本研究為探討2009年莫拉克颱風期間，高雄旗山溪與荖濃溪流域內土石流災害之降雨、地質材料，以及地形等3項因子特性，以及其工程地質特性與發生機制，針對研究區域內廬山層、桂竹林層，以及南莊層三個不同案例之土石流事件進行現場地質及地貌的調查、地質材料試驗、影像判釋，以及降雨資料分析。 從現場調查結果顯示，廬山層土石流事件，以及南莊層土石流事件之主要地質材料來源為發生部中，由山嶺延伸至河道的大型崩塌地，大量的崩塌土石進入到河道後，與河道中逕流混合後順流而下，形成土石流。桂竹林層土石流事件沿線發達之不連續面，與坡面形成平面與楔型破壞幾何模狀，崩積物進入河道中，再加上河道中之水流沉積物，以及前次土石流所殘留之堆積物，便成為該區土石流的主要土石來源。從坡體上各崩塌地的分布結果可以發現，約有51.0 %的崩塌屬於涵蓋範圍從河道至山嶺的大型崩塌地，其次為靠近河道處的崩塌地約佔32.4 %，顯示當集水區內的崩塌地，大部分都分布在接近河道的位置上時，崩落的土石容易受到雨水的沖刷被搬運至河道中，成為土石流發生時所需的地質材料。 地形分析結果顯示，當集水區面積越大、河道長度越長，且平均海拔高度越低時，河道搬運堆積物的能力較強，土石流中之地質材料，來自河道沉積物的比例越高。此外，當水系密度以及面積高度積分值越高時，集水區內之侵蝕作用越旺盛，因此集水區內崩塌率也越高，由崩塌直接提供土石流地質材料比例越高。 地質材料試驗結果顯示，當岩石強度越低且單位體積節理密度越高時，溝谷的地質材料供應速率越大，在暴雨事件時，邊坡易發生破壞而使地質材料進入河道中，成為土石流的地質材料來源。 從降雨資料顯示，當有效累積雨量大於1100 mm或是降雨強度大於50 mm/hr時，本研究之三個土石流事件的集水區內便可能發生土石流。
This study is aimed to investigate the rainfall, sedimentological and morphological characteristics of debris flow occurred in the catchments of the Chishan river and Laonong river during 2009 Typhoon Morakot, and the links between engineering geological characteristics and triggered mechanism of debris flows. The study methods include field geomorphological investigations, satellite images, geomaterial testing and rainfall analysis of three debris flows occurred in the Lushan Formation, Nanchuan Formation and Kueichulin Formation. According to the interpretations of the satellite images and field investigations, landslides located near the river and expanded to hilltop in the source area of debris flows in the Lushan Formation and Nanchuan Formation become the main source of geomaterial when the debris enter the channel and cause the debris flow. The rock discontinuities is well-developed in the transportation area of debris flow in the Kueichulin Formation, formed various types of failure models, such as dip slope and wedge failure, which provide a large volume of deposited materials. The deposited materials, river sediments, deposited materials left by the former debris flow and the geomaterial which eroded on the both sides of valley while the debris flow occurred, have become the main geomaterial source of the debris flow. About 51.0 % of the landslides located near the river and expanded to hilltop and about 32.4 % of the landslides located near the river. Consequently, more deposits were transported into the river during the typhoon and become the triggering factor of debris flow occurrence. According to the morphology analysis, the big area of catchment, long length of river, and low elevation may be corresponding to the high sediments transport ability; therefore, the portion of geomaterial which comes from river sediments in debris flow would be higher. Furthermore, the higher the drainage density and hypsometric integral, the higher the landslide ratio will be; therefore, the portion of geomaterial which comes from landslides would be higher. The experimental results show that the low strength of rock and high number of discontinuity per cubic meter may induce the high geomaterial recharge rate. While during storm events, failure is easy to occur on slope, bringing the geomaterial alone to the channel, and become the main source of the debris flow. The result of rainfall analysis demonstrated that when the regional rainfall intensity surpass 50 mm/hr or the cumulative rainfall exceed 1100 mm, debris flow may be induced.