Study On The Model Of Regulation Of Nansi Lake Flood And The Different Flood Water Level

With the development of the economic society, the discrepancy between service discharge and consumptive use is more troublesome in the Nansi Lake area. It has happened5severe dry lake events here since1980s, especially in2002, which was a fatal blow to the ecological system in the Nansi Lake. They aroused general concern. The precipitation is uneven distribution of time and space because it is prevailed over by monsoon climate. About70%-80%of the annual precipitation falls in one or two rain events during rainy season which normally last from June to September. Thus, the level of control for the flood hydrograph, which is caused by the one or two rain events, directly determines annual situation of service discharge and consumptive use. From the angle of flood control and management, We have insisted that it is secure when floods go into the sea for a long time, which makes insufficient water resource lost fast in rainy season. According to analysis and calculation of the runoff data for45years from1956～2000, the mean annual drain discharge exceeds1720X106m3and the water will flow away intensively in the rainy season.This study stands on the point how to mitigate the discrepancy between service discharge and consumptive use and improve ecological system in the Nansi Lake area. It comprehensively uses the methods and theories of hydrology, hydrometeorology, hydrological statistical analysis, statistical analysis of water resources and risk analysis, and develops a hydrological model composed of advent of freshet, which provides theoretical ground and technology support to increase water resource security assurance.The Nansi Lake Flood Control Model divides the nansi lake into three series lakes,which are Nanyang Ru, Dushan Hu and Weishan Hu.The narrow shallow section among the three lakes can be as two plain rivers,and a "Three Lakes Two Rivers" flood control model is established and generalized.The Nansi lake is generalized as a treelike river network, the Saint-Venant equations is used to describe the law of motion of the flood, and the four-point implicit scheme in Preissmann is choosed to discrete the treelike river network, the Nansi lake hydrodynamic flood regulation model is established, which is better to simulate the flood evolution of Nansi lake. Adjustment of Staged Limited Level of The Nansi lake divides the flood seasons of Nansihu Lake Drainage Area into three periods, which are the pre-flood season (June1to June30)、 the main flood season (July1to August20)and the later flood season (August21to September30).According to the calculation of50-year frequency of design floods Regulation into the lake, when the limit water level of the later flood season elevate from34.2m to34.5m,the flood water level will be increased from37.00m to37.07m. the limit water level plays an important role in utilizable benefit when it is raised in the later flood season, when the limit water level of the later flood season elevate from34.2m to34.5m, the fill storage ratio of non-flood season will be increased from3.70%to25.93%.Assessment the flood limit water level by using multi-objective fuzzy recognition decision completely.