Abstract: Cascade reservoirs on the upper Yangtze, after operation, will significantly change their downstream conditions, e.g. water and sediment conditions, river regime, and navigation conditions. This paper develops a 2D water-sediment mathematical model for the reach from Shuifu to Luzhou (or Shuilu reach in short) downstream of the Xiangjiaba dam. On the basis of verification, this model has been applied to calculation and analysis of riverbed scour and silting in this reach after impoundment of the Xiangjiaba and Xiluodu reservoirs, focusing on the changes in river regime and navigation conditions in some typical shoals. The results show that after the impoundment the downstream channel takes an overall scour trend, which can be demonstrated with three general changes. First, in curved reaches the flows tend to take a straightforward path though the river pattern remains curved; second, in braided reaches the branches tend to decay while the main channel to be scoured deeper, favorable to navigation, but local deposition will happen in some reaches, creating new shoals; last, the difference in elevations of floodplain and channel will be increased as a result of silting on point bars and scour in main channel, which aggravates local adverse flow patterns and deteriorates the navigation conditions in torrential shoals.