Environmental DNA （eDNA） technology is a key tool for river health assessment. It shows great application potential in the biological analysis of aquatic ecosystems. However， the relationship between eDNA and sediments that are widely present in water bodies is complex， and eDNA is also affected by water flow， which seriously restricted the promotion and application of eDNA technology. Therefore， it is necessary to investigate the influence of sediment and water flow on the degradation of eDNA. This study took Ctengodon Idella， an important freshwater cultured fish in China， as the research object to explore the influence of water flow and sediment on the persistence of eDNA of grass carp. The results show that： ① In flowing water bodies， the degradation rate of the eDNA accelerates with the increase of flow rate. ② The presence of sediment accelerates the degradation rate of eDNA in water. Compared with the thickness of sediment laying， the sediment partical size has a greater impact on eDNA degradation. ③ Notably， in still water， the eDNA degradation rate decreases with the increase of sediment partical size. While in flowing water， water interference leads to the opposite eDNA degradation pattern， that is， the degradation rate of eDNA increases with the increase of sediment partical size. The study emphasizes that the impact of the sediment response method is critical in planning or interpreting eDNA studies and provides a valuable reference for the application of eDNA technology in aquatic ecosystems.

To explore the ecological effects of “water diversion project from Yangtze River to Taihu Lake” on the water bodies in the receiving lake area， the simulated indoor experiment was constructed using an aquatic microcosm model in a period of 11 days. The Gonghu Bay area of Taihu Lake was used as the receiving water body， and three groups of Wangyu River water with different nutrient levels O， M， E （Oligotrophic group， Mesotrophic group， Eutrophic group） were introduced to study the dynamic response process of the water ecological environment of the receiving water body under the influence of water diversion at different nutrient levels. The purpose is to provide a basis for the rational formulation of water diversion scheduling plans and the optimization of the scheduling effect of the “water diversion project from Yangtze River to Taihu Lake”. The results showed that： during the experiment， total nitrogen （TN）， nitrate nitrogen （NO₃ ^--N）， ammonia nitrogen （NH₄ ⁺-N）， total phosphorus （TP）， soluble reactive phosphate （SRP） and total organic carbon （TOC） in oligotrophic group and mesotrophic group decreased significantly. The effect of eutrophic water diversion group was worse than that of oligotrophic group and mesotrophic group. Water diversion increased the Shannon-Wiener diversity and Pielou’s evenness index in this water ecosystem. Density of diatoms and other non-cyanobacteria increased. Meanwhile， the growth of cyanobacteria was under competitive stress. The effect of oligotrophic group and mesotrophic group was better than that of eutrophic group. Simultaneously， the results of redundancy analysis showed that： pH， DO， SiO₃ ^2--Si， TDS， NO₃ ^--N， and SRP of the receiving water body were the main environmental factors influencing the distribution of phytoplankton community in this experiment.

To investigate the along-range variation characteristics of flow velocity and longitudinal dispersion coefficients of water flow in open channels under the influence of floating vegetation， in this paper， a three-dimensional numerical simulation was carried out by the k-ε model in Fluent software， and compared with the results of flume tests. On the basis of reasonable model validation， the vertical distribution characteristics of longitudinal time-averaged flow velocity of water with different depths of root into water and coverage rates of floating vegetation were investigated. The enhanced N-zone model served as the basis for the analysis of the longitudinal dispersion coefficient. The results showed that the vertical structure of floating vegetated flow could be divided into vegetated flow layer， non-vegetated flow layer and near-riverbed layer. The depth of the vegetation root into the water and the covering rate were connected to the maximum longitudinal velocity， which was found in the non-vegetated flow layer. While the longitudinal velocity in the near-riverbed layer and non-vegetated flow layer increased with increasing coverage rate and depth of vegetation root into water， the longitudinal velocity in the vegetated flow layer decreased with increasing coverage rate and depth of vegetation root into water. The greater the vegetation coverage rate and the depth of root into water， the greater the velocity difference between the vegetated flow layer and the non-vegetated flow layer. The longitudinal dispersion coefficient showed a tendency of first increasing and then decreasing along the streamflow direction， with the sharpest dispersion in the middle and lower reaches of the vegetation zone， and was positively correlated with the depth of vegetation root into water and coverage rate.

To investigate the spatial distribution characteristics of sediment grain size parameters in the surface sediments of rivers， this study collected 115 surface sediment samples from eight typical rivers in Maoming City， based on the geographical environment and the course of the rivers in the city. The collected samples were analyzed using a laser particle size analyzer. The study revealed that only three particle size components， namely sand， silt， and clay， were detected in the surface sediments of rivers in the research area. Silt was identified as the predominant component， with all eight rivers exhibiting silt content exceeding 50%. The content of sand and clay was similar， both registering below 20% in the studied rivers； however， they displayed contrasting distribution patterns within the river systems. The average grain size of surface sediments in the study area falls within the range of 4.37 to 7.3φ， indicating a relatively small variation. The sorting coefficients range from 1.53 to 2.48， suggesting overall poor sorting. Skewness values range from -0.09 to 0.73， with most sediments exhibiting positive skewness. Kurtosis values range from 0.70 to 1.17， indicating a generally flat peak. Specifically， sediments from the Jianjiang River and Luojiang River demonstrate a trend of low sorting coefficients and large average grain sizes. In contrast， sediments from the Xiaodong River and Huanghua River exhibit a pattern of high sorting coefficients and small average grain sizes. The average grain size of the main stream of the Jianjiang River， midstream > downstream > upstream， showed a trend of increasing and then decreasing. The main stream of Huanghua River showed a decreasing trend in particle size， and the sediment tended to be coarse-end. The average particle size of Luojiang River main stream showed a decreasing trend， and the river flow was not easy for fine grain deposition. The conclusions of this study on the characteristics of particle size parameters and grain size distribution provide data support and theoretical reference for related studies.

In order to identify the priority management area of nonpoint source pollution in the Zuli River basin， the Zuli River basin， a first-class tributary of the Yellow River， was selected as the research object based on the SWAT model. The study firstly simulated the spatial distribution of total nitrogen loads from nonpoint sources in the basin， and analyzed the change of total nitrogen loads in the basin from the perspective of the interannual and inter-monthly changes. The upstream and downstream relationships in the sub-basins and the role of the river channel in retaining the pollutants were considered. The Yellow River confluence in the basin is the water quality impact monitoring point. Based on the total nitrogen pollution intensity of the sub-basins relative to the entire basin， non-point source pollution priority management area were divided. The results show that the SWAT model is applicable in the Zuli River basin， and the Nash efficiency coefficients are higher than 0.5 using SWAT-CUP software for the simulation values of runoff and water quality for parameter rate fixing.From the simulation results， it can be concluded that there is a large difference in total nitrogen loads in each sub-basin， and the total nitrogen loads of the sub-basins located in the upper reaches of the basin are small， and those sub-basins with large loads are mainly distributed in the outlet of the river. From 2001 to 2022， the trend of total nitrogen load in the whole watershed was approximately the same as that of annual precipitation； and the seasonal change was obvious， with the highest total nitrogen load in summer. According to the intensity of total nitrogen pollution， the sub-basins were divided into three types of pollution priority management zones， and it was found that the sub-basins that need to prioritize the management of non-point source pollution during the 20-year period were distributed along the main channel of the Bitter Water River， which is the upper reaches of the Zu Li River， from the south to the north. The results can provide a reference for the management of nonpoint source pollution and ecological restoration and protection in the Zuli River basin.

Percolation phenomenon widely exists in various physical processes in natural world， and percolation theory has been widely used and studied in many fields. In contrast to traditional seepage theory taking hydraulic conductivity as the main parameter， percolation theory offers a distinctive approach to understanding the permeability of porous media. This may be a more reasonable approach to solve complex seepage problems such as when the gas phase invades the water-saturated porous medium，the characterization of gas phase motion in immiscible two-phase flow systems in porous media. Porous media， conceptualized as an interconnected network of pores and throats， can be likened to nodes and bond connections in the percolation model. This unique perspective allows the application of percolation theory to porous media， providing a theoretical framework for analyzing both saturated and unsaturated hydraulic conductivities using the critical path analysis method in the percolation theory. The derivation begins with Poiseuille's equation， a fundamental equation governing fluid flow. Hydraulic conductance and critical volume fraction for percolation become essential concepts in this theoretical exploration. By integrating these concepts with Poiseuille's equation， the relationship between saturated hydraulic conductivity and critical pore radius is established. To further refine the theoretical framework， on this basis， the porosity is given in the form of a probability density function of the pore radius and the concept of equilibrium radius is introduced into the formula derivation process， this addition enhances the model's accuracy by accounting for the distribution of pore sizes within the porous media. As a result， the expression for unsaturated hydraulic conductivity finally obtained. The applicability of the unsaturated hydraulic conductivity expression was analyzed by comparing the measured data of two soil samples in the Rijtema database and predicted values. It was found that the expression of the unsaturated hydraulic conductivity given in this article is close to the measured value only in the range far away from the percolation threshold， that is， when the saturation is greater than 90 percent， while at small saturation， even errors of several orders of magnitude were produced. The generation of these errors is related to the assumptions and approximation processing in the aforementioned derivation process of unsaturated hydraulic conductivity and the complexity of the topology when approaching percolation. The result is that the closer to the critical saturation， the less accurate the predicted value is.

As the Loess Plateau is the most frequently affected area by landslides in China， and rainfall is the main influencing factor for the scour and instability of loess slopes， so it is particularly important to understand the law and mechanism of water infiltration on the surface scour of different slopes and inside the slope body. In this paper， the slope soil we studied is from Heifangtai loess in Gansu Province. Indoor triaxial shear tests were carried out on loess with different water contents. Rainfall scour tests and model box slope water holding capacity monitoring tests were designed and carried out under different vegetation protection. Sensors were used to monitor the volumetric water content and matrix suction of the slope. The displacement of the slope under different rainfall intensities were measured and analysed， and the flow and sand production of different vegetated slopes were recorded. The results are as follows： The cohesion and internal friction angle of the soil body show a quadratic function with the water content. The bare slope has the shortest flow production time， the least water infiltration， and the slope surface is relatively easier to produce runoff， thus entering the slope erosion stage. The increase in slope gradient leads to an increase in slope runoff velocity， which strengthens the water resistance of the slope surface， and the slope erosion decreases with the increase in slope gradient. The decrease of the matrix suction of the soil body under the effect of heavy rain and rainstorm is significantly faster than that under the effect of light rain and medium rain. The stable value of matrix suction is the largest under light rainfall and the smallest under heavy rainfall.

Ammonium Perfluorooctanoate （APFO） is a hard-to-degrade， bioaccumulative and toxic per- and polyfluoroalkyl substances （PFAS） that poses a serious threat to the environment and biological health. Although mass spectrometry is effective in detecting PFAS， it is expensive. High-performance liquid chromatography （HPLC） method is a lower-cost detection method， but the existing technology has low stability， reproducibility and efficiency.This study successfully established an HPLC method with aqueous perchloric acid and acetonitrile as mobile phases capable of separating and detecting APFO. The study systematically investigated the effects of mobile phase volume ratio and pH on the detection of APFO. The results showed that the best APFO peaks were obtained under the conditions of aqueous perchloric acid∶acetonitrile= 60∶40， pH=3.5. This method consumed less than 15 minutes per sample， and the limit of quantification of the method was 1.01 mg/L. This method achieved similar sensitivity to other HPLC methods using simpler operation and less time and cost， and showed good linearity in the concentration range of 2~50 mg/L. The precision and accuracy experiments showed that the relative standard deviation of the method was within 9%， and the spiked recoveries were between 97.35% and 104.80% for actual water samples， which demonstrated anti-interference for determining complex samples. This study showcases the method's significant potential for efficient and economical detection of high-concentration PFAS in water treatment material development during initial stages.

This study focuses on the river habitat in the Liaohe irrigation district of northwest Jiangxi Province as the research scope， aiming to develop an evaluation index system and application model for large-scale irrigation districts. The assessment system of river habitat quality in the Liaohe irrigation district was screened using bibliometrics and analytic hierarchy process， and the river habitat degradation index and the index of river habitat quality were created based on the examination and analysis of the water environment and riparian habitat in the irrigation district. The findings demonstrated the geographical statistical significance of river water quality， riparian vegetation， economic structure， land use， riverbed substrate and other factors. The average habitat value among the 32 reaches that were evaluated was 2.54， with a range of 1.37 to 3.92. Among them， 28.13% had medium habitat quality， 21.88% had poor habitat quality， and 25% of the river reaches had exceptional habitat quality. According to the statistical findings， river habitats were distributed spatially as follows： upstream section > middle section > downstream section. Jing'an area > Fengxin area > Anyi area； countryside area > agricultural area > village area > urban area. According to the river habitat degradation index， 31.25% of the river reach was clearly impacted by human activity. The quality of the habitat in rivers was significantly correlated negatively with habitat deterioration. Between 2000 and 2020， the irrigated area's river habitat quality first declined and then progressively improved. The impact of human activity on the Liaohe irrigation district are becoming more and more evident， exhibiting the traits of the conversion of forested and farmed land into water areas and construction sites.

Making full use of modern technological means to improve the accuracy of runoff forecasting plays an important guiding role in basin flood and drought disaster defense and joint scheduling of reservoir groups. However， existing deep learning models have problems such as lack of model transparency and poor physical interpretability. To address the above problems， in this study， a conceptual hydrological model EXP-Hydro is embedded into the P-RNN layer of recurrent neural network， and a deep learning hybrid model Hybrid-DL coupled with physical mechanism is modeled. The hybrid model adopts a differential framework to realize the deep bidirectional fusion of conceptual model and neural network， which is able to train the parameters of conceptual model and neural network at the same time. And an application study is carried out in the upper reaches of Qingjiang River as an example. The results show that compared with RNN， EXP-Hydro， BP and SVM models， the Nash efficiency coefficient （NSE） of the Hybrid-DL model increases by 6.08%， 21.01%， 37.09% and 73.92%， the root-mean-square error （RMSE） decreases by 10.82%、33.73%、54.70% and 95.57%， the KGE efficiency coefficient increases by 4.78%、12.68%、26.79% and 55.74%， and the peak error TPE decreases by 4.96%、13.12%、252.84% and 297.81%. The Hybrid-DL model has good robustness and adaptability， and can provide a reliable theoretical tool for runoff forecasting in the upper reaches of Qingjiang River and even in other basins.

The medium and long term forecast of runoff in areas with little data is related to the medium and long term power generation of power plants， and also has a strong guiding effect on the short term economic operation of power plants. The Yalu River basin is an important clean energy base in Northeast China. Since North Korea controls more than half of the area of the Yalu River basin， it is difficult to share its runoff data with China， which brings certain obstacles to the medium- and long-term runoff forecast of the Yalu River basin. Taking the inflow runoff of Shuifeng Reservoir in Yalu River Basin as the research object， six model methods， namely phase space reconstruction model （local method， global method）， LSTM model， wavelet analysis-LSTM model， coupled phase space reconstruction （local method， global method） and wavelet analysis model， were used to forecast the inflow runoff of Shuifeng reservoir in the medium- and long-term. The accuracy of the prediction results of the above six models was compared by mean absolute error， mean absolute percentage error and qualification rate. The results show that the coupled phase space reconstruction （global method） and wavelet analysis model are used to forecast the annual runoff. In the monthly scale runoff forecast， the results of coupled phase space reconstruction （local method）， wavelet analysis model and wavelet analysis-LSTM model are better from January to May， while the coupled phase space reconstruction （global method） and wavelet analysis model have obvious advantages from June to December. In the 1-year forecast period， the wavelet analysis-LSTM model has a good effect. For the ten-day runoff prediction， the effect of wavelet analysis-LSTM model is better in the 1-day forecast period， and that of coupled phase space reconstruction （global method） and wavelet analysis model in the 3-day forecast period has obvious advantages. The study will support the formulation of medium - and long-term operation plans for Shuifeng Reservoir and downstream power plants.

This paper takes reservoir real-time flood forecasting as the research object， aiming at the problem that the forecast lead time for flood prediction of small and medium-sized river basins is short and the natural forecast period of river basins is difficult to meet the production requirements of hydraulic project， studies the reservoir real-time flood forecasting method， and builds a reservoir real-time flood forecasting model based on meteorological and hydrological coupling. Firstly， a 24-hour precipitation forecast model is established by using short-time proximity extrapolation technique and STMAS-WAF mesoscale weather model. Then the results of meteorological forecast are coupled to hydrological forecast to achieve the spatio-temporal scale matching of meteorological and hydrological. Finally， a precipitation forecast correction method based on the feedback of incoming water forecast results is established， and the precipitation forecast results in the future 24 h are revised on a rolling basis according to previous rules. The revised precipitation forecast is input into the hydrological model to predict the incoming water from the reservoir in real time， so that the hydrological model can be accurately input from the source， and the real-time flood forecast of the reservoir with high precision and long forecast time can be realized. The problem of insufficient forecast period of traditional hydrological model is solved. The Xin?anjiang Reservoir is taken as an example to carry out a case study of the model， and the coupled meteorological and hydrological forecast scheme of Xin?anjiang Reservoir is formulated to carry out real-time flood forecast of the reservoir， and the influence of different rainfall input forms on the forecast accuracy is discussed. The results show that： the model takes into account the bidirectional feedback of meteorology and hydrology， and improves the real-time flood forecast period of the Xin?anjiang Reservoir from about 6 hours to 18 hours， ensuring that the forecast accuracy within 18 hours is above 80%. Compared with two traditional methods that do not consider precipitation forecast and use unmodified precipitation forecast， the effective forecast period of the new method is increased by 200% and 29% respectively， effectively extending the real-time flood forecast period of reservoirs， improving the flood forecast service ability， and providing an effective method for real-time flood forecast of reservoirs.

Reservoir water supply regulation calculation is an important technical means to achieve rational spatial and temporal allocation of river water resources. The conventional reservoir water supply regulation calculation method has a clear process and simple operation， but the calculated water supply volume is not the optimal value. Aiming at the shortcomings of conventional water supply regulation method， an optimization model is constructed in order to improve the calculation accuracy of the reservoir water supply scale. The model’s goal is maximizing the total water supply of the reservoir during the calculation period， and it’s constraint contains the water supply guarantee rate and maximum damage depth of each water supply object. Based on the principle of equivalent transformation， the nonlinear constraint conditions of the water supply guarantee rate for water supply objects in the model are linearized， and Cplex linear solver is used to solve the model. The analysis results of Zhangfeng reservoir water supply project show that： Compared with the conventional method， the average annual water supply volume of Zhangfeng Reservoir calculated by the optimization model increases by 9.48 million m3， with an increase of 7.5%， and the water supply benefits increases significantly. The average water level of the reservoir decreases by 6 meters compared with the conventional method， and the number of changes in water storage and discharge increases， which fully utilizes the multi-year regulation effect of Zhangfeng Reservoir. The number of maximum damaged months for water supply objects is greater than that of the conventional method， but it still meets the design water supply guarantee rate requirements of each water supply object， indicating that the optimization model achieves the purpose of reducing the maximum damage depth by increasing the number of maximum damaged months. The average annual outflow rate decreases by 0.2 m3/s compared with the conventional method， but it can ensure that all months of the long series meet the ecological flow requirements within the river. The water shortage and water shortage process in two typical continuous dry periods from 1997 to 2002 and from 2008 to 2010 in the Qinhe River basin are similar to the results of the conventional method， which conforms to the actual situation and verifies the rationality of the model. The optimization model can modify the objectives and constraints according to actual needs， can accurately control the water supply guarantee rate and maximum damage depth of each water supply object， and also has portability， which makes it more flexible to use.

The assessment of urban flood risk plays a crucial role in preventing flood disasters， yet there is limited research on road safety risk assessment. Taking Xiushan County， Chongqing Municipality， as the study area， road safety risk was assessed using the MIKE FLOOD coupled model. The results indicate that surface water depths are mainly concentrated between 0.05 to 0.15 meters， and the spatial distribution of water depths under different return periods （P=1%~20%） is generally consistent. The duration of water accumulation is mainly between 60 to 90 minutes， and the water accumulation flow velocity is mainly greater than 0.8 meters per second. In some areas of the old city， the infrastructure safety risk is primarily at a very high level （water depth >0.4 meters）， while in other areas， it is predominantly at a slight risk level （water depth <0.5 meters）. Pedestrian safety risk of the old city is primarily at level III （hazard index 1.25~2） in some areas， while in other areas， it is primarily at level I （hazard index <0.75）. The traffic operation conditions on most road sections are mainly at the unimpeded level （retention coefficient >0.7）， but some road sections are interrupted during heavy rainfall （retention coefficient = 0）. The research findings can provide scientific basis for traffic control and passage warning before urban flooding occurs.

Under the combined influence of global climate change and high intensity human activities， the natural water cycle in many river basins has been disrupted. The runoff series show obvious non-stationary characteristics， which brings certain challenges to water resource planning， management， forecast and regulation. Revealing the non-stationary characteristics of runoff series can effectively deal with complex water problems under global climate change， and is important for reducing the difficulty of hydrological analysis and improving the accuracy of runoff prediction. This study takes Lancun Station in the upper reaches of Fenhe River as the research object to analyze whether the annual and monthly runoff series of the station from 1958 to 2016 are stationary. Firstly， from the perspective of stochastic hydrology， Mann-Kendall test method and wavelet analysis method are used to identify the trend， abrupt change and periodic characteristics of the runoff series. On this basis， the Ng-Perron unit root test is introduced from the perspective of statistical hydrology. A suitable test equation is selected by Mann-Kendall trend test and scatterplot method， and Generalized Least Squares （GLS） regression potential is applied to the runoff series. The Modified information criterion （MIC） is used to calculate the optimal time lag order and determine whether the runoff series is non-stationary. The results show that there are trends， abrupt changes and periodic components in the runoff series， which are non-stationary runoff series. At the same time， the Ng-Perron unit root test shows that the annual and monthly runoff series of the station has non-stationary characteristics at 1% significance level. Compared with the traditional unit root test method， Ng-Perron unit root test adopts more robust modified test statistics to significantly adjust the horizontal distortion in the case of small samples， which has better test level and efficacy， and can obtain more reasonable test results. The research results provide reference for the further improvement of the non-stationarity test theory of runoff series and the development and application of runoff prediction model.

In view of the demand for water saving and water network construction in China， as well as the serious uneven temporal and spatial distribution of water resources， and the great differences in economic development level and population size among different regions， the data of water consumption， industrial added value and population structure of each provincial administrative region from 2000 to 2020 are used. The LMDI index decomposition method and GDP constant price conversion method were used to analyze the difference of total water use， water use structure change， and the intensity and contribution ratio of driving effects of water use intensity， industrial structure， economic scale and population size in each region from two perspectives of time and space， aiming to support China's water resources planning and management as well as water use structure adjustment. From the perspective of time， economic growth is the most important driving factor for the increase of total water use in China. The decrease of industrial water use intensity and industrial structure adjustment， especially the decrease of water use intensity and proportion in the primary industry， are the main factors inhibiting the increase of regional total water use. The effect of water use intensity is slightly greater than that of industrial structure， while the increase of population size has no obvious effect on the increase of total water use. Therefore， China's water consumption control should be based on the strategy of improving water use efficiency and optimizing and upgrading the industrial structure. From the perspective of space， the four driving effects in the major regions of China promote or inhibit the increase of total water use steadily. In order to narrow the spatial difference of water consumption in different regions of China， inland areas such as Southwest and Northwest of China need to vigorously develop economic scale on the basis of optimizing the industrial structure； meanwhile， Northwest of China also urgently needs to improve water use efficiency in the primary industry； while East China can properly control the population size， the northeast and northwest need to control the population outflow.

In order to gain a deeper understanding of the changing law of water-sand relationship in the Jialing River， based on the annual runoff and sediment load data of Beibei Hydrological Station at the outlet of the Jialing River from 1965 to 2022， the Mann-Kendall test， double cumulative curve method and the physical genesis method were used to diagnose the variation points of water and sediment relationship， and the marginal distribution function and Copula function of the runoff and sediment load were preferred through the AIC， BIC， and RMSE， and the optimal Copula function was determined， and the water-sediment joint distribution model of the Jialing River basin was established. The established model was then used to calculate the probability of water and sediment abundance and depletion encounter， joint and co-occurring recurrence periods in the basin， and then to compare and analyse the univariate and joint variables design values of water and sediment. The results show that： ① The water and sediment relationship changed abruptly in 1989， and the water and sediment correlation before the change was stronger than that after the change. ② The optimal marginal distributions of the water and sediment series in 1965-1989 are Logn， and the optimal joint distribution model of water and sediment is the Gumbel Copula model， while the optimal marginal distributions of runoff and sediment in 1990-2022 are Gamma and GP respectively， and the optimal joint distribution model of water and sediment is the Frank Copula model. ③ The synchronous probability of the two stages of water and sediment sequences is 59.77% and 61.14% respectively， both of which are greater than the asynchronous probability， and the probability of occurrence of the extreme cases of “abundant water and sediment depletion” and “depleted water and sediment abundance” is extremely low， which indicates that there is a large correlation between the probability of water and sediment， and the water and sediment conditions are relatively stable. ④ The design value of the joint variable is larger than the univariate one， and the design value of runoff and sediment load calculated by the joint distribution of the two variables is more reliable. The joint recurrence period of water and sediment is concentrated near 2 years， and the majority of the co-occurrence recurrence period is less than 50 years. By exploring the characteristics of the joint change of water and sand in the Jialing River basin， this study can provide a reference for water and sand regulation， disaster prevention and mitigation in the basin.

Runoff is the main carrier of soil erosion. Accurate prediction of runoff is crucial for soil erosion forecast and reservoir safety management in the Three Gorges Reservoir. To optimize the SCS-CN model's calculation method for soil antecedent moisture content and assess the model's applicability before and after improvement in the Three Gorges Reservoir area， this study introduced the antecedent precipitation index to characterize soil moisture and set an upper limit threshold based on measured soil saturated moisture content， thereby improving the SCS-CN model. Using the rainfall-runoff data from the Zhongxian Soil and Water Conservation Monitoring Station from 2019 to 2022， the applicability of the model before and after improvement under different rainfall types and land uses was evaluated. The results show that among the two initial models and two improved models， the improved model based on MSCS-CN （M4） has higher simulation accuracy for runoff depth， and the Nash efficiency coefficient （NSE） is improved by 134% compared with the original SCS-CN model （M1）， especially for the case of saturated soil water content in the antecedent period where the NSE is improved to 0.74， and the introduction of the maximum antecedent precipitationindex（API _max） as the upper limit of the antecedent precipitation index can reduce the overestimation of the predicted values of high runoff events in previous models. In addition， the improved model M4 is well applicable to the main flow-producing rainfall types （high rainfall intensity） and the main land uses （croplands and orchards） in the Three Gorges Reservoir area， and effectively improves the runoff simulation accuracy for the small rainfall-producing events and the land use types with high erosion risk （the Nash efficiency coefficients for Rain Type II， croplands， and orchards are 0.66， 0.69， and 0.75， respectively）. Overall， the improved model M4 improves the accuracy of runoff simulation， and is more suitable for the runoff generation mechanism and land use types of the Three Gorges Reservoir area， which can provide a valuable reference for runoff prediction and soil and water loss prevention and control work in the Three Gorges Reservoir area.

Soil moisture is a crucial parameter for the exchange of matter and energy at the land-atmosphere interface. Timely and accurate acquisition of soil moisture information is of paramount importance for drought monitoring， water resource management， and crop yield estimation. In this study， utilizing Sentinel-1 SAR remote sensing data and Sentinel-2 optical remote sensing data， the relationship between various optical vegetation indices and measured vegetation water content was systematically analyzed. The Fusion Vegetation Index （FVI） was preferentially selected to establish vegetation water content estimation model，which was combined with the vegetation microwave scattering model—Water Cloud Model （WCM） to correct the impact of vegetation layer on SAR backscattering signals. On this basis， a surface microwave scattering model—Oh model was used to construct the backscattering coefficient simulation database， and soil moisture retrieval for the summer maize-covered surface under both VV and VH polarizations was achieved through the application of the Look-Up Table （LUT） algorithm. The results indicate that， for surfaces covered by dense vegetation like summer maize， vegetation water content characteristics can be better reflected by FVI， enabling the accurate correction of the impact of vegetation layers on SAR backscattering coefficients. The vegetation water content inversion model based on FVI achieved an R ² of 0.693 and an RMSE of 0.303 kg/m². After vegetation correction， the correlation between soil moisture and SAR backscattering coefficients increased by 21.6% and 27.9% for VV and VH polarizations， respectively. Compared to VH polarization， VV polarization is found to be more suitable for soil moisture retrieval， with an R ² of 0.672 and an RMSE of 0.048 m³/m³ between retrieved and measured soil moisture values. The findings of this study provide robust support for the remote sensing observation of soil moisture information in densely vegetated surfaces.

This study has carried out the three-point bending test with the digital image correlation technology （DIC） to explore the mechanism of size effect on the tensile properties of clay， and the tensile crack failure process of compacted clay beam under the condition of geometric similarity and non-geometric similarity （the change of sample height h， thickness b） is analyzed from macro and micro perspective. The results showed that： The increasing of the size of geometrically similar and non-geometrically similar specimens prompted the increasing of the peak load of the specimens. The tensile strength σ _t of soil is significantly affected by the size effect and σ _t of geometrically similar soil beam linear decreases with the increase of sample size. When only increasing the soil beam h， σ _t increases at first and then decreases. When the soil beam b is changed， σ _t decreases first and then increases with the increase of b， in which the change of b has less influence on σ _t. By introducing the meso-evaluation index： Local strain degree ε _a， it is concluded that the ε _a of geometrically similar specimens increased with the increase of size， while the ε _a of non-geometrically similar samples increased at first and then decreased with the increasing of h or b.

Rainfall is an important cause of deposit slope instability in engineering area. How to evaluate the influence of saturated-unsaturated seepage flow on the stability of deposit slope under rainfall condition？ The challenge lies in accurately obtaining the unsaturated seepage parameters of deposit body.Taking Meijiatai landslide control project as the research object， unsaturated hydraulic parameters and boundary water level are obtained by using saturated-unsaturated finite element analysis and dynamic inversion of seepage field based on monitoring data， and then limit equilibrium method is used to analyze the change of landslide stability. The results show that the groundwater level at the back edge of the slope changes dynamically from 692.0 m to 694.5 m， and the groundwater level in the slope varies from 3.0 m to 12.0 m under the influence of the back edge recharge and rainfall infiltration. After the drainage measures were implemented， the groundwater level decreased by 9.0 m， and the variation amplitude was reduced to 1.0~5.5 m. At the same time， the range of the transient saturation area of the weak accumulation zone in the middle of the landslide was reduced by 84.5%， and the saturated area at the foot of the slope was suppressed below Highway 1， which played a great role in drainage and pressure reduction. There are three instability modes of landslide： shallow slide along the central weak zone， shallow slide along the lower front， and cut out from Highway 1 along the old slide zone. The stability decreases significantly during rainfall infiltration， and the stability coefficient decreases to 0.82， 0.99， and 0.98 respectively， which is less than the stability safety coefficient of 1.05. Under comprehensive management measures， the stability coefficients are increased by 0.28， 0.13 and 0.19 respectively， and the current stability coefficients are 1.10， 1.12 and 1.17 respectively. The stability coefficients of each instability mode are greater than the stability safety coefficient， and the landslide is in a stable state. The research results can provide reference for similar engineering management design and seepage stability analysis.