本研究於苗栗縣三義鄉火炎山一號坑進行土石流現地監測，分析2017年五次土石流事件對地形及地貌的影響。火炎山從2012年10月至2018年，整體溪床呈現淤積情形，其中上游段坡度增加，其餘區段變化則不顯著，土石流停至坡度大致落在10.8至11.8度之間。相較於2016年前的土石流事件，火炎山土石流的降雨強度與降雨延時門檻值有下降的趨勢。本研究分析2016年至2017年間八次土石流事件的雨量相關特性，歸納出土石流發生時的時雨量是影響土石流移動距離之重要因子。由三維地聲儀所得到土石流的地聲訊號，得知土石流主要頻率介於15至40赫茲之間。所測得訊號進行振幅法與脈衝法轉換，可有效降低訊號資料儲存量。使用振幅法轉換能降低背景雜訊，使土石流通過時所產生之峰值較為顯著；使用脈衝法則能大量降低訊號儲存量，但門檻值之選擇會影響對土石流發生的判釋。本研究定義火炎山一號坑，各地聲測站的土石流門檻值，測站一(Geo1)垂直向、南北向以及東西向之門檻值依序為20、50、4000 μm/s；測站二(Geo2)各方向之門檻值則均為20 μm/s。;This field study is located at the Houyenshan of San Yi, Miaoli, Taiwan, and the influence of five debris flow events on landforms in 2017 is analyzed. The whole terrain of Houyenshan has been silted up since October 2012, but only the slope of the upper reach increased, and the threshold of rainfall intensity for debris flows in the Houyenshan area declines. The rainfall characteristics of the eight debris-flow events from 2016 to 2017 have been analyzed, and the important factors affecting the moving distance of debris flows are summarized. The deposition angles for debris flows are generally within the range of 10.8 to 11.8 degrees. The ground motion velocities caused by debris flows are measured by two three-dimensional Geophones. The main vibration frequencies of the debris flows are between 15 - 40 Hz. The velocity thresholds of Station Geo1 in Z, Y, X directions are 20, 50, 4000 μm/s, respectively. While the thresholds of all directions of Station Geo2 are 20 μm/s.
