2022 Volume 10 Issue 1 Pages 136-144
In October 2019, a typhoon caused major damage along the Chikuma River, including the structural failure of major roads along the river and of bridge piers. To mitigate flood damage, it is useful to develop a flow pattern evaluation method for detecting high-risk river reaches against bank erosion during a flood. This study focuses on the turbulent energy distribution along the riverbank, which was increased by several flow patterns, such as secondary flows in curved channels, high velocity downstream from a weir, three-dimensional flow around a pier, and water surface fluctuations along the bank — all of which induced bank erosion. The three-dimensional flow structures were investigated using the bottom velocity computation (BVC) method for several instances of bank erosion in three rivers: the Chikuma River, which suffered riverbank erosion damage due to the heavy rainfall brought by Typhoon 19 in October 2019, and the Misasa and Seno Rivers, where massive riverbank erosion occurred due to heavy rain in July 2018. All bank erosions in the reaches in this study are found where the turbulent energy takes a local maximum.
