Bed Evolution of Group-bar-featured Reach Before and After Three Gorges Reservoir Impoundment

Mutual influence and interdependence of depositing bars in alluvial river are very complicated. Expressive form of the interaction varies with river boundaries and incoming water and sediment. This paper deals with evolution process of the multiple bars by example of Shashi reach, the first sandy sub-reach downstream from Three Gorges Project (TGP). Difference of bars evolution between pre-dam and post-dam and its causes are revealed through field data analysis. Conclusions show that: partial adjustment occurs on the bars taking form of enlarging-shrinking and dispersing under the new flow and sediment regime. The feature that evolution process is dominated by the Lalin sidebar, which will take form of central bar and point bar under different fluvial condition, is maintained despite of reservoir impoundment.