NATIONWIDE EVALUATION OF POTENTIAL FLOOD DAMAGE REDUCTION BY RIPARIAN VEGETATION REMOVAL IN JAPAN

Abstract

 This study aims to grasp the potential flood damage reduction effect of riparian vegetation removal in Japan. We calculated changes in flood damage before and after riparian vegetation removal through the estimation of roughness coefficients of river channels using the normalized vegetation index obtained from satellite images and the calculation of damage based on flood inundation analysis. The damage reduction rate was estimated to be 1.3% whole of Japan when vegetation was removed in river channels where Strahler's stream order was four or higher. The class A river systems with the highest damage reduction rates were the Sekikawa River system (16.3%), Tokachi River system (14.7%), Oita River system (13.6%), Tenjin River system (11.7%), and Oyabe River system (10.9%). We also estimated the damage reduction rate depending on the section of riparian vegetation removal. The result shows that the flood damage reduction effect of vegetation removal in river channels with Strahler's stream order of five or higher is approximately 80% of the flood damage reduction effect of vegetation removal in river channels with Strahler's stream order of four or higher.