On the non-uniform sand river bed, the armor layer at the bottom of the bridge pier local scour pit will affect the maximum local scour depth of the bridge pier. Through a flume model experiment, the sediment gradation, relative coarseness, and non-uniformity of the armor layer at the bottom of the local scour pit on the bridge pier were studied. The results indicate that the median particle size of the sediment in the armor layer at the bottom of the local scour pit on the bridge pier increases with the increase of the local scour depth on the bridge pier, and its relative coarsening degree increases with the increase of the Froude number, while the degree of non-uniformity decreases with the increase of the Froude number. A formula for calculating sediment particle grading in the armor layer at the bottom of the local scour pit on the bridge pier has been proposed. The applicability and reliability of the proposed formula is verifies by the measured data.

Exerting huge economic and social benefits, the construction and operation of water conservancy projects have an impact on the ecological environment of upstream and downstream reaches. However, it is also an effective way to regulate and improve the ecological environment by rationally optimizing the water storage and release process of the reservoir and carrying out targeted ecological management of the reservoir. From the perspective of ecological flow constraints, through data investigation and analysis, the appropriate flow ranges of the Yangtze River main stream conducive to the natural reproduction of the four major Chinese carps, Chinese sturgeon and the control of estuary salt tide intrusion were determined. Then, the optimal scheduling model of the Three Gorges Reservoir was established considering the downstream ecological flow constraints. Multi-objective reservoir ecological dispatching model is emphasized. The results show that the ecological flow of the lower reaches of the Three Gorges Reservoir was basically guaranteed during the wet season from May to September, but the ecological water shortage was prone to occur in different degrees in other seasons, especially in the dry years. For the optimal scheduling, the power generation and the monthly maximum ecological water shortage rate showed a positive relationship, indicating that the two scheduling objectives could not reach the optimum simultaneously. The power generation of the optimal scheduling in a typical dry year was between 80.2 billion and 83.5 billion kW·h, and the monthly maximum ecological water shortage rate was between 24% and 48%. The optimal scheme obtained by multi-objective dispatching can basically coordinate the ecological and power generation needs. On the basis of the downstream ecological flow needs, the power generation benefits increases by 4.07% compared to the design scheme.

The regulation and storage capacity of a river channel plays an important role in the safety of drainage in polder areas. In order to study the factors related to the actual effective regulation and storage capacity of a river channel in polder areas, this paper adopts the unsteady flow model and the water balance method to calculate the regulation and storage capacity of a single river channel. The calculation results of the two methods show that the main influencing factors of the regulation and storage capacity of a river channel are the water depth corresponding to the starting regulation level, the roughness of the river channel, the length of the river channel and the cross-section morphology, etc. For the backbone drainage channel with large discharge, the actual effective regulation and storage capacity is the storage capacity from above the water surface line corresponding to the designed discharge to the maximum water level. The research results have certain reference value for the planning and design of drainage in polder areas.

With the transformation of the southwest power grid with a high proportion of hydropower into an UHV AC-DC network structure, ultra-low frequency oscillations have occurred in the power grid. According to the characteristics of the hydropower unit governor, a small disturbance model of the hydropower unit was established. The impact of various parameters of the hydropower unit governor on the system stability in primary frequency modulation was discussed by using the eigenvalue analysis method, and the power mode and the opening mode were compared. Finally, the impact of the opening mode and the power mode with AGC was studied. The results show that the parameter adjustable range of the opening mode is larger than that of the power mode, but it is more easily affected by AGC. This study lays a foundation for further research on suppression methods of ultra-low frequency oscillations.

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 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.

In order to study the characteristics of the hydraulic transition process of accidental pump stoppage before and after the pipeline optimization of pumping station water delivery system, based on the actual project, Bentley Hammer software was used to establish a mathematical model of the pumping station water delivery system with two pumps in parallel units to study the effects of the most unfavorable water hammer parameters such as water hammer pressure and unit speed before and after the pipeline optimization under different two-stage valve shutdown schemes. The results show that the maximum water hammer pressure decreased by 3.76%-8.85%, the minimum water hammer pressure increased by 4.89%-8.85%, and the maximum reversal speed increased by 1.47%-81.35% after pipeline optimization; The fast shutdown time had a significant effect on the most unfavorable water hammer parameters, and the most unfavorable water hammer parameters of the pumping station water delivery system all occurred before than before the optimization after pipeline optimization. It shows that the pipeline optimization effectively improved the water hammer characteristics and the safety of the pumping station water delivery system.

In order to enhance the real-time flood forecasting accuracy in the Linyi River Basin, a TOPKAPI grid model was developed based on the underlying surface characteristics of the Linyi River Basin. The TOPKAPI model simulation results were corrected at different lead times using BP neural networks and LSTM models. Furthermore, a stacking approach was applied, employing the Transformer model as a secondary learning tool to refine the corrections made by BP and LSTM. The results indicate that after real-time correction with the BP and LSTM models, the improvement of the simulation accuracy of the TOPKAPI model is obvious, with better correction results for shorter lead times. Following the stacking method for secondary learning, the correction results is the best, effectively enhancing the flood forecasting accuracy in the Linyi River Basin.

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.

Based on the spillway tunnel of Kangsu Reservoir Project, the RNG turbulence model and VOF model in FLOW 3D software was used to study the flow characteristics of the spillway tunnel. The flow velocity and relative energy dissipation rate under different conditions of the original design scheme was analyzed, and compared with the model test. The reliability of the numerical simulation was verified. In view of the problems in the original design scheme, such as the water-wing in the upstream transition section of the spillway tunnel, the far drive hydraulic jump in the stilling basin, and the downstream gully flow not returning to the channel, the modified scheme was proposed. The results show that the modified scheme can effectively reduce the water wing phenomenon, and can effectively reduce the downstream gully flow velocity and the riverbed scouring by adding multi-level energy dissipation, which can provide a reference for the design.