Splash Projection Distance for Aggregated Soils
Résumé
Splash is an essential process in interrill erosion because it detaches soil fragments from their substrate and transports them. However, splash measurements are difficult to interpret and relatively little is known about the influence of particle characteristics on the spatial distribution of splash. The objective of this work is to study the splash distribution of different size fractions for aggregated soils. We used a recently proposed theory for spatial distribution by splash to interpret experimental data on the radial distribution of soil fragments splashed by simulated rainfall. A laboratory device with five concentric rings was used to determine average splash lengths for 16 fragment size fractions (0.05 to >2000 µm) of four soils. Sieved soil (3- to 5-mm size fraction) was exposed to simulated rainfall at 29 mm h–1 and with a time-specific kinetic energy of 252 J m–2 h–1. We interpreted the measured masses of fragments splashed into the different rings using an approximate solution of the exponential splash distribution theory applied to the experimental design. We demonstrated that the theory is valid for bulk aggregated soil as well as for individual fragment size fractions. The derived average splash lengths ranged from 4 to 23 cm, depending on the fragment size and soil. Splash lengths were greatest for soil fragments of 100 to 200 µm, and decreased for finer and coarser size fractions. Comparison of these findings with physically-based theory suggests that the coarser fragments, 50 to 2000 µm, are transported as single airborne particles, whereas the smaller ones, <50 µm, are transported in groups in splash droplets. This interpretation is consistent with observations reported in the literature.