Relationships Between Rainfall Intensity and the Interrill Soil Loss-Slope Steepness Ratio as Affected by Antecedent Water Content

Rainfall intensity (I), antecedent water content, and slope steepness affect soil loss from interrill areas. Objectives of this field study were to (i) test the validity of the assumption that interrill soil loss is a function of I2, (ii) determine effect of antecedent water content on interrill erodibilities (Ki) for two slope steepnesses, (iii) evaluate the slope factor used in the water erosion prediction project (WEPP), and (iv) evaluate the product of I, flow discharge, and slope steepness as a possible interrill erosion model. Four soils, ranging in texture from sandy loam to clay, were exposed to sequences of simulated rainfall at three intensities (50, 70, and 100 mm h−1). Soil loss and runoff were measured from air-dried and prewetted flat plots and from air-dried and prewetted ridged plots. For each plot type (slope steepness), b values for E = alb varied between air-dried and prewetted conditions with no apparent trend. Values of b ranged between 0.91 and 2.05, although most b values did not approach 2.0. Prewetting had no effect on Heiden clay and Cecil sandy loam Ki values for the model E = KiI2, but it decreased Ki values for Miami silt loam and Broughton clay by at least 21 and 31%, respectively. Increased slope steepness associated with ridged plots reduced the degree of surface sealing as indicated by decreased soil strength. Values of Ki for E/Sf = KiI2, where Sf = WEPP slope factor, were different for different slopes. Sf was a function of soil type, antecedent water content, and individual interrill erosion processes controlling sediment delivery.