Modelling soil losses from the ardeche rangelands

A simple equation is needed to predict soil loss on a storm-by-storm basis and on a hill-slope scale. In response to this need a modelling procedure is proposed that incorporates not only the relation between soil loss and one or more determining factors at individual locations in different source areas (interrill, pre-rill and rill areas) but also the spatial variation in this relation among locations within a source area. The initial version of the relation presented here considers soil loss only as a function of erosivity and rainfall and runoff erosivity factors are used for interrill areas and for pre-rill and rill areas respectively. About 85% of the variation in soil loss at individual locations in each source area is explained by erosivity. The influence of erosivity, however, is found to vary with the size of the area under consideration. In addition, this scale-dependence varies with the type of erosion occurring. Modelling soil loss becomes much more effective if this effect is taken into account. The rainsplash and interrill erosion equations presented are very site-specific. This means that modelling these types of erosion on a hillslope scale will involve the introduction of many erosion determining factors. The rill and pre-rill erosion equations are less site-specific. Accordingly, fewer factors are required to describe these erosion types. On a hillslope scale a pre-rill erosion model for instance based only on erosivity can explain as much as 76% of the variation in soil loss.