NUMERICAL INVESTIGATION OF THREE DIMENSIONAL FLOW STRUCTURES AND TURBULENCE ENERGY DISTRIBUTIONS IN BANK EROSION REACHES DURING LARGE FLOOD EVENTS

Abstract

 In October 2019, a typhoon caused major damage in the Chikuma River, including structure failures of major roads along the river and bridge piers. In order to mitigate the flood damage, it is useful to develop a flow pattern evaluation method for detecting the high-risk river-reaches against bank erosion during a flood. This study focuses on the turbulent energy distribution along riverbank, because it was increased by several flow patterns inducing bank erosion, including secondary flows in curved channel, high velocity downstream from a weir, three dimensional flow around a pier and water surface fluctuations along the bank. The three dimensional flow structures are investigated with bottom velocity computation (BVC) method for several bank erosions cased in the three rivers: Chikuma River, which has been suffered riverbank erosion damage due to the heavy rain fall brought by typhoon 19 in October 2019, Misasa River and Seno River, where massive riverbank erosions have occurred due to heavy rain in July 2018. All the bank erosions in the reaches in this study are found where the turbulent energy takes a local maximum.