Estuarine suspended sediment is transported in a mixed nonuniform way under unsteady flows. Sediment of different grain sizes has different characteristics and transport behavior and has a different effect on the ecological system. Therefore classification and fractionization of the mixed sediment are required before the flux is estimated. A fuzzy clustering approach is applied to the classification of suspended fine-grained sediment in the Changjiang Estuary. Two populations are objectively found by considering the standard grain-size distribution statistics of each cluster. The critical grain size of ~10 &mgr;m in diameter is the size limit for cohesive sediments. A grid with equal cell areas is used to estimate fractional sediment fluxes through an estuarine cross section since this type of grid introduces less statistical error in the flux calculation. The sediment transport mechanism is analyzed. ¿ 2001 American Geophysical Union