In both USLE and RUSLE, slope length is defined as the
horizontal distance from the origin of overland flow to the
point where either the slope gradient decreases to a point where
deposition begins, or runoff becomes concentrated in a defined
channel (Renard et al., 1997). However, in a real twodimensional
landscape, overland flow and the resulting soil
loss do not really depend upon the distance to the divide or
upslope border of the field, rather on the area per unit of
contour length contributing runoff to that point. For this reason,
the slope length unit should be replaced by the unitcontributing
area. To model upslope drainage area, the steepest
descent algorithm, multiple flow algorithm and the flux
decomposition method have been proposed for calculating the
contributing area of each grid cell in a grid-based digital
elevation map (DEM). The flux decomposition method is well
suited to the Taipingxi watershed because it accounts for
complicated flow divergence and convergence patterns that are
common in highly mountainous terrain. Therefore, the flux
decomposition method outlined by Desmet and Govers (1996b)
was selected as the flow routing algorithm in this study.