Detachment and sediment transport from interrill areas under wind -driven rain
Abstract
Wind-driven rain erosion and the combined effect of wind and rain on erosion process has not been studied widely although wind has long been recognized as an important factor in water erosion. A wind-tunnel study under wind-driven rains was conducted to determine the effects of horizontal wind velocity and direction on physical raindrop impact, interrill detachment and transport processes. Windless rains and the rains driven by horizontal wind velocities of 6 ms−1, 10 ms−1, and 14 ms −1 were applied to three agricultural soils packed into a 20 by 55 cm soil pan placed at both windward and leeward slopes of 4.0, 8.5, and 11.3 degrees. Inclined raingauge measurements showed that the impact frequency of wind-driven raindrops on sloping soil surfaces varied extremely depending on wind-velocity and direction. Rain energy was measured by the splash cup method and a kinetic energy sensor. Measurements indicated that an exponential relationship existed between the energy of simulated rainfall and the applied horizontal wind velocity. Soil detachment and rainsplash transport rates were assessed by the amount of splashed particles trapped at set distances on a 7-m uniform slope segment. Different soil detachment rates occurred depending upon wind velocity and direction under wind-driven rains. Parameters such as fluxes of energy and momentum, which are widely used to predict the soil loss in windless rains, were found to be insensitive to this kind of spatial variability in soil detachment. However, introducing angle of rain incidence as a directionally effective parameter significantly improved the ability of rainfall parameters to account for the variations. Accordingly, the parameters based on the normal impact velocity and impact frequency explained ≥82% of the variation in the detachment rates. Airsplash transport was described by relating transport rate to rainfall parameters and wind shear velocity by a log-linear regression technique, and average airsplash trajectory was predicted by the momentum loss. Sediment transport by rain-impacted shallow overland flow was also adequately described by the selected rainfall and flow parameters. Comparing the contribution of airsplash and thin flow transport as sub-processes of interrill erosion, it is concluded that the airsplash is a significant process that should not be neglected in accurately predicting interrill water erosion.
Degree
Ph.D.
Advisors
Norton, Purdue University.
Subject Area
Soil sciences|Environmental engineering|Civil engineering
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