The outline of the disastrous circumstances on torrential streams in Hidaka region due to the typhoon No.10, 2003 (prompt report)

Abstract

The typhoon No. 10 with heavy rainfall had attacked to Hokkaido from August 8 to 10, 2003. This paper promptly reports the outline of the sediment related disaster. The authors had carried out aerial reconnaissance and field surveillance to detect the disastrous circumstances due to the heavy rainfall. The most heavily damaged areas were Ribira River, Wenteshikan River and Bin River; upstream of the Atsubetu River, where had been extremely deposited sediment and woody debris. The results show that there were shallow landslides on the hill slopes, bank erosion, sediment yield (runoff) from gullies and temporal retention of woody debris on existing check dam basins in upper streams. In lower streams, large amount of sediment and woody debris were also deposited on the riverbed. The maximum size of woody debris was approximately sixty centimeters in diameter and twenty meters in length. The Prefectural Government of Hokkaido will carry out the emergency measures against remained sediment and woody debris. We concurrently study the totalized measures against sediment related hazards through the study committee with the forest agency.