摘要：In recent years, heavy rainfall leading to floods, landslides, and debris-flow hazards have had increasing impacts on communities in Japan because of climate change and structural immobilism in a changing and ageing society. Decreasing the rural population lowers the human vulnerability in the mountains, but hazards can still leave the mountain to the plains and sea, potentially carrying drifted-wood. The paper aims to measure the distribution of wood-debris deposits created by the 2017 Asakura disaster and to rethink the distribution and spatial extension of associated disaster-risk zoning. For this purpose, the authors: (1) digitised and measured the distribution of drifted-wood, (2) statistically analysed its distribution, and (3) calculated the potential impact force of individual drifted timber as a minimum value. The results have shown that there is a shortening of the wood debris as they travel downstream and that the geomorphology has an important control over deposition zones. The result of momentum calculation for different stems’ length show spatially differentiated hazard-zones, which limit different disaster-risk potentials. From the present finding, we can state that we (1) need to develop separate strategies for sediments and wood debris (2) and for wood hazards, zonation can be generated depending on the location and the size of the deposited trees that differs spatially in a watershed.
