;The in-situ monitoring of debris flows in Hoyenshan,Miaoli,Taiwan was performed in this study by exploring the events of May 28, 2015 and several sporadic small debris flows then after. The debris-flow event in June 13, 2016 with a maximum flow height of 2 m, and its ground vibration frequency is within the range of 30-40Hz. According to the CCD images, particle sizes and then flow velocities, the flow type can be categorized into the gravelly debris flow. Most of the debris flows were triggered by short rainfall. The study found that the rainfull threshould for Hoyenshan debris flows has been declining in recent years.
