Journal of the Japan Society of Erosion Control Engineering, Vol.59,No.1,2006
Quantitative study of the area of damage and the amount of lost or trapped
timber
in a riparian forest in the Appetsu River basin caused by Typhoon 0310 (Etau).
Kenji YAMADA Yu NAGASAKA Hajime SATO Toshiyuki TSUSHIMA Tomoyuki ABE
Abstract
We estimated the damaged area of riparian forest and the volume of timber lost
from or trapped by the riparian forest in the Appetsu River basin, caused by Typhoon
0310 (Etau). This typhoon caused heavy damage in the Hidaka and Tokachi districts
of Hokkaido, Japan. Using photo]retouching software, the damage was classified
into three categories (lost, fallen, or intact) according to the color and tone
of aerial photographs taken just after the flood. About 33 hectare of the riparian
forest were lost, and 67 hectare were fallen. The area of lost forest was the
greatest along the main stream (upper]middle reach), while less area was lost
on each branch. The area of fallen forest was the greatest on the main stream
(middle]lower reach). The estimated 11,000m3 of fallen timber were trapped by
the riparian forest, which exceeded the 8,000m3 of wood lost from the riparian
forest. Therefore, in this flood, the riparian forest served as a sink for woody
debris rather than a source. Most of the lost forest was located around the center
of the inundated area, where the power of the water was likely greatest during
the flood.
Key words: Typhoon 0310, damage classification, woody debris, riparian forest
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