Study On Calculation Method Of Overtopping Risk Analysis For Embankment Dam

The dam is the great wealth in the development of human society, which plays a vital role in modern society. On one hand, the water shortage situation in non-flood season can be reduced through retaining water during the flood period by reservoir, and the flood risk imposed on downstream can also be cut down with the help of reservoir regulation. On the other hand, it needs to be pointed that the existence of reservoir will bring the new risk of dam failure inevitably, especially for the embankment dam. Flood is the main reason causing overtopping accident of reservoir. Therefore, it is particularly important to conduct the study of flood characteristics. On the basis of the introduction about risk analysis, the overtopping risk for embankment dam is conducted. A new method used for calculating the value of overtopping risk, based on an improved Monte Carlo method, is proposed, and the hydrological frequency analysis method which is closely related to the calculation of overtopping risk is also studied. According to the disadvantage of these methods, a new theory for analyzing hydrological frequency is proposed. Finally, the methods mentioned above are applied in practical project taking Dahuofang Reservoir in Liaoning Province as an example. The main contents in this paper are as follows:(1) On the basis of introducing relevant theory and method of risk analysis, an improved Monte Carlo method used to calculate overtopping risk is proposed. The combined Important Sampling and Latin Hypercube Sampling method is adopted instead of the traditional Monte Carlo sampling method, which can improve the sampling efficiency, and reduce the effort of computation, in the aspect of sampling effect and convergence effect.(2) Due to the fact that the existence of random variable frequency analysis error will influence the calculation results of random variable design values, the uncertainty of frequency analysis is taken into account when studying the overtopping risk in this paper. In addition, the corresponding calculation method of overtopping risk is also given.(3) A new approach for flood frequency analysis based on the probability density evolution method (PDEM) is proposed, which can avoid the problem of linear limitation for flood frequency analysis in a parametric method and avoid the complex process for choosing the kernel function and window width in the nonparametric method. Based on basic principle introduction of PDEM, the flood frequency analysis model is established, and the corresponding solution method, as well as the detailed process of calculating design values of flood frequency, is also given.(4) The robustness of flood frequency analysis model built based on PDEM is investigated using Monte Carlo simulation, and the conclusion that the method proposed in this paper is prior to the commonly used parameter method from the perspective of robustness, is obtained. In order to further study the properties of the method proposed in this paper, the Shihmen Reservoir in Taiwan and Dalai Hydrologic Station in Nen River, are selected to have the numerical investigation. The results indicate that the flood frequency curve obtained by the PDEM has a better agreement with the empirical frequency than that of the parametric method widely used at present. The method based on PDEM is an effective way for hydrological frequency analysis. In addition, the PDEM can also be treated as the reference of parameter method when conducting frequency analysis, in order to analyze and verify the reasonability of assuming population distribution by parameter method.(4) The overtopping risk analysis is conducted with the example of Dahuofang Reservoir in Liaoning Province. Moreover, the effect of whether the uncertainty factor is considered or not, and only the flood factor, as well as that of combined flood & wind, on the calculation results are all discussed. Numerical results show that, both of wind and uncertainty have an impact on the overtopping risk values, in particular, the effect of wind is more obvious. According to the calculation results, some recommendations about regulation and operation for the reservoir are suggested, with the anticipation to increase the effectiveness and profit under the prerequisites that the safety of dam can be ensured.