VELOCITY AND KINETIC ENERGY OF RAINDROPS BY A DYNAMIC RAIN GAGE

Abstract.

Knowledge of raindrop velocity is very important to calculate kinetic energy and, therefore, erosivity either by natural rains or by sprinkler irrigation systems. Several methods are used to estimate kinetic energy, being the majority, based on rain intensity. This research presents a new method able to measure the drop velocity, designated as Dynamic Rain Gage System (DRGS). Simulated rains were investigated even under windy conditions to measure the velocity of drops and their kinetic energy, at International Center of Eremology at Ghent University in Belgium. Results were compared to data obtained by a LASER disdrometer (PARSIVEL) and it can be concluded that this new method is very accurate for evaluating velocity or kinetic energy of rains. Conditions were simulated to vary rain intensity by increasing the water pressure from 1.0 to 1.5 and 2.0 bars; wind velocity set to zero and to 6.4 m/s horizontally; different vertical distance from the sprayers and positions (under sprayer and in between sprayers). These variations allowed investigating the effects of wind and rain intensity on velocity and kinetic energy of raindrops. Measurements of velocity and rain intensity at ICE wind tunnel allows concluding that the UFLA DRGS can potentially measure the drop velocity since, by turning on all directions, might better integrate the velocity vectors compared to the Parsivel LASER system. Winds such as 6.4 m s-1 can decrease the kinetic energy of rain under the sprayer and increase it under and between sprayers.