STUDY ON THE BEHAVIOUR OF SANDBAR IN A RIVER CHANNEL AT THE BABAME RIVER

Abstract

 Local heavy rain was caused flood damage in July and August 2017, May 2018 in Akita prefecture. High water level was observed in Babame river. Recently, it was frequently happened flood damage resulting from local heavy rainfall in Japan. Babame River was the largest Class B rivers in Akita Prefecture. Left hand side bank was scouring due to this damage. It was important to grasp sandbar shape and channel condition. This study proposed to maintain channel using UAV (Unmanned Aerial Vehicle) to take aerial photographs. Because it was important that regularly grasping of actual condition in channel management. At the first, about 50 aerial photographs were taken along a river from ground to 150 m height. Then, aerial photographs were taken to overlap 80 % of the photographs horizontally and vertically. It was taken aerial photographs from September, 2017 to November, 2018. This study was chosen 5 times in case of low water level and high water level. Then, this aerial photographs captured SfM(Structure from Motion) technique. It evaluated quantitatively the relationship between the behavior of sandbar and water level. The behaviour of the sandbar formation grasped from the aerial photographs. Sandbar area, length, and width was measured in this area. In this study, evaluation of sandbar width was important to grasp constriction of the channel and erosion of sandbar in channel management.