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, 000 m3 of fallen timber were trapped by the riparian forest, which exceeded the 8, 000 m3 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.
