近年來由於全球氣候異常,降雨量豐沛且強度集中,加上台灣地形陡峻、坡短流急、表土沖蝕量大,每當在颱風暴雨期間,常誘發重大的土砂災害,不但造成生命財產的損失,且耗費大量社會成本。因此,若能針對降雨影響集水區坡地之土壤沖蝕進行持續地觀察與分析,將有助於瞭解坡地表土受降雨沖蝕的影響。 土壤沖蝕應屬地域性相關之研究,現階段台灣的土壤沖蝕研究仍顯不足,缺乏全台土壤沖蝕的現地調查資料。本研究針對大安溪、曾文溪及其鄰近流域之上游集水區進行土壤沖蝕的調查及資料庫的建置;研究中配合天秤颱風事件計算現地沖蝕深度之量測,推算其土壤沖蝕量。更參照試區自然環境,運用USLE 公式推算土壤沖蝕指數,進而探討不同自然環境下,降雨對土壤沖蝕之影響。本研究亦針對試區土樣進行現地及室內土壤試驗,並參考水土保持技術規範(2012)所提出之室內試驗方法,推估各試區之土壤沖蝕指數,並經比較後選定並繪製最適合本研究範圍之土壤沖蝕指數分布圖。 結果顯示,現地試區內不論何種土壤特性,當累積雨量增加,則土壤沖蝕量亦有隨之增加的趨勢。在相同觀測期間之累積雨量下,當現地試區之坡度越陡、透水速度越快、剪力強度越低時,其相對應之土壤沖蝕量則有越大的趨勢。但表土硬度的高低似乎與土壤沖蝕量的多寡並無一致之趨勢。而以本研究之推估公式推算天秤颱風之土壤沖蝕量將有顯著之成果,但仍有部分落差。本研究亦繪製研究區土壤沖蝕指數空間分布圖,可作為估算研究範圍全區降雨誘發土壤沖蝕量之參考。
With more and more concentrated extreme rainfall events as a result of climate change, in Taiwan, mass cover soil erosion occurs frequently and leads to sediment disaster in high and precipitous region during typhoons or torrential rain storms, causing a lost to the property and even the casualty of the residents in the affected areas. To make the execution of the regulation of slope land development more efficiency, construction of evaluation model for regional landslide potential is very important. Soil erosion is one of the topics of regional research and the associated study in Taiwan is not adequate. The field investigation data of soil erosion all over Taiwan are not complete. In this study, we selected upstream watershed near the Daan river and the Zengwen river to be the study area. We calculate the depth of the field erosion for heavy rainfall events during Typhoon Tembin to estimate the volume of soil erosion. The USLE (Universal Soil Loss Equation) is employ to estimate the index of rainfall-based soil erosion under different natural environment. The index of soil erosion is also by laboratory test recommended by Technical Regulations for Soil and Water Conservation. Finally, the optimal distribution map for index of soil erosion is ploted after comparing those indexes. The results show that the volume of soil erosion increases with accumulated rainfall regardless of field soil characteristics. Under the sameaccumulated rainfall, the volume of soil erosion also increases with slope and permeable rate, but decreases with shear strength of soil. However, the volume of soil erosion is not proportional to the hardness of cover soil. The proposed empirical formula can be used to roughly estimate the volume of soil erosion caused by Typhoon Tembin. The developed optimal distribution map for index of soil erosion can be used to estimate the volume of soil erosion in research area caused by rainfall.