Long duration, high intensity rainfall associated with typhoon storm events causes landsliding and surface runoff. Surface runoff in turn leads to erosion. Debris sediment from landsliding and surface erosion contribute to river sediment yield. The size of the landslide and depth of the soil that the landslide takes place in effect the total landslide volume. Soil depth has been found to not only be related to depth but also the terrain curvature. In this study, soil depths have been measured from the trunk stream and tributaries of the Shih-Men watershed to establish a rational and reliable empirical equation for soil depth relative to topological characteristics. The hope of this study is that the empirical formula can be used to guide estimates of landslide volume for a given disaster event. The availability of such an empirical equation would help mitigation strategies and project management in response to sediment disasters that affect an entire watershed.