THE EFFECT OF WIND ON RAINDROP IMPACT AND RAINSPLASH DETACHMENT

Abstract

In winddriven rains, variations in raindrop trajectory and frequency are expected due to the changes in the angleof raindrop incidence. This article presents experimental data on the effects of horizontal wind velocity on rainsplashdetachment. In a wind tunnel facility equipped with a rainfall simulator, windless rains and rains driven by horizontal windvelocities of 6, 10, and 14 m s1 were applied to three agricultural soils packed into 20 55 cm soil pans with both windwardand leeward slopes of 7%, 15%, and 20%. Rain intensity was directly measured with inclined raingauges oriented with respectto the prevailing wind direction. These measurements showed that the actual amount of rainfall intercepted on the soil surfacevaried widely depending on the angle of rain incidence, which was a function of the rain inclination and slope gradient andaspect. A twodimensional numerical model was used to estimate winddriven raindrop trajectories. Rain energy was alsomeasured by a kinetic energy sensor. Theory and measurement showed that an exponential relationship existed between theenergy of simulated rainfall and the applied horizontal wind velocity. The experiments led to the conclusion that the windnot only increased the resultant raindrop impact velocity but also altered the angle of raindrop incidence, resulting in variableraindrop impact frequency and impact angle. Accordingly, differential rainsplash detachment occurred depending on thechanges in raindrop trajectory and frequency with wind velocity and direction. There were significant differences in thedetachment rates between the aspects, and the rates were as much as 44 times greater in the windward slopes than in the leeward slopes.