Abstract:

The water flow and sediment in Yangtze River have changed remarkably since the operation of Three Gorges Reservoir. To provide guarantee and basis for the simulation of hydrological conditions in sediment model calculation, we statistically analysed the variation of sediment in the middle-lower Yangtze River since the Three Gorges Reservoir impoundment. On this basis, we carried out detailed research on the sediment problem of hydrological year of designed frequency which is often selected in sediment model calculations and tests. We proposed the method and approach of dealing with sandy sediment in sediment model which is to deduce the sediment process of designed flood according to the relationship between flow rate and sediment transport rate. Moreover, in consideration of project safety, we proposed to take the lower enveloping curve of flow rate versus sediment transport rate as the basis of determining sediment process. Through this method, the sediment condition in hydrological year of designed frequency when sediment load decreases could be well reflected.

Key words: Three Gorges Project, middle-lower reaches of Yangtze River, sediment model, bed material load, hydrological year of designed flood frequency