Author(s): Naoki Fukuoka; Hiroyuki Nagano; Haruyuki Hashimoto
Linked Author(s):
Keywords: Debris flow; Driftwood; Woody debris; Numerical simulation; Sozu River; Hiroshima prefecture
Abstract: The 2018 debris flow event in the Sozu River resulted in significant deposition of driftwood in the middle reach and sediment in the downstream reach. This paper presents a numerical simulation for examining behavior of driftwood and sediment during the debris flow event. This simulation is based on a flow model which has frontal flow of driftwood only and the following main flow of sediment-water mixture with driftwood in the surface. The simulation results show that the quantity of sediment and driftwood outflow from the mountain area was about 63,000 m 3 and 1,100 m 3, respectively. The former agrees well with the result from laser aerial survey. The latter is of the same order of magnitude as the amount of driftwood deposited in the middle reach. The simulation also reveals that considerable sediment deposition in the downstream reach occurred during the peak rainfall and before the landslide. Immediately after the landslide, a larger amount of driftwood was carried from the landslide location. This caused channel blocking at the two bridges in the middle reach. The simulation method provides satisfactory result in predicting the debris flow event, although the values of all coefficients in the basic equations of the simulation were determined independently of this study.
Year: 2020