| Poyang Lake water level is suffered from the dual impact of five rivers(Gan River,Fu River,Xin River,Rao River,Xiu River) and the Yangtze River. The five rivers flood season generally is in March to July, the main flood season is in April to June, and the Yangtze flood season often is in May to October. Poyang Lake water level gradually increase with five rivers flooding into the lake, but only five rivers are in the flood, Poyang Lake water level generally is not the highest level for the year. Fiver rivers water supply reduce in July to September, but mainstream of the Yangtze River entered the main flood season. Poyang Lake is maintained in a hight level by Yangtze River, as a result,the water level rises rapidly. According to the material statistics 1991-2007 year on Hukou station, the year maximum high-water all appears in July in the year of the Hukou station water level to be higher than 20.00m.Therefore, Poyang Lake year maximum high-water is mainly controlled by the Yangtze River flood.Based on the ready-made research results,this paper,according to the initial period movement plan of the Three Gorges Reservoir,applys the establishment flood evolution model and simulates the variation of the Poyang Lake water level and discharge after the running of Three Gorges Reservoir. Analyzing the Poyang Lake flood level frequency and the chang tendency of the Three Gorges Reservoir running,which provide the safeguard for the Poyang Lake area economical development and the science flood prevention for the middle and lower reaches of the Yangtze River.This article main research content is as follows:(1) Collecting the yearly maximum water level data from 1950~2007of Hukou station,and the dayly water level and discharge materials in 1991-2007,which are analysist to the serial of the maximum water level and the monthly maximum water level in May and June yearly. And arrive at the Poyang Lake flood frequency at present,applying the P- III frequcency simulation and analysis curve;(2) According to the characteristic of the middle and lower reaches of the Yangtze River,establish the Great Lake Flood Evoluton Model,divising 4 computing element in Yichang to Hukou: Yichang to Shashi, Shashi to Chenglingji, Chenglingji to Hankou,Hankou to Hukou. And makes simplification processing to the Yichang to Hukou's branch,only considered the big branch the influence,the Yichang to Shashi section only considers Qing River's inflow and Songci and Taipingkou's outflow;The Shashi to Chenglingji section only considers the Xiang River, Zi River,Yuan River and Li River of the Dongting Lake;The Chenglingji to Hankou only considers Hanjiang River's influence;The Hankou to Hukou section only considered the Gan River, Fu River, Xin River,Rao River and Xiu River's influence;(3) According to the operation plan of the Three Gorges Reservoir in the initial period,simulate the change of the water level in Hukou station,based on the accumulation and release process,applying the flood evolution model in middle and lower reaches of the Yangtze River.Statistics the serical of the maximum water level and the month maximum water level in May and June year after year,and obtains the high water mark change tendency influence in Poyang Lake flood season and the month maximum water level chang tendency influence in May and June of the Three Gorges Reservoir in the initial period using the P-III frequcency simulation and analysis curve;The result indicated that,the maximum water level change influence value in Poyang Lake is 0-0.7m of the Three Gorges Reservoir movement in initial period,the average is 0.12m.And enlarge the frequency in Poyang Lake flood season high water mark -20.00m ,by 25% increases to 43.5%.The running of Three Gorges Reservoir in initial period,affected the monthly maximum hight water level,most seriously is in May. The affected scope is 0.02-1.63 m,with average of 0.85m.The affected scope in June is from 0.02-0.93m,with average of 0.45m.
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