RELATIONSHIP BETWEEN THE EROSION OF VEGETATION AND THE CHANNEL EVOLUTION IN THE OI RIVER

Abstract

In this paper, the relationship between the channel evolution and the vegetation washout during a flood event in a braided stream was studied by using the spatial data that was obtained by the operation of an Unmanned Aerial Vehicle (UAV). The study site was the downstream region of the Oi River where the fully developed braided stream has long been observed. In this region, a relatively large flood event occurred on October 23, 2017. The vegetation regions on this site were evaluated before and after the event in order to extract the specific regions where the vegetation was vanished after the flood. By using Digital Surface Model (DSM), the vanished regions of the vegetation were classified into the two classes, one is the covered by the bed material, and the other is the eroded by the channel migration. The results show that the thickness of the bed materials was relatively small on the regions where the vegetations were covered. On the other hand, the higher vegetations were only vanished on the eroded regions. By comparing the locations of these eroded vegetation regions to several longitudinal profiles of low water channels, it was implied that the step-pool-like structures may provide more possibility to yield the lateral channel migration in the braided stream.