Stoss Slopes Of Dunes Research Articles

Late‐Holocene wind‐field evolution at the southern Baltic coast as revealed by GPR data from the Mrzeżyno dunefield, NW Poland

All dunes within a dunefield usually show a similar response to the wind regime. However, in the late‐Holocene coastal dunefield in NW Poland the surface topography suggests that slipface orientation may vary significantly with distance from the coast, which is rarely reported in the literature. The dunefield was stabilized with forest in the mid‐19th century, preserving a unique record of atmospheric circulation in the South Baltic region at the end of the Little Ice Age. To elucidate the Holocene processes occurring along the study site a pseudo‐3D GPR data set was collected. Six grids of parallel GPR lines combined with 400 m of GPR profiles (2D) were collected across the dunefield and displayed using GOCAD for interpretation and geostatistical analysis. The geophysical data revealed that the larger dunes almost entirely consist of steeply laminated facies. Most importantly the pseudo‐3D data, supported by geostatistical estimates of strata dip directions, revealed the existence of three zones parallel to the coastline with the mean dip direction almost perpendicular to the coast in the northern coastal strip and almost parallel to it in the southern part. Spreads of the dip directions in pseudo‐3D GPR data sets recorded on the stoss slopes of dunes and crests suggested initial deposition on transverse dunes, which later were transformed into barchanoid dunes. This can probably be linked to changes in the wind regime, i.e. reduction in velocity of the northern and northwestern winds leading to reduced sediment supply from the coast. While the data provide a new interpretation of Holocene dunefield dynamics at this site, they also suggest that the minimum number of pseudo‐3D GPR grids required to establish general trends using geostatistical analysis should be at least 10, with even more data needed at larger, or more complex dunefields.

A review of Computational Fluid Dynamics (CFD) airflow modelling over aeolian landforms

Abstract Aeolian landforms occur on all earths’ continents as well as on Mars, Titan and Venus and are typically formed where sediment is eroded and/or deposited by near surface wind flow. As wind flow approaches an aeolian landform, secondary flow patterns are created that cause wind to deviate in both speed and direction, producing complex patterns of sediment erosion, deposition and transportation. Computational Fluid Dynamics (CFD) modelling of wind flow has become a common tool to predict and understand secondary wind flow and resulting sediment transport. Its use has progressed from simulating wind flow over simple two dimensional dune shapes, to calculating a multitude of flow parameters over a range of increasingly complex landforms. Analysis of 25 peer reviewed journal articles, found that CFD has been crucial to providing additional insight to flow dynamics on the stoss slope of dunes, the structure and nature of wind flow separation in the lee of landforms and information on localised wind flow variations in large-scale dune fields. The findings of this assay demonstrate that further research is required regarding the parameterisation and modelling of surface roughness, the incorporation of accurate sediment transport to wind flow models, and the prediction of topographic surface changes. CFD is anticipated to be increasingly utilised in aeolian geomorphology and this work aims to be a starting point for aeolian geomorphologists wishing to better understand and review the utilisation of the technique to date.

Aeolian Sand Ripples: Experimental Study of Fully Developed States

We report an experimental investigation of aeolian sand ripples, performed both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed, we can identify three regimes: appearance of an initial wavelength, coarsening of the pattern, and finally saturation of the ripples. We show that both initial and final wavelengths, as well as the propagative speed of the ripples, are linear functions of the wind velocity. Investigating the evolution of an initially corrugated bed, we exhibit nonlinear stable solutions for a finite range of wavelengths, which demonstrates the existence of a saturation in amplitude. These results contradict most of the models.

Airflow up the stoss slope of sand dunes: limitations of current understanding

The windward (stoss) side of a sand dune acts as a streamlined obstacle in the path of the wind. Continuity principles necessitate compression of the flow field up the stoss slope of a dune, and shear stress must progressively increase as the flow accelerates. Measurements in transverse flow over thirteen dunes at Padre Island, Texas, the Algodones, California, and White Sands, New Mexico, confirm that velocity profiles on the stoss slope are not log-linear, and that flow acceleration occurs very close to the surface within an internal boundary layer. As a consequence, in the overlying flow where measurements have historically been made, an overall decrease in shear stress occurs up the slope. The actual shape of the velocity profiles, and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means.