Author
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Stout, John |
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Zobeck, Teddy |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/18/1996 Publication Date: N/A Citation: N/A Interpretive Summary: We report here results from a comprehensive field study of the wind erosion process within a single agricultural field during a regional dust storm in the Southern High Plains. The field, located in Wolfforth, Texas, was observed as the wind strength grew, peaked, and later weakened. Sediment transport was monitored by an array of samplers spaced across the field and dby a particle impact sensor. Meteorological information was obtained from 10-m tower. Attempts were made to relate the observed temporal and spatial variations of sediment transport to meteorological factors and soil surface conditions. Results indicate that the critical threshold spanned the point at which the most susceptible grains become dislodged to the point where the entire surface becomes mobile. The pattern of mass flux variation across the field was dependent upon the height of measurement. The near surface flow was mainly composed of large saltating grains that were easily ytrapped by surface roughness. Whereas farther from the surface the mode shifted distinctly toward smaller sizes. We developed a new method for graphically visualizing the relative contribution of various grain sizes to the mass flux at each height. The resulting contour plot clearly depicts the zones of saltation, suspension, and the transitional region between these regimes. Technical Abstract: The goal of this study was to obtain a detailed account of the wind erosion process within a single agricultural field during a regional dust storm in the Southern High Plains of West Texas. Sediment transport was measured by an array of samplers spaced across the field and meteorological information was obtained from a 10-m tower. Measurements reveal that threshold spans a range of wind speeds (around 6-8 m/s). Measurements of mass flux at a fixe point show substantial temporal variations that reflect changes of wind strength and perhaps changes in surface erodibility. The pattern of mass flux variation across the field was dependent upon the height of measurement. Near-surface transport (z<0.25 m) was found to vary according to surface conditions, especially roughness. Fine dust, measured at heights greater than 70 cm, was less affected by local surface conditions but reflect conditions upwind of the sampling point, where the dust was generated. The mass flux profile within the fully-developed surface layer (z<0.25m) was found to follow a modified power-law function. The near surface portion of the mass flux profile was mainly composed of large saltating grains whereas from the surface the mode shifted distinctly toward smaller particle sizes. We show that it is possible to visualize the zones of saltation, suspension, and the transitional region between these regimes. |
