Interrill soil erosion and slope steepness factors

Interrill erosion models assume a constant slope steepness term as a function of slope angle. To test the hypothesis that the slope steepness term varies with antecedent soil moisture and soil texture, we determined the effect of slope steepness on soil loss for five soils from clay to silt loam in texture with wet or dry antecedent soil water contents. Interrill sediment yield (wash), splash detachment, runoff, and sediment size were measured in laboratory erosion pans under simulated 90-min, 72 mm h(-1) rainfall at 9 and 20% slopes. As slope steepness increased, splash decreased for three soil treatments and increased for the other five treatments. Splashed sediment and sediment yield were not correlated. Change in splash with increased slope steepness was correlated (r = 0.96) with change in sediment yield. Mean weight diameter (MWD) of splash was, on the average, about twice the MWD of wash. The MWD of both splash and wash was significantly (r = 0.0001) influenced by soil type and antecedent moisture, but MWD of splash and wash was uncorrelated with amount of splash and wash, respectively. The results emphasize the importance of quantifying terms in erosion equations in relation to specific erosion processes.