Analysis of design flood in middle and lower reach of the Yangtze river

The Yangtze river is a storm flood river with a distant source and a long stream,and large storm floods occur occasionally in this river basin.The stem stream of the Yangtze river comes out of the Three Gorges reach at Yichang and then flows into the middle-lower plain and river-net area.The river runs in the vast alluvial plain with river nets crisscrossing and lakes standing next to each other.In the plain area,the relations between the river and lakes are very complicated and the river dikes are high on the river's two banks.For large floods,dike failure or purposeful flood diversion and storage as well as variations in flood-regulating function of rivers and lakes made flood series observed at control stations in the middle and lower area have obvious incompatibility.Based on analyzing the flood characteristics in the middle and lower Yangtze river,a total inflow analysis method is used to analyze the design floods at main control stations of the middle and lower Yangtze river.Analysis results show that design floods of total inflows obtained by analysis are reliable,and can meet the requirement of the flood control planning.