本研究利用坡長20m的USLE標準試驗區,以5m寬之草帶為基本單位,分別配置於20m坡長的上坡面、中上坡面、中下坡面及下坡面,並利用地表逕流量及土壤流失量之現場實測,進行可加性及Foster and Wishmeier複合坡公式的探討。 經由可加性探討中得知,土壤流失量以上游坡長愈短而下游坡長愈長的分離組合最符合可加性原理;地表逕流量則以上游坡長愈長而下游坡長愈短的分離組合最符合。複合坡探討中可得知,在草帶的條件下,植生加權土壤流失比例公式(VWSLC)優於Foster and Wishmeier所提出的土壤流失比例公式(SLC);而估算土壤流失量,則以修正係數修正複合坡公式所估算出的土壤流失量效果最佳。經過一連串的驗證得知,本研究所提出的植生加權與草帶上、下游分別修正的做法可以解決Foster and Wishmeier複合坡公式的缺點。
When Foster and Wischmeier proposed an irregular-slope equation in 1974, a limitation was imposed due to the nature of the sediment transport process so that soil loss from slopes involved in deposition process could not be estimated. Therefore, field experiments were set up in this study on USLE standard plots with various grass location configurations along the slopes. The objectives of this study are to test the concept of commutativity and to seek alternative to release the limitation of the irregular-slope equation through field experiments. Soil loss may follow the rule of commutativity when amount of soil loss generated from short upper slope segment is added to long lower slope. Surface runoff may also follow the rule of commutativity provided that runoff from long upper slope segment being added to the short lower slope. Vegetation weighted soil loss coefficient formula (VWSLC) proposed by this study has proved to be superiors to soil loss coefficient formula (SLC) that formed the backbone of Foster and Wischmeier irregular-slope equation. Through VWSLC and proper correction factors for segments before and after grass strip respectively, soil loss estimation can be greatly improved.