Slope Angle‐Interrill Soil Loss Relationships for Slopes up to 50%

Abstract

Abstract Soil loss data were collected from 1.2‐m long by 0.6‐m wide plots under 76 mm/h simulated rainfall for two soils at slopes from 3 to 50%. Soil loss and soil loss ratio (soil loss at any slope ÷ soil loss at 9% slope) were related to the sine of slope angle in degrees. Second‐ and third‐degree polynomial equations fit the data best. An equation for the Hillgate soil showed that the soil loss ratio increased rapidly up to 35 to 40% slope and then became nearly constant. This may be partly due to the experimental conditions of short slope length but is realistic because at high slope angles there is less direct raindrop impact on the soil surface. The equation for the Contra Costa soil loss ratio yielded a curve much below the Hillgate curve at slopes between 15 and 40%. These data suggest that soil properties and slope effects are not independent. The experimental conditions are not meant to be representative of field conditions but the data represent the effect of slope steepness on interrill erosion by raindrop impact and overland flow.