Journal of Natural Disaster Science

Field Survey and Simulation of the Powder Snow Avalanches at Yokokura and Ohara, Fukui Prefecture, Japan

Masayoshi SUGIMORI
Senior Researcher, Snow Management and Construction Technology Research Center
Fukui Prefecture, Kasuga, Fukui 910-8107, Japan
Hiromasa KITAGAWA
Principal, Arado Elementary School
Inami, Arado, Katsuyama, Fukui 911-0045, Japan
Fumio ITO
Research Associate, Department of Physics, Faculty of Education, Fukui University
Bunkyou, Fukui 910-0017, Japan
Masahiro UMEDA
Researcher, Building and Repairs Section, Fukui Prefecture
Ohte 3-chome, Fukui 910-8580, Japan
and
Yusuke FUKUSHIMA
Professor, Department of Civil and Envir. Engineering
Nagaoka University of Technology, Kamitomioka, Nagaoka, Niigata 940-2188, Japan

(Received 11 June, 1999 and in revised form 6 September, 1999)

Abstract

Two large-scale powder snow avalanches damaged a wide area of Japanese cedar forests and destroyed a bridge on a forestry road at Yokokura and Ohara in Katsuyama City, Fukui Prefecture, Japan in February 1996. Field surveys and numerical simulations of these avalanches were made. The numerical model presented consists of the conservation equations for air and snow particles, a momentum equation, and an equation for the kinetic energy of turbulence. This model can account for increases and decreases in the mass of snow particles in an avalanche caused by the erosion and the deposition of the snow layer on a mountain slope. The height of each avalanche was estimated to be at least 30 m from field surveys. The speed, concentration and level of turbulence also were well simulated. The maximum speeds of the simulated avalanches are 39.7 and 50.6 m/s. Results of a numerical analysis based on the fluid dynamic model well simulates the scale and destructive force of each avalanche, the estimated respective destructive forces being 59.2 kPa for Yokokura and 53.0 kPa for Ohara.

Key words

surface avalanche, powder snow avalanche, disaster, simulation, destructive force