The problem of standard disconnection often exists in the two-level drainage mode of plain river network cities in China. As a result, when heavy rainfall occurs, the hydraulic characteristics and drainage capacity of pipe network system are affected by both rainfall intensity and water level of drainage water, making it difficult for waterlogging to discharge out. Therefore, taking the municipal drainage system and water drainage system of Suzhou Industrial Park as an example, the multi-scenario flood process simulation based on SWMM was carried out, and the analysis showed that when the river water level was between 1.70 m and 2.30 m, the main reason for the water accumulation in the study area was the insufficient capacity of the current pipe network system itself, and the river water level aggravated the water accumulation. When the water level exceeded 2.30 m and keep rising, the drainage capacity of the pipe network system decreased sharply, and the river level gradually became the main factor restricting the flow capacity of the pipeline and aggravating the degree of water accumulation. It is suggested that the maximum water level for river drainage control in the study area should be around 2.30-2.32 m. This conclusion can provide reference for urban river level regulation to improve urban drainage and waterlogging capacity.

There are some problems in construction, such as inaccurate material parameters and unclear influence of shield operation parameters on ground settlement. Based on a water-rich sand layer shield construction diversion tunnel, an orthogonal experiment is designed by setting the index of ground surface settlement, and a three-dimensional numerical simulation is used to analyze sensitivity of different material’s parameter. Mechanical parameters of materials are inverted according to the observed settlement. The subsidence lines under different excavation pressures, different synchronous grouting pressures and different speeds of the shield are calculated. The result shows that the surface subsidence is most sensitive to the change of internal friction angle of sand layer. Increasing the internal friction angle of the sand layer and the elastic modulus of the lining will reduce the settlement. The speed of the shield has a great influence on the subsidence. Increasing the speed of the shield, the maximum settlement of the surface settlement curve will increase, and the width of the "settlement tank" will also increase. The maximum settlement and the width of "settlement tank" decrease with the increase of excavation chamber pressure or synchronous grouting pressure.

In view of the complex and changeable construction site and high difficulty in construction of water conservancy safety, the risk assessment of all hazard sources is the premise of safety control of a project. The traditional LEC method has the defects of large influence of subjective factors and unclear weight of each hazard source. Based on the introduction of expert credibility, the background differences between risk evaluation subjects were converted to quantitative analysis, and the subjective impairments was modified. This paper combined fuzzy comprehensive evaluation method with traditional LEC method to establish the risk evaluation index system. By calculating every index weight factor with the modified risk values in LEC method, the risk assessment was converted from qualitative to quantitative by membership degree matrix and the defection of imprecise weight factor in LEC method was solved. Finally, a verification of Xinmeng River shows that the objectivity of risk assessment of hazard sources has been improved significantly through the modified method, which provides scientific basis for the risk hierarchical control of water conservancy safety.

To explore the temporal and spatial distribution and attribution of mountain torrent disaster risk in Sichuan Province, the spatial distribution difference and high-risk areas of mountain torrent risk during 1990-2020 were studied by AHP and cluster analysis methods, and the changing characteristic and driving reason were investigated. The results show that the risk of mountain torrent disasters increased from the west to the east in Sichuan Province. High-risk areas mostly existed in areas with dense river networks and high exposure and vulnerability, such as Meishan, Zigong, Neijiang, Ziyang, Suining, Guangan and Nanchong. From 1990 to 2020, the risk of mountain torrents showed an increasing trend in Sichuan Province. The proportion of areas with high and above risk increased from 17% to 34%. Increased risk levels were concentrated in central Sichuan, and most of them were from moderately high and relatively high risk transformed into high risk. In the past 30 years, the risk of mountain torrents has shown a downward trend in Sichuan Province, while the greater GDP and population density had changed vulnerability and disaster prevention capacity, leading to increasing risk level of mountain torrents in local areas. The results can provide theoretical guidance and practical support for forecast and early warn in flood disaster and disaster prevention and mitigation in Sichuan Province.

Conductivity is an important parameter to measure water quality. High-frequency monitoring of water conductivity plays an important role in water quality management. Due to the complexity of field conditions, equipment failure often leads to data loss. In order to improve the high-frequency monitoring data, machine learning model was used to predict the conductivity content in water body based on the meteorological and physical indexes obtained from high-frequency monitoring. The results show that the random forest regression model has the best prediction effect, with its determination coefficient R² reaching 0.996, root mean square error (R_RMSE) 1.31 μS/cm, and mean relative error (M MRE) 0.38%. The pH value contributed the most and was the dominant factor affecting the conductivity. The results are conducive to optimizing the field high-frequency monitoring system platform, improving the high-frequency monitoring data, which provides scientific basis for water quality management.

The selection of a suitable, efficient and accurate numerical model for groundwater flow is an important basis for numerical simulation work. The analytical solution of water level of seepage calculations of fully penetrating well in a phreatic aquifer was compared with the numerical solution of water level of structured conventional model, structured encrypted model and two unstructured encrypted models to analyze the degree of fit and error. The results show that the accuracy of the numerical simulation of all four models is quite good, and the average absolute error is less than 0.1, R² is greater than 0.98. Compared with the structured traditional model, the accuracy of the structured encryption model is the best, the unstructured 4-level encryption model is the second and the 3-level encryption model is the worst; The accuracy of the unstructured four-level encryption model is slightly worse than that of the structured encryption model, but the number of mesh is reduced by 90%. It is a highly applicable, efficient and accurate numerical model for groundwater flow, which improves the computational efficiency and makes up for the poor applicability of multi-point encryption of the structured encryption model.

In order to explore the cause of the flow pattern problem in the forebay of the pumping station at the diversion operating condition in Taihuzhuangyuan in Changzhou City, and find the corresponding solution, the three-dimensional turbulent numerical simulation method was used to calculate the inlet flow pattern after the prototype of the lock station and the addition of the diversion pier. By analyzing the flow uniformity and weighted average angle of the inlet section in each case, it can be concluded that the flow pattern of the forepbay is mainly caused by the large diffusion angle. The longer a single diversion pier is added to the forebay, the better the rectification effect will be. Compared with the single pier, the combined pier can weaken the recirculation region more and improve the inlet flow pattern. The research results can provide reference for engineering practice.

Aiming at the problem of sluice flow, based on the smooth particle hydrodynamics method (SPH), the boundary treatment method was improved, and the main parameters of repulsion force were re-calibrated, which can avoid non-physical oscillation with n₁=4 and n₂=2. At the same time, the comparison and selection of water replenishment modes were carried out, and it was clear that the bottom hole water replenishment mode with 3 m elevation difference in the optimal water replenishment mode can reduce the net outflow of particles from the upstream water body. On this basis, the numerical model of the flow through the gate impacting the stilling pool downstream was established, and the process of the flow from the sluice to the stilling pool was simulated. The results show that at the initial time, the maximum pressure at the bottom of the upstream water is 127.4 kPa; At the 7th second, the average velocity at the right end of the stilling pool is 7.07 m/s, at the 19th second, the average velocity at the right end of the stilling pool decreases to 1.4 m/s. Thus, the SPH method can accurately simulate the changes of flow velocity, pressure and flow pattern in the discharge process.

The selection of instability criterion is particularly important when the finite element strength reduction method is used to analyze slope stability, but a consensus has not yet been reached. Based on ABAQUS finite element software, the method of total displacement mode combined with cusp catastrophe theory was proposed to judge the safety coefficient of slope. For a classical slope case, the safety coefficient was calculated by using calculation non-convergence, abrupt change of displacement of characteristic point, plastic zone penetration and abrupt change of total displacement mode as the instability criterion, and compared with Spencer method. The results show that the new criterion has a clear meaning, is less subject to human interference, has a wide range of application, and has certain advantages over the traditional three criteria.

The flood discharge tunnel of large pumped storage power stations will be subject to high speed water flow, sand transport erosion and external water pressure during operation period, and the tunnel may suffer from local damage such as lining cracking, spalling and falling blocks, which will have a negative impact on its long-term use. Taking the flood discharge and sand drainage tunnel of the Fengning Pumped Storage Power Station as the research object, this paper firstly carried out robot-based real-time video, high-definition image and multi-parameter gas collection to realize the inspection of nearly 2 km cavern section. The defects of the tunnel were classified into structural and functional defects and graded. Then, the stability of the tunnel envelope was initially evaluated by combining the monitoring data within the tunnel for the past 6 years. Finally, numerical analysis methods were used to analyze and evaluate the forces on the tunnel envelope and lining structure under different operating conditions. The results show that the flood discharge and sand drainage tunnel has good service performance in the current state. The results of the study are of reference value for the operation and maintenance management of existing power stations and for the inspection of similar tunnels.