INVESTIGATION OF QUANTITATIVE SANDBAR MONITORING USING UAV AND SEDIMENT ANALYSIS AT BABAMEGAWA RIVER

Abstract

Large-scale flood damage was caused one after another by typhoons and heavy rains in Japan. In 2023, Japan's Akita Prefecture suffered severe flood damage due to record heavy rains. Therefore, investigating the mechanism of riverbed variation in rivers was important for flood control planning. It was necessary to understand the particle size distribution of riverbed materials in river planning and sediment outflow forecasting. However, in many cases, the grain size considered in numerical calculations was only for the surface layer because collecting sediment requires heavy labor, and it has not been studied much in the depth direction. In this study, sediment was collected from multiple locations on the sandbar in the middle reaches of the Babamegawa River, which was a class B river in Akita Prefecture. Then, the particle size analysis was performed in the cross-sectional and longitudinal directions. Sediment was collected, and changes in particle size were confirmed before and after the flood. In addition, assessing observations of sandbars using UAV were carried out to evaluate the behavior of sandbars. As a result, it was found that D50 increases or decreases depending on the scale of the flood in both the transverse and longitudinal directions. In the depth direction, changes in particle size were confirmed even at a depth of 70 cm, which was the deepest part investigated in this study.