| The semi-arid rangelands of southern New Mexico are important areas for active sand movement because of the mesquite-dominated desert ecosystem. Accelerated wind erosion in the mesquite shrublands is attributed to the development of elongated patches of bare soil ("streets") that create a complex distribution of the nabkhas on the surface. Research was undertaken to understand the relationship between surface roughness, wind flow and sediment transport. To understand the effects of wind properties, measurements were taken for near surface wind speed, shear stress and saltation flux. Measurements of near surface wind speed and shear stress were ratioed to regional wind speeds (at 18 m) to make comparisons of wind data between wind directions. Measurements of saltation flux were ratioed to the largest value of flux for comparison purposes. Results show that as winds change direction lambda values also change. Lower lambda, associated with mesquite streets, show higher near surface wind speeds and sediment movement. Higher lambda values show lower near surface wind speeds and reduced sediment movement. Average shear stress values show no significant difference as lambda values change; however, detailed inspection of shear stress on a sensor-by-sensor basis show that winds flowing over the roughness with low lambda values create more widespread shear stresses. The results suggest that the width of the roughness, orientation and distribution affect the shelter areas in the lee of the roughness, which in turn affect sediment transport. |
