坡面型土石流與溪流型土石流之地形特性

臺灣位於歐亞大陸板塊與菲律賓海板塊之交界，板塊運動造就了發達的斷層及褶皺等地質構造，地質破碎加上劇烈天氣，土石流災害頻傳。土石流依其地形可分為坡面型與溪流型兩種，近年來已有許多坡面型土石流之相關研究，但雖有地形及產狀特徵等描述，卻較少定量分析與區分土石流類型之準則，無法將其與溪流型土石流明確區分。本研究希冀能建立溪流型土石流與坡面型土石流之區分準則，並探討兩者地形特性之差異，作為爾後坡面型土石流之相關研究參考。　　本研究以集水區地形特徵觀點，探討溪流型土石流與坡面型土石流之地形特性差異。研究採用高屏溪流域2009年莫拉克颱風期間發生之土石流事件，溪流型土石流案例16筆及坡面型土石流案例47筆，建置地文因子分析資料庫，選出溪流型與坡面型土石流之顯著不同之地形特徵，進而訂定二型土石流之區分準則。而後應用判釋結果，探討溪流型土石流與坡面型土石流之地形差異。　　依據研究結果，代表性集水區流動段河道／河岸坡度比0.4，可做為溪流型與坡面型土石流之區分閾值，溪流型及坡面型土石流案例之正判率分別為93.8%及95.7%，整體正判率可達95.2%，判釋結果良好。　　綜述地文因子分析結果，坡面型土石流之集水區面積、發生區面積、流動段長度及集水區高差等三者皆小於溪流型土石流；坡面型土石流之流動段坡度（溪床坡度）較溪流型土石流陡，但集水區、發生區及流動區之平均坡度（區域平均坡度）則無顯著差異；溪流型土石流之有效集水指標較坡面型土石流小，代表溪流型土石流之發生區面積占集水區之比例較小；坡面型土石流之流動段河道／河岸坡度比大於溪流型土石流，代表溪流型土石流之地形演化階段高於坡面型土石流；溪流型土石流之流動段深寬比大於坡面型土石流，代表溪流型土石流之災前溪床槽化程度較坡面型土石流大。

關鍵字

土石流類型；坡面型土石流；溪流型土石流

並列摘要

Taiwan is located at the boundary of Eurasian Plate and Philippine Sea Plate, fractured geological fragmentation caused by more geologic structures the frequent earthquakes induced many debris flow hazards. Debris flow torrent could be classified into two types, channelized and hillslope debris flow. Many studies have been focused on hillslope debris flows in recent years, many descriptions of the geomorphology characteristics were discussed, although the quantitative analysis and the distinguish criterion on two types of debris flow were lacked. This study attempt to establish the criteria for the interpretation of channelized and hillslope debris flows, and to explore the differences of the two in the topographic characteristics. 　　The debris flow inventory used in the study that occurred by Typhoon Morakot in Kaoping River in 2009, 16 cases of channelized debris flows and 47 cases of hillslope debris flows were surveyed and established a topographic factor database. Based on above, distinguish criteria to the channelized debris flow and the hillslope debris flow were developed, and discussion on the topographic characteristics of channelized and hillslope debris flows were carried out. 　　The result shown that, the gradient ratio of river bank slope to river channel (B/C gradient ratio) of transporting section of catchment, 0.4, could be as the distinguish threshold of channelized and hillslope debris flows. In this case, the positive judgment rates of the case of channelized and hillslope debris flow are 93.8% and 95.7%, respectively. The good overall positive judgment rate 95.2% were achieved. 　　The catchment area, initiation area, length of transporting section, and height difference of the hillslope debris flow are all lower than those of the channelized debris flow. The gradient of the transport section (stream bed gradient) of the hillslope debris flow is steep than that of the channelized debris flow. Moreover, there is no significant difference in the average gradient of the catchment area, initiation area and transportation area. The ratio of effective watershed area of the hillslope debris flow is higher than that of the channelized debris flow, which means that the initiation area of the channelized debris flow has less area percentage to river watershed area. The B/C gradient ratio of hillslope type debris flow is higher than that of channelized type, which represents that the terrain evolution stage of the channelized-type flow is higher than that of the hillslope type. The depth-width ratio of the transporting section of the channelized debris flow is greater than that of the hillslope-type flow, which means that the degree of river troughing of channelized debris flow is greater than that of hillslope debris flows.