Analyzing rainfall intensity effects on interrill splash and wash processes

Directional splash and wash sediments from a Rhodic Eutrustox (Wahiawa silty clay) were measured at 4, 9, 18, 27, and 36% slopes under simulated rainfall with 45, 65, 90, and 135 nun h(-1) intensities. The rainfall intensity effects on erosion rates were well described with a power function model: E = aI(b), where E is the erosion rate and I is the rainfall intensity. However, values of a and b are different for splash (b=0.5similar to1.4, a =13similar to28) and for wash (b=2.1similar to4.6 and a<0.003). This indicated the fundamental differences between the two processes, i.e., splash is sediment detachment and transport by raindrops and wash is sediment transport by raindrop impacted overland flow. It was also shown that rainfall intensity effects were dependent on slope steepness since the b-values for both splash and wash increased with increasing slope angle. The study suggested that interill splash and wash be modeled separately with more fundamental erosivity parameters such as rainfall kinetic energy or flow rate coupled with a slope factor.