The drought in the Fenhe River Basin has the characteristics of serious disaster and wide range of influence, which has a great blocking effect on the development of local society economy, so it is of great significance to accurately evaluate the drought situation in the basin. Based on Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Runoff Index (SRI), the data were grouped with Tyson polygons. A new comprehensive drought index Comprehensive Index (CI) was constructed by Caussian Copula function. Mann-Kendall trend test was used to test the trend of CI annual series, and the run-length theory was used to extract drought features. It is found that CI can respond well to both hydrological and meteorological droughts. The number of M-K trend series of CI sequence is -3.78. There is a trend towards drought in the upper reaches of the Fenhe River. The intensity of drought in 1970 is the smallest, which is 0.06. Four years from 2013 to 2016 appeared continuous drought, and the maximum intensity is 2.66.

In view of the case that the high wave wall changes from inclined to vertical near the dam slope and crest, numerical simulation and physical model tests were used to mutually verify the calculation of wave run-up. The working conditions of different wave elements and water depth in front of the dam were analyzed to study the impact of high wave walls on wave run-up in the reservoir. The results show that when the same wave factor is applied to different reservoir depths, the wave run-up shows an inverted parabolic trend with the reservoir depth; The maximum wave run-up occurs at the intersection of the vertical section of the wave wall and the slope section; When the water depth in front of the wall is higher than the intersection of the vertical section and the slope section, the wave run-up calculated by the standard method is larger compared with the results of mathematical and physical models. The finding can provide a reference for the refined design of the top elevation of high wave walls considering the impact of wave run-up in the design of earth-rockfill dam.

Support Vector Machine (SVM) has advantages in small sample simulation prediction, but there is subjectivity in the selection of penalty factor C and kernel function parameter γ in SVM. Therefore, the Harris Hawks Optimization (HHO) algorithm was used to optimize C and γ in the SVM. And then the HHO-SVM mode was established to predict water quality in the Xiyuan tunnel section of Lake Dianchi Caohai. The results show that the prediction accuracy of the water quality prediction model based on HHO-SVM is higher than that of the SVM based on genetic algorithm (GASVM) and the SVM based on whale optimization algorithm (WOA-SVM). It is proved that the HHO is feasible to optimize the parameters in SVM, and HHO-SVM can be used in water quality prediction.

Aiming at the impact of large-scale ecological water replenishment (four times of ecological water replenishment in Beijing section of Yongding River) on the long-term cut-off river, a MIKE 11 hydrodynamic model was established. The variation characteristics of runoff and infiltration capacity before and after water replenishment were quantitatively evaluated by scenario simulation analysis. The results show that the inflow runoff sequence of Guanting Reservoir can be divided into three stages: natural stage, human weak interference stage and human strong interference stage. During the three ecological replenishment periods from 2019 to 2020, the flow of the main section of the Beijing section of Yongding River is much larger than the ecological flow of human strong interference stage. In the autumn of 2021, the loss of permeability coefficient and leakage of ecological water supplement was the lowest, indicating that the leakage of Yongding River was significantly reduced through three consecutive years of large-scale ecological water supplement. Taking the ecological replenishment in autumn of 2021 as an example, the fitting functions of channel storage and replenishment flow, submerged area and replenishment flow, submerged area and channel storage, permeability coefficient and replenishment flow were established, which can provide some guidance for the development of ecological replenishment in Yongding River. The results of this study can effectively guide the optimization and formulation of ecological water supplement scheme in the Beijing section of the Yongding River, and provide reference for the comprehensive management of the Yongding River Basin and the exploration of ecological restoration of long-term river courses in North China.

Affected by global climate change and human activities, extreme weather events such as drought and rainfall have led to landslides and other disasters in the reservoir dam. At the same time, the impact of evaporation and rainfall on the seepage and stability of the dam slope has not been considered in the design specifications for roller compacted earth-rockfill dams. Taking an earth-rockfill dam as the research object, a finite element calculation model was established to study the impacts of evaporation, rainfall and reservoir water level changes on the pore water pressure, saturation line and safety factor of anti-sliding stability of the earth-rockfill dam. And the cause mechanism of landslide was analyzed in combination with geological exploration and monitoring data. The results show that evaporation and rainfall have a great impact on the pore water pressure of the soil within 0~2 m of the downstream dam slope. The difference between the measured water level of the piezometer and the saturation line calculated by the finite element method is less than 0.4 m. At the initial stage, evaporation improves the stability of the dam slope, but evaporation causes the surface fill of the dam body to shrink and crack continuously, providing a channel for rainfall infiltration. With the increase of the number of rainfall and evaporation cycles and the rising of the reservoir water level, the cracks continue to increase, and the local stagnant areas near the bottom of the cracks are interconnected to form a saturation zone, which leads to the instability and damage of the shallow dam slope downstream of the dam. The research results provide a scientific basis for improving the design specifications of earth-rockfill dams and the early warning of reservoir dam landslides.

In order to study the impact of the dam break of the Huiling tailings pond in Guangxi on the downstream region, a three-dimensional model of the tailings pond region conforming to the actual terrain was established with the help of GOCAD and Rhino software. In addition, PFC3D discrete element simulation software was used to simulate the state of dam break when the tailings pond runs to the final accumulation elevation +490 m, and the possible submerged range of tailings discharge and the area affected by tailings debris flow were analyzed. The results show that the evolution rate of tailings debris flow increases rapidly to the maximum value in a short time after dam break, and then decreases gradually. The farther away from the dam site, the faster the reduction of tailings debris flow evolution rate is. When the evolution time of dam break is 1 100 s, the furthest evolution distance of tailings is 1 215 m at the foot of tailings dam, the maximum width of the drainage body is 853 m, and the maximum depth is about 30 m. In the process, many sensitive points are submerged. The research provides decision-making information for early warning, personnel evacuation and flood relief of tailings pond accident.

The shear performance of heterogeneous concrete is very important. In this paper, the parallel bonding model of particle discrete element was used to simulate the direct shear test process of concrete to reveal the shear characteristic and failure mechanism of concrete. The impacts of meso parameters, such as contact modulus, contact stiffness ratio, particle friction coefficient, tensile strength, ratio of cohesive strength to tensile strength, and contact friction angle, on the results of concrete direct shear test results were studied by controlling the variable parameters. The shear deformation resistance of specimen has a significant linear relationship with the contact elastic modulus. The contact stiffness ratio has little impact on the shear test results. Particle friction coefficient, contact tensile strength, ratio between cohesion strength and tensile strength, and contact friction angle have a significant effect on the shear strength parameters. Contact tensile strength, ratio between cohesion strength and tensile strength, and contact friction angle could affact the curve form after peak of shear stress vs. horizontal displacement. This paper provided a reference for particle discrete element simulation of direct shear test of concrete specimens.

To decrease the costs associated with wave energy conversion and improve the performance of wave energy converters (WECs), a multi-float WEC that also serves as a breakwater is proposed, and its hydrodynamic performance is explored through physical model tests. The control variable method was used to investigate the free water surface, the dynamic response of the floats, and the energy conversion of the device under different PTO damping loads and wave conditions. These tests allowed for an analysis of the wave energy capture, as well as the device’s ability to prevent and dissipate waves. The test results show that the device functions well as a breakwater, with an average transmittance of 0.48 under typical test conditions, meaning that less than a quarter of the wave energy is transmitted to the rear of the device. Moreover, the device can effectively convert wave energy, with K_e exceeding 20% within the range of 0.64≤kh≤1.39 under suitable PTO loads.

In the construction of hydropower projects under the same dam site, the height of water-retaining structures is a key index affected by many factors. In this paper, the responses of three design dam height schemes of a water-retaining structure under static and dynamic superposition conditions were analyzed. The results show that although the dead weight and reservoir water pressure of the arch dam increase with the increase of the dam height, the ground motion response of the arch dam does not all increase with the increase of the dam height. In this calculation case, the beam compressive stress and arch compressive stress on the upstream surface of the arch dam increase with the increase of the dam height, the beam compressive stress on the downstream surface decreases with the increase of the dam height, and the arch compressive stress first decreases and then increases with the increase of the dam height, the forward displacement and openness first increase and then decrease with the increase of the dam height. The research results can provide a reference for the design of water-retaining structures.

The change of channel storage capacity is an important content of river evolution analysis. In the past, the section method was mostly used for simplified calculation. However, in the complex river pattern with multistage branching or tributaries, the section method often needs to be dealt with separately, and the calculation efficiency is low. By introducing the water surface width ratio of the branching channel, optimizing the distribution of the calculated area of the section at the branching point, adding the section, estimating the storage capacity of the channel in the missing section near the tributary estuary, and using the topographic method to restore the section spacing under different water levels, the calculation model of the section method under the complex river pattern is improved. The comparison results show that the calculation accuracy of tank storage capacity is greatly improved by using the above method, which can provide a reference for batch calculation of tank storage capacity under various complex river types.