Field observations of unit weight of flowing debris flows by force plate in Sakurajima, Japan

Tsuyoshi OSAKA, Eiichi TAKAHASHI, Masaru KUNITOMO, Takao YAMAKOSHI, Yukinori NOWA, Hiroshi KISA, Tadanori ISHIZUKA, Rei UTSUNOMIYA, Koji YOKOYAMA and Takahisa MIZUYAMA

This is a prompt report of the observation results obtained by new equipments installed into the Arimura river in Sakurajima, Japan for field measurements of normal stress and cross section of moving debris flow. The normal stress was continuously obtained by the force plate designed by McArdell et al. (2007). The cross sections of debris flow were continuously obtained by a laser scanner. The data obtained in a debris flow event occurring on June 21, 2012 show that volumetric sediment concentration of the debris flow was around 40% at the time of the peak flow and decreased to around 30% with decreasing flow rate. The data obtained by the equipments show that normal stress and cross sectional area of debris flow observed were considered to be precise enough because values and temporal change of the data can provide reasonable explanations to the phenomena observed through video images. The data obtained by the field observations in Sakurajima are expected to be utilized not only to improve the method to design sabo dams but also to enable us to set more appropriate parameters of numerical simulations for obtaining debris flow inundation area.