This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sediment beds.It is found that the heterogeneity of the sediment exerts an influence on detailed bed topographies around the spur dyke,but does not influence the typical features of scour-deposition morphologies.The mean grain size and the geometric standard deviation of the bed sediment are two important and practical parameters in characterizing the changes of the bed morphologies and the bed compositions around the spur dyke.The sediment sorting process plays a crucial role in the grain size distribution,and the process occurs longitudinally,laterally and vertically.In the proximity of the spur dyke,the bed is generally coarsened from upstream to downstream and sand ribbons consisting of fine particles are observed.Within the scour hole,the bottom sediment is coarser than that at the top. This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke. A series of experiments are conducted with different types of sediment beds. It is found that the heterogeneity of the sediment exerts an influence on detailed bed topographies around the spur dyke, but does not influence the typical features of scour-deposition morphologies. The mean grain size and the geometric standard deviation of the bed sediment are two important and practical parameters in characterizing the changes of the bed morphologies and the bed compositions around the spur dyke. the sediment sorting process plays a crucial role in the grain size distribution, and the process occurs longitudinally, laterally and vertically. the proximity of the spur dyke, the bed is generally coarsened from upstream to downstream and sand ribbons consisting of fine particles are observed.Within the scour hole, the bottom sediment is coarser than that at the top.