A SWAT model of the upper Paraná River basin in Brazil was constructed to test its applicability in largescale watershed. The sensitivity parameters of the model were analyzed. Then the model was calibrated and validated using 17 runoff stations. The results show that the soil evaporation compensation coefficient (ESCO) and the SCS runoff curve number (CN2) are the most sensitive parameters for the sub-basins with a high density of rain gauged stations, the model could simulate the discharge well after calibration, and the R² values of 11 stations among 17 calibration stations were greater than 0.5; Affected by factors such as insufficient precipitation data and changes in land use, the model in validation period did not perform as well as in the calibration period. Thus, the SWAT model could be used as an effective tool for large-scale watersheds, but the simulation accuracy largely depends on the quality of precipitation data.

In light of the difficulty of traditional single runoff prediction models to describe future variation in runoff, a monthly runoff prediction model named AVMD-GPR-CK based on adaptive variational modal decomposition (AVMD) and Gaussian process regression (GPR-CK) with physically composite kernel was proposed. In the proposed model, the runoff series was decomposed into several subseries using AVMD. Then subseries were separately modeled according to their own characteristics, and the final prediction result was the superposition of the subsequence prediction results. The AVMD-GPR-CK was applied to forecast the future 1-12 months runoff at Xiangjiaba station in the Jinsha River basin. The results show that the deterministic coefficient of the AVMD-GPR-CK model is greater than 0.94, and the mean absolute percentage error (M_MAPE) is within ±17% for all leading times, and the M_MAPE is inside ±10% for leading times within 10 months. Furthermore, the accuracy of the AVMD-GPR-CK is significantly better than those of the commonly used BP, GRNN, RBF, and RELM models.

Revealing the characteristics of basin runoff evolution and quantitatively identifying the contribution of driving factors is essential for adaptive water resources management and water security in basins. Based on the measured monthly runoff series from 1960-2015 at the NO.2 hydrological station in the source area of the Ulungur River and the meteorological and human water and soil resources development and utilization image data for the same period, the sliding removal wavelet analysis method, the Mann-Kendall trend test method and the sliding t test method were used to analyze the evolution trend and mutation characteristics of the hydrometeorological elements sequence. The elastic coefficient method based on the Budyko hypothesis was used to identify the contribution rates of climate changes and human activities to runoff change in the study area. The results show that there is a non-significant upward trend in runoff series, a significant upward trend in precipitation series and a significant downward trend in potential evapotranspiration series in the Ulungur River source area; The runoff series changed abruptly in 1995, with the sensitivity coefficients of runoff to precipitation, potential evapotranspiration and subsurface characteristics increasing by 8.8%, 25.0% and 7.8% respectively in the change period 1995-2015 compared to the base period 1960-1994; The contribution of changes in precipitation and potential evapotranspiration and subsurface characteristics parameters to runoff changes are 39.2%, 7.0% and 53.8% respectively. The runoff changes in the study area are driven by a combination of human activities and climatic elements, with human activities being the main driving factors.

Aiming at the cumbersome problem of applying the Markaviev method to calculate the bed-forming flow rate, the geomorphic work diagram method was proposed to simplify the calculation of the bed-forming flow. Based on the measured water and sediment data from 1960 to 2014 at the four hydrological stations of Huayuankou, Gaocun, Aishan and Lijin in the lower reaches of the Yellow River, the Markaviev method and the geomorphological method were used to calculate the bed-forming flow of the four stations over the years. The results show that the differences in the bed-forming flow over the years at the four stations in the lower reaches of the Yellow River calculated by the two methods are small and the downward trend is similar. Compared with the Markaviev method, the geomorphic work diagram method is more convenient and accurate to calculate the bed-forming flow.

Due to the disturbance of human activities and the influence of climate change, the water area of Mudong Lake, the core area of Huixian Wetland, the largest karst landform original wetland in the Lijiang River Basin, has shrunk and faced severe ecological and environmental risks. Using the Sentinel remote sensing image data of 65 scenes from 2017 to 2021, the water area of Mudong Lake was extracted by random forest classification. The temporal and spatial changes of the water area of Mudong Lake in the past five years were analyzed to explore the correlation between the water level and area of Mudong Lake. The results show that the water area of Mudong Lake has been relatively stable in the past five years, but the changes in the wet and dry periods are obvious; The area changes are mainly distributed in the northern part of the lake area; The correlation between water level and area is relatively good, and the correlation coefficients of different water periods are different; The correlation coefficients of the wet periods and dry season are 0.90 and 0.60, respectively.

Optimal allocation of water resources is an important method to effectively relieve the contradiction between the supply and demand of water resources in regions. The traditional butterfly optimization algorithm (BOA) has some defects, such as low search accuracy, slow convergence speed, easy to fall into local optimization and can not be directly used to solve multi-objective optimal allocation of water resources problems. It was improved by introducing the methods of fast non dominated sorting, congestion and elite strategy, and the superiority of the ameliorative butterfly optimization algorithm (ABOA) was verified by using ZTD function. Finally, the ABOA was applied to the optimal allocation model of water resources in Handan, and the scheme with the least water shortage was selected as the final scheme from the Pareto front. The Handan water resources optimal allocation in 2035 (p=50%) yielded a total water demand of 2.74 billion cubic meters, a total water distribution of 2.44 billion cubic meters, and the water shortage was 298 million cubic meters, and the water shortage rate was 10.9%. Domestic and ecological water demand could be fully met. However, the primary, secondary and tertiary sectors were still facing water shortages in different regions, which need to be alleviated by water conservation. The research results can provide a new reference for the solution of multi-objective optimal allocation of water resources.

In order to enhance the efficiency and rationality of water resources allocation in Minjiang River, a water allocation index system including the monitoring rate of water intake, the rate of water quality of control sections meeting the standards and the early warning of discharge was established from the perspective of water resources management and assessment effectiveness. And then the quantitative calculation of the water intake of each water-taking city and the importance of each index were carried out by the comprehensive weighting method which combines the subjective and objective factors. The results show that the results of water intake distribution are consistent with the actual of water diversion, and the demand of water resources in Chengdu, Meishan and other cities in the middle reaches of Minjiang River is large, which can provide a basis for water resources regulation and water rights trading in Minjiang River. The supervision rate of water intake and the rate of water quality of control section are of great weight among the 6 new indexes, which provides an idea for constructing a new index system of water allocation. The results of water diversion take into account both the health of rivers and the requirements of water environment, and try to directly link the benefits of water resources management with water diversion, which can provide reference for actual water diversion, and urges each area to have the emphasis to continue to do well the water resources management and the appraisal related work.

The problems, such as unreasonable development of small hydropower and the neglect of the river ecological flow demand, can negatively impact the hydrological ecology of the lower reaches and damage the habitat environment of aquatic organisms. Taking the Xiaxiang hydropower station in the Dahuan River Basin of Guangxi Zhuang Autonomous Region as the research reach, carp was selected as the target fish. Based on the suitability curve of carp velocity and water depth, using the habitat simulation, the characteristics of hydrodynamic distribution and carp mass habitat area distribution under 11 flow conditions were analyzed. The results show that the suitable ecological flow of target fish in dry season is 9.38 m³/s, and the minimum ecological flow is 6.25 m³/s. The comparative analysis was carried out by using the hydrology method, and the suitability of the minimum ecological flow was evaluated by three evaluation indexes. The results show that the suitable ecological flow and the minimum ecological flow of the habitat simulation are reasonable and suitable. The research results are of great significance to ensure the ecological environment health of the downstream rivers of small hydropower stations.

In order to understand the temporal and spatial characteristics of blooms in the Three Gorges Reservoir, the temporal and spatial changes of dissolved oxygen, Chlorophyll-a and other indicators were analyzed, and the growth characteristics of algae was screened, which can provide reference for the early warning of blooms under the condition that no blooms occurred in Xiangxi River bay of the Three Gorges Reservoir in June 2020. The results show that the thermocline and the surface layer of the inverted weight current block the vertical hydrodynamic exchange, and then promote the presence of oxygen thermocline at the bottom of the water surface. Consecutive sunny days in summer may increase the chance of bloom outbreaks from 7:00 to 11:00 and from 14:00 to 17:00. There is a lag in bloom outbreak. Algae growth cannot be characterized only by the density of algae in monolayer water, so it is necessary to use the average density of algae in the vertical migration range for further bloom warning.

As an important factor in the ecological environment of lakes, aquatic plants play a key role in the restoration and management of lakes. The water blocking effect of aquatic plants has a significant impact on the flood storage and discharge process of lakes, so the impact of aquatic plants on the roughness has become an important part of the hydraulic research of ecological lakes. The height of aquatic plants is closely related to the roughness of lakes. The elastic modulus of aquatic plants is an important mechanical property parameter for calculating its deformation. The stem of aquatic plants is simplified as a cantilever beam with variable cross-section. Through the bending deformation test of eight aquatic plants, the tensile force, displacement and other parameters are measured, and the elastic modulus value is calculated. The basic range of the measured elastic modulus change of eight aquatic plants is obtained. The comparison shows that the elastic modulus of these aquatic plants increases with the growth age or total length.