SOIL SLOPE GRADIENT INTERACTIONS IN EROSION BY RAIN-IMPACTED FLOW

Slope gradient is a factor influencing interrill erosion. Results of l aboratory experiments using artificial rainfall with 20 soils with wid ely differing susceptibilities to interrill erosion were analyzed in t erms of the effect of slope gradient on interrill erosion through a mo del that considers the effects of both raindrop impact and surface wat er flow on interrill erosion. Three forms of response were identified. In one form, interrill erosion rate increased with slope gradient at decreasing rate. This form was associated with soils with large stable aggregates that formed a highly protective layer (erosion pavement). In another form, the interrill erosion rate increased with slope gradi ent at an increasing rate. This form was associated with rilling in pr eviously unrilled interrill areas as slope gradient increased Half of the soils produced surface crusts that were highly resistant to rillin g. For these soils, the effect of slope gradient was linear. A common relationship for the effect of slope gradient on interrill erosion doe s not occur for all soils because different soils respond to the appli ed erosive stress in different ways.