|Present study discusses the formation process of present geomorphology and sediment size distributions of bed material of Seri River, Japan to identify the physical meanings of the data measured in a low water stage after six years of a large flood event. Numerical simulations are conducted to reproduce present channel morphology using a specified flood series based on 2013 event as well as on floods from 2014 to present. Planform of the channel shape, cross-sectional geometry, and lateral and longitudinal sediment size dis-tributions of bed material are reproduced well. Numerical results suggest that the present channel morphology is mainly determined by the flood event of 2013. The flood events from 2014 to present only contribute to small scale adjustments in sediment size distribu-tions of riverbed material, lateral and longitudinal channel geometry as well as channel planform.