Debris flows running from mountainous gullies are often with destructive high velocities, large buried depth and great number of coarse particles and may cause serious slope disasters. By analyzing the geophone and acoustic signals, real-time CCD images and the rainfall data in the gully 1 catchment at Houyenshan, Miaoli, one
can classify the debris flow into two different flow patterns such as viscous debris flows and diluted debris flows based on their flow characteristics. This paper studies the rainfall-induced debris-flow event on May 22, 2013. The multi-temporal digital elevation model produced by airborne and terrestrial LiDAR was also adopted to map the location of wave surge and nature levees after debris flow events. Frequency distribution of surface runoff is higher than that of debris-flow events. The frequency spectrums of surface runoffs are 30 to 45Hz, while the frequency spectrum of debris flows are 10 to 32Hz. Through verifying both geophone and acoustic monitoring systems by the CCD images,it can be concluded that the signals of geophone sensors, by frequency spectrum analysis and judging signal duration and their amplitudes can be regarded as the basis of debris-flow warning system.
Key Words : Debris flow, Houyenshan, rainfall, natural levées, geophone signals.