Abstract

The characteristics of the soil topography are usually influenced by the distribution of rainfall in typhoon season, steep terrains and fragmental geology; as a result, severe soil erosion often occurs in Taiwan. The aim of this study was to evaluate the relationship between the rainfall event and soil erodibility factor by collecting fifty nine measured erosion data from nineteen experimental sites among the six main rivers in the southwestern part of Taiwan. Three methods were employed to estimate the soil erosion factors; soil and water conservation design, soil test and regression with in-situmeasurement of erosion. The test results showed that the soil erosion factors (SEFs) of Southwestern Rivers ranged from 0.015 to 0.03. The SEFs obtained using the soil tests were smaller than the SEFs from the soil and water conservation design specifications. For the SEFs of the five soil types (clay, silty loam, silty clay loam, very fine sandy loam and sandy), the result obtained from the test exhibits a wider range between 0.016 and 0.042. Moreover, from the investigation, it was found that the observed erosion was smaller than the one estimated by the USLE, which implied possible overestimation in using the equation.

Key words: Soil loss, erodibility factor, universal soil loss equation (USLE), rainfall conservation, Taiwan hillslope.