One dimensional bed deformation model is very useful in obtaining long�]term and long�]reach bed deformation characteristics. However, sediment discharge will be underestimated by assuming a rectangular cross�]section. Furthermore, when cohesive material is exposed at scoured areas in rivers, erosion of bed tends to be suppressed. Sediment transport rate is also suppressed on bed composed of cohesive material. In the present study, in order to improve the estimation of the sediment transport rate, the model that we suggest here does not assume cross�]sections as rectangular shapes; the bed elevation change is considered in the transverse direction but the water surface elevation is constant in the transverse direction. Furthermore, sediment transport and bed deformation characteristics on bed composed of cohesive material are discussed with attention focused on sediment sorting, based on the results obtained from numerical model of bed deformation and the model is applied to the Tonle Sap River in Cambodia. The results show that the change in sediment discharge with bed configuration is calculated automatically using the suggested model. The sediment discharge obtained by the suggested model is greater than that using a rectangular cross�]section model. Furthermore, the transverse change in sediment size has been reproduced by considering the sediment transport width change. The temporal change of sediment size distribution on bed with cohesive material is faster than that on bed with non�]cohesive material, because sediment is transported to downstream area without bed erosion process.

Key words�Fgeneral cross�]section, cohesive material, non�]cohesive material, one dimensional bed deformation analysis, Tonle Sap River