PRACTICAL DEVELOPMENT OF A RISK EVALUATION METHOD FOR EROSION TYPE LEVEE BREACH BASED ON THE EXISTING RIVER CONDITIONS ~ CASE OF DAMAGE IN THE CHIKUMA RIVER IN THE OCTOBER 2019 FLOOD ~

Abstract

 A risk evaluation method for erosion type levee breach based on understanding the existing river conditions was proposed. The method was developed for 97.5 to 106.5 km of the Chikuma River, which suffered a left bank levee breach during the Typhoon No. 19 flood in 2019. The risk evaluation was conducted using the information available prior to the 2019 flood, and the levee breach area, which was located on the opposite bank of the attacking point of river flow before the flood, was detected as high risk area. The practical issues found in the process of developing the method were systematically organized in a series of flows leading to the evaluation results, and the constraints for solving each issue, the target level required for technological development, and the necessity of acquiring river channel and structure data that affect the risk evaluation in practice have been concretely presented.