Studying the spatial and temporal changes in aeolian sand transport in a wind tunnel using 3D terrestrial laser scanning

Abstract

The spatial and temporal changes in aeolian sand transport are important in modelling wind erosion and parameterizing sand dunes and ripples. In this study, we explored the wind erosion processes that occur in sand beds using a Trimble 3D laser scanner. We found that the erosion intensity varied with distance along the sand bed and that the sand bed surface could be divided into three zones. In the pre‐bowl zone, the sand bed surface showed small and uniform variation, indicating weak erosion intensity in this zone. Downwind of the pre‐bowl zone, the bowl zone developed where the sand surface was eroded seriously and a kind of morphology analogous to blowouts occurred. The post‐bowl zone, which followed the bowl zone, was characterized by alternating accumulation and erosion. Wind velocity affected the spatial development of this bed morphology, whereas the erosion duration only affected the erosion depth. We developed an equation of the form QL = Qsat/(1 + e(−10(L‐s)/k)) to describe the relationship between sediment flux (QL) and bed length (L) in the pre‐bowl and bowl zones and found the fitting coefficients R2 were very high (1.0, 0.98, 0.97 at wind velocities 10.0, 11.0 and 12.0 m s−1, respectively). Using a fine spatial resolution for the measurements revealed features of the sand flux profile that were missed at coarser resolution. However, it will be necessary to use a longer sand bed to study the full length of the post‐bowl zone. Highlights The erosion intensity at different sites of the sand bed was studied. The roughness of the bed surface increased with increasing erosion duration. A sigmoid curve could describe the changes of erosion along the fetch length.

Field investigation of the fetch effect and essential conditions for saturated sand flow

“…Starting from the non‐erodible upwind boundary ( L = 0) and moving downwind (from 0 to 100 m), C increased with increasing fetch length; however, the rate of increase decreased gradually with increasing L . The relationship between C and L agrees with sand flux data obtained in several earlier studies (Andreotti et al, 2010; Selmani et al, 2018; Wang et al, 2020). When the fetch length increased from 80 to 100 m, C displayed minor changes under most wind conditions, indicating that the sand transport rates gradually approached constant values when the fetch length exceeded 80 m; however, the exact fetch length at which the sand transport rate becomes constant must be studied further.…”

“…A gobi surface is a representative example because the lack of erodible sediment makes it extremely difficult to entrain enough particles to achieve saturation. Although the sand particles on the surface are all erodible at a certain wind velocity, it becomes difficult for the sand flow to become saturated because of the development of surface microtopography in the form of ripples (Wang & Zhang, 2021;Wang et al, 2020). These bedforms, in turn, extract some of the wind's momentum (Lancaster et al, 2010;MacKinnon et al, 2004).…”