HYDRAULIC CONDITIONS AND MECHANISMS OF WOODY DEBRIS JAM ON RIVER CHANNELS ON HOKKAIDO HEAVY RAIN DISASTER IN 2016

Abstract

In this paper, the relationship between the hydraulic characteristics of river channels and the existing hypothesis of mechanisms of woody debris jam was evaluated by using the GIS analyses on the field observation and the numerical calculation results of the Hokkaido heavy rain disaster in 2016. The target regions were the confluence of the Satsunai River and the Tottabetsu River and the upstream region of the Otofuke River. The intensive field surveys of the geometries of river channels and the debris jam were executed on these sites, in which the aerial LiDAR systems or the on-site observation were applied. These high-resolution geometries and the exact distributions of the locations of debris jam were applied to the GIS, and the relationships between the information and the numerical results of the flow are quantitatively examined. The results confirmed the hypothesis of the existing study, in which the flow velocity around the water surface is the important factor of the transport of woody debris into the underwater.