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United States Department of Agriculture

Agricultural Research Service

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Research Project: DISTURBANCE ASSESSMENT AND MITIGATION OF GREAT BASIN RANGELAND Title: Rainfall and sheet power equation for interrill erosion on steep hillslope

Authors
 Shin, Seungsook - Pierson, Frederick Al-Hamdan, Osama - Williams, Christopher

 Submitted to: American Geophysical Union Publication Type: Abstract Only Publication Acceptance Date: September 28, 2012 Publication Date: December 3, 2012 Citation: Shin, S.S., Park, S.D., Pierson, F.B., Al-Hamdan, O.Z., and Williams, C.J. 2012. Rainfall and sheet power equation for interrill erosion on steep hillslope. Presented at the American Geophysical Union Annual Fall Meeting, December 3-7, 2012, San Francisco, CA. Technical Abstract: Splash and sheet erosion processes dominate on most undisturbed hillslopes of rangeland. Interrill soil erosion should consider the influence of both raindrop and sheet flow to work of soil particles detached by raindrop impact and transported by rainfall-disturbed sheet flow. Interrill erosion equations that combine the influence of both rainfall and runoff have been proposed by several researchers. However most approaches to modeling interrill erosion have been based on statistical relationships given the inherent complexity in derivation of broadly-applicable physically-based erosion parameters. In this study, a rainfall and sheet power equation to evaluate interrill sediment yields (Qs) was derived from the sum of rainfall power and sheet power expressed by rainfall intensity: Qs=a(cos'/L){a sin' ' I(t)^(11/9)+ß tan'^(1/2) ' (1-fr(t))^(5/3) I(t)^(5/3)}^b, where I(t) is rainfall intensity, ' is slope angle, fr(t) is infiltration rate, a, b, a, and ß are coefficients, sin' I(t)^(11/9) is the rainfall power term, and tan'^(1/2) (1-fr(t))^(5/3) I(t)^(5/3) is the sheet power term. The rainfall power ratio and sheet power ratio decreased and increased with increased rainfall intensity, respectively. The sheet power term depended greatly on infiltration rate controlled by rainfall intensity, vegetation cover, and soil condition. The rainfall and sheet power equation assuming that a and ß is 0 was evaluated using field data from plots on steep hillslopes and showed the better correlation with sediment yields than rainfall kinetic energy, runoff discharge, or interrill equations based on rainfall intensity and runoff discharge founded in the literature. This equation successfully explained physical processes for soil erosion that rainfall power is dominant under low rainfall and sheet power is dominant under heavy rainfall. Additional experimental data is needed to assess coefficients of the power equation to determine the relative quantities of rainfall power and sheet power and to evaluate the erosion efficiency of interactions between raindrop impact and sheet flow and soil erodibility.