Sand dunes, dune fields, playa lakes, playa sediment plumes, blowouts, and scour streaks can be recognized from LANDSAT imagery (resolution ∼80 m) and high-altitude aerial photography (resolution ∼5 m). The abundance of such features in the southern Wyoming test area confirms a major wind corridor with local areas of extremely strong winds indicated by concentrations of eolian features. The abundance of sand and semiarid climate of the area are also important factors in the development of eolian features.
Elongate eolian features indicate the direction of flow of strong winds through the area. Streamlines interpreted from these directional indicators parallel streamlines derived from wind measurements obtained by over-flights at low altitudes with specially instrumented aircraft. The streamlines interpreted from imagery yield only a two-dimensional representation of the flow pattern. But, in areas of stably stratified flow, this plan view provides a first approximation of the flow pattern useful for identifying high wind-energy areas. Smaller wind channels within the Wyoming wind corridor display energies at least two to three times greater than adjacent areas.
The dimensions and types of eolian features that develop in a high-wind area are greatly influenced by moisture, vegetation, sand supply, cementation, and other factors such that wind strength and/or persistence does not correlate strongly with either the type or dimensions of eolian features. Dune spacings and other harmonic distribution patterns observed in the eolian features, however, correlate with certain windflow patterns. Spaced dune groups and playa clusters are found in areas where gravity waves develop in the near-surface air-flow. Diagonal alignments of eolian features are interpreted to be the result of helical circulation cells aligned parallel to the main flow direction. Strong turbulence is characteristic of scoured areas on the lee side of topographic highs. These local characteristics of windflow can have important effects on average wind energy and on the performance of wind-driven energy systems; thus, they are critical in siting of wind generators and other structures.
Relative estimates of average wind velocities can be made by correlating the streamline data and eolian activity in a region of unknown wind energy to a similar area where wind measurements are available. Direct estimates of average wind velocity may also be possible by computations relating average wind velocity to the average migration rates of dunes. Field observations suggest that the dunes are most active during summer and autumn months. Wind velocity estimates derived from the Wyoming dunes should represent the strong summer winds rather than the extremely strong winter winds that sweep the area while the dunes are frozen. Conversely, blowouts with playa lakes are most active in the autumn and winter months (after spring runoff has evaporated). Thus, the playa lake blowouts should develop in response to the stronger autumn and winter winds. Length-to-width ratios of playas and playa plumes were tested as possible indicators of average wind velocities. The shape ratios of playas in the Northern Laramie Basin test area indicate a mature (very active) playa field (indicative of extremely strong winds), but correlations of shape ratios with other data have, so far, failed to yield quantitative estimates of mean wind velocities.
The wind/landform relationships observed in each of the three test areas were employed in compiling a wind-energy prediction map for the southern Wyoming test region. This map shows the dominant patterns of windflow in the southern Wyoming wind corridor and the location of areas of extreme winds within the corridor. The map indicates areas of particularly high wind-energy potential and regions where special flow conditions persist. Mean wind velocity values obtained from permanent meteorological stations are plotted on the map for reference.
