The Influence of Bedrock Location and Soil Characteristics on Rainfall-Runoff and Large-Scale Landslides

大規模崩塌多與地質及構造條件有關，其中基岩位置即為因素之一。由於地質構造探勘，大多費時且昂貴，許多研究嘗試由降雨-逕流關係來探索地質構造。本研究使用 IRIS 模式模擬降雨、入滲及逕流過程，並預測崩塌發生之時間與規模。結果顯示，如以中間流結束時間作為指標，較能明顯區隔基岩位置與逕流之關係。模擬結果亦指出，崩塌規模主要受土壤剪力強度控制，而土壤保水性及透水性僅影響崩塌時間或崩塌機率。因此，大規模崩塌易發生於土壤摩擦角較小且土層保水性高、透水性較低之地區。本研究亦發現，即使雨場型式不同，同一坡面崩塌時，土層中的水含量幾乎相同，此特性應可作為崩塌預警之指標。Generally, the causes of large-scale landslides are related to geological conditions and tectonics,and bedrock location is one of the important factors. Since the investigation of geological structure is usually time-consuming and expensive, many researchers have tried to explore a geological structure by analyzing groundwater flow. This study uses an integrated Rainfall-Infiltration-Slope stability (IRIS) model to simulate the process of rainfall-runoff and predict the time of occurrence and the scale of large-scale landslides. The simulation results show that the bedrock location influences runoff, and the end time of interflow offers a better index for detecting the bedrock location when using runoff data. The simulation results also indicate that the soil strength dominates the scale of landslides, and the soil hydraulic characteristics only affect the time of occurrence (or probability) of landslides. Accordingly,large-scale landslides tend to occur in areas which have a lower angle of internal friction, higher water retention,and lower hydraulic conductivity. Moreover, the water contents of the soil are almost same in areas where landslides occur even if under the different rainfall patterns. That is, the water contents of soil can be used as an effective index for predicting landslides