Field determination of drag forces and shear stress partitioning effects for a desert shrub (<i>Sarcobatus vermiculatus</i>, greasewood)

Abstract

Drag coefficients ( C d ) for the desert shrub greasewood ( Sarcobatus vermiculatus ) were developed from force versus wind speed data collected with an omnidirectional force balance. The average C d for a small (0.6 m high, 0.5 m wide) shrub and a larger (1.6 m high, 1.3 m wide) shrub were 1.425 (±0.103) and 0.435 (±0.200), respectively. These values are much larger than similarly shaped solid elements and previously reported values for creosote bush ( Larrea tridentata , C d = 0.485) and an artificial tree (0.4). The greater C d value for greasewood probably results from factors related to porosity and vegetation structure that gives this shrub‐type greater momentum extracting potential. The drag coefficients for the greasewood shrubs were found to show dependence upon flow Reynolds numbers &gt;6×10 5 , corresponding to wind speeds greater than 18 m s −1 at 10 m. The developed greasewood C d values were used in a shear stress partitioning model that indicated they would be extremely effective at reducing wind‐generated sediment transport at low‐percent coverage.