Implications of gravel content on aerodynamic parameters, sand flux, erosion and accumulation during deflation processes over Gobi

The deflationary process of the Gobi Desert contributes to the release of atmospheric dust and may lead to sand hazards. This process is influenced by the presence of gravel on the desert surface. While extensive research has been conducted on the impact of gravel coverage on sand transport, there is lack of studies examining the wind-sand characteristics across varying gravel content in mixed beds of sand and gravel. In a series of wind tunnel experiments, aerodynamic parameters, sand flux, and both erosion and accumulation amount were measured across beds with differing gravel contents. The findings revealed that the maximum roughness and friction velocity were observed at a 35 % gravel content. As gravel content increased, both the sand flux density (q) and the total sand flux within 30 cm (q_t30) declined, whereas the saltation height (h₅₀) increased. Both the deflation rate and the sediment entrainment rate showed a decrease as the gravel content increased from 15 % to 55 %. Although particle flux density exhibited significant fluctuations, no clear correlation with gravel content was found. The deflation process is accompanied by distinct stripes of sand accumulation at 15 % and 25 % gravel contents, owing to the saturated sand flow characterized by a high sand entrainment rate and particle flux density. In contrast, a gravel content of 55 % exhibited stability with only minor deflation, corresponding to a low sand entrainment rate and particle flux density, thus approaching an equilibrium state. This observation indicates that increasing gravel content effectively slows the deflation rate.