Sediment discharge in the Tokachi region, Hokkaido, caused by Typhoon No. 10 (Lionrock), 2016

Nobutomo OSANAI, Mio KASAI, Shin]ichiro HAYASHI, Shin'ya KATSURA, Takahisa FURUICHI, Mari IGURA, Muneaki KOSAKA,
Takeshi FUJINAMI, Shigeru MIZUGAKI, Takaaki ABE, Masanori NUNOKAWA, Atsushi YOSHII, Katsuya MOMIJI, Yasuharu WATANABE,
Yasuhiro SHIONO, Tomoyoshi MIYAZAKI, Masayo SAWADA, Tomoya HAYAKAWA, Akira MATSUOKA, Tetsuro SAEKI, Chiaki INABA,
Naomi NAGATA, Naoki MATSUOKA and Ryoko INOUE

Soon after three typhoons (No. 7, 11, and 9) hit Hokkaido in August 2016, Typhoon No. 10, Lionrock brought a large amount of orographic rainfall on the eastern slope of the Hidaka Range from August 29 to 31, which caused substantial discharge of sediment. Nine tributaries of the Tokachi River, from the Panke]Shintoku in the north to the Totsutabetsu in the south, discharged the huge volume of sediment by debris flows and experienced bank erosion and flooding, which caused damages in residential area, railway, expressway and national highway and so on. For example, the Pekerebetsu River discharged at least 0.63 million m3 of sediment, the largest amount in approximately last 50 years. Bank erosion and flooding caused aggradation of the river bed and blockage at bridges (many drift wood were included in the sediment) and washed away several houses in the center of Shimizu Town. The sites of the substantial sediment discharge (e.g., Totsutabetsu, with the total precipitation of 530mm, and Nissho, with 367mm) coincided not with an area of the heaviest precipitation (Notsuka, with 713mm) but with granite geology. The sediment was mainly composed by granite boulder and fine material which came from gently sloping periglacial terrain.

Key wordsFHokkaido, Tokachi, Hidaka mountains, debris flow, granite