The effect of roughness density of gobi beds on the entrainment of sediment by wind: A wind tunnel study

Abstract

Although gobi is a major source of dust storms in northern China, few studies have investigated the effect of roughness density (λ) of gobi beds on aeolian sediment entrainment. This wind tunnel study quantitatively evaluated the effect of λ on aeolian entrainment from gobi beds with λ of 0.05–0.51 using Rt and RQ. Rt referred to the ratio of the entrainment threshold for a bare sand bed to those of gobi beds; RQ was the entrainment rate ratio, whose calculation was just reversed with Rt. The results indicated that a two-to five-fold increase in entrainment threshold and 41.4–100% of entrainment rate was attenuated within an experimental friction velocity (u*) range of 0.40–0.63 m s−1. Moreover, the variation of RQ with λ was almost negligible, as λ reached 0.176, 0.203, 0.313, and 0.375 for u* values of 0.40, 0.49, 0.54, and 0.63 m s−1, respectively, which were specific for the Gobi Desert with their typical gravel beds. This study also indicated that for higher u* of 0.54 and 0.63 m s−1, aerodynamic entrainment plays a significant role in aeolian entrainment, whereas at lower u* of 0.40 and 0.49 m s−1, splash entrainment exerts a greater impact.