REPRODUCTION IN FLOOD WATER LEVEL OF OPPE RIVER AND TOKIGAWA RIVER AND LOWERING EFFECT OF FLOOD WATER LEVEL DUE TO VEGETATION MANAGEMENT AFFECTED BY TYPHOON HAGIBIS

Abstract

 The flood water level was reproduced where breach of river dike occurred at the confluence of Oppe River and Tokigawa River in the flood event of Typhoon Hagibis. We compared the estimination of flood water level using a two-dimentional numerical model with roughness coefficient, and tree height and thick growth of vegetation added. The estimated flood water levels were substantially coincident with the maximum flood trace heights along the river. We showed the rise of flood water level in Oppe River and Tokigawa River with vegetation affected by Typhoon Hagibis. We also evaluated the lowering effect of flood water level due to vegetation management that was demonstrated by changing the vegetation location and the percentage of vegetation. 40% tree removal near the breach location of Oppe River is found to be the most effective way in the condition of the least tree removal area of this study.