The internal contradiction between flood risk and power generation benefit can be alleviated by studying the flood season and flood limit level of reservoir.It is of great significance to adjust the floodwater storage in flood season. In this paper, based on the normal distribution theory improved fuzzy set analysis method, according to the inflow flood of cascade reservoirs downstream Jinshajiang River, the flood season is divided into stages. The flood limit water level of cascade reservoir is determined by the mapping relationship between subordinate degree and flood control storage capacity.A intertemporal sampling method is proposed to correct the staging results and flood limit water level. The research results show that the end of the pre-flood season of cascade reservoirs downstream Jinshajiang River is July 15, and the beginning of the post-flood season is September 16, and the reasonable flood limit water levels of the four reservoirs from upstream to downstream are 962m, 800m, 575m and 374m respectively. The rationality of the stage flood limit water level is tested by the flood process with different typical flood magnification. The results of the lower stages of the Jinshajiang River and the stage water level of each reservoir can improve the economic benefits such as reservoir power generation and improve the utilization ratio of flood resources in flood season to a certain extent.
In order to provide a theoretical basis for real-time flood control, reduce the flood disaster in the lower reaches of Jinsha River and the upstream Yangtze River (the section in Sichuan Province, also known as the Chuanjiang River), as well as alleviate flood control pressure of the downstream Three Gorges Project flood encounter characteristics between the lower reaches of Jinsha River and the Chuanjiang River were discussed in detail based on Copula Function Method. AIC criterion and OLS criterion were applied in the paper to evaluate the fitting effect of four Archimedean Copula function models, and Frank Copula function with the best effect was selected for the flood encounter analysis subsequently. The result shows that: the proportion of the maximum 3d, 7d, 15d, 30d flood volume of the lower reaches of Jinsha River in the composition of the Chuanjiang River increases in sequence. Frank Copula function has very small errors in the flood encounter problems of the lower reaches of Jinsha River and Chuanjiang River, with higher credibility, its calculation results are consistent with the flood encounter laws of the two rivers. The frequency of occurrence of the largest flood peak in the two rivers in different months is significantly different. The co-occurrence probability of floods with peak flow greater than 50-year flood for the two rivers is 0.15%. Therefore, by taking full advantages of the flood co-occurrence characteristics, it’s extremely practicable to reduce not only the flood control pressure of Chuanjiang River but also the downstream Yangtze with the cascade reservoir operation in the lower reaches of Jinsha River.
The flood in small basin specializes in quick confluence, high peak value, hard to forecast and serious destruction effect, and once the flood disaster happens. It will put a great threat to the safety of the lives and properties of the resident alongside the river. Rational determination of design flood peak is crucial to the determination of scale, safety and benefit of the projects such as regulation of small basin, river renovation, danger eliminating and reinforcement of dangerous reservoirs and so on. Most of the small basins in China either lack gauged flood data or the catchment area of the project is quite different from the catchment area of the hydro-station, while the rainfall (metrological) data within this basin is relatively abundant. So, rational utilizing available gauged flood data to calculate the design flood of the project place whose catchment area is quite different from the hydro-station’s and utilizing available rainfall data to figure out the design flood are becoming particularly important. The rational method, (comprehensive) instantaneous unit hydrograph, hydrologic analogy, regional comprehensive method, experience formula and some other often-used methods which are often used in the flood calculation of small basin are systematically introduced in this paper. Taking Tingxi Basin in Fujian Province as an example, the above mentioned methods are applied and verified in the four places of Zaoshui hydro-station (10.5km2), Lower dam basin of Xiamen pumping storage power station (12.1km2), Wufeng hydro-station (50.1km2), and Tingxi Water Reservoir (100.8km2), the rationality of the results are analyzed, and the difference of those methods are compared in this paper. On the basis of these things, the application scope and condition of these methods are concluded, and a set of design flood calculation methods of small basin are relatively systematically summarized.
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