Surface Erosion from Landslide Site in Weathered Granite Area and the Analysis by Using USLE.

Abstract

To quantify the amount of surface erosion from landslides in the weathered granite area of central Japan, a soil trap was installed at the base of a landslide site in Matsukawa watershed, Nagano Prefecture for a 2-yr period. The average surface erosion from the landslide site was 1, 200 ton/ha/yr with no difference between the two years. This value is a bit larger than previously believed. Both rain and frost heaving had significant influences on the amount of surface erosion; rain produced 59% of total surface erosion. Erosion by frost heaving varied widely between the two years of monitoring. The rainfall factor of USLE and some rainfall indices for surface erosion are estimated with a high confidence level when comparing the rainfall factor with known rainfall indices for surface erosion. The soil erodibility factor used in the USLE calculations is half the value of immature soil. By using this value of soil erodibility, the USLE provides an effective estimate of surface erosion from landslide sites during rainfall periods.