Guidelines for the Energetic Characterization of a Portable Drip-Type Rainfall Simulator for Soil Erosion Research

The results of the energetic characterization of two drip-type rainfall simulators, differing in the length of their capillary tubes, are presented. The rainfall kinetic power and momentum were measured using a single capillary tube and applying weighing and photographic techniques to determine the raindrop mean equivalent diameter and fall velocity, respectively. The measurements highlighted that the simulated rainfall intensity is the only variable affecting raindrop diameter, and the increase in the capillary tube length produces a reduction in rainfall intensity and raindrop diameter. Finally, an empirical relationship relating fall velocity with raindrop falling height and diameter found in the literature was developed and positively tested using both the experimental data of the velocity measurements from the present research and the literature. Relationships to estimate the rainfall kinetic power and momentum based on the knowledge of mass and raindrop falling height were proposed and positively tested for the two simulators in the present investigation. In conclusion, operative guidelines for a drip-type simulator characterization are proposed in this paper, considering that the knowledge of the geometric characteristics of the capillary tube, pressure head, and falling height values are fundamental to having a complete energetic characterization of the rainfall simulator.