土壤沖蝕研究乃一地域性極高的科技,在臺灣地區土壤沖蝕試驗研究成果仍然不足,缺乏現地土壤沖蝕指數(Km)調查資料。經濟部中央地質調查所(Central Geological Survey, MOEA)委託財團法人成大研究發展基金會防災中心,從民國 96 年開始,對臺灣地區易淹水地區上游集水區地質調查及資料庫的建置,在高屏地區不同土壤設置 19 處研究試區,觀測土壤受降雨沖蝕的情形,從民國 98 年至 100 年 5 月止,共觀測 112 筆資料進行研究與分析。以研究試區所採取土壤,依水土保持手冊試驗方法,配合由現地量測之沖蝕深度,利用 USLE 公式反推得到推估的 Km 值,與水土保持手冊查表值和盧光輝依據USDA土壤質地分類所訂定值比較,探討 Km 值的適用性與通用性。從結果得知,在五級坡以上之試區無法適用 USLE 公式估測沖蝕量;相同土壤質地之土壤沖蝕指數差異性甚大,只能做為附近無調查試區或無查表 Km 值時之參考值;進行現地觀測時,設置試區初期累積雨量(小於 1000mm)的調查數值,由於表土受到擾動,不宜列入分析。現地量測土壤沖蝕量顯示以 USLE 公式套用目前慣用的Km 值可能高估坡地土壤沖蝕量,此結果可能與臺灣的強降雨、高陡坡及年輕地質等區域特性有關。依本研究的分析結果,沖蝕樁觀測時間至少應達2 年,使各相關因子已可達到明顯的關係;土壤沖蝕指數可設定一區間而非單一數值估算土壤沖蝕量。
Soil erosion is highly regionalized technology, and soil erosion tests and the relevant researches in the Taiwan are still insufficient to verify the local data. The Institute for Research and Development Foundation, Disaster Prevention Center, National Cheng Kung University, has been commissioned, since 2007, by the Ministry of Economic Affairs to conduct geological survey and establish database for upstream watershed of the areas being prone to flooding in Taiwan. 19 research sites containing different soil types were set up in the Kaohsiung-Pingtung region. From 2009 to May, 2011, totally 112 data sets of soil erosion relating to rainfall were observed and analyzed. Soil samples collected from the 19 sites were processed based on the method regulated in the water and soil conservation manual. The Km values of the 19 different soils, cooperating with the erosion depths measured in-situ, were inversely calculated by use of the USLE equation. The study then investigated the reasonableness of Km values of different soils by examining the disparity among the calculated, the tabulated in the soil and water conservation manual (SWCM), and the designated, suggested by Guang Huai Lu on USDA soil classification basis, Km values, The results revealed that USLE formula is not applicable for estimating amount of erosion on 5th grade or steeper slopes in the test areas. Soil erosion index could diverse greatly in same soil type, and can only be used as reference for nearby regions without tabulated Km values. While conducting in-situ observation, the initial accumulated rainfall (less than 1000mm) in the test area should be excluded in the analysis due to disturbance in top soil. The measured amounts of soil erosion suggested that the USLE equation using the SWCM and Lu’s Km values tend to overestimate the erosion. The overestimation may be due to heavy rainfall, steep slopes, and young geology in Taiwan. This study results show that erosion observation should last at least 2 years until all relevant factors can achieve a clear relationship. Soil erosion index may be located in an interval instead of a single value to estimate the amount of soil erosion.
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