Reservoir operation rules, as an important tool to guide reservoir operation, are not only the decision-making reference in the reservoir planning and design period, but also one of the key technologies affecting the comprehensive benefits of the reservoir in the operation and management period. Therefore, based on the historical operation data of reservoirs in the upper reaches of the Yangtze River, the number of periods, early water level, inflow, outflow and current inflow were selected as the influence factors to form the input factor set combined with the reservoir operation principle and operation characteristics. Comprehensively considering the characteristics of operation data and the principle of decision tree, the end of period water level was determined as the model output and then the corresponding simulated water level evaluation index was proposed based on the reservoir regulation capacity. The correlation coefficient and mutual information were used as the correlation evaluation index of model input factors, and the tree Parzen evaluator was introduced to optimize the number of input factors and algorithm super parameters. Finally, the reservoir operation rule extraction model based on decision tree and its integrated model was established and the reservoir operation rule integrating historical operation process and expert experience was formed. The experimental results show that the decision tree and its integrated model have strong ability and applicability in the extraction and application of reservoir operation rules.

Due to the uncertainty of runoff, there are certain risks when formulating hydropower station power generation plans. In this paper, the concept of spectral risk measurement in economics was introduced in reservoir dispatch to quantify risk, and a benefit-risk equilibrium optimization model was established, which can reflect the attitude of decision makers to risk through different risk aversion coefficients and confidence values according to the actual situation of the power station. Taking the Three Gorges Power Station as an example, the results show that compared with the traditional model of maximum power generation benefit, the proposed benefit-risk equilibrium optimization model can effectively reduce the risk caused by the uncertainty of inflow in hydropower stations under the condition that the loss of power generation income is extremely small.

The reservoir flood control operation problem has the characteristics of multi-stage, nonlinear and multiple complex constraints. The research of solution method will help to improve the effect of flood control optimal operation. Differential evolution algorithm (DE) has a good effect in the application of reservoir optimal operation, but it is prone to premature convergence and fall into local optimum due to the random search strategy. In order to balance the global and local search ability of DE, this paper proposed an improved differential evolution algorithm SDE, which is used to improve the search ability by considering the differential mutation strategy of fitness ranking and to improve the development ability by random selection mechanism. The related numerical experiments verified that the SDE convergence is significantly better than that of the DE, GA, PSO, and ACOR. The results of case study show that the SDE is better than POA and DE in terms of the feasible solution, calculation time, accuracy, convergence stability and speed. The average flood-peak rate of the SDE is 0.17%-4.26% higher than the POA, and is 0.13%-1.26% higher than the DE.

The Gaoxin District and Jinshui District were selected as the representatives of the new and old urban areas of Zhengzhou to explore the evaluation indexes that affect the risk of rainstorm waterlogging in cities and the importance of each index, and a risk index evaluation system covering natural and social factors was established. The importance of each evaluation index in new and old urban areas was determined by using random forest model. The results show that for both new and old urban areas, the sensitivity of disaster-inducing environment is the most important first-level indicator. Among them, imperviousness and pipe density are the most important tertiary indicators for surface and subsurface disaster-preventing environments, respectively. The risk of disaster-causing factors is the least important for Jinshui District and Gaoxin District, and the importance of rainfall is much greater than that of rain type. The difference between the old and new urban areas is mainly reflected in the stability of disaster-bearing body, whose importance is 0.23 and 0.09 for Jinshui District and Gaoxin District. The conclusion can provide some reference for the prevention and control of rainstorm waterlogging disaster in Zhengzhou.

Aiming at the problem of urban waterlogging caused by heavy rainstorms in coastal cities, this paper takes Fuzhou City as an example and constructs a fined coupling model of urban one-dimensional drainage network and two-dimensional land surface hydrodynamics based on Infoworks ICM. The model was applied to the analysis of rainstorm waterlogging in Gutian Road area of Fuzhou during Typhoon "Lubi" in August 2021, which verified the high simulation accuracy of the model. Based on this model, the rainstorm waterlogging process in Gutian area under different recurrence periods was analyzed, and two "sponge" reconstruction schemes were proposed. It is found that increasing the pipe diameter is more conducive to improving the waterlogging situation in the study area. The study can be used to accurately calculate the process of urban underground drainage and land area water in Fuzhou City, which provide technical support for the real-time decision of flood control and drainage in coastal cities.

To further promote the construction of sponge cities, system dynamics and Morris, EFAST sensitivity analysis methods were used to analyze the regional differences in the benefits of sponge facilities in residential areas. The research conclusions are as follows: The comprehensive incremental cost benefit and economic, environmental, and incremental social benefits of Shenzhen, Beijing, Lanzhou sponge facilities in operation for 20 years accounted for 1 504.5 (69%, 23%, 8%), 352.4 (54%, 28%, 18%), and 2.0 (27%, 53%, 20%) ten thousand yuan, respectively. The sensitivity of the comprehensive benefit parameters of sponge facilities from high to low is sorted as average annual precipitation, rainwater recovery rate, economic loss caused by water shortage, etc. Among them, the rainfall and rainfall characteristics limit the benefit value of Beijing and Lanzhou. The low of water use in Lanzhou also affects the benefit value.

Influenced by terrain and construction costs, the water flow of the flood drainage ditch outside the surrounding wall of the construction project in hilly regions should be minimized as much as possible. However, the capacity of existing or planned small reservoir in the low-lying areas of mountain flood gully outside the walls of construction projects is usually small and difficult to expand, which cannot meet the normal requirements of reservoir flood control. Aiming at this kind of engineering technical problems, this paper proposes a technical scheme with the construction of a small empty reservoir for flood prevention and drainage in construction projects. Compared with the normal reservoir flood regulating system, the storage capacity in this system can be greatly reduced, and the downstream flow reduction requirements can be met. The function and design points of the empty storage capacity peak cutting and flood regulating system are elaborated in detail combined with the actual engineering cases, which aim to provide important technical support and experience for the flood prevention and drainage project of small watershed in mountain and hilly regions.

Under the background of global climate change, river flood risk assessment is of great significance to disaster prevention and mitigation in river basins. By analyzing the spatiotemporal change characteristics of floods in the Nanliu River Basin from 1960 to 2021, a flood risk assessment index system was established for flood risk assessment. The results show that the interannual variation of flood disaster in Nanliu River shows a fluctuating upward trend; 1993 was a big catastrophe year of flood disaster change; On the whole, the upstream basin, the middle river valley and the downstream estuary plain are the flood prone areas, and the flood risk shows a distribution pattern of high in the southeast and low in the northwest, which is consistent with the characteristics of historical flood data. The results can provide scientific basis for the comprehensive management of Nanliu River Basin.

Aiming at the shortcomings that traditional water weirs cannot measure the sand content of runoff and the traditional measurement methods are not accurate, it is difficult to realize online measurement in the field of dam water weirs. By analyzing the negative correlation between the sand content of the water flow of the water weir and the gray value of the image, sand volume measurement technology was proposed to automatically measure the sand content of the water flow of the weir. The test results show that the deviation between the detection result of sand content and the actual value is low, and it is a convenient, efficient and real-time determination method. The research results have certain reference value for dam seepage monitoring.

Based on the finite element method, this paper numerically analyzes the stress behavior and its adverse effects when diaphragm of dam foundation axis shifts downstream during operation, and proposes remedial measures and reference critical values. The results show that when the axis does not shift, diaphragm of dam foundation is only subjected to bending moment and produces local tensile stress, but its influence is not obvious. When the axis is shifted downstream and the offset is less than 30 cm, diaphragm of dam foundation is subjected to the combined action of pressure and bending moment, resulting in stress concentration and adverse effects. In the case of no other processing, when the axis does not shift and the offset is less than 15 cm, it can be temporarily not processed; If the axis offset to the downstream is more than 15 cm and not more than 27 cm (measured maximum offset), in the subsequent construction, the concrete base needs to be widened downstream at least 20 cm, which can reduce the tensile stress extreme of diaphragm of dam foundation and weaken the stress concentration, so as to improve the stress behavior of diaphragm of dam foundation. The finite element simulation provides a reference for the safety evaluation and treatment measures when diaphragm of dam foundation is eccentric.