A STUDY ON SPATIAL FLOW STRUCTURES AND WOODY DEBRIS TRANSPORT BY USING OBSERVATIONAL DATA OF DEBRIS ON EXISTING RIVER FLOWS

Abstract

In this study, mechanisms of woody debris transport and spatial flow structures on an existing river, Nukabira River of the Saru River system, were investigated by using numerical models and reexamining observational results. The results of the field observation that the number of debris were counted in each sub-region of a monitoring area during a flood event in 2010 show that locations of highly concentrated areas of woody debris vary widely in response to the discharge and the debris size. The particle based numerical model of woody debris was additionally applied in order to investigate the details of the debris motions. The results of the calculation show that the woody debris concentrated to the regions where the vorticity was relatively low in the existing channel. The results also imply that the inertia of debris is one of the important issues, in particular in the cases where the discharge and the size of debris are small, because it determines the responsiveness of woody debris motions to small flow structures which was generated by the exposed incised channels.