Relationship between variation of sediment carrying flows and readjustmentof riverbed in the lower reaches of Yellow River

Alluvial river possesses the capability of self-adjustment conforming the variation of runoff, sediment and river boundary conditions. Remarkable changes occur to the lower reaches of Yellow River since 1986,such as the reduction of flood peaks and reduction of occurrence frequency of effective floods. Since then the River is under the long-term action of small discharge. In this paper, the characteristics of the flow-sediment variation and the corresponding adjustment of riverbed shape are studied based on the observation data. It is found that the silting or erosion of the river is closely related to the annual average incoming sediment coefficient(ratio of sediment concentration to river discharge). When the annual average incoming sediment coefficient is less than 0.015, the river reaches the critical state in which deposition will not take place. So that it is very important to provide a certain incoming discharge for forming the reasonable shape of river channel by means of the optimized operation of Xiaolangdi Project. The configuration of riverbed must consist of main channel and flood plain.