Abstract: Analysis on the measured flow and sediment data of the middle reaches of the Yangtze River as well as the section data indicates that the adjustment of channel morphology at Shashi station is delayed to the variation of flow and sediment conditions. In order to obtain the regularity of delayed response of Shashi section, we improved the delayed response model for river evolution in the Yellow River in three aspects: 1) define the cross section area at the annual average low water level of Shashi section as the characteristic variable of the delayed response model; 2) introduce the “yearly combined flow” ;3) use the piecewise function in the iterative formula of the model. The results show that the determinant coefficient R² of delayed response model for river evolution at Shashi section is between 0.7 and 0.8.

Key words: alluvial river, river bed evolution, variations of incoming flow and sediment, delayed response, section area, Shashi station of Yangtze River