Study On Theory And Method Of Some Key Problems In Reservoir Flood Control

For the current problems in reservoir flood safety design and operation management, several key problems are listed and studied, including the establishment of reservoir flood standard, calculation of design flood, flood spatial pattern analysis of cascade reservoirs, risk model of reservoir overtopping, optimized scheduling model of reservoir level on flood season based on allowable risk, and problems of flood handle during construction on the lower reaches of cascade reservoirs. First, the reasons of flood control standard on the high side of our country are preliminarily analyzed and some advise on how to establish the flood control standard of cascade reservoirs are presented. Then, the optimization model of design flood enlargement realized by computer is established, it makes the risk evaluation method and calculation precision of overtopping risk be improved effectively. Next, the optimized scheduling model of multipurpose reservoir with the allowable (or the affordable)risk level in flood season is established, it effectively solves the conflict between the flood control and hydropower production. At last, the influence on construction diversion of upper cascade reservoirs and uncertain factors during construction diversion are analyzed, and the calculation method of hydrologic risk during construction diversion is prensented. The study on these key problems, will enrich furtherly the theories on flood safety design and operation management of reservoir in our country, it has some significant meanings both in theory and in practice.(1) Through the comprehensive review on flood control standard development at home and abroad, the influence factors on reservoir flood standard are analyzed, the higher reasons of flood standard in our courtry is got. When using the pattern of Russia and U.S mechanically, the misunderstanding was produced, it is not change to adapt the real situation of our country, the economy is not better consided in the establishment of flood standard. The suggestions on how to establish flood standard (included series reservoirs) are given, these are two approaches, one is to degrade the standard for flood control of project by improving the classification indexes of project and buildings. The other is to degrade the flood standard directly, but keeping the classification index steady.(2) Aiming at the problems in conventional hand-work method of typical flood enlargement ,which need longer time and is arduous, even the randomicity is bigger , the flood enlargement optimization model has been established in this paper. Considering the combined hydrographs is similar to different paths that the ants find foods, the advanced colony algorithem, i.e., Ants Colony System algorithem was introduced to solve the model, and the efficiency and effects of calculation of design flood can be improved. The advantage of flood enlargement by computer can be taken all recorded floods as typical flood to gain the design flood hydrograph, so the method is safer for project.(3) In studying the design flood spatial pattern, JC method in structure reliability theory was introduced. By means of the method, the worst spatial pattern and the probability what happened can be gained, It is a new method for deriving the cascade reservoir design flood and complement some conventional methods.(4) On the basis of the usual overtopping risk model and the computation method, Latin Hypercubic Sampling method is used instead of Simple (Standard) Random Sampling method, bounded distribution density function instead of unbounded distribution density for hydrological random variables, and nonparametric density estimation was taken to estimate density function, which indeed affects the distribution feature of reservoir water level variable. The improvement above, which proved by study example, improve the computational accuracy and efficiency of reservoir overtopping risk effectively.(5) Based on the permitted risk level in flood period, multipurpose reservoir optimized scheduling model in flood period was established, the model considered not only reservoir flood safety (presented by permitted risk level) but also making reservoir impoundment as much as possible. Since the conception of risk have been presented in scheduling,the model becomes more reasonable and reservoir flood ability is adequately made use of. The study case indicated that the model have mediated the contradiction between flood control and flood benefit effectively.(6) The paper analyzed the effects of cascade reservoir on downstream construction diversion and the method reducing the flow of construction diversion is presented by regulating upstream reservoirs: one way was lowering flood standard of upstream reservoir, but may greatly increase the flood risk of upstream reservoir. The other is changing operation mode of upstream reservoir, lowering flood limited level in flood period and turning part beneficial reservoir capacity into flood control reservoir capacity consequently. The way of reducing downstream construction diversion flow by lowering upstream reservoir flood limited level, the computation of flood benefit loss and designed construction investment cost was more easier, as long as the investment saving is more than flood benefit loss, the scheme will be reasonable in economy. As for the other indexes which cannot present by currency, such as the shorter construction period, construction difficulty decreasing and so on can also be analyzed and selected by comprehensive analysis. So the second way was frequently adopted in practical construction design.(7) This paper has analyzed the uncertain factors in construction diversion and showed that the main uncertain factor is hydrologic factor. The hydrology computational function of the risk of construction flood has been given by illustrating the construction diversion of GongboXia hydroelectric plant in Yellow River's upstream and Shuhe, satisfactory results were gained. This research achievement is also used well for reference to the domestic similar cascades.