STUDY ON THE BEHAVIOR OF SANDBAR IN A RIVER CHANNEL AT THE BABAMEGAWA RIVER

Abstract

A flood disaster was frequently happened resulting from local heavy rainfall in Japan.Many farmlands and housing were damaged terribly in 2017 and 2018. A high water level was observed in the Babamegawa River which was the largest Class B river. The embankment on the left bank at Babamegawa River was collapsed owing to scouring was caused by a sandbar at the downstream side. Like this, streamflow was greatly influenced by a sandbar, so it was important to understand the behavior of the sandbar. However, only one percent of rivers were conducted Periodic Vertical and Cross-sectional Survey while all Class A river were conducted measurement mainly because there were too many Class B river to measure. In this study, it was carried out that investigation using UAV to manage rivers easily. The Sandbar was taken the photographs from 150 m above the ground from September 2017 to November 2018 and The sandbars’ area, length, and width were calculated with SfM (Structure from Motion technique). These data were investigated sharply when the water level was decreased below ordinary. Moreover, it was important to remark the width of sandbar as a contraction of channel and loss of sandbar were needed to grasp for river management.It was found that the embankment was broken to slip by losing base performing the numerical calculation.