Suspended solids transport along the Ayase River reach is numerically simulated using a one-dimensional and one-layer model. The concept of the erosion velocity is used which is determined qualitatively based on experiments. The simulation is satisfactory under the condition of a constant fall velocity of suspended solids W sub o value both at spring and neap tides. In case of a storm runoff, in which the runoff rate is not negligible, longitudinal changes of the w sub o value with the salinity level provide a useful tool in obtaining a satisfactory simulation. However, relevant values of w sub o with the runoff scale are not now known. Under hydraulic conditions that cause a definite salt wedge to form, the simulation model cannot be applied.