THE IMPACT ANALYSIS OF THE RELATIONS BETWEEN DONGTING LAKE AND THE THREE OUTLETS OF JINGJIANG RIVER AFTER THE THREE GORGES PROJECT OPERATION

Since impoundment on June 1,2003,the Three Gorges Reservoir(TGR) began to play comprehensive roles in flood control,power generation,and navigation,etc.In order to study the changes of erosion,hydrological response,relationship between river and lake,variations in the condition of water and sediment movements in the Dongting Lake area since the operation of TGR.Hydrological and sediment observation data were analyzed systematically to understand the water and sediment in-and-out of the TGR.In addition,by applying the BP Neural network,variation coefficient and accumulation curve of water and sediment were calculated or depicted,to study the material transportation from the Dongting Lake to the Changjiang(Yangtze) River,and the variation of water and sediment within the lake.Results show that:(1) in inter-annual and inter-decadal scales,reduction of precipitation in the upper reaches of Changjiang River and the construction activities of TGR are the main factors causing variation of materials in the lake;(2) the sharp decrease of flow-in water and sediment downstream the TGR has caused siltation at the Sankou Section(the three outlets of Jingjiang River) and the demise of other two tributaries who are no longer function as a normal river; and(3) the accumulated amount of sediment in Dongting Lake in 2003—2011 is merely 2301×104 t,a 95.6% reduction of that in 1994—2002.In addition,using BP neural network could simulate precisely the amount the runoff and sediment in Dongting Lake,providing a tool for effective utilization and scientific management over the complicated river-basin system.