Characterizing the Kamphorst rainfall simulator for soil erosion investigations

• Rainfall intensity, I s , depends on pressure head, H , and water temperature, T. • I s is the only variable that affects the mean mass of a single drop. • For falling height, h less than 1.3 m the raindrop fall velocity, v is function of h. • Rainfall kinetic power and momentum are function of I s and h. • The Kamphorst characterization needs to know the nozzle geometry, H , T , and h. In this paper, the results of the characterization of Kamphorst’s rainfall simulator obtained by laboratory experiments carried out at the Department of Agricultural, Food, and Forest Sciences of the University of Palermo, are presented. At first, the rainfall uniformity distribution was positively verified considering several pressure heads (ranging from 1.9 cm to 11.9 cm) and water temperatures (from 24 °C to 27 °C), achieving a uniformity coefficient ranging from 96 to 99 %. Then, using a single nozzle, the simulator has been characterized in terms of kinetic power and momentum by applying both a photographic and a weighing technique. In particular, terminal drop velocity was measured by the displacement of a single raindrop measured between two consecutive frames, while the mean mass of single drops was evaluated by weighing a fixed number of drops. The analysis of the experimental data highlighted that the rainfall intensity, which increases with water temperature and pressure head, is the variable affecting the measurement of the single raindrop mass. Measurements also showed that an increase in rainfall intensity determines a decrease in the mean mass of the raindrops and an increase in the number of raindrops that fall in the unit time and area. This circumstance allowed to justify the increasing trend of the rainfall kinetic power and momentum with rainfall intensity. The measurements allowed to develop empirical relationships relating kinetic power and momentum with the simulated rainfall intensity and falling height of the raindrops. Finally, a theoretical expression suggested in the literature for estimating simulated rainfall intensity was positively tested.