Morphodynamic characteristics of echo dunes in the Cele oasis-desert transition belt
In Cele oasis-desert transition zone,echo dunes generally develop from upwind of the nabkhas,so,the morphological indexes of echo dunes,the sediment runoff,wind speed,and particle size characteristics of geomorphic parts of echo dune were analyzed by mathematical statistics,it is helpful to reveal the effect of wind-drift sand and vegetation on the morphology and material composition of the dune.The results indicate that:1)The shape of a mature echo dune is crescent,and the morphological characteristics of scrub and nabkhas af-fect the morphological characteristics of the echo dune.The width of the echo dune increases gradually with the increase of the width of the nabkhas.In the early stage of dune formation,the height of the echo dune does not increase significantly with the height of nabkhas,and in the later stage,the height of echo dune increases gradually with the increase of nabkhas height.2)The wind speed is the minimum when echo dune vortex trough airflow recoils,whereas the wind speed is the maximum when the flanking airflow undergoes bypassing.3)The sediment transport is the largest at the flanks and the smallest at the vortex trough at five geomorphic parts of the echo dune.The closer the each geomorphic part is to the horizontal ground,the greater the sediment transport is.The eigenvalue λ of wind-sand flow is greater than 1 in all five geomorphic sites,and wind erosion and transport processes dominate in each geomorphic site,greater scrub thinning or dieback can cause dissipation to occur in the echo dune.4)The sandy material on the surface of the echo dunes consists mainly of very fine sand,fine sand,and extremely coarse silt.The greater the wind speed is,the bigger the sand particles that are carried by the wind-drift sand are.The particles carried by the wind on the flank are the biggest,and the particles carried by the wind on the leeward slopes of nabkhas are the smallest.The average grain size of the surface sand of the echo dunes is coarser than that of the nabkhas.The morphological characteristics of the back echo dunes and nabkhas affect the flow field changes and the spatial differentiation of the sand particle characteristics in different geomorphological sites.
万方数据
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