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.

Aiming at the shortcomings of insufficient population diversity, easy to fall into local optimum, and slow initial solution speed of intelligent water drops algorithm (IWD), an improved IWD algorithm (IIWD) was proposed, which introduces the Logistic chaotic initialization method and the differential variation operator of the difference evolution algorithm (DE), and improves the neuronal update mode of the self-organizing mapping algorithm (SOM) and introduces it into the sub-update process of the optimal individual of the IWD algorithm. The IIWD was applied to the peak shaving scheduling of cascade reservoir groups. Compared with IWD and DE, the efficiency of the IIWD was verified.

Taking the upper reaches of the Yangtze River at Guangyang Dam as an example, a physical model was constructed to analyze the changes of water depth and flow field in the corresponding river section before and after the implementation of the continuous pool-riffle type natural habitat restoration technology scheme. And then the effects of the habitat restoration scheme on fish spawning grounds, habitats, overwintering activities and waterways were discussed. The study show that after the implementation of the habitat restoration scheme, the area of the slow flow area in the test reach increased significantly, and a local slow flow was formed between the group of spur-dike, which was conducive to fish spawning and habitat; The implementation of the scheme did not adversely affect the vessel traffic in the channel of the river.

Based on the chloride ion diffusion model and aggregate gradation theory, the mesoscopic model of recycled concrete random polygonal aggregate was constructed using PYTHON and COMSOL. The validity of the model was verified by the existing experimental results. The calculation and analysis of the chloride ion erosion resistance of recycled concrete under different working conditions such as the diffusivity of new and old mortar, the thickness of old mortar and the replacement ratio of recycled aggregate was carried out. And then the diffusion law of chloride ion in recycled concrete and the influence law of critical factors on the chloride ion erosion resistance were studied. The results show that the simulation results are close to the experimental values, and the method can better simulate the diffusion of chloride ions in recycled concrete. The relationship curve between chloride concentration and depth shows discontinuous characteristics. With the increase of diffusion coefficient of new and old mortar, the chloride ion content increases gradually. The chloride ion erosion resistance of recycled concrete decreases with the increase of the thickness of old mortar and the replacement ratio of recycled aggregate.

In order to study the sponge urban transformation scheme of existing communities, taking an existing community in Hongshan District of Wuhan as an example, a SWMM rainfall-runoff model was established. Different LID combination schemes were determined according to the feasibility analysis of site conditions, space requirements and underlying surface characteristics. The runoff control and pollution load of each combination scheme under different recurrence periods in the study area were simulated. The simulation results of each combination scheme were analyzed from the ecological, social and economic aspects. The results show that the ecological and social benefits of biological retention facilities were high. The combination of LID facilities for laying infiltration trench, vegetative swale and biological detention facility has the best effect on runoff control, flood peak and pollutant reduction in the study area, and has good social and economic benefits, which is the best scheme.

In view of the serious cavitation erosion and local cracks of water turbine runner after the capacity expansion and transformation of four runners in Shangyoujiang hydropower station in 1998, JF3057 turbine runner with excellent hydraulic performance was developed through numerical analysis and optimization design in 2017 for the innovation of unit ^#2 of the power station. The measured results of the prototype turbine after innovation show that the new runner has greater output and higher efficiency, and the vibration and the shaft runout are normal, but strong noise and metal roar within a certain load range exist in the turbine. In 2018, the strong noise and metal roar were basically eliminated after the blade outlet edge modification. After 5-year operation test and periodic inspections of the runner, the cavitation phenomenon of the new runner has been greatly improved, and the transformation of No. 2 turbine has been successful.

Analyzing the dynamic evolution and current situation of development and utilization of water resources is of great significance to the sustainable development and protection of water resources. The data of 1997-2020 water resources bulletins of 10 water resources zones, including Songhua River, Liao River, Hai River, Yellow River, Huai River, Yangtze River, Southeast China, Pearl River, Southwest China, and Northwest China, were selected to analyze the dynamic evolution of water resources and the current situation of development and utilization in these zones by using Kendall rank test. The results show that there are spatial differences in the dynamic evolution of water resources in China with the Yellow River region showing a highly significant increasing trend, the Songhua River basin showing a significant increasing trend, the Huai River basin showing a non-significant decreasing trend, and the rest of the basin showing a non-significant increasing trend. The Songhua River and Yangtze River basin show a weakly significant increasing trend, while the Liao River, Hai, Huai and Southeast rivers basin show a non-significant decreasing trend; The other water resources basin all show a non-significant increasing trend. The proportion of surface water is the largest, groundwater is the second largest and other water uses is the smallest. The water consumption of agriculture and industry in China's water use structure is on a highly significant downward trend after 2013, which corresponds to an increase in the efficiency of water use in agriculture and industry, a stable level of water use in domestic use and an increase in ecological water use year by year.

In view of the problem that hydraulic concrete buildings in cold regions are vulnerable to early freezing injury during pouring construction and may affect the later healthy service, in order to study the strength damage law of early frozen concrete and optimize its ratio, Box-Behnken (RSM-BBD) response surface method was used to optimize the experimental design. The RSM response surface model was established by taking water binder ratio, fly ash content and air entraining agent content as variables. A GA-BPNN strength prediction model was constructed to predict the strength of early-frozen concrete accurately. Compared with the RSM model, the results show that the GA-BPNN has more accurate prediction performance and can optimize proportion design more efficiently. The goodness of fit R² and average relative error e_MRE by the GA-BPNN strength prediction model are 0.998 5 and 2.13%, respectively. The relative error between the predicted value of the optimal strength ratio and the experimental value is about 1%. The application of GA-BPNN strength prediction model can realize the efficient optimization of concrete freezing strength and its ratio.

In order to illustrate the influence mechanism of flow distribution on slope of urban asphalt road, two-dimensional shallow water equations were applied to simulate runoff characteristics on asphalt slope. Comprehensive sensitivity analysis was performed on multiple factors (cross slope, longitudinal slope, slope width, slope length, rainfall intensity and roughness coefficient) which caused different degrees of ponding on asphalt slope. The maximum flow depth was taken as the sensitivity analysis index. Both range and variance analysis were performed, through which the sensitivity ranking of the influencing factors were obtained and the significance level can be clarified as well. The results show that under overflow drainage condition, cross slope, pavement width and rainfall intensity have significant effects on flow depth; Slope length has no significant effect on flow depth. Flow depth is negatively correlated with cross slope, and positively correlated with rainfall intensity, pavement width and slope length, and negatively correlated first and then positively correlated with the roughness coefficient. The research results can provide reference for engineering practice.

With the development of the city, the contradiction between urban water supply and spring protection has become increasingly prominent, and the groundwater resources must be developed reasonably under the premise of ensuring that the spring water is not affected. Monthly rainfall and water level data of Botu Spring Group from 1990 to 2005 in Jinan area were selected to analyze the characteristics of rainfall recharge and the lagging response of water level in spring area to precipitation by statistical method. When the average of three-point movement of precipitation starts to correlate with water level in spring area, the average of ten-point movement of precipitation has the strongest correlation with water level in spring area. The current spring water level is closely related to the comprehensive rainfall in the first ten months. After ten-point moving average treatment of precipitation, through comparative analysis of groundwater exploitation data in urban area, east of Jinan and west of Jinan, it is proved that water level in spring area is closely related to groundwater hydrology unit in urban area and west of Jinan, and there is no hydraulic connection with groundwater hydrology unit in east of Jinan, so groundwater unit in east of Jinan can be reasonably exploited.