[Objective] This study aims to clarify the laws of sediment deposition and the distribution characteristics of pollutants in the Yangtze River Basin. To fill the research gap regarding the spatio-temporal evolution of flocs and their driving factors along the mainstream from the Three Gorges Reservoir （TGR） Area to the Yangtze River estuary， this research systematically explores the variation rules of flocs and identifies their key influencing factors， so as to provide theoretical and practical support for sediment regulation and pollutant research in the basin. [Methods] Combining published literature and in-situ field measurement data of sediment flocculation collected from the TGR Area to the Yangtze River estuary，this paper conducts a comprehensive analysis on the spatio-temporal variation characteristics of sediment flocs.Field observations and statistical analyses are adopted to quantify the particle size，effective density and settling velocity of flocs in different river sections，different seasons and different water depths. Meanwhile，the correlations between floc properties and hydrodynamic conditions， sediment concentration， salinity and organic matter are further discussed to determine the dominant factors affecting floc formation and development. [Results] Obvious flocculation of fine-grained sediment was observed throughout the reach from the TGR Area to the Yangtze River estuary.The floc particle size ranged from 22.0 μm to 58.0 μm in the TGR Area， 25.4 μm to 101.4 μm in the middle and lower mainstream of the Yangtze River， and 32.6 μm to 179.0 μm in the Yangtze River estuary. During the flood season， the floc particle size first decreased and then increased along the river from the TGR Area to the estuary. In the dry season， the average floc particle size at each monitoring station from Chenglingji to Datong in the middle and lower mainstream was larger than that in the estuary. Vertical distribution of floc size varied across regions： at Hankou and Hukou stations， floc particle size gradually increased from the water surface to the bottom layer. There was no significant difference in the effective density of flocs among different regions in the flood season. In the dry season， the effective density of flocs in the estuary was notably higher than that in the middle and lower mainstream. In terms of settling velocity， the ranges were 0.13~0.61 mm/s for the TGR Area， 0.30~0.68 mm/s for the middle and lower mainstream， and 0.46~2.32 mm/s for the estuary. At Xuliujing station， the settling velocity of flocs presented an upward trend from the surface layer to the bottom layer. Weak hydrodynamic conditions， fine primary sediment particles and high sediment concentration were conducive to the formation and growth of flocs along the entire study reach. Salinity exerted a prominent promoting effect on sediment flocculation in the estuary area， while organic matter was a vital factor that intensified flocculation in partial sections of the middle and lower mainstream. [Conclusions] This study quantitatively reveals the spatio-temporal distribution patterns and vertical stratification features of floc particle size， effective density and settling velocity along the Yangtze River from the TGR to the estuary， and clarifies the differentiated controlling mechanisms of multiple environmental factors on flocculation in different river segments. The findings improve the basic theoretical system of cohesive sediment movement in large river basins. Practically， the research results offer important references for the prevention and control of waterway， lake and reservoir sedimentation in the Yangtze River Basin， as well as the investigation on distribution， migration and transformation of pollutants. Furthermore， the differentiated influence rules of hydrodynamic force， salinity and organic matter summarized in this paper can provide a new research perspective for follow-up studies on river sediment dynamics and pollutant migration in similar large river systems.

[Objective] This study comprehensively investigated the applicability， failure mechanisms， and adaptability characteristics of different bank protection structures to provide theoretical basis and technical support for structural optimization， engineering design， and the development of new ecological revetment technologies under complex river conditions in the middle reaches of Yangtze River. [Methods] Typical bank collapse cases and operational data from engineering practices in the middle reaches of the Yangtze River were collected and analyzed. Representative revetment structures， including riprap， articulated concrete mattresses， gabions， geotextile sand pillows， pebble mattresses， precast concrete blocks， Reno mattresses， geogrid stone mattresses， and vegetative revetments， were systematically investigated. Their mechanical properties， protection mechanisms， failure modes， and improvement measures were summarized by integrating previous physical experiments， numerical simulations， field observations， and engineering applications. A comprehensive evaluation framework accounting for ecological， hydrological and sediment conditions and riverbed evolution processes was established. [Results] Riprap revetment remains the most widely used protection type in the middle reaches of the Yangtze River， while ecological concrete， Reno mattresses， and gabions have been increasingly adopted， reflecting a shift from conventional engineering protection to environmentally oriented designs. Revetment stability is jointly influenced by hydrodynamic conditions， water level fluctuations， riverbed deformation， bank material properties， structural parameters， and construction quality， among which flow scouring is the dominant factor responsible for structural failures. After bank protection works are implemented， channel deformation tends to shift from lateral migration to vertical erosion， resulting in deep-channel encroachment and severe toe scour. Consequently， failures usually initiate from underwater toe protection. Different revetment structures exhibit distinct characteristics. Traditional structures such as riprap and dry masonry show favorable economic performance but relatively poor ecological adaptability， whereas vegetative revetments provide the highest ecological benefits but insufficient resistance to strong hydraulic disturbances. Articulated concrete mattresses， gabions， and Reno mattresses exhibit balanced flexibility and integrity. Geogrid stone mattresses possess strong hydraulic adaptability but relatively high construction and maintenance costs. Comprehensive evaluation demonstrates that ecological concrete revetments perform well in hydraulic， ecological， and economic aspects and exhibit obvious advantages in overall adaptability. [Conclusions] The adaptability of bank protection engineering in the middle reaches of the Yangtze River is characterized by the coupling effects of multiple factors， and structural stability depends not only on the properties of the revetment itself but also on river regime evolution， hydrological conditions， and maintenance practices. For reaches subjected to severe scouring and strong flow attacks， rigid-flexible combined structures with high erosion resistance should be preferentially adopted， whereas ecological revetments with good permeability and environmental compatibility are more suitable for relatively stable reaches. Compared with traditional structures， new ecological revetments integrating structural stability and ecological functions exhibit better comprehensive adaptability， among which ecological concrete shows great development potential. The proposed multi-dimensional evaluation framework enables a systematic comparison of different revetment types and provides a new analytical approach for revetment optimization and bank collapse prevention. Future studies should strengthen the integration of bank protection engineering with river regime prediction and intelligent monitoring technologies to improve the long-term adaptability of revetment systems under continuously changing hydrological and sediment conditions.

[Objective] Since the operation of Xiaolangdi reservoir in 1999， continuous erosion has happened in the lower Yellow River. As of 2023， the accumulated erosion volume of Tie-Li reach （from Tiexie station to Lijin station） in the lower Yellow River has reached 2.2 billion m³. However， the erosion efficiency gradually decreases from 13.6 kg/m³ to 6.3 kg/m³. It is important to realize the temporal and spatial accumulation variation law of continuous erosion in the lower Yellow River in order to estimate the erosion potential. [Methods] Through collecting the annual erosion volume data from 2001 to 2024 for different sub-reaches， the temporal and spatial accumulation variation law of continuous erosion in the lower Yellow River is analyzed. Based on the river spatial non-equilibrium sediment transport theory， and combined with the temporal delayed response model of sediment transport capacity adjustment during the processes of erosion and sedimentation of river bed， a temporal and spatial accumulation variation model of continuous erosion volume is proposed， and then is used to simulate the temporal and spatial accumulation variation of continuous erosion in the lower Yellow River and predict the future erosion potential. The model parameter ϕ is calibrated based on the measured spatial accumulation erosion data of 2017， the model parameters K_（0） and β is determined based on the measured temporal accumulation erosion data from 2001 to 2017 of the Hua-Li reach. These calibrated parameters are used to simulate the temporal and spatial accumulation erosion from 2018 to 2024 of the different sub-reaches for model validation and the performance is evaluated using the certainty coefficient and the Nash-Sutcliffe efficiency coefficient. [Results] Data analysis results show that the temporal and spatial accumulation variation law of continuous erosion in the lower Yellow River shows a set of different growth curves， and the growth rates present a first fast and then slow down change trend， finally gradually tending towards 0. The simulation results of the temporal and spatial accumulation erosion volume show that the simulated and measured values are in good agreement， the values of the certainty coefficient and the Nash-Sutcliffe efficiency coefficient are 0.98 and 0.99. The sediment transport capacity coefficient K decreased to 0.005 4 kg·s/m⁶ by 2024. The continuous erosion in the lower Yellow River is approaching equilibrium. If further erosion is desired， it is necessary to optimize the water and sediment combination conditions. If the average discharge increases by half to 1 191 m³/s and the sediment concentration decreases by half to 1.98 kg/m³， the erosion potential can increase to 860 million m³. [Conclusion] The high model precision illustrates the rationality of the proposed temporal and spatial accumulation variation model of continuous erosion volume. As a macro accumulation model， the proposed model in this paper is not suitable to simulate different annual erosion volumes of different sub-reaches of the lower Yellow River and the spatial accumulation variation law. But after long term self-adjustment， its macro temporal and spatial accumulation variation law conforms to the model proposed in this paper reflecting the macro fluvial process tend towards equilibrium. In the future， from a micro perspective of the different independent year， how to finely simulate the annual erosion volume of different sub-reach and the complex spatial accumulation variation law in the lower Yellow River is still to be further studied.

[Objective] In 2024， the Xin’anjiang Reservoir experienced the largest inflow flood since its construction due to persistent and intense rainfall during the Meiyu season. The return periods of the maximum 5-day and 7-day inflow volumes both reached the 50-year level. This study conducts a post-event assessment based on the actual forecasting and operation process. [Methods] Multi-source and multi-model quantitative precipitation forecasts were assimilated to analyze the rainfall intensity characteristics of typical historical floods. Representative forecast rainfall time series were optimized under unfavorable， moderate， and favorable conditions with phased temporal distribution， extending forecast lead time while reducing rainfall uncertainty. The Xin’anjiang three-component runoff generation framework was applied to construct a basin-wide flood forecasting model， coupled with reservoir operation rules to form an integrated forecasting-operation modeling scheme. Hourly rolling forecasts were performed based on real-time rainfall and operational information. Considering multiple objectives such as controlling maximum reservoir level， ensuring downstream safety discharge， and managing flood-peak staggering with the mainstream， iterative forward-and-reverse scenario simulations generated 215 forecast scenarios， providing precise support for ten rounds of gate operation decisions. [Results] A comparative assessment of the two major floods in 2024 and 2020 shows that although the 2024 event involved larger rainfall and greater inflow volume， the forecasting was more refined， the regulation was earlier and more proactive， and the peak staggering with the Lan River was more precise. This demonstrates that the integrated forecasting-operation model can effectively support multi-objective risk control， achieving the systemic goal of “zero major disaster and zero casualty”. [Conclusion] The full-process summary highlights that dynamic and accurate forecasting is the key to scientific operation， comparative scenario analysis supports refined decision-making， and the principle of “early action， rapid response， and incremental adjustment” is more conducive to basin-wide flood risk reduction.

[Objective] This study aims to analyze the spatiotemporal distribution and probabilistic characteristics of multi-level meteorological droughts at the seasonal scale in Guangxi， China， with a focus on seasonal continuous drought events. The study quantitatively analyzes drought frequency trends， identifies the optimal probability distribution function for seasonal precipitation， and assesses the joint probability of consecutive seasonal droughts with the goal of providing more scientific basis for drought risk management in Guangxi. [Methods] Using daily precipitation data from 18 meteorological stations （1960-2020）， we calculated the Standardized Precipitation Index （SPI） for four seasonal scales and classified drought thresholds into four levels （mild， moderate， severe， and extreme）. The GAMLSS （Generalized Additive Models for Location， Scale and Shape） model compared six probability distributions （Gamma， Normal， Lognormal， Gumbel， Weibull， and Logistic） to fit precipitation sequences， and the Gamma function was selected as the optimal model based on the AIC （Akaike Information Criterion）. Five Copula functions （Clayton， Frank， Gaussian， Gumbel， and t-Copula） were used to construct the joint distribution of continuous seasonal drought， and the optimal Copula function was determined using the squared Euclidean distance （OSL）. Spatial interpolation techniques were applied to visualize regional drought probabilities. [Results] The SPI in spring showed a decreasing trend （-0.005 8/a）， indicating an increase in drought frequency， while the SPI in summer （0.007 6/a）， autumn （0.002 1/a）， and winter （0.015 3/a） showed an increasing trend， indicating a decrease in drought frequency. Based on the fitting results of the GAMLSS model using six probability distribution functions for the seasonal precipitation series in Guangxi， the gamma function appeared most frequently in the optimal and suboptimal distributions， indicating that the gamma function can effectively describe the characteristics of precipitation changes. The seasonal frequencies of different drought levels at various stations show that mild droughts （30%-48%） are more common in summer， while moderate droughts （20%-37%）， severe droughts （10%-27%）， and extreme droughts （5%-17%） are more likely to occur in autumn. The gamma distribution performs exceptionally well， with the difference between theoretical and empirical frequencies not exceeding 11%. Different regions in Guangxi exhibit significant differences in consecutive drought characteristics. Among the four consecutive seasons of spring-summer， summer-autumn， autumn-winter， and winter-spring， the probability of consecutive droughts， moderate droughts， severe droughts， and extreme droughts is higher and more widespread during the winter-spring season. The probability range for consecutive winter-spring droughts is 13.1%-20.9%， primarily distributed in the southern coastal areas of Guangxi， central Guangxi， and northeastern Guangxi， with the highest probability of drought occurring in the northwestern part of Wuzhou City. Regions with a higher probability of severe consecutive droughts are distributed in Liuzhou， Laibin， Qinzhou， and Baise. Regions with a higher probability of severe and extreme consecutive droughts are distributed in Liuzhou， Laibin， Qinzhou， and Baise， among which Liuzhou has the highest probability of severe and extreme consecutive droughts during the spring-summer season， with probabilities of 7.1% and 3.9%， respectively. [Conclusions] The study revealed differences in seasonal drought trends in Guangxi， with spring becoming increasingly dry， while other seasons exhibit a trend toward greater moisture. The robustness of the gamma function in precipitation modeling highlights its practicality in drought frequency analysis. Crucially， the Copula-based joint probability analysis identified winter and spring as the most susceptible periods for consecutive droughts， particularly in regions dominated by karst topography. These findings provide scientific basis for adaptive drought management strategies， emphasizing the need to prioritize addressing composite drought risks in regional water resource planning.

[Objective] The urban agglomeration in the middle reaches of Yangtze River Basin is a key region in the “Rise of Central China” strategy. Dense population and high-level industrialization have led to severe contradictions between water supply and demand. By calculating the connection values of regional water resources carrying capacity （WRCC）， this research aims to provide scientific references and empirical support for optimizing regional water resource allocation， promoting sustainable socioeconomic development， and informing policy practices for high-quality water conservancy development within the Yangtze River Economic Belt. [Methods] Based on multi-year statistical data from Hubei， Hunan， and Jiangxi provinces， we applied the fuzzy analytic hierarchy process （FAHP） to calculate indicator weights， set pair analysis （SPA） to evaluate the WRCC by quantifying the connection numbers between the system and carrying grades， and the standard deviational ellipse （SDE） method to analyze the spatial distribution pattern and evolution trajectory of WRCC. [Results] （1） The WRCC of the urban agglomeration in the middle reaches of Yangtze River were increasing， with the average connection number increasing by 0.20； （2） Water allocation and pollution control have been optimized， with connection numbers for water use per GDP unit and urban sewage treatment rate increasing by more than 0.70； （3） Northern cities exhibit lower WRCC， and the SDE centroid has shifted from the east to the northwest， indicating improved spatial balance in WRCC. [Conclusions] Although the WRCC of the study region has been continuously improving， there are still spatial differences. It is necessary to strengthen water resources regulation and control capabilities in the high-consumption industrial areas and high-population density areas in the northern part of the urban agglomeration. The findings provide scientific evidence and decision-making support for water resource optimization and regional coordinated management in the middle Yangtze River region.

[Objective] This study aims to reveal the seasonal concentration characteristics and spatial differentiation patterns of precipitation in Tianjin from 1980 to 2023 by quantifying long-term seasonal trends， characterizing the spatial patterns of Precipitation Concentration Degree （PCD） and Precipitation Concentration Period （PCP）， and establishing a bivariate risk assessment method based on PCD-PCP joint return periods using Copula functions. The innovation lies in the first application of Copula-based PCD-PCP coupled analysis to the hydrometeorological field of Tianjin， providing support for extreme flood prevention. [Methods] Daily precipitation data from 13 meteorological stations in Tianjin during 1980-2023 were employed. The Mann-Kendall trend test and Sen’s slope estimator were used to detect monotonic trends in seasonal and annual precipitation. The vector-based PCD and PCP indices were calculated to quantify precipitation concentration uniformity and peak timing. Inverse distance weighting （IDW） was applied to visualize spatial patterns. The distribution characteristics of PCD-PCP under specific scenarios were analyzed based on copula joint distribution. [Results] Seasonal precipitation in Tianjin is highly uneven. Summer dominates with a mean of 383.6 mm （70.1% of annual total）， while winter precipitation is extremely low （11.5 mm） but shows the highest interannual variability （extreme value ratio： 180.50）. Summer precipitation exhibits a significant increasing trend， which may elevate the risk of extreme precipitation events， whereas the increased variability of autumn precipitation could prolong the urban waterlogging risk window. Spatially， annual precipitation exhibits a stable “higher in the north and lower in the south” pattern across the 1980s-2010s. The spatial pattern of PCD shows limited variability， with values predominantly ranging from 0.68 to 0.73. A high-value zone is identified in the Binhai New Area （PCD≈0.73）， reflecting strong precipitation concentration within a short annual window， whereas lower values in Jizhou and Wuqing suggest a more even precipitation regime. In contrast， PCP exhibits a west-east gradient， increasing from approximately 201 in the west to 207 in the east （mid-to-late July）， indicating spatial asynchrony in precipitation concentration timing. Temporally， PCD shows substantial interannual fluctuations （0.50-0.85）， yet its long-term trend remains stable， as evidenced by decadal means ranging from 0.69 to 0.71. PCP also exhibits notable interannual variability （180-220） but demonstrates a significant decadal delay， progressing from 198.5 in the 1980s to 203.7 in the 2010s， a trend intrinsically linked to the phenomenon of summer rainfall shifting to autumn in the Beijing-Tianjin-Hebei region. The copula-based analysis reveals a non-independent relationship between PCD and PCP， whereby higher PCD values tend to coincide with PCP falling within the annual peak precipitation period. The 50-year precipitation event corresponds to the combination of high PCD and a specific PCP， indicating that this extreme scenario arises from the simultaneous deviation of both variables from their normal states. Under this scenario， PCD is significantly above the multi-year average， and PCP falls within the main summer flood season. This concurrence of high precipitation concentration and flood season timing will substantially elevate the risk of urban waterlogging and basin flooding. Therefore， responding to extreme precipitation events requires attention not only to increases in total precipitation but also to high temporal concentration and its coincidence with the main flood season. [Conclusion] This study systematically quantifies the seasonal concentration characteristics and spatial differentiation of precipitation across Tianjin. Summer dominates both the total amount and long-term trends. PCD is spatially homogeneous but interannually variable， whereas PCP shows a clear west-east gradient. Under the 50-year precipitation event， Tianjin faces credible extreme flood hazards. Future work should incorporate climate model projections to assess non-stationarity in the PCD-PCP dependence structure under warming scenarios.

[Objective] Current research on water demand prediction primarily focuses on improving prediction accuracy， while studies on interval prediction of water demand remain limited. This study aims to further improve prediction accuracy， reduce error interval and reflect the actual regional water demand by incorporating the Kolmogorov-Smirnov （K-S） normal interval estimation into BP （back propagation） neural network model. [Methods] In view of a wide range of water demand influencing factors， limited sample series， and significant demand fluctuations in Jiangsu Province， we coupled the K-S normal interval estimation with particle swarm optimization （PSO） and BP neural network. Specific processes are as follows： the degree of influence and the number of key factors were preliminarily identified through principal component analysis （PCA）， followed by the calculation of grey relational grades （GRG） to determine the final water demand influencing factor index. This index was utilized as input for both BP and PSO-BP neural networks. The final model was then selected by comparing performance indicators， including relative error， Nash-Sutcliffe efficiency （NSE）， and coefficient of determination （R²）. Using multiple fitting iterations of the PSO-BP neural network， the sample size was expanded， and the K-S normality test and normal interval estimation were performed to further narrow the relative error intervals of the water demand prediction results. [Results] 1） Eight primary influencing factors of water demand were identified for Jiangsu Province： population， GDP， added value of secondary industry， added value of tertiary industry， per capita urban domestic water consumption， per capita rural domestic water consumption， irrigation water quota per mu （1 mu≈666.7 m²）， and water consumption per 10 000 yuan of industrial added value. 2） Both BP and PSO-BP neural networks exhibited strong performance in fitting historical water demand data， demonstrating their feasibility for future water demand prediction. Specifically， the PSO-BP neural network outperformed the standard BP network in the relative error of water demand prediction. The maximum relative errors for the training， validation， and testing samples were 2.23%， 0.88%， and 1.19%， respectively， with an average training error of 1.03%. The NSE and R² reached 0.98 and 0.99， respectively. 3） The selection of sample size significantly influenced the prediction results of water demand. With the increase of the sample size， the average value of samples was closer to the real value， and the overall prediction results of samples were more stable. The increase of sample size would reduce the benefit of improving the accuracy of the overall prediction results. 4） The K-S normality test and normal interval estimation stabilized the prediction results， substantially narrowed the error intervals， and better reflected the actual water demand. At a 95% confidence level， the relative error intervals of water demand prediction in 2021， 2022， and 2023 in Jiangsu Province were reduced to -0.23%-0.09%， -0.28%-0.01%， and -0.28%-0.02%， respectively. [Conclusion] The KS-PSO-BP neural network coupled model significantly reduces the error range and provides more stable and accurate prediction results that closely align with actual water demand in Jiangsu Province. The model serves as an effective method for regional water demand prediction and offers valuable guidance for future water resources planning in Jiangsu Province.

[Objective] This study aims to clarify the driving mechanisms and spatiotemporal propagation characteristics of water level fluctuations in the river section about 40 km downstream of the Wudongde hydropower station during its operation. The primary objectives are to： （1） quantify the dual impacts of unsteady flow from the hydropower station and the backwater effect from the downstream Baihetan Reservoir； （2） reveal the spatial attenuation patterns of water level variation； and （3） propose safety thresholds for water level variation in navigable waters. [Methods] Twelve high-frequency water level monitoring stations （SD1-SD12） were deployed along the river section 40 km downstream of the dam， and water level data were collected at 5-minute intervals. Four intensive monitoring activities were conducted， covering key operational periods including the impoundment period， drawdown period， flood season， and low-water level operation of the Baihetan Reservoir. The correlations among flow variation from the Wudongde hydropower station， water level of the Baihetan Reservoir， and downstream water level variation were quantified using statistical methods， including linear regression and correlation analysis. In addition， the spatial gradients and temporal attenuation of daily and hourly water level variation were calculated and analyzed. [Results] 1） The water level fluctuations downstream of the Wudongde Dam exhibited a bidirectional coupled driving mechanism， consisting of unsteady flow and reservoir backwater effects. In the near-dam reach （0-15 km）， the station’s flow was the primary driver of water level variation， with the water level response coefficient remaining stable at 0.12-0.15 m per 100 m³/s （R²>0.99）. Conversely， the far-dam reach （> 35 km） was dominated by the water level of the Baihetan Reservoir， exhibiting slow-varying， reservoir-controlled behavior with relatively stable water levels. 2） Downstream water level fluctuations exhibited a three-stage attenuation pattern. In the near-dam reach （0-15 km）， water level variation decreased rapidly， with a maximum daily attenuation rate of 0.41‰， and was strongly correlated with flow fluctuations （R²=0.85）. In the transition zone （15-35 km）， the interaction of nonlinear waves increased the variability of the attenuation rate （0.02‰-0.31‰ per day）， leading to a sharp weakening or disappearance of the correlation with flow. In the far-dam reach （>35 km）， the backwater effects of the Baihetan Reservoir stabilized water levels. 3） Water level regulation at the Baihetan Reservoir exerted a dampening effect on wave peak propagation. For every 10 m decrease in reservoir water level， the propagation distance of the flow peak increased by an average of 2.3 km （R²=0.96）. The nighttime flow peak at the Wudongde Dam occurred between 16：00 and 24：00， and flow levels exceeded daytime peaks by more than 40%. When the daily and hourly flow variations at Wudongde exceeded 5 000 m³/s and 1 500 m³/s， respectively， the resulting water level variation （3.2 m/d and 1.2 m/h） exceeded the shipping safety thresholds （3.0 m/d and 1.0 m/h）. [Conclusion] Downstream water level fluctuations are governed by a bidirectional coupled mechanism of unsteady flow and reservoir backwater effects， and exhibit a distinct three-stage attenuation pattern. This study identified the nonlinear superposition phenomenon in the transition zone （15-35 km） for the first time based on prototype observations， revealing that opposing wave phases （flow waves and backwater waves） generated complex peak interference effects. Furthermore， navigation safety thresholds are determined， and a “spatiotemporal peak-staggering” management strategy is proposed. This strategy involves dynamic zoning control， such as restricting navigation in the high-risk near-dam reach （0-15 km， SD1-SD4） during the peak period of 16：00-24：00.

[Objective] To address water quality deterioration in Dianchi Lake caused by combined agricultural and urban non-point source pollution as well as confluence of rainwater and polluted water， this study constructed a Bayesian Network （BN） risk assessment framework. This framework integrates pollution identification， spatial tracing， and probabilistic inference to support “zoning management and targeted restoration” strategies in Dianchi Lake. [Method] Water quality data from 10 national control sections （2021-2024） in Dianchi Lake were pre-processed by eliminating outliers and interpolating missing values. Total Phosphorus （TP） was identified as the typical pollutant via Spearman correlation analysis. A BN structure was constructed based on TP concentrations using a hybrid algorithm： a Most Weight Supported Tree （MWST） derived from the Mutual Information matrix， node ordering via Breadth-First Search （BFS）， and structural optimization using the K2 score function. Parameters were learned using the Expected Maximization （EM） algorithm after discretizing data according to the Surface Water Environmental Quality Standard （GB3838-2002）. Model performance was evaluated using Leave-One-Out cross-validation. The validated BN was applied to assess water quality risk through forward prediction， sensitivity analysis， reverse tracing， and causal chain identification. [Result] The model achieved an average validation accuracy exceeding 80%. In 2025， the probability of lake-wide water quality exceeding Class IV standards is <15%. By 2035， the probabilities of exceeding Class III standards are projected as follows： DQ （66%）， LJY （59%）， GYSD （42%）， CHZX （41%）， DCN （38%）， HKX （29%）， BKY （26%）， GYSZ （22%）， and GYSX （14%）. Sensitivity analysis indicated that water quality at HKX is most significantly influenced by HWZ （0.469 2）， BYK （0.367 5）， and GYSZ （0.186 7）. When HKX water quality is Class V， the probability of Class V conditions at BYK， GYSZ， GYSD， LJY， and HWZ exceeds 40%； when HKX is Class IV， the probability of Class IV conditions at BYK， GYSZ， GYSD， LJY， HWZ， and DCN exceeds 80%. The identified causal pollution chain is HWZ→BYK→GYSZ→GYSD→LJY. [Conclusion] The MWST-BFS-K2 hybrid algorithm effectively quantified water quality risk in Dianchi Lake. In 2025， the risk of exceeding Class IV standards is extremely low lake-wide. By 2035， DQ faces high risk； LJY， GYSD， and CHZX face medium risk； while DCN， HKX， BYK， and GYSZ face low risk. The risk of exceeding Class III standards at GYSX is negligible. The pollutant migration path follows “HWZ→BYK→GYSZ→GYSD→LJY.” Management should prioritize blocking pollution transmission from GYSZ to GYSD. Water quality fluctuations at HWZ， BYK， and GYSZ significantly impact HKX. Key pollution sources for Haikou River include BYK， GYSZ， GYSD， LJY， HWZ， and GYSX in 2025， with DCN replacing GYSX as a priority area by 2035. This framework provides a scientific basis for the ecological management of plateau lakes.

[Objective] Significant sediment deposition occurs at the estuaries of small and medium-sized rivers in the Three Gorges Reservoir Area （TGRA）， which can easily lead to endogenous pollution. Investigating the water environment pollution risks associated with sediment deposition in these typical rivers is of great significance for the water environment protection of the TGRA. [Method] Taking the Nixi River and Zhuyi River—typical small and medium-sized rivers located in the perennial backwater zone—as study subjects， this study evaluated the water environment pollution risks through sediment deposition surveys and analyses of the physicochemical properties， nutrient contents， and heavy metals in the sediments. [Results] （1） Significant sediment deposition was observed at the estuaries of both rivers， with silt accounting for over 76% of the sediment. Sampling sites closer to the estuaries exhibited higher proportions of clay and silt， and lower proportions of sand. （2） In the Nixi River， the spatial distribution of total nitrogen， hydrolyzable nitrogen， and available phosphorus showed a consistent trend， increasing from the upstream section to the estuary. Conversely， in the Zhuyi River， the average total organic carbon content in the sediment was higher than that in the Nixi River， but it decreased from upstream to the estuary. （3） The maximum comprehensive sediment pollution indices for the two rivers were 0.7 and 0.8， respectively， indicating a low overall risk. However， the maximum mass fractions of organic nitrogen reached 0.110 7% and 0.103 1%， respectively， indicating slight exceedance and a potential risk of release into the water body. Organic pollution in the Nixi River was primarily affected by the confluence and reservoir water level fluctuations， whereas in the Zhuyi River， it was mainly driven by human activities in the upstream urban areas of the bay. （4） The maximum potential ecological risk indices for multiple heavy metals were 68.07 and 123.94， respectively， indicating low pollution levels. [Conclusion] The overall water environment risk in the Nixi and Zhuyi rivers is currently low. However， sudden water quality deterioration occasionally occurs， primarily caused by the exceedance of phosphorus-containing substances and easily oxidizable small molecules. Further improvement and management of the water environment require not only controlling agricultural non-point source pollution but also emphasizing sediment dredging and endogenous pollution control. Additionally， comprehensive measures must be implemented in the Zhuyi River to reduce low-molecular-weight pollutants and prevent sudden water pollution incidents.

[Objective] The intrinsic mechanisms underlying the spatiotemporal heterogeneity of nutrient removal efficiency and the regulatory role of aquatic plant rhizosphere effects in micro-scale surface flow constructed wetlands （SFCWs） remain unclear. This study aims to address the following issues： （1） Elucidate the spatiotemporal distribution patterns of nitrogen （N） and phosphorus （P） removal efficiency； （2） Reveal the correlation mechanisms among microbial community structure， metabolic potential， and N/P removal； and （3） Evaluate the effects of the plant rhizosphere and three typical plant species on microbial community structure and N/P metabolic potential， providing a basis for the design and maintenance of micro-scale SFCWs. [Method] Using a specific wetland as a case study， water quality monitoring and high-throughput microbial sequencing were employed to systematically analyze the spatiotemporal characteristics of N/P removal and their microbial driving mechanisms. The regulatory mechanisms of substrate types and plant rhizospheres on microbial community composition and metabolic potential were also clarified. [Results] （1） The ammonia nitrogen removal rate remained stable （89.3%-95.8%）， while the total nitrogen removal rate exhibited seasonal variation： summer （75.6%） > autumn （64.9%） > spring （54.3%） > winter （21.9%）. This process was closely related to the succession of functional bacterial communities and changes in metabolic potential. N-cycling functional bacteria， including Kosakonia， Bacillus， Noviherbaspirillum， Ellin6067， and Anaeromyxobacter， were significantly enriched in spring and summer， resulting in significantly higher N metabolic potential compared to autumn and winter. （2） The total phosphorus removal rate， co-regulated by microbial action and adsorption/sedimentation， showed seasonal variation （summer 74.9% > spring 65.6% > autumn 59.8% > winter 46.7%）. Microbial influence on seasonal fluctuations was evidenced by the significant enrichment of P-cycling functional bacteria， such as Massilia， Bacillus， Saccharimonadales， and Gemmatimonas， in spring and summer， with P metabolic potential significantly higher than in autumn and winter. （3） Spatially， N/P metabolic potential demonstrated stability. Although substrate types （gravel， non-rhizosphere soil， and rhizosphere soil） significantly altered bacterial community composition， no significant differences in N/P metabolic potential were observed among substrates. This provides empirical evidence for the weakened rhizosphere boundary effect and the maintenance of metabolic homeostasis via functional redundancy at specific scales in micro-scale wetlands. [Conclusion] In space-constrained SFCWs with low pollution loads， water temperature dominates the biochemical reaction rates of N/P transformation. Alkaline pH and an appropriate increase in total nitrogen concentration synergistically promote P removal. Microbial community distribution is influenced by nutrient substrates and environmental factors. Based on these findings， the following optimization strategies are proposed： （1） Install a pre-treatment unit for total phosphorus at the inlet to mitigate the risk of endogenous release caused by substrate saturation； （2） Utilize aquatic plant root systems to promote the enrichment and spread of denitrifying bacteria， while reducing the reliance on precise plant species configuration； （3） Based on the succession characteristics of functional bacteria， apply targeted inoculation of highly efficient microbial agents for N/P removal； and （4） Maintain stable system operation through water temperature regulation， pH optimization， and nutrient load management.

[Objective] Soil temperature， moisture content， electrical conductivity， and pH in the water-level-fluctuating zone are fundamental to assessing soil physical， chemical， and biological characteristics and conducting ecological restoration. This study aims to clarify the impact of varying flood intensity of the Hubei section of the Three Gorges Reservoir on soil properties in the water-level-fluctuating zone. [Method] This study divides the water-level-fluctuating zones of various counties in the Hubei section into four gradients： no flooding （>175 m）， light flooding （175 m）， moderate flooding （170 m）， and severe flooding （<170 m） zones. In May 2024， in-situ monitoring of soil temperature， moisture content， electrical conductivity， and pH was conducted in different flooding intensity zones. Statistical and spatial analysis were used to reveal their spatial variability characteristics. [Results] （1） The average values of soil temperature， humidity， electrical conductivity， and pH in the Hubei section of the water-level-fluctuating zone of the Three Gorges Reservoir are 32.45 ℃， 12.58%， 41.34 S/cm， and 6.75， respectively. During the monitoring period， soil temperatures ranged from 26.4 ℃ to 43.3 ℃， the average soil moisture content was 12.58%， the soil electrical conductivity showed significant variation， and the mean pH of the soil was 6.75. （2） The variability of soil properties in the water-level-fluctuating zone of different counties were varied. The soil temperature of Yiling exhibited a decreasing trend as the intensity of flooding decreased. The soil moisture of Zigui decreased as the flooding intensities decreased. The electrical conductivity of Xingshan was generally high， with most values exceeding 60 S/cm. The pH of Badong was consistent with other counties and districts， showing no obvious patterns of change， and remained stable between 6.0 and 7.0. （3） Soil temperature exhibited the highest coefficient of variation under moderate flooding. Under moderate， light， and no flooding conditions， the coefficient of variation decreased as flooding intensity decreased， with the lowest variability observed under no flooding conditions. Soil moisture variability was largely consistent under severe and moderate flooding conditions； the variability was basically consistent under light flooding and no flooding. The variability of electrical conductivity did not show a clear pattern with changes in flooding intensity. Under severe flooding， the coefficient of variation was the highest， while under no flooding， the coefficient of variation was the lowest. The variability of pH across different flooding intensities was generally low across counties， with the highest variability observed in the moderate flooding zone. （4） In terms of the order of variability in soil properties， Yiling and Zigui were consistent， while Xingshan and Badong were consistent. The variability of soil properties in Yiling and Zigui was as follows： electrical conductivity > soil moisture > soil temperature > pH， while that in Xingshan and Badong was as follows： electrical conductivity > soil temperature > soil moisture > pH. Geographic location and spatial distance may be the primary factors influencing these differences. [Conclusion] This study presents a preliminary analysis of the variability characteristics of soil properties in the Hubei section of the Three Gorges Reservoir area under different flooding intensities based on limited data. Further monitoring with multiple frequencies and indicators （such as carbon， nitrogen， and phosphorus） is needed to reveal the spatiotemporal variability patterns of soil properties in the Three Gorges Reservoir area and provide technical support for targeted ecological restoration efforts.

[Objective] The northern Guangxi region is a typical karst rocky desertification area in China， where ecological restoration faces severe challenges. Current applied research on bryophyte-based ecological restoration mainly focuses on the Loess Plateau and the karst areas of Guizhou Province. However， studies focusing on the karst area of northern Guangxi Province—characterized by unique eco-geographical conditions （subtropical monsoon climate， favorable hydrothermal conditions， and limestone-dominated bedrock） and severe rocky desertification—remain relatively limited. In particular， research on the environmental adaptability of bryophytes and their functions and effectiveness in localized restoration practices is relatively scarce. [Methods] This study was conducted in the experimental area of Pingfeng Mountain in Qixing District， Guilin City. Three bryophyte species—Barbula unguiculata， Bryum paradoxum， and Hyophila involuta—were selected as the research objects. Through water-holding capacity test （for drought adaptation）， high-temperature resistance test （for surface high temperature adaptation）， acid and alkali resistance test （for soil and acid rain adaptation）， and erosion resistance test （for soil and water conservation assessment）， their environmental adaptability and ecological restoration potential were quantitatively evaluated. [Results] （1） All three bryophyte species exhibited significant water-holding capacity， with H. involuta showing the highest water-holding rate （581.71%）. This capacity enabled this species of bryophytes to effectively store water in the rocky desertification areas of northern Guangxi， contributing to improved soil moisture conditions. However， its high-temperature resistance was weak. After treatment at 60 ℃， some tissues turned black and necrotic. （2） B. unguiculata and B. paradoxum had water-holding rates of 408.88% and 389.82%， respectively， and demonstrated stronger resistance to high temperature， acid and alkali， and erosion， indicating better adaptability to the high-temperature and arid conditions of the rocky desertification areas in northern Guangxi. Among them， B. paradoxum achieved a plant density of 102 plants/cm² at pH=6， and its crust thickness （2.54 mm） and dry weight （0.311 g/cm²） were significantly higher than those under other treatments. （3） All three bryophyte species exhibited a certain degree of tolerance to different pH conditions. B. paradoxum showed the best growth performance in weakly acidic environments， indicating its good adaptability to acidic soil. （4） Bryophytes effectively reduced soil erosion， especially on steep slopes. B. unguiculata and B. paradoxum exhibited better erosion resistance than H. involuta， making them suitable for rocky desertification areas with large slope gradients to reduce soil loss. At a slope gradient of 30°， the soil erosion amounts of B. unguiculata and B. paradoxum （71.1 g， 67.2 g） decreased by more than 62% compared with bare soil （187.8 g）. [Conclusion] Considering the high water-holding capacity， strong environmental tolerance， and excellent erosion resistance of B. unguiculata and B. paradoxum， they are suitable for rocky desertification areas with large slope gradients to reduce soil loss and hold great potential for ecological restoration in the rocky desertification areas of northern Guangxi. They can not only improve soil moisture conditions but also effectively reduce soil erosion and enhance ecosystem stability， making them suitable as pioneer plants for ecological restoration in rocky desertification areas.

[Objective] This study represents the first systematic quantification of soil erosion in large-scale tea plantations within the hilly region of southern Anhui Province， aiming to provide critical insights for soil and water conservation strategies. [Methods] We built a comprehensive soil erosion factor dataset through integration of field-measured soil parameters and multi-source geospatial data. Based on the CSLE （Chinese Soil Loss Equation） model， we analyzed the characteristics of soil erosion in tea plantations and evaluated the influences of topography and soil types in Fengle River Basin. [Results] （1） The 2022 average soil erosion modulus of Fengle River Basin was 2 953.24 t/（km²·a）， with 43.02% of the watershed area experiencing erosion. The area of soil erosion was mainly classified as mild erosion and decreased with increasing erosion intensity. The overall soil erosion intensity exhibited a spatial pattern of higher values in the northwest and lower values in the southeast. （2） Tea plantations exhibited an average soil erosion modulus of 9 621.59 t/（km²·a）. The soil erosion area in tea plantations covered 27.76 km²， accounting for 68.19% of the total tea plantations and 12.55% of the basin’s total erosion area. Among the eroded tea plantations， mild erosion accounted for 47.14%. The area of soil erosion in tea plantations gradually decreases with the increase of erosion intensity level. The overall spatial distribution of soil erosion intensity revealed higher erosion levels in the northern regions and lower levels in the southern regions. （3） Average erosion modules exhibited a unimodal relationship with elevation， peaking at 500-1 000 m. The proportion of soil erosion area in tea plantations at altitudes of 200-500 m reached 75.81%， followed by the 500-1 000 m zone， with minimal loss in other altitude ranges. Regarding slope changes， the average soil erosion modulus and erosion area of tea plantations in Fengle River Basin both exhibited increasing trends with slope， reaching maximum values at slopes of 25°-35°， and then slightly decreasing at slopes above 35°. Tea plantations in slope zones above 25° accounted for 75.44% of the total erosion area， classified as having extremely intense erosion intensity， with severe forms of soil loss. （4） The average soil erosion modulus of tea plantations ranked： litho soils > skeletal soils > yellow earths > red earths > paddy soils > purplish soils. Erosion area of tea plantations distribution followed： red earths > skeletal soil > paddy soil > yellow earths > purplish soils > litho soils. （5） Combining topography and soil impacts， in terms of average soil erosion modulus， severe erosion combinations included skeletal soil with slope 25°-35°， limestone soil with slope 25°-35°， and purple soil with slope >35°. There were 12 extremely intense， 4 intense， and 5 moderate erosion combinations. The top three erosion contributors were red earths with slope >35°，red earths with slope 25°-35° ，and red earths with slope 15°-25° ， accounting for 69.92% of the total erosion area in tea plantations. Other combination conditions had a minimal erosion area. [Conclusion] Fengle River Basin is characterized by pronounced soil erosion factors， including high rainfall erosivity （R-factor）， low vegetation coverage （C-factor）， steep slope gradients （LS-factor）， and poor soil erodibility （K-factor）. Fengle River Basin’s tea plantations face serious soil erosion issues. Tea plantations are widely distributed on high and steep slopes， while soil and water conservation measures are limited. These regions are the key areas for preventing soil erosion and promoting sustainable development of the tea industry in the future.

[Objective] To provide technical support for the precise regulation of upstream and downstream floods， the scientific arrangement of excess flood volume management， and the timely organization of emergency evacuation， we construct a risk assessment system for the operation of flood storage and detention areas （FSDAs） to accurately evaluate their dynamic operational risks. [Method] We construct an operational risk assessment system for FSDAs based on the coupling of Remote Sensing （RS） and Geographic Information Systems （GIS）. Combined with a two-dimensional hydrodynamic model and a set of operational schemes based on flood diversion volumes， the flood routing process at various stages was simulated. The dynamic risk characteristics of FSDA operation， specifically the “flood diversion volume-water level-loss-population relocation” relationship， were extracted. The Honghu Lake East Sub-block FSDA was selected as a typical case for risk analysis. [Result] （1） There is a strong linear relationship between the flood diversion volume and the average water level in the Honghu East Sub-block FSDA. For every 0.5 billion m³ increase in flood diversion volume， the average water level rises by 0.57 m. （2） The variation of various risks with flood diversion volume is comprehensively affected by loss rates and land cover distribution. Direct economic losses in this area increase most rapidly when the flood diversion volume ranges from 2.0 to 4.5 billion m³， while indirect economic losses and relocated populations grow fastest during the initial stage of flood diversion （volume <0.5 billion m³）. （3） When the flood diversion volume reaches 2.0 billion m³， the entire area is inundated， requiring the complete relocation of 183 700 people. When the volume exceeds 2.5 billion m³， the economic loss structure shifts from being dominated by indirect losses to direct losses， with secondary and tertiary industry losses stabilizing at 980 million RMB. At a flood diversion volume exceeding 3.0 billion m³， the fishery output value in the area is completely lost， amounting to approximately 3.6 billion RMB. At a volume of 6.0 billion m³， the direct and indirect economic losses are approximately 17.36 billion RMB and 6.55 billion RMB， respectively. [Conclusion] The dynamic risk assessment method established in this study can be extended to other FSDAs. The dynamic correlation characteristics of “flood diversion volume-water level-loss-population relocation” can simulate in real-time the changes in inundation extent， economic losses， and population risks under different diversion schemes. This provides a quantitative basis for selecting the timing and magnitude of flood diversion， supporting refined trade-offs in cross-regional flood volume allocation. However， the nighttime remote sensing and population distribution data used in this study have relatively low accuracy， making it difficult to apply the method to smaller FSDAs. Future research should focus on improving the accuracy of fundamental data.

[Objective] Flash floods in hilly small watersheds occur frequently， posing severe threats to the lives and property of residents in riverside villages. Existing research lacks sufficient understanding of disaster mechanisms at the village scale and under compound conditions， making it difficult to accurately reflect real risks. This study develops a comprehensive risk assessment framework based on multiple scenarios to provide scientific support for the governance planning and risk management of riverside villages. [Methods] Based on the disaster chain from rainfall to flood inundation and to disaster formation， we constructed a complete risk assessment framework. First， we collected the basic geographic， hydrometeorological， and socioeconomic data of the study area， and designed different compound scenarios considering field conditions， and then calculated the joint occurrence probabilities of these scenarios using the Copula function. Subsequently， a coupled hydrological hydrodynamic model was built to simulate the flood evolution processes under various scenarios. On this basis， a loss calculation model for affected entities was applied to estimate direct economic losses. Finally， risk probabilities and loss values were integrated to derive a risk index that comprehensively reflects the long-term risk level of the region. [Results] The inundation area expanded significantly with increasing return periods， from 37 980.81 m² under a 5-year return period to 272 788.74 m² under a 100-year return period， with particularly noticeable growth between 20- and 100-year return periods. Compound scenarios markedly aggravated disaster losses. Under a 100-year rainfall condition， compared to the scenario without bridge blockage or downstream backwater （direct economic loss of 9.988 3 million CNY）， the direct economic losses under the scenarios of 50% bridge blockage， downstream backwater， and both combined increased to 10.262 9 million， 10.240 1 million， and 11.292 3 million CNY， respectively. The loss under the combined scenario was notably higher than that under any single-factor scenario， highlighting the amplification effect of compound disaster factors. Additionally， the Copula function indicated that bridge blockage and downstream backwater exhibit significant joint occurrence probabilities under the same return-period rainfall， confirming the objective basis for the compound disaster scenarios involving dual conditions. The expected loss from flash floods in Beichenjiagou Village， Rizhao City， was calculated as 501 600 CNY using the risk degree model. [Conclusion] This study successfully constructed and applied a flash flood risk assessment framework integrating compound scenario analysis incorporating the entire disaster chain process. It comprehensively reflects the entire process of flash flood formation， disaster triggering， and loss generation in small watersheds. By introducing compound scenario analysis， the study enhances the characterization of chain disaster mechanisms， quantifies the amplification effect of bridge blockage and downstream backwater on disaster losses， and underscores the critical role of key hydraulic engineering nodes in risk prevention and control. Furthermore， the study quantifies disaster risk as the expected loss value of the study area， offering a quantitative basis for determining economic inputs in disaster prevention and mitigation， as well as for formulating insurance and risk management strategies.

[Objective] To address the limited adaptability of traditional numerical methods for water hammer under complex boundary and uncertain conditions， as well as the constrained convergence efficiency and prediction accuracy of Physics-Informed Neural Networks （PINNs） in strongly nonlinear transient flows， this study proposes a PINNs-based framework for transient pressure prediction in pipelines aiming to enhance the prediction accuracy of pressure variations in pipeline hydraulic transients. [Methods] In this framework， the continuity and momentum equations are embedded into the neural network loss function， and automatic differentiation is employed to solve the governing partial differential equations， enabling high-accuracy pressure simulation under limited labeled data conditions. Furthermore， an improved Locally Adaptive Activation Function （LAAF） is introduced by incorporating a trainable offset parameter β， while a mini-batch gradient descent strategy is adopted to enhance the model’s training stability and prediction robustness. [Results] Numerical case studies demonstrate that the proposed model effectively captures the transient characteristics of water hammer pressure. Compared with the Baseline-PINNs model and LAAF2-PINNs model， it achieves significantly higher predictive accuracy， with the relative L₂ error reduced by 37.32% and 23.83%， respectively. In addition， sensitivity analysis of wave velocity， verification under multiple initial flow velocity conditions and generalization ability analysis demonstrate that the improved model has superior generalization ability and robustness. [Conclusions] The proposed M-LAAF2-PINNs model provides a novel and effective approach for achieving high-precision water hammer transient analysis under limited observational data and uncertain boundary conditions， offering superior technical support for pressure monitoring， parameter inversion， and intelligent scheduling in long-distance pipeline systems.

[Objective] The strength characteristics and underlying mechanical mechanisms of expansive soil treated with microbially induced calcite precipitation （MICP） remain insufficiently understood. Investigating the effect of varying calcium ion concentration on the strength of MICP-treated expansive soil can provide critical guidance for its engineering applications. [Methods] Sporosarcina pasteurii （CGMCC 1.3687） was selected for microbial solidification using the mixing method. This study systematically investigated the mechanism by which different calcium ion concentrations—the core variable—affect the strength characteristics of treated expansive soil. Through a series of consolidated quick shear tests， the relationship between calcium ion concentration and strength parameters was analyzed to elucidate the mechanism by which regulating calcium carbonate formation enhances soil strength. [Results] The results indicate that MICP treatment significantly enhances the shear strength of expansive soil， altering its mechanical behavior from the strain-hardening mode of untreated soil to a dual-mode response： strain-softening under low confining pressure and strain-hardening under high confining pressure. Soil treated with Ca²⁺ solution exhibited higher shear strength than the untreated control. Specifically， cohesion （c） and the internal friction angle （ϕ） followed a unimodal trend with increasing Ca²⁺ concentration， peaking at 1.5 mol/L （c=42.5 kPa， ϕ=18.4°）. This represents a 269.6% increase in cohesion and a 10.2% increase in the internal friction angle. A concentration of 1.5 mol/L was identified as optimal， maximizing calcium carbonate yield and cementation. Lower concentrations resulted in insufficient Ca²⁺， while higher concentrations inhibited bacterial activity； both scenarios reduced calcium carbonate production and soil strength. [Conclusions] This study confirms that MICP technology significantly improves the strength of expansive soil. The strengthening mechanism is attributed to a significant positive correlation between calcium carbonate content and strength indices.

[Objective] While the mechanical properties of rock-concrete composites and basalt fiber-reinforced concrete have been widely studied， research on their combined performance after high-temperature exposure remains limited. This study investigates the use of basalt fibers to enhance the high-temperature performance of granite-concrete composites， aiming to evaluate their efficacy in mitigating thermal damage. [Method] Granite， plain concrete， and granite-basalt fiber concrete （GBFC） composites with four fiber volume fractions （0%， 0.1%， 0.2%， and 0.3%） were tested. Following high-temperature treatments at ambient temperature and 200 ℃， 400 ℃， and 600 ℃， static uniaxial compression and splitting tensile tests were conducted to evaluate compressive strength， tensile strength， failure modes， and damage factors. Scanning electron microscopy （SEM） was also employed to analyze microstructural evolution. [Result] （1） The composites exhibited continuous medium mechanical behavior， characterized by plastic failure under uniaxial compression and brittle failure during splitting. Their compressive and tensile strengths fell between those of pure granite and concrete， trending closer toward the concrete values. （2） Basalt fiber incorporation improved both strength metrics and failure modes at elevated temperatures， with a 0.2% fiber content identified as optimal. （3） The damage factor increased progressively with temperature； specifically， the GBFC damage factors were 0.103 5 at 200 ℃， 0.339 1 at 400 ℃， and 0.702 7 at 600 ℃， indicating severe structural degradation at the highest temperature. （4） SEM analysis revealed that uniaxial compression primarily damaged the concrete matrix， while the interface and granite remained relatively intact. High-temperature treatment exacerbated concrete deterioration but had minimal impact on the interface and granite. Basalt fibers acted as bridging and crack-arresting agents within the concrete matrix， effectively mitigating crack initiation and propagation when added in appropriate amounts. [Conclusion] These findings provide valuable references for understanding composite mechanical properties， optimizing tunnel construction， and guiding post-fire evaluation and repair strategies for tunnel infrastructure.

[Objective] To address the stability issues of rock ridges during the blasting demolition of the large cofferdam for the unit expansion project at Wuqiangxi Hydropower Station， this study proposes an optimized blasting scheme， aiming to prevent the sliding instability of the remaining thin rock ridge after layered blasting under the influence of fracture seepage. [Method] A discrete fracture seepage-stress coupling model was employed to evaluate the excavation sequence， slope height-to-width ratios， and seepage stability of the downstream slope of the rock ridge. The stability of the rock ridge under various blasting schemes and slope height-to-width ratios was analyzed considering fracture seepage. By integrating safety factors and failure slip modes， the optimal blasting sequence and a reasonable downstream slope height-to-width ratio were determined， providing precursor information on potential failure modes of bedded rock masses under seepage conditions. [Result] （1） Based on the engineering characteristics and blasting challenges， a demolition design for the intake cofferdam was formulated： blasting the outer earth-rock cofferdam during the dry season， thinning the inner side of the cofferdam， removing the top concrete cofferdam， and blasting the remaining rock ridge in a single pass. This scheme prevents the instability of the remaining thin bedded rock ridge under fracture seepage while minimizing risks to existing structures. （2） At slope height-to-width ratios of 1∶0， 1∶0.3， and 1∶0.5， the failure mode was global， with failure boundaries comprising a composite slip surface of the concrete-rock interface， weak interlayers， and bedding planes. At ratios of 1∶0.7， 1∶0.9， 1∶1.1， and 1∶1.3， the failure mode transitioned to local bedding slip instability. As the ratio increased， the tensile failure boundary at the trailing edge moved further from the toe of the excavated slope， and the thickness of the unstable rock layer decreased， indicating an evolution toward shallow bedding slip failure. [Conclusion] Considering both the safety factor and the failure slip mode， a slope height-to-width ratio of 1∶0.7 was determined to be optimal for the downstream slope excavation， as the safety factor exceeded 1 and the failure mode transitioned from global to local. The proposed scheme effectively controls the deformation and instability risks of the reserved thin-walled rock ridge. These findings provide valuable references for the demolition of large cofferdams and the stability evaluation of rock ridges under fracture seepage conditions.

[Objective] Based on suction-controlled triaxial isotropic compression tests on compacted loess， this study establishes a soil-water characteristic curve （SWCC） and hydraulic conductivity prediction model that accounts for compression deformation. This work aims to provide an accurate and convenient method for predicting the SWCC and hydraulic conductivity of compacted loess under compressive deformation， facilitating seepage analysis in loess embankment engineering. [Method] This study takes the Q₂ compacted loess samples from the Phase I Project of mountain flattening and city construction in Yan’an New Area as the research object. Four sets of isotropic compression tests under different constant suctions （y=25， 37， 50， 100 kPa） were conducted by using a GDS unsaturated triaxial apparatus. Building upon the test findings， a power function related to the void ratio is introduced into the four-parameter Fredlund-Xing model to establish a SWCC model considering compressive deformation. The model has fewer parameters， requiring only 7 parameters； the tests are simple， as the model parameters can be obtained only through suction-controlled compression tests and saturated permeability tests； （3） the model also considers the influence of adsorbed water on the hydraulic conductivity. The proposed model is applied to predict the SWCC and hydraulic conductivity curve of Yan’an compacted loess within a wide suction range， and the predicted results are compared with measured test data. [Results] （1） Compressive deformation causes a significant mechanical wetting effect， specifically manifested as follows： a. during the constant suction loading process， the degree of saturation of the samples increases significantly with the development of compressive deformation； b. in the process of compressive deformation， the SWCC of the samples shifts overall to the right as the void ratio decreases， and the air entry value increases significantly. （2） The proposed model can accurately predict the SWCC and hydraulic conductivity of compacted loess under any void ratio within a wide suction range， and its prediction accuracy in the high suction range is significantly higher than that of the Gallipoli model and the CCG model. In addition， the proposed model is used to predict the influence of compressive deformation. During compressive deformation process， as void ratio decreases， the soil-water characteristic curve of compacted loess gradually shifts to the upper right， and the air entry value increases significantly. In the low suction range， the hydraulic conductivity of compacted loess decreases with the decrease of void ratio， while in the medium and high suction ranges， the hydraulic conductivity increases with the decrease of void ratio. The response of the hydraulic conductivity of compacted loess to compressive deformation is essentially caused by the change of the cross-sectional area of water flow and flow paths due to the change of micro-pores. [Conclusion] The proposed model provides a reliable tool for understanding the soil-water characteristics and permeability behavior of compacted loess under compressive deformation. It not only improves the accuracy of seepage analysis in loess filling projects but also provides a theoretical basis for evaluating the stability and safety of engineering structures built on compacted loess.

[Objective] In typical plain tidal river networks at the Yangtze River Delta front， dense waterways and frequent navigation significantly impact levee safety through channel operations and bed scour. Focusing on two typical levee structural types along the Huangpu River and its main tributaries， this study investigates the scour response under the coupling of structural dimensions and scour depth. The findings aim to provide a scientific basis for accurately identifying high-risk bank sections， optimizing bank protection structures， and enhancing the targeted management of levee engineering in tidal navigable rivers. [Methods] To examine the scour resistance sensitivity and its variation of levee structures in tidal navigable rivers， the theoretical scour depth was calculated based on the actual operating conditions of a navigable tributary in the upper Huangpu River. Using these calculated values as a reference， finite element models were developed to analyze the displacement responses of gravity-type and pile-founded levees under coupled conditions of varying structural dimensions and scour depths. This approach allowed for the determination of the scour resistance sensitivity and evolutionary trends for different levee structural types. [Results] The scour resistance sensitivity of gravity-type levees is primarily influenced by the base slab width and embedment depth. When the base slab width is <4 m or the embedment depth is <2 m， a toe scour 0.5-1.0 m triggers a sharp increase in the displacement rate at the wall top. Conversely， when the base slab width exceeds 5 m or the embedment depth exceeds 2 m， further increasing the dimensions yields significantly diminishing returns in scour resistance. The scour resistance sensitivity of pile-founded levees is mainly governed by the pile length. When the pile length is <15 m， the displacement growth rate accelerates markedly once the scour depth 1.0-1.5 m. Beyond a pile length of 15 m， the effectiveness of increasing pile length to enhance scour resistance weakens. [Conclusion] （1）The sensitivity of different structural types to toe scour must be fully considered during the selection and sizing of levee structures in tidal navigable rivers. Under the given typical boundary conditions， the scour resistance sensitivity increases with the base slab width， embedment depth， and pile length. However， beyond certain thresholds， the marginal gain in sensitivity decreases， making it economically inefficient to further improve scour resistance solely by enlarging structural dimensions. Instead， altering the structural type or controlling the scour depth is recommended to enhance levee safety. （2）For the design of gravity-type levees， it is advisable to maintain a base slab width of ≥4 m and an embedment depth of ≥3 m. If the anticipated scour depth exceeds 1 m， gravity-type structures are not recommended. For existing gravity levees， the impact of scour should be mitigated through strengthened vessel traffic management and the installation of protective structures. （3）For the design of pile-founded levees， the pile length should be controlled at ≥15 m. When the anticipated scour depth reaches 1 m， measures such as enhanced vessel traffic management and protective structures should be implemented to reduce scour impacts. The proposed structural dimensions and structural adaptability under varying scour conditions provide a scientific basis for the design and management of levees in tidal navigable rivers.

With the increasing internationalization of geotechnical engineering projects in China and the growth of international engineering cooperation， the demand for referencing and applying foreign technical standards in engineering practice is growing. As a widely used in-situ testing method， the technical requirements and application of plate load test （PLT） results vary across different standard systems. To facilitate international engineering practice and standard alignment， this paper provides a comparative analysis of the similarities and differences between current domestic and foreign PLT standards from three aspects： standard systems， testing methods， and data interpretation. The analysis reveals the following：（1） In terms of standard systems， foreign standards typically focus on specific fields by proposing mandatory provisions and technical requirements， featuring a relatively concise structure. （2） Regarding testing methods， foreign standards are primarily principle-based and guidance-oriented， imposing higher requirements on engineers to conduct tests based on actual field conditions. （3） In data interpretation， domestic standards usually determine the allowable bearing capacity directly from the load-settlement curve. In contrast， foreign standards derive the allowable bearing capacity by back-calculating strength parameters under specific conditions and applying ultimate bearing capacity theories. This study provides a valuable reference for conducting PLTs and analyzing results under foreign standard frameworks.

[Objective] The Bishan-Tongliang Line is an east-west municipal express railway in the suburbs of Chongqing， aimed at promoting rapid development in the western Chongqing area. During the construction of the Yunwu Mountain Tunnel—a critical control project—a sudden water inrush occurred in the adit. This study aims to accurately identify the causes of the water inrush， providing a scientific basis and technical support for waterproofing measures during construction and the identification of water inrush sources in similar tunnel projects. [Method] Taking the water inrush in this tunnel as a case study， potential water-conducting channels were analyzed based on a comprehensive review of regional engineering geology， hydrogeological characteristics， and the features of the adit water inrush. Through laboratory and field tests， as well as physical and chemical analysis methods， the differences and correlations between water samples from regional aquifer channels and the inrush water were investigated to achieve accurate and efficient identification of the water inrush source. [Result] The regional groundwater primarily consists of red bed fissure water， detrital rock pore-fissure water， and carbonate karst water. Potential sources of the adit water inrush include surface water leakage， bedrock fissure water， water accumulated in mined-out coal areas， water inrush from water-conducting faults， and karst water. Through a comprehensive multi-factor analysis combining field investigations， physical methods， and chemical methods， it was identified that the water inrush originated from confined fissure water in sandstone strata interbedded within impermeable shale， supplemented by reservoir water recharged through water-conducting faults. [Conclusion] This study provides a universal methodology for identifying water inrush sources in tunnel engineering under complex geological conditions. This approach involves predicting potential water inrush factors by integrating regional engineering and hydrogeological characteristics， followed by systematic investigation and comparative analysis of each factor using field surveys， physical methods， and chemical methods to accurately and effectively identify the source of tunnel water inrush.

[Objective] The overall performance of prefabricated dams depends on the cementitious materials between precast blocks. However， current research on the impact of the deterioration of cementitious material performance on the overall performance of the prefabricated dam remains insufficient. [Method] Taking the No. 3 water-retaining dam section of the main dam at the Lushui hydro-junction as the research object， numerical simulations were conducted combining thin-layer elements and the finite element method. The impact of the bonding performance of cementitious materials between precast concrete blocks on the overall performance of the dam was quantitatively analyzed. Furthermore， the differences in the impact of performance deterioration in various types of joint cementitious materials on the prefabricated dam were investigated. [Results] （1） As the degree of deterioration of the cementitious joint materials increased， the displacement of the prefabricated dam gradually increased. When the deterioration of the cementitious material reached 90%， the displacement increased by approximately 21% compared to the baseline condition. （2） With the increasing deterioration of the cementitious material， the area of the maximum principal stress in the precast blocks gradually expanded， with the high-stress regions primarily concentrated at elevations of 30 m to 36 m on the downstream side. （3） As the deterioration worsened， the proportion of closed cementitious joints in the prefabricated dam gradually decreased， while the proportion of open joints increased， leading to an increase in dam displacement. （4） The deterioration of the horizontal cementitious joint materials had the most significant impact on the dam’s performance. When the deterioration of the horizontal joint cementitious material reached 80%， the thin-layer elements in a non-closed state were mainly located on the horizontal joints near the downstream side at elevations of 33 m to 38 m in the assembly area. [Conclusions] Thin-layer elements can effectively simulate the state changes of cementitious joints， demonstrating the feasibility of applying them to the performance calculation of prefabricated dams. The deterioration of cementitious materials leads to increased displacement and stress in the assembly area of the prefabricated dam， thereby threatening its safety performance.

[Objective] To reveal the differences in seismic performance between hardfill dams and concrete gravity dams， this study investigates the nonlinear seismic response of the Oyuk dam （a typical hardfill dam） in Turkey and the non-overflow section of the Xiangjiaba gravity dam in China. [Methods] Numerical models of the Oyuk dam and the non-overflow section of the Xiangjiaba gravity dam were built using the finite element method. We employed the Westergaard method to simulate the hydrodynamic pressure of reservoir， the concrete damage plastic model to represent the nonlinear material behavior of dam body， and the massless foundation model to avoid the motion amplification effect of the foundation. The seismic failure process and anti-sliding stability of the two types of dams were investigated under ground motions with different peak ground accelerations （PGAs）. The failure zones and controlling failure patterns of two dams were summarized. The seismic performance of two dams was compared using the failure indicator， cumulative plastic dissipation energy， and the anti-sliding stability safety factor. [Results] The failure zones of hardfill dam mainly occurred at dam heel， dam toe， and the upstream and downstream faces in the middle part of the dam. In contrast， the failure zones of gravity dam were mainly located at dam heel， locations of downstream slope change， and the upstream and downstream faces in the upper part of the dam. For hardfill dam， the controlling failure pattern was the penetration between failure zones on the upstream face and the downstream face， whereas for gravity dam， the failure pattern was the penetration from the downstream face to the upstream face. The symmetrical dam section of hardfill dam significantly enhanced its anti-sliding stability. The minimum anti-sliding stability safety factor of hardfill dam under the operating basis earthquake （0.24g） was 2.44， while that of gravity dam under design peak ground acceleration （0.222g） was 1.53. The anti-sliding stability safety factor of both dam types gradually decreased with increasing PGA. The safety factor for gravity dam decreased to 1.0 at PGA=0.5g， while that for hardfill dam remained at 1.17 at PGA=0.8g. Based on the failure indicator and the anti-sliding stability safety factor， the ultimate seismic capacity of gravity dam was determined at 0.45g-0.50g， whereas that of hardfill dam at 0.75g-0.80g. [Conclusion] This study reveals the differences in nonlinear seismic performance between hardfill dam and gravity dam. The ultimate seismic capacity of hardfill dam is significantly higher than that of gravity dam. In the construction of hydraulic engineering projects in high seismic regions， hardfill dam is an effective alternative dam type.

[Objective] Cracks induced by hydration heat and associated temperature stress in mass concrete present a critical technical challenge in ultra-high voltage （UHV） substations. Focusing on typical mass concrete for UHV projects， this study systematically investigates the mechanisms by which the combination of fly ash， slag， and inhibitors affects the hydration heat of cementitious composite systems. [Methods] Using typical mass concrete as a case study， a series of hydration heat tests were conducted to investigate the influence of a composite system incorporating fly ash， slag， and inhibitors on the hydration heat of cement. Based on these experiments， a rational control strategy is proposed. [Results] Incorporating slag powder， fly ash， and inhibitors significantly delays the onset of the accelerated hydration phase and reduces total hydration heat. The inhibitory effect of citric acid exhibits a positive correlation with the dosage of mineral admixtures； specifically， citric acid primarily extends the peak time at lower admixture levels， whereas it induces complete process inhibition at higher concentrations. Nano-zinc oxide effectively mitigates early-stage hydration exothermicity； however， rapid subsequent reactions （exceeding 100 hours） may cause thermal stress concentration within cement-based materials， thereby accelerating the risk of cracking. Consequently， zinc oxide is not recommended for controlling hydration temperatures in mass concrete applications. Furthermore， the synergistic use of slag powder， fly ash， and inhibitors influences nucleation and crystal growth during hydration， resulting in an increase in kinetic parameters while simultaneously reducing hydration rates across all stages （evidenced by decreasing K_NG， K_I， and K_D）. Notably， the combination of tartaric acid and fly ash demonstrates the most pronounced effect， achieving a 97.4% reduction in the peak hydration temperature， which is far superior to the 30% to 50% efficiency of conventional material-based temperature control. Additionally， the control system combining inhibitors， mineral admixtures， and water cooling effectively reduces the temperature gradient to below 8.5℃/m， a performance significantly better than traditional temperature control indices. [Conclusions] The type and dosage of retarders should be determined comprehensively during the construction phase of mass concrete， considering their effects on workability， mechanical properties， and durability. From an economic perspective， although the cost of using tartaric acid is slightly higher than that of traditional methods， its remarkable effectiveness at low dosages significantly mitigates cracking， reduces subsequent maintenance costs， and enhances overall economic efficiency. Therefore， these achievements provide scientific support for mix proportion design and temperature control strategy optimization， offering practical guidance for temperature regulation and crack prevention during the construction of UHV substations.