Deformation of Step-Pool Bedform by Passing of a Sediment Wave

Abstract

The data of water discharge and sediment yield monitored since 1986 at the outlet of the Kurabone basin which is a headwater of Chikuma river system were examined from the viewpoint of the passing of a sediment wave at a point of the stream. As a result, the passing process of a sediment wave was demonstrated by revealing temporal changes in response of sediment yield to peak discharge. In the last of its process, pools temporarily filled with sediment and some of boulders creating steps were moved. As a result of analysis of hydraulic conditions for the flood which caused the deformation of step-pool bedforms, it was considered that a superior mobility of the mixed sediment, which is caused by such effects of mixing as smoothing, exposure and collision, played an important role for moving the boulders creating steps.
Therefore, the passing of a sediment wave caused by a large amount of heterogeneous sediment supplied from the upstream is an important factor in deforming step-pool bedforms.