Splash detachment of sand particles under varying contact stress field of wind‐driven raindrop impact

• Published in: Earth surface processes and landforms 2021-11, Vol.46 (14), p.2870-2883
• Main Authors: Erpul, Günay, Gabriels, Donald, Pınar, Melis Özge, Sagun, Çağlar, Cornelis, Wim
• Format: Article
• Language: English
• Subjects: Atmospheric precipitations; Compressibility; Contact stresses; Energy flux; Energy transfer; Factorial analysis; Interfacial shear strength; Kinetic energy; Moisture; Obliquity; Rain; Raindrop impact; Raindrops; Rainfall; Rainfall intensity; Sand; Sand & gravel; sand detachment; sand moisture state; Sand particles; Shear strength; size‐dependent properties; Statistical analysis; Stress distribution; stress field partitioning; Variance analysis; Variation; Wind; Wind effects; Wind stress; Wind tunnels; Winds; wind‐driven rain (WDR)
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.5214

The effects of wind‐driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two‐dimensional experimental set‐up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind‐free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s−1 and rainfall intensities of 50, 60, 75 and 90‐mm h−1 to assess the sand detachment rate (D, in g m−2 s−1). The effects of sand moisture state (dry and wet) on the detachment of different‐sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KEx and KEy, respectively, in J m−2 s−1) along with their vector sum (KEr, in J m−2 s−1) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KEr, KEx and KEy with the sand size and three‐way interaction of KEx, sand size and moisture were statistically significant. These results can be explained by size‐dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind‐driven oblique raindrops (KEx/KEy). Further analysis of the variation of the unit sand detachment rate (Du = D/KEr = g J−1) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on Du that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non‐cohesive particle detachment rates, to some extent interacted with size‐dependent compressibility and interface shear strength of sand grains. Wind has an important effect on impact parameters of raindrop during rains accompanied by wind; therefore, wind‐driven rain erosion processes could differ from those of both wind‐driven eolian and windless, to a great extent. This article has a specific focus on splash detachment of non‐cohesive sand by wind‐driven rains. Under differential two‐dimensional‐stress fields, the interaction between compressive and shear stresses stemmed from various incidence angles of wind‐driven raindrop fall trajectory prominently determined the magni