay mouth toward the bay head.
[Objective] As a new type of support anchor, the Glass Fiber-Reinforced Plastic (GFRP) screw anchor is increasingly used in engineering practice due to its simple construction, light weight, high strength, corrosion resistance, and cost-effectiveness. Previous calculation formulas for uplift bearing capacity of screw anchors mostly based on artificially defined boundaries between shallow and deep embedment, resulting in large differences in critical embedment depth ratio H/D (where H is the embedment depth and D is the anchor plate diameter) given by different scholars. This study aims to propose a calculation formula for uplift bearing capacity based on the generalized unified failure surface morphology, providing theoretical support for the design of GFRP screw anchors in engineering practice. [Methods] Using finite element numerical simulation software ABAQUS, numerical simulations of the uplift performance of GFRP screw anchors under different embedment ratios were conducted. The maximum uplift bearing capacity of vertical GFRP screw anchors in soil and the evolution of the failure surface morphology of anchored soil were investigated. [Results and Conclusion] (1) The load-displacement curves of GFRP screw anchor during uplift in anchored soil could be divided into three stages: the elastic stage, the local plastic stage, and the penetration failure stage. In the elastic stage, the load and displacement showed linear relationship, with the slope of the curve representing the equivalent stiffness of the anchor plate-soil system. In the local plastic stage, plastic deformation occurred in the local soil zone, deformation of the anchored soil gradually increased, system stiffness decreased, load-displacement relationship became non-linear (indicated by a gradually decreasing curve slope), and the interaction between the GFRP screw anchor and the anchored soil began to exhibit non-linear characteristics. In the penetration failure stage, the resistance of the anchored soil reached its ultimate value, cracks in the anchored soil became interconnected, the soil failure surface formed, and the curve entered a stable phase where the load no longer changed with displacement increase. The uplift bearing capacity factor Nγ showed a trend of initial increase followed by gradual stabilization with embedment ratio, which matched well with experimental results from other scholars, thereby verifying the simulation’s validity. The turning point occurred near H/D=9, suggesting that an embedment ratio H/D=9 could be considered as the critical embedment ratio distinguishing shallow from deep embedment. (2) Numerical simulation showed that during uplift, the anchored soil could be divided into three zones based on stress state: conical active zone formed by compaction above the GFRP screw anchor, passive zone extending outward along screw anchor edge influenced by extrusion from soil within failure surface, and transition zone between active and passive zones in plastic state. The soil within the failure surface consistently extruded the soil outside failure surface. Except for the outermost region, which might be in a state of at-rest earth pressure, the soil on the failure surface was generally in a state of passive earth pressure. With increasing embedment ratio, the failure surface morphology of the anchored soil underwent a dynamic evolution from “trumpet” shape➝“goblet” shape➝“light bulb” shape. No distinct “critical embedment ratio” between shallow and deep embedment for GFRP screw anchors existed. (3) By integrating the maximum uplift bearing capacities obtained from numerical simulations and the evolution patterns of the failure morphology in the anchored soil, a generalized unified failure surface model that did not require distinguishing between shallow and deep embedment for the soil anchored by GFRP screw anchors was proposed. This model was derived by introducing a cubic term based on the “trumpet” shape (with inclined linear boundaries) failure surface. On this basis, a calculation formula for the uplift bearing capacity under different embedment depths of GFRP screw anchors was derived, and the formula was compared and validated with numerous experimental results from domestic and international studies. The results demonstrated that the proposed calculation formula could effectively predict the maximum uplift bearing capacity under different embedment depth ratios.
[Objective] To explore the impact of freeze-thaw environments on the strength of guar gum-modified loess, direct shear test, unconfined compression strength test, Brazilian splitting test, and bender element small-strain test are conducted to examine the strength degradation and deterioration characteristics of guar gum-modified loess before and after freeze-thaw cycles. [Methods] In this experiment, cationic guar gum was selected for specimen preparation. The specimens were subjected to freeze-thaw cycles in a sealed environment. In the bender element tests, a single-pulse sine wave was used as the input signal at a frequency of 1 kHz. The initial arrival method was adopted to determine the travel time, from which the wave velocity was calculated. [Results] After freeze-thaw cycles, the tensile strength, uniaxial compressive strength, and shear strength of guar gum-modified loess decreased, but all remained greater than that of untreated loess subjected to freeze-thaw cycles. The strength degradation of guar gum-modified loess after freeze-thaw cycles was influenced by the coupling effects of water content and guar gum content, with water content having a more pronounced effect than guar gum content. Microscopic analysis revealed that guar gum formed filamentous cement by bonding with water molecules, which linked soil particles and restrained their movement. Consequently, the strength of the modified loess was notably enhanced. However, during the freeze-thaw cycles, the simultaneous damage of the above-mentioned cement and loess particles was the main reason for the more pronounced strength degradation of guar gum-modified loess than that of untreated loess. The shear wave velocity of loess modified by guar gum before and after freeze-thaw cycles was measured using bender element tests. The functional relationships of shear wave velocity with compressive strength and tensile strength of loess were established, revealing a good correlation with uniaxial compressive strength. [Conclusion] The research findings systematically reveal the influence of freeze-thaw action on guar gum soil stabilization technology, and a novel method is proposed to evaluate the strength degradation of modified loess with wave velocity. This provides environmentally friendly materials and new insights for soil stabilization in the loess regions of northwestern China, while offering a theoretical basis for the further application of guar gum in geotechnical engineering.
[Objective] This study investigates how soluble salts in clay redistribute under an applied direct-current electric field during electro-osmotic drainage and how the redistribution affects dewatering and consolidation efficiency. The study quantifies the spatiotemporal evolution of salt content through bulk electrical conductivity, distinguishes the individual effects of salinity and water content on conductivity, and infers ion-migration trends and their implications for the combined dewatering and desalination performance of saline clays. [Methods] Laboratory conductivity calibrations were conducted on remolded clay across practical ranges of water content and soluble-salt concentration. Based on these data, an empirical relationship was established that linked soil bulk conductivity to pore-fluid salinity while explicitly incorporating water content, enabling the conversion of measured conductivities into estimates of salt content. Subsequently, a one-dimensional electro-osmotic consolidation test was conducted. Segmented voltage, local conductivity, cumulative drainage, and current were monitored and recorded. Using this calibration, time-lapse conductivity profiles were processed to reconstruct salt-content distributions and their evolution. This method could provide a framework to monitor and interpret coupled ionic transport and water removal during electro-osmosis. [Results] Calibration showed that conductivity increased with both salinity and water content. However, when water content was considered, salinity accounted for a larger share of the variance in bulk conductivity. Accordingly, conductivity served as a reliable in-situ indicator of salt content during electro-osmosis. The electro-osmotic test revealed a distinct zonation of salt content consistent with electromigration toward the cathode. At the anode, salt content declined rapidly during the first 2 hours and then stabilized at approximately 2.0 g/L until the end of the test. In the mid-section, salt content also decreased over the first 2 hours, showing the smallest reduction among the three regions, followed by an increase and subsequent decline. By 6 hours, it temporarily exceeded the initial salinity. This peak reflected the convergence in the middle zone of cation fluxes migrating from anode to cathode and anion fluxes moving in the opposite direction. After 6 hours, the mid-section salinity decreased progressively and, at the end of the test, fell below that of the anode region. The cathode experienced the most pronounced change, showing a continuous decline throughout energization. By 8 hours, the cathodic zone had nearly approached a salt-free state. During electro-osmosis, the soil potential field was strongly modulated by both water content and salinity, producing spatially differentiated potential distributions that evolved over time. Water content and drainage rate exhibited non-uniform dynamics among regions and ultimately formed a moisture gradient of Anode < Middle < Cathode. Salinity exerted a pronounced control on potential pathways and transmission efficiency. Therefore, its evolution should be incorporated explicitly in design to optimize treatment outcomes. The combined evidence demonstrated that electro-osmotic drainage in saline clay could achieve two outcomes simultaneously: accelerated consolidation and effective removal of soluble salts. The latter mitigated adverse effects of high salinity on subsequent construction, including corrosion risk and strength variability, thereby improving the suitability of the treated ground. [Conclusion] This study delineates the migration and distribution patterns of soluble salts in high-salinity clays under electro-osmotic drainage, offering a new perspective for treatment and practical guidance for engineering application. Operationally, a critical point is reached when salinity in the cathodic zone drops to a very low level. Continuing energization beyond this point leads to sharply diminished drainage efficiency and disproportionately increased energy consumption. At the design stage, measuring soil electrical conductivity and conducting pre-tests to characterize the salinity-moisture relationship are recommended, thereby informing the required energization time. In practice, continuous conductivity monitoring provides a comprehensive indicator of overall dewatering progress. Wider adoption of these insights is expected to facilitate broader and more effective application of electro-osmosis in geotechnical engineering.
[Objective] This study systematically investigates the influence of particle shape on the mechanical properties of soil-rock mixtures, with a particular focus on strength and deformation characteristics. It aims to address the current knowledge gap regarding the specific mechanisms through which particle shape affects the mechanical behavior of such materials. By establishing quantitative relationships between shape parameters and mechanical response, the study aims to provide a scientific basis for predicting and controlling the settlement of soil-rock mixture subgrades in engineering practice. [Methods] High-strength α-hemihydrate gypsum powder was utilized to fabricate rock-like particles with controlled shapes. The Brazilian shape parameter (Y) was employed to quantitatively characterize particle morphology. A series of consolidated-drained triaxial tests were conducted using a medium-pressure triaxial apparatus to systematically evaluate the mechanical properties of soil-rock mixtures containing particles with different shape coefficients. The testing program included comprehensive measurements of peak deviatoric stress, internal friction angle, cohesion, and other shear strength parameters under different confining pressures. Microstructural analysis was performed to observe particle breakage patterns and stress transmission mechanisms. [Results] The experimental results revealed significant shape-dependent mechanical behavior. As the particle shape coefficient Y increased, the peak deviatoric stress of the specimens initially increased and then tended to stabilize. With increasing Y, the internal friction angle and initial shear angle φ0 gradually decreased, while the cohesion exhibited a corresponding increase. The increment of shear angle Δφ showed a non-monotonic trend, first decreasing and then increasing. The shape coefficient was found to alter the stress transmission path within the particle skeleton, leading to preferential breakage of large-sized particles. When Y increased from 0.63 to 0.73, the failure mode transitioned from edge damage to localized rupture, and ultimately to complete fragmentation. Ellipsoidal particles (Y≥0.69) exhibited stress concentration at the long-axis ends, resulting in localized fracture concentrated in the shear band region. In contrast, near-spherical particles demonstrated uniform stress distribution and exhibited surface spalling. [Conclusion] This study successfully establishes the quantitative relationship between particle shape and mechanical properties of soil-rock mixtures, revealing the underlying mechanisms of shape effects. The findings demonstrate that particle shape significantly influences the strength, deformation, and failure characteristics through its control on stress transmission and particle breakage patterns. The study provides a scientific basis for the prediction and design of soil-rock mixture subgrade settlement, offering practical guidance for engineering applications. Future research should focus on extending these findings to field-scale conditions and developing predictive models that incorporate shape effects for improved design accuracy.
[Objective] During the parameter inversion process of groundwater models, frequent calls to the forward model result in excessive computational demand and prolonged processing time, which severely limits their practical applicability. To address the high time consumption in groundwater model inversion, this study proposes a coupled inversion algorithm capable of rapidly identifying unsteady permeability coefficients. [Methods] The proposed algorithm coupled the parameter inversion process with reduced-order model training, where the reduced-order model was employed instead of the original model for parameter inversion calculation, thereby reducing total inversion time. During the iteration process, the sum of squared errors between the reduced-order model calculation values and observations was used as the objective function, and an improved differential evolution algorithm with strong global search capability was employed as the optimization method for parameter inversion. In each iteration, the parameters that best matched the observations were identified as optimal, and snapshots of these optimal parameters were calculated to train the reduced-order model, thereby enhancing the inversion accuracy in the next generation. To enable the reduced-order model to accurately capture the time-domain response characteristics of the original model, a uniform snapshot strategy was employed to collect time-step snapshots. Based on the characteristics of the coupled inversion algorithm, the relative error of the reduced-order solution corresponding to the optimal parameters was calculated at all nodes within the time domain, and iteration was terminated when the maximum error fell below a preset threshold. [Results] Taking a two-dimensional pumping well model as an example, the proposed method was compared with an inversion approach based on the original model. The results indicated that: (1) For unsteady seepage parameter inversion, compared with the optimal time snapshot strategy, using a uniform snapshot collection strategy to construct the reduced-order model could achieve higher computational accuracy, while the reduced-order model had a lower average order. (2) While maintaining inversion accuracy comparable to that of the original model, the proposed algorithm could reduce computational time by approximately 95.37%. (3) Near the optimal parameters, the reduced-order model obtained by the proposed method showed almost identical responses to the original model. However, the error increased significantly when moving away from the optimal solution. (4) The effects of observation error, mesh density, and inversion dimensionality on the inversion accuracy of the proposed algorithm were consistent with those of the original model, but the computational time of the proposed algorithm was less than 5% of that of the original model. (5) The proposed algorithm was less affected by the order of the original model, and the increase in the computational time was proportionally smaller than the increase in model order, indicating higher computational efficiency for high-order models than for low-order ones. (6) Compared with low-dimensional inversion problems, the proposed algorithm exhibited greater time-saving efficiency in handling high-dimensional cases, suggesting stronger robustness against the curse of dimensionality. (7) Under different convergence accuracies, the proposed algorithm could consistently reproduce the results of the original model without a significant increase in computational time even as accuracy improved. [Conclusion] The proposed coupled inversion algorithm in this study, as a deterministic finite element-based inversion framework, innovatively couples the training process of the reduced-order model with the parameter inversion process and significantly improves the computational efficiency of parameter inversion.Characterized by a simple structure,ease of implementation, and no need for posterior error calculation,the algorithm has significant engineering application value and promising prospects for broad application.
[Objective] The steel volute of a pumped storage power station is the part of the flow passage structure subjected to the highest internal pressure, bearing cyclic water pressure during operation and facing potential risk of low-cycle fatigue failure. At present, a fundamental issue in predicting low-cycle fatigue life of steel volutes in pumped storage power stations lies in the scientific determination and input of the fatigue load spectrum. [Methods] Static analysis of the composite structure was performed on the Abaqus finite element platform. Based on water level monitoring data, static monitoring results, and unit operating modes, the prototype load spectrum, rainflow-counting load spectrum, and constant-amplitude load spectrum were respectively compiled. [Results] By comparing with the fatigue life prediction results based on the prototype load spectrum, the reliability of the load spectrum compiled by the rainflow-counting method was verified. The sequence of cycle amplitudes and extremely small amplitude loads in rainflow counting had minimal impact on fatigue life prediction results, indicating that the rainflow-counting method could serve as a simplified input approach for low-cycle fatigue loading of steel volutes. The fatigue life prediction results based on the constant-amplitude load spectrum were close to those based on the prototype spectrum. For this pumped storage power station, constant-amplitude loading could be used as a simplified input for fatigue loading. However, it should be noted that the drawdown depth of the water level at this power station was relatively small. In such cases, whether the prototype load spectrum, rainflow-counting load spectrum, or constant-amplitude load spectrum was used, the range of cyclic amplitude variation was limited. For power stations with small water level drawdown depths, the fatigue load spectrum of the steel volute could be simplified to a constant-amplitude form. However, for power stations with relatively large water level drawdown depths, whether the above conclusions were applicable required further investigation. [Conclusion] The findings of this study can provide a reference for compiling low-cycle fatigue load spectra for steel volutes. According to the prediction results, there is no risk of low-cycle fatigue failure during the operation period of the power station. However, certain limitations in the calculations of this study may lead to an overestimation of prediction results for the following three reasons. (1) Only the impact of hydrostatic pressure on the steel volute is considered, while variations in water hammer pressure during transitions of unit operational states are not taken into account. (2) Seasonal variations in water temperature inside the steel volute significantly affect the timing and spatial distribution of contact closure between the steel volute and concrete, and neglecting temperature effects may underestimate the stress level in the steel volute. (3) During operation, the steel volute and concrete jointly bear the internal water pressure. Cracking in the concrete weakens its restraining effect on the steel volute, leading to an underestimation of the stress level in the steel volute in calculations.
[Objective] Dam deformation is comprehensively influenced by multiple components such as water level, temperature, and time-dependent effects, exhibiting characteristics of nonlinear time series. Currently, traditional and single models struggle to fully capture the complexity and diversity of dam deformation data, resulting in limited predictive performance and interpretation ability. To solve the above problems, this study aims to propose an efficient and interpretable dam deformation prediction method through the combination and optimization of multiple prediction models. [Methods] First, the least absolute shrinkage and selection operator (LASSO) was used to efficiently screen numerous environmental variables, both simplifying model input and explaining the reliability of factor selection.Then,the long short-term memory (LSTM) network was employed to predict dam deformation, and the attention mechanism was introduced to enhance the extraction of important information.Finally,the bagging algorithm was used to integrate the prediction results of multiple models, further improving the accuracy, stability, and generalization ability of the overall prediction. By combining the advantages of LASSO regression feature selection, LSTM model with attention mechanism, and bagging ensemble algorithm, a multi-model coupled method was proposed. [Results] To validate the effectiveness and applicability of the coupled model, this study took the deformation monitoring data of a roller-compacted concrete gravity dam as the research object for prediction analysis. When the number of features was relatively large, the LASSO variable selection method reduced model complexity by adding L1 regularization term and selected features with important influence on dam displacement, enhancing the interpretability of factor selection. Combined with this method, multiple LSTM models with attention mechanism were integrated for parallel training and prediction, reducing potential overfitting problems in single models and improving generalization ability and prediction efficiency of the coupled model. The trained model was used to predict and validate the test set data. The residual values of the coupled model were small, and residual distribution had strong randomness, indicating high prediction accuracy. The fitting results of each measurement point were smooth and agreed well with the measured data, and the prediction results were stable without showing any “distortion” phenomenon. Using the same dataset and identical proportion division, LSTM multi-factor model, stepwise regression prediction model, LASSO regression model, LASSO-LSTM model, and the coupled model were compared and analyzed. The results showed that the coupled model proposed in this study significantly outperformed other models in overall prediction trend and the prediction accuracy of partial fluctuations. The average MAE, MSE, and RMSE at each measurement point were 0.052, 0.005,0.067 mm, respectively. The coupled model could more accurately capture the dynamic changes of dam deformation, providing a simple and efficient method for prediction model research. [Conclusion] This study constructs a coupled prediction model with high accuracy, stability, and interpretability. The main innovation lies in the effective selection of key environmental variables through LASSO, simplifying model input and improving its interpretability; the use of LSTM to capture the time-series features of dam displacement data, while the incorporated attention mechanism helps the model focus on important features in time series; and the bagging algorithm that significantly improves the generalization ability of model by training multiple sub-models in parallel. Based on actual case analysis, the coupled model not only demonstrates higher accuracy in dam deformation prediction,but also outperforms commonly used models in interpretability and stability.The coupled model based on interpretable variable selection provides a reference for the optimization of subsequent combined models.Future research directions can shift from single measurement points in different dam sections to multiple measurement points in the same dam section.This will involve analyzing the location of measurement points and the relationships between different points,thereby enabling the construction of a comprehensive multi-point coupled model.
[Objective] Current micromechanical models pay limited attention to parameter uncertainty and interactions, which makes it difficult for their response results to reflect the dispersed nature of the properties of cement-based materials. Therefore, it is necessary to explore an analysis method that can simultaneously capture the effects of multiple parameters and their interactions on the responses of micromechanical models of cement-based materials. [Methods] To address the discrete distribution of response results in existing micromechanical models and to identify and control the influencing factors causing this phenomenon, a multi-scale micromechanical model of cement-based materials was constructed in this study. Cement-based materials were divided into four scales: calcium silicate hydrate gel, cement paste, cement mortar, and concrete. Considering the mineral composition of cement phases, aggregates, and the ITZ, a multi-scale micromechanical model capable of accounting for the randomness of input parameters was proposed. Meanwhile, probabilistic methods were applied to the constructed micromechanical model, and global sensitivity analysis was employed to quantify the effects of input parameter uncertainty on the elastic modulus of cement-based materials. [Results] The results showed that the proposed model exhibited good applicability in simulating the relationship between elastic modulus and hydration degree of cement-based materials across multiple scales and showed good agreement with experimental results. The discreteness of the model response results mainly originated from the cross-scale propagation of input parameter uncertainty, indicating that uncertainty at the concrete scale incorporated the uncertainties of input parameters at the mortar and cement paste scales. The total-order sensitivity indices, ranked from largest to smallest, were the elastic modulus of sand and coarse aggregates, the volume fraction of sand and coarse aggregates, the elastic modulus of hydration products, the volume fraction of cement clinker, and the elastic modulus of cement clinker. To identify the dominant sources of uncertainty within the model framework, particular attention should be paid to the elastic modulus of sand and coarse aggregates, whereas the volume fraction and elastic modulus of cement clinker can be regarded as insensitive factors. [Conclusion] Screening the number of input parameters has important practical significance for reducing computational complexity and improving the efficiency of model response analysis.
[Objective] This study aims to reveal the exothermic properties and hydration mechanism of low-heat Portland cement (LHC) (hereafter referred to as low-heat cement) mixed with fly ash, the composition of pore solution during hydration, and the evolution mechanism of hydration products. [Methods] Long-term exothermic tests were conducted on the cementitious materials, and a quantitative relationship between heat release and hydration progress was established, from which the hydration state was obtained. Based on the theory of Gibbs free energy minimization using GEMS software, thermodynamic calculations were performed to construct a cement hydration model, whose validity was verified through comparative analysis between simulated and measured Ca(OH)2 contents in neat paste. [Results] (1) The exotherm from low-heat cement hydration was mainly concentrated within 28 days. Fly ash significantly reduced the hydration heat of low-heat cement: a 20%-50% replacement ratio resulting in a reduction of 14.6%-32.7% in total exotherm after 720 days of hydration. Predictive models for exotherm and degree of hydration of the cementitious system were established. At hydration stabilization, the degree of hydration of low-heat cement reached 86.0%, and the reaction degree of fly ash was 53.3%. (2) The Ca(OH)2 content calculated by the cement hydration model showed small deviation from measured values, indicating that the developed model adequately characterized the hydration process of low-heat cement. The cement was dominated by dicalcium silicate (C2S). Compared with ordinary and medium-heat Portland cements, it produced more calcium silicate hydrate (C-S-H) gel and less Ca(OH)2, which explained its higher later-age strength. (3) Different types of C-S-H were found to exhibit distinct saturation indices, ranked from highest to lowest as C1.5S0.67H2.5, C0.83S0.67H1.83, C1.33SH2.17, and C0.67SH1.5 (the last being unstable). All types showed linear positive correlations with the saturation index of Ca(OH)2, as well as with OH- and silicon ion concentrations, and a negative correlation with calcium ion concentration, with the relevant relationships established. (4) After fly ash incorporation (0-25%), the ettringite (AFt) content in the cementitious system gradually decreased to zero, while the monosulfate (AFm) content continuously increased. (5) At low fly ash dosages (0-20%), Si phases in fly ash first reacted with Ca(OH)2 to form C-S-H with a higher Ca/Si ratio, increasing the average from 1.61 to 1.63. At higher dosages (20%-50%), C-S-H content decreased by 16.5%, and both Ca/Si ratio and pH declined markedly, primarily due to exhaustion of CH, reduced Ca phase, and increased Si and Al phases. At very high dosages (65%-80%), severe deficiency of Ca phase along with excess Si, Al, and Fe phases and lower pH caused extensive dissolution of C-S-H and a reduction in its Ca/Si ratio. (6) A relationship among pH, solution composition, and product saturation indices was established. At pH=12.86, the saturation indices of the above products were highly similar. When pH≤12.86, significant changes in the stable states of the products occurred. [Conclusion] Incorporation of fly ash further reduces the exotherm of low-heat cement, and heat release is significantly positively correlated with hydration progress. At low dosages, both the content and properties of C-S-H gel are improved, which benefits macroscopic mechanical performance and durability. pH 12.86 appears to be the pH inflection point for the stable state of hydration products, which should be considered when designing low-heat cement concrete with high fly ash dosages.
[Objective] The water source area of the Middle Route of the South-to-North Water Diversion Project faces issues such as water quality safety risks, dual challenges in scheduling, and a lack of coordinated monitoring due to fragmented and decentralized management. This study aims to construct a holistic collaborative management mechanism for the water source area and to provide a reference for the “four unifications” management practice, thereby ensuring the high-quality development of the Hanjiang River Basin and the achievement of the goal of “a continuous flow of clean water going northward forever”. [Methods] Based on the theoretical foundation of holistic governance theory and the classic SFIC collaborative management analysis model, the study systematically drew on the collaborative management experiences of the Murray-Darling River and the North American Great Lakes. By analyzing 232 policy documents and 21 relevant important speeches, nine key elements were extracted and summarized into three dimensions: collaborative bodies, basin-wide coordination, and support and safeguard. Finally, the holistic collaborative management mechanism for the water source area was constructed. [Results] The study constructed a five-dimensional holistic collaborative management mechanism model for the water source area of the Middle Route Project of South-to-North Water Diversion Project, consisting of “initial conditions - catalytic leadership - institution design - collaboration process - outcome assessment”. Initial conditions focused on enhancing the motivation for collaboration among multiple bodies. Catalytic leadership coordinated and integrated efforts by improving communication and coordination mechanisms. Institutional design ensured the fairness and legality of collaboration through the establishment of a comprehensive legal system. The collaboration process created a virtuous cycle of cooperation among multiple bodies. Outcome assessment continuously optimized collaborative results. Based on this model, five policy recommendations were proposed: establishing a unified management institution for the water source area, unlocking market potential to promote overall synergy, improving coordination and compensation mechanisms, ensuring the sufficiency and stability of various resources, and perfecting the legal and regulatory system of the water source area. Research on holistic collaborative management not only enriched the theory of system governance but also provided practical guidance for the management of water source areas in water diversion projects, serving as an effective reference for the transition from local to holistic collaboration. [Conclusion] This study overcomes the limitation of previous research on water source area collaborative management that focused primarily on local collaboration, concentrating instead on the holistic collaborative management of the water source area of the Middle Route Project of South-to-North Water Diversion Project. Based on the theoretical foundation of holistic governance theory and the SFIC model, and drawing on the collaborative management experiences of the Murray-Darling River Basin and the North American Great Lakes, the study analyzes laws, regulations, policies, and key speeches from a holistic collaborative management perspective, distills the key elements of holistic collaborative management, and then constructs the holistic collaborative management mechanism for the water source area. Five targeted policy recommendations were proposed. The study provides a reference for addressing the challenges of fragmented and decentralized management in the water source area, and is of great significance for ensuring the smooth operation of the Middle Route Project, supporting the construction of the national water network, and promoting the synergistic development of ecology, livelihood, and economy along the route.
[Objective] Taking the deeply buried Liupanshan tunnel of the Bailong River Diversion Project as the research background, this study aims to systematically investigate the distribution characteristics of the in-situ stress field along the tunnel alignment and to assess the rockburst risk of hard-rock sections under high-stress conditions, thereby providing a scientific basis for early-stage project planning, construction safety control, and support design. [Methods] A comprehensive approach combining field testing, numerical simulation, and theoretical analysis was employed. (1) Geological survey and deep-borehole hydraulic fracturing tests were conducted to obtain measured in-situ stress data from representative boreholes along the tunnel alignment. (2) Based on the measured data, a three-dimensional geomechanical model was established, and a multivariate regression inversion method was used to invert the initial in-situ stress field of the entire study area. (3) By integrating the Russenes criterion, the Turchaninov criterion, and the criterion of the ratio of chamber damage depth, a multi-criterion comprehensive evaluation of rockburst risk was conducted for the hard-rock sections. [Results] (1) In-situ stress characteristics: Along the tunnel alignment, horizontal stress was dominant, and the maximum horizontal principal stress was mainly oriented in the NEE-EW direction, forming a small angle with the tunnel axis, which was favorable for surrounding rock stability. The stress magnitude increased with depth and was significantly influenced by faults and valley topography, resulting in localized stress concentration and stress differentiation. (2) Inversion verification: A comparison between the measured data and inversion results from the deepest borehole ZK2301 showed good agreement in the deep zone, verifying the reliability of the inversion model. (3) Rockburst risk: The multi-criterion assessment indicated that rockburst risk increased with burial depth along the tunnel alignment: no rockburst at depths ≤197 m; weak rockburst at depths of 197-344 m; moderate rockburst at depths of 344-629 m; and strong rockburst at depths >629 m. Sections with strong rockburst risk accounted for a relatively large proportion of the entire tunnel, mainly concentrated in hard-rock zones with high burial depths. [Conclusion] The in-situ stress along the Liupanshan tunnel is generally at a moderate-to-high level, providing conditions conducive to rockburst occurrence. The selected tunnel axis orientation is reasonable and favorable for surrounding rock stability. However, strong rockburst risk exists in hard-rock sections with large burial depths. Therefore, it is recommended that appropriate rockburst monitoring and mitigation measures should be implemented for high-risk tunnel sections during construction. This study provides critical guidance for the safe construction of the project and offers valuable reference for rockburst prediction and prevention in similar deeply buried hard-rock tunnels.
[Objective] Identifying the main areas and driving factors of eutrophication in Fengjiangkou Reservoir can provide guidance for water quality protection in the online regulation reservoir of the water resource allocation project in northern Hubei Province. [Methods] Taking Fengjiangkou Reservoir as the study area, water quality monitoring and meteorological and hydrological data collection were conducted. The comprehensive nutrient status index method and the partial least squares regression method were used to analyze the spatiotemporal variation characteristics of nutrient status in Fengjiangkou Reservoir and its influencing factors. [Results] There were significant spatiotemporal differences in indicators such as permanganate index, ammonia nitrogen, total phosphorus, total nitrogen, and chlorophyll-a. These indicators were higher during the irrigation period than during other periods, and higher in the estuary areas of the Fengjiangkou River and Shahedian River than in other waters, making them the key periods and water areas for pollutant control in Fengjiangkou Reservoir. In the estuary area of Fengjiangkou River, chlorophyll-a concentration was significantly positively correlated with TN concentration (P=0.02), TP concentration (P=0.05), and diffuse radiation (P=0.04). In the estuary area of the Shahedian River, chlorophyll-a concentration was significantly positively correlated with TN concentration (P=0.02) and TP concentration (P=0.02), indicating that TN concentration, TP concentration, and diffuse radiation intensity might be the main factors affecting the nutrient status in the estuary area of Fengjiangkou River, while TN concentration and TP concentration were the main factors affecting the nutrient status in the estuary area of Shahedian River. Although indicators such as air temperature and wind speed showed no significant correlation with chlorophyll-a concentration, each indicator exhibited a clear correlation with chlorophyll-a concentration under given conditions. During the irrigation period, the nutrient status of the Fengjiangkou River and Shahedian River estuary areas was mildly eutrophic. Contribution analysis results showed that permanganate index (20.6%), total nitrogen (11.0%), and nitrogen-to-phosphorus ratio (9.3%) were the main water quality indicators affecting eutrophication in the estuary area of Fengjiangkou River, while total phosphorus (15.6%), ammonia nitrogen (12.3%), pH (10.1%), and total nitrogen (8.3%) were the main water quality indicators affecting eutrophication in the estuary area of Shahedian River. Both normal radiation and diffuse radiation contributed over 10% to the occurrence and decline of eutrophication in the estuaries of Fengjiangkou River and Shahedian River, making them the main meteorological driving factors of eutrophication in Fengjiangkou Reservoir. [Conclusion] To synergistically ensure the water quality safety in Fengjiangkou Reservoir, recommendations are proposed, including reducing watershed non-point source pollution during the irrigation period, regulating algal biomass in the reservoir bay, and implementing water environment monitoring and intelligent management.
[Objective] The Xianglushan Tunnel is a challenging and key control project of the Central Yunnan Water Diversion Project. Branch Tunnel No.7 of the Xianglushan Tunnel, located in Songgui Town, Heqing County, Dali Prefecture, Yunnan Province, generally lies at a depth of 600-1 300 m, with a maximum burial depth of 1 415 m. High external water pressure is regarded as a major threat to its safety. Existing studies on tunnel external water pressure have mostly assumed homogeneous strata, paying relatively little attention to geological structures. The influence of geological structures—particularly the presence of aquitard layers above the tunnel—remains to be investigated in depth.[Methods] A typical deep-burial section of the Central Yunnan Water Diversion Project was investigated through field observations and numerical simulation to study the external water pressure acting on the tunnel lining. The effects of geological structures and seepage control measures on the external water pressure were analyzed to provide a reference for the design and construction of deep-burial tunnels.[Results] During in-situ drilling, groundwater in the tunnel was identified as fissure groundwater. Obvious water inflow occurred if a borehole intersected water-conducting fissures; otherwise, the boreholes remained essentially dry. Monitoring data from five piezometers installed in the tunnel over nearly one year indicated that the external water pressure around the unlined tunnel during construction was relatively low, only several meters of water head. Numerical simulation of the seepage field revealed that higher rock permeability and shorter distance between the tunnel and water-conducting structures increased both external water pressure and seepage discharge. Impermeable linings, while blocking water, caused an increase in external water pressure. Drainage holes, while reducing external water pressure, resulted in an increase in tunnel seepage discharge. Under specific geological structures and seepage control measures, tunnel excavation and drainage may only cause local groundwater drawdown around the tunnel, without affecting the regional phreatic surface.[Conclusion] In the model of this study, an aquitard layer with relatively low permeability exists above the tunnel, which limits the influence range of tunnel drainage. As a result, drainage only forms a localized desaturation zone between the tunnel and the aquitard, exerting minimal effect on groundwater above the aquitard. This localized desaturation explains the phenomenon observed in tunnel projects in water-rich areas, where the regional phreatic surface is high while the external water pressure acting on the tunnel remains relatively low. Near the tunnel face, equipotential lines are densely spaced, and the hydraulic gradient is relatively large, whereas a smaller gradient prevails behind the face. This indicates that greater seepage pressure is imposed near the tunnel face, explaining why seepage-induced failures frequently occur in this area.
[Objective] Water intake structures of reservoir connection projects are characterized by large water level fluctuations, bidirectional flow, and operating modes affected by pipeline roughness, leading to a relatively complex hydraulic regulation process. Poor intake design or unreasonable regulation can easily cause a series of problems. To analyze the key hydraulic issues of water intake structures in reservoir connection projects, this study took the Gongming-Qinglinjing Reservoir Connection Project as the research object. The hydraulic characteristics of bidirectional water intake and layered control intake were systematically investigated, and key issues and corresponding measures that needed to be focused on in the design of various types of water intakes were proposed. [Methods] Firstly, the hydraulic calculation method was used to analyze the hydraulic characteristics of the main conveyance line under different operating conditions and to assess the impact of roughness variation on flow conveyance capacity and water intake operating conditions. On this basis, hydraulic model tests were conducted to examine the flow patterns and local hydraulic characteristics of the bidirectional water intake and layered control intake under typical scheduling conditions. Finally, regarding the transitions between free surface and pressurized flow as well as closed hydraulic jump in the connecting tunnel behind the gate of the layered control intake, optimization recommendations were proposed from the perspectives of engineering measures and operational scheduling. [Results] (1) the selection of roughness had an important impact on the project’s water conveyance capacity, water intake hydraulic characteristics, and project hydraulic scheduling. When the roughness increased from 0.011 to 0.016, the pipeline head loss increased by 108.2%-111.6%. Under maximum roughness conditions, the water conveyance capacity of the project must be ensured, while under small roughness conditions, particular attention must be given to the flow connection characteristics at the water intake. (2) Under inflow conditions, at bidirectional water intakes, the water surface in the reservoir area and the diversion channel was stable, the flow velocity was relatively small. After entering the intake tower, the flow velocity increased, with no adverse flow patterns such as vortices or recirculation. Under outflow conditions, the flow at the water intake was smooth. The main flow increased in velocity after entering the diversion channel from the forebay, generating symmetrical recirculation on both sides. (3) During gate-controlled discharge, the layered control intake exhibited a free jet flow pattern. The jet impacted the wall of the energy dissipation well, fell to the bottom, and then entered the connecting tunnel section in an open-channel flow state. Adverse flow patterns such as closed hydraulic jumps might occur in the connecting tunnel. (4) Regarding the issue of closed hydraulic jumps, feasible preventive measures were proposed from the perspectives of engineering solutions and operational scheduling. (5) Reservoir connection projects had complex operating conditions. After the project was commissioned, the actual roughness of the main tunnel should be inversely calculated based on monitoring data, and the hydraulic control methods should be adjusted in a timely manner. The research findings can provide references for the design and operational scheduling of water intakes in similar water diversion projects.
[Objective] During the construction of water-rich disintegrated dolomite tunnels, water and sand inrush disasters are prone to occur frequently, seriously affecting construction progress and project safety. [Methods] The Chenaju Tunnel of the Central Yunnan Water Diversion Project was taken as the research object. Considering the main factors affecting the suitability of water and sand inrush treatment schemes, and in combination with the characteristics of disintegrated dolomite strata and the formation mechanism of water and sand inrush, ten evaluation indicators were selected from four aspects: rock mass characteristics, groundwater conditions, tunnel length and burial depth, and the environmental impact of water and sand inrush. Key factors such as the disintegration degree of dolomite, unfavorable geological structures, external water pressure, and water richness were incorporated into the evaluation system, compensating for the insufficient consideration of disintegrated dolomite characteristics in existing evaluation systems. A suitability evaluation system for water and sand inrush treatment schemes applicable to disintegrated dolomite strata was established. A game theory-based combined weighting method was adopted to balance the weights calculated by the Analytic Hierarchy Process (AHP) and the CRITIC method, thereby improving the scientific rationality of weight allocation for evaluation indicators. The TOPSIS method was applied to rank the suitability of treatment schemes, and the suitability was classified into four levels: Grade Ⅰ (excellent), Grade Ⅱ (moderate), Grade Ⅲ (low), and Grade Ⅳ (poor). Combined with obstacle factor diagnosis, the key factors restricting suitability were quantified and identified. [Results] The results showed that, by comprehensively considering the main disaster-causing factors of water and sand inrush in disintegrated dolomite tunnels—such as the deterioration of rock mass characteristics, groundwater seepage and external water pressure driving effects, and the hydraulic channel effect of unfavorable geological structures—as well as engineering constraints including technical feasibility, economic efficiency, and treatment difficulty, the established evaluation system was able to accurately reflect the particularity of disintegrated dolomite strata, identify the main factors restricting the suitability of water and sand inrush treatment schemes in disintegrated dolomite tunnels, and produce evaluation results that were consistent with actual engineering conditions. [Conclusion] The key factors included in the evaluation system, such as the disintegration degree of dolomite, unfavorable geological structures, external water pressure, and water richness, fully reflect the characteristics of disintegrated dolomite rock masses, including low strength, poor self-stability, and high sensitivity to external disturbances, highlighting the complexity of water and sand inrush formation in disintegrated dolomite strata and its constraining effect on treatment schemes. When disintegrated dolomite tunnels pass through water-rich tunnel sections, the risk of water and sand inrush increases significantly. Under special unfavorable geological conditions, when disintegrated dolomite tunnels encounter high-frequency and large-scale water and sand inrush events, rerouting to avoid high-risk areas shows superior suitability.
