It is of great significance for the long-term planning and allocation of Nanjing water resources to analyze the current situation of Nanjing water consumption, make reasonable prediction of Nanjing water consumption and master the future water demand. The analysis of water consumption in Nanjing from 2009 to 2019 showed that industrial and agricultural water consumption accounted for a large proportion of total water consumption in Nanjing, which played a crucial role in the change of total water consumption. The combined model of grey GM(1,1) model and Elman neural network was used to forecast the water consumption of all districts and the total water consumption of Nanjing. The results show that the grey Elman neural network model has a good prediction effect on the total water consumption of Nanjing City from 2009 to 2019. The relative errors of the forecasts were all less than 3.5%, and the average relative errors of the predicted results over the years were 1.55%; The relative error of the forecast results is less than 8.5% in the forecast of the water consumption of all districts in Nanjing in 2019. The model used in this paper can accurately predict the water consumption of Nanjing, which is of great significance to effectively control the regional water consumption and realize the principle of "four water and four determinations".

To explore temporal and spatial variations of extreme precipitation in the Rolling Hilly Region of Northeast China, a set of extreme precipitation evaluation indicators was established using the daily precipitation data from 79 meteorological stations covering the period from 1981 to 2015. The intensity, frequency and persistence of extreme precipitation were analyzed using various methods, including linear trend estimation, coefficient of variation, Mann-Kendall test, R/S analysis, and GIS spatial analysis. The results show that from 1981 to 2015, the overall extreme precipitation showed a weakening trend in the Rolling Hilly Region of Northeast China; R×1day, R×5day, R12D, R50D, and CRED decreased at rates of -0.5 mm/10a, -2.1 mm/10a, -0.2 d/10a, 0.02 d/10a and 0.03 d/10a, respectively. The inter-decade variation of the intensity index showed a state of "rise-fall-rise", and the annual change of frequency index and persistence index showed a "fall-rise" form, which increased by 12.5%-15% in the 2010s compared with the 2000s. The C_V value of frequency index R50D is 0.45, which fluctuates sharply, and the C_V value of other indices is less than 0.2, and the fluctuation range is small. R50D and CRED experienced abrupt changes in 1988 and 1990, respectively, and exhibited an increasing trend before the mutation points and a weakening trend after that. Extreme precipitation increased during the 1990s, weakened in most areas during the 2000s, and intensified in both frequency and intensity in the northern high-altitude areas of the Rolling Hilly Region of Northeast China in the 2010s, while it reduced in the Southern Regions. This study can provide a theoretical basis for formulating strategies to cope with extreme precipitation risks in the Rolling Hilly Region of Northeast China.

In order to coordinate the balance between water resources supply and demand and promote the sustainable use of water resources in Wuhan City, this paper conducts a comprehensive evaluation and simulation of the water resources carrying capacity of Wuhan based on the improved TOPSIS method and system dynamics, and realizes a combination of static evaluation and dynamic prediction. The results show that the overall water resources carrying capacity of Wuhan City fluctuates and increases from 2010 to 2020, and the overall level is in a critical state; By simulating the development of Wuhan City from 2021 to 2035, the water resources carrying capacity of Wuhan City under the conventional development model has exceeded the limit and it is difficult to maintain the demand; The economic priority model sacrifices resources and environment for economic speed up, which shows the most serious water resources; The environment-friendly model can reduce water consumption and improve the ecological environment, but the economic development is also limited to a certain extent; The integrated development model, from the perspective of coordination and balance, can achieve resource conservation and environmental protection while satisfying the steady and rapid economic development, and obtain the maximum economic and ecological benefits with the minimum water consumption, achieving the harmonious development of human and nature.

Pressure fluctuation in the flow field around a tidal current turbine is one of the key factors affecting the safe and stable operation of the turbine. To evaluate the effects of the duct and the duct-to-rotor clearance ratio δ on the pressure fluctuation characteristics of the tidal current turbine, three-dimensional transient CFD methods and slip-grid techniques were used to perform three-dimensional numerical simulations of the bare turbine and the ducted turbine with the blade tip clearance of δ=0.02D and δ=0.06D, respectively, under the optimal operating conditions (T_TSR=4). By analyzing the unsteady flow phenomenon of the flow field around the turbine, the pressure pulsation and frequency-domain vibration characteristics of the turbine under three different working conditions were obtained. The results show that the pressure fluctuation amplitude of the turbine is basically increasing from the root to the tip of the blade; The addition of a duct can effectively reduce the pressure fluctuation amplitude of the turbine; δ has less impact on the pressure fluctuation coefficient of the turbine and more impact on the vibration characteristics in the frequency domain of the pressure fluctuation; The main frequency of the pressure fluctuation of the turbine is mainly concentrated near the leaf frequency of the corresponding operating conditions. In addition, it is also found that the pressure fluctuation of turbine blade suction surface is stronger than the pressure surface, and the addition of duct can effectively reduce this fluctuation.

In order to deal with the serious problem of siltation in the main channel of the Yellow River Diversion Irrigation Area in Zuncun Village, Shanxi Province, a field water and sediment test was carried out on the main channel. The distribution law of suspended sediment in the channel, the relationship between channel flow and sediment deposition, and the sediment carrying capacity of the channel flow were explored by using the vertical suspension index and the planning solution method, so that it could express the sediment carrying capacity of the flow within a certain range. The critical suspended flow corresponding to the channel particle size was put forward. It was beneficial to prevent siltation by adjusting the flow according to the working conditions and particle size. The sediment carrying capacity formula was optimized. The conclusions are as follows: When the diversion flow is 4.46-24.52 m³/s, the sediment content in the channel is between 0.9-4.0 kg/m³, and the sediment content is positively correlated with the flow velocity. The channel flow can be properly adjusted to more than 39.6 m³/s to effectively suspend the sediment with large particle size. The correlation between the optimized sediment carrying capacity formula and the measured value of the main channel sediment reaches 0.828, which indicates that this formula can reflect the current sediment concentration to a high degree, and provide support for the design and analysis of the balance of channel erosion and deposition in the later stage.

The health of the water cycle is a key factor in high-quality regional development. The prediction of water cycle health state is of great significance to the coordinated development of regional water resources system, economic and social system and ecological environment system. Taking Zhengzhou City as a typical research area, this study constructed a DPSIR model for urban water cycle health evaluation, and analyzed the evolution process of water cycle health status in Zhengzhou from 2010 to 2020 by using entropy weight fuzzy comprehensive evaluation method. The system dynamics model and entropy weight fuzzy comprehensive evaluation method were used to predict the health status of water cycle in Zhengzhou from 2021 to 2030 under five types of comprehensive coordination type, economic development type and water resources optimization type. The results show that the health status of water cycle in Zhengzhou has been developing well in the past decade, and the indicators of per capita GDP, urbanization rate and intelligent water resources management have reached the "healthy" state. Under the five prediction scenarios, the urban water cycle reaches the state of "subhealth" or above, and under the comprehensive coordination scenario that takes into account economic development, ecological protection and water resources optimization, the water cycle health status of Zhengzhou reaches the state of " health", and this scheme is the optimal scheme. The results can provide theoretical basis and technical support for ecological protection and high quality development in Zhengzhou City.

The phased trend recognition of deformation monitoring sequences for dams can deepen the understanding of the evolution laws of deformation monitoring sequences at different time scales, which is of great significance for the safe operation and management of dams. The heuristic segmentation algorithm (BG algorithm) is adopted to identify the mutation points of deformation monitoring sequences for dams, which can effectively avoid the interference of mutation points in trend recognition. On this basis, the segmented sub-sequences are trend identified using an improved ITA method, which can retain the internal correlation of the sequences and has good applicability. The engineering case analysis shows that the proposed method can effectively identify the mutation points in the deformation monitoring sequences for dams, divide the monitoring sequences into sub-sequences with stable trends, and identify the changing trends of each sub-sequence.

The identification of key influencing factors and their critical values for the prevention and control of water bloom in lakes is of great significance. Taking Wuhan South Lake as the study area, based on hydrological, water quality and meteorological monitoring data, Pearson Correlation Analysis, Gray Correlation Analysis and Principal Component Analysis were used to screen and identify key environmental factors with high correlation with chlorophyll a concentration, and the critical values of key environmental impact factors were analyzed by the Receiver Operating Characteristic (ROC) curve method. The results show that the COD_Mn, total phosphorus, total nitrogen, water temperature and air temperature had strong correlations with chlorophyll a concentration and were the key factors for water bloom outbreak, with the critical values of 6.25 mg/L, 0.146 mg/L, 0.725 mg/L, 27.05 ℃ and 22.35 ℃, respectively. It was found that the accuracy of the ROC curve method for solving the critical values of COD_Mn, total phosphorus, total nitrogen and other environmental factors with small daily variation was better than that of environmental factors with large daily variation such as air temperature and water temperature, and the ROC curve method has a greater advantage in determining the critical values of nutrient concentrations for water blooms in lakes.

A study was performed on the stress characteristics of the urban emergency flood-control box—a new equipment made of polymer material. The finite element analysis method was used to study the stress, strain and deformation characteristics of the flood control box under different water retaining heights. The results show that the stress concentration area of the box is mainly appeared at the water retaining surface and the two sides; With the increase of the water retaining height, the difference of water level between inside and outside of box as well as the maximum stress and the deformation are gradually smaller. Compared with the ABS, LLDPE, HDPE and PP materials, the deformation of the flood control box with ABS material is relatively smaller under the same conditions. An optimization study was carried out on the scheme of the flood-control box. And the stress, strain and deformation of the optimization scheme under the same conditions are greatly improved. The maximum stress decreases from 16.09 MPa in the original form to 7.31 MPa in the optimized form, and the maximum deformation decreases from 0.78 cm to 0.13 cm. The mechanical characteristics of the box structure are obviously improved.

At present, the issue on the influence of mixed arrangement of variable and constant speed units on the load rejection transition process under the complex water delivery system with multi-units sharing multi-tunnels is scarce. Based on the transient flow theory of one-dimensional pipeline, this paper established the mathematic model of hydraulic transition process of variable-constant speed pumped storage units that four units share two tunnels in the diversion system and one tunnel in the tailrace system by using the characteristic method, and discussed the influence of the mixed arrangement of variable and constant speed units on regulation guarantee parameters under the load rejection condition by combining with practical engineering examples. The results show that regulation guarantee parameters during the load rejection transition process under the layout of two variable speed units sharing one diversion hole are safer than those under the layout of variable speed units sharing different diversion holes in the region with higher power generation efficiency.