Abstract:It is easily to develop a landslide or debris flow in mountain area because of the earthquake or the rainstorm. After the disaster, a large congeries can often be formed in the river bank，which can cause large influence on sediment scouring and deposition in the river reach. Based on the movable bed experiment and some results gotten from fixed bed experiment, the relationship between river bed deformation and velocity distribution was studied. The range of the scour and deposit area and the position of the maximum scour pool according to different inflow condition and different dimension of congeries were analyzed too. It was found that the main conclusions are as follows：The scour area would appear at downstream the edge of the congeries，and the deposition area often appear in the recirculation zone downstream the congeries. The range of the scour and deposit area would increase with the increasing of flow discharge. The bed deformation around the congeries was caused by the contraction and turbulence of flow near the congeries，and the maximum scour position was influenced mainly by flow expansion and adjustment. The maximum scour and deposit position mainly influenced by inflow condition，but the distance between the two positions was mainly affected by the size of the congeries.