Field observations of wind profiles and sand fluxes above the windward slope of a sand dune before and after the establishment of semi-buried straw checkerboard barriers

Abstract

Abstract Straw checkerboard barriers are effective and widely used measures to control near-surface sand flow. The present study measured the wind profiles and sand mass flux above the windward slope of a transverse dune before and after the establishment of semi-buried straw checkerboards. The 0.2 m high checkerboards enhanced the aerodynamic roughness length to larger than 0.02 m, which was two to three orders of magnitude higher than that of the bare sand. The modified Charnock model predicted the roughness length of the sand bed during saltation well, with C m = 0.138 ± 0.003. For the checkerboards, z 0 increased slowly to a level around 0.037 m with increasing wind velocity and the rate of increase tended to slow down in strong wind. The barriers reduced sand flux and altered its vertical distribution. The total height-integrated dimensionless mass flux of saltating particles ( q 0 ) above bare sand followed the relationship ln q 0 = a + b ( u ∗t / u ∗ ) + c ( u ∗t / u ∗ ) 2 , with a peak at u ∗ / u ∗t ≈ 2, whereas a possible peak appeared at u ∗ / u ∗t ≈ 1.5 above 1 m × 1 m straw checkerboards. The vertical distribution of mass flux above these barriers resembled an “elephant trunk”, with maximum mass flux at 0.05–0.2 m above the bed, in contrast with the continuously and rapidly decreasing mass flux with increasing height above the bare sand. The influences of the barriers on the wind and sand flow prevent dune movement and alter the evolution of dune morphology.