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Comparison of Rainfall Energy and Soil Erosion Parameters from a Rainfall Simulator and Natural Rainfall

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2007 ASAE Annual Meeting  072230.(doi:10.13031/2013.23501)
Authors:   William T Gilmore, Allen L Thompson, Neil I Fox
Keywords:   Distrometer, droplet size distribution, gamma function, ponding, wind

Natural rainfall was compared to simulated rainfall from a gravity-fed simulator on the basis of droplet size distribution (DSD), kinetic energy (KE), and time to ponding. Natural rainfall drop DSDs from convective storms more closely fit an exponential rather than a positive shape factor gamma curve as previously assumed. Rainfall KE determined from fitted gamma curves underestimated KE compared to calculations using actual droplet size frequencies due primarily to under-prediction of larger droplet sizes. A combination of wind and high rainfall intensities resulted in horizontal KE-values that were over 50% of the total energy beyond which gravity-fed simulators can replicate. Surface ponding was delayed for natural events by up to 55% when compared to similar rainfall intensities using rainfall simulators. Soil loss from small soil beds was problematic under natural rainfall due to splash-out and wind directional influence. The ability to vary the splash screen distance below rainfall drippers using simulated rain compensated for some of the DSD variability of natural rainfall as simulated in the laboratory.

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