Laserfiche WebLink
West Elk Mine <br /> <br /> <br />2.04-120 Rev. 08/94- TR71, 06/95- PR06, 03/06- PR10;05/22- MR462 <br />then associated with light and variable winds was able to occur and the surface air joined with the <br />faster, more freely moving gradient flow at higher elevations. This effect occurred at all three sites, <br />with the winds at Site 3 coupling about an hour sooner than those at Sites 1 and 2. <br /> <br />Another contributor to the rise in wind speed during this period was upslope flow conditions arising <br />primarily from convection due to the more intense heating of the canyon or mountain sides and tops <br />than heating of the valley or canyon bottoms. This convection upslope flow was generally in the <br />direction of the gradient flow and was further reinforced by the mechanism described previously. <br /> <br />As the sun dropped later in the day, the vertical mixing began to diminish. This resulted in less <br />vertical transfer of horizontal momentum from the upper level gradient flow to the surface layer and <br />hence the wind speeds diminished at all three sites. As the sun set, the nocturnal surface-based <br />inversion began to form. Once again, this resulted in the beginning of a drainage flow situation. As <br />these drainage flows funneling through the canyon began to dominate at Sites 1 and 2, the average <br />wind speed increased to its nighttime maximum. Being above the intense drainage layer, Site 3 <br />experienced light drainage winds from higher terrain directly to the south which remained about 4 <br />and 5 mph throughout the night. <br /> <br /> Wind Speed and Direction <br /> <br />Because of the extreme topographical influence on the wind flows over the area, joint frequency <br />distribution data between wind speed and direction, or wind roses, were developed for different <br />segments of the day at each site. Complete data listings of all of these frequency distributions were <br />compiled and are graphically presented in Exhibit 24. Each wind rose showed the percentage of <br />time over the reporting period that the wind blew from a particular direction by plotting a bar in the <br />compass direction from which the wind blew, with a length proportional to that percentage of <br />occurrence. <br /> <br />At Sites 1 and 2 between midnight and 8:00 a.m., the drainage flow through the canyon was well <br />established and virtually all winds during this period came out of the southeast. Although the major <br />valley axis at this point runs from east-southeast to west-northwest, there is a bend in the canyon <br />about 3,000 feet to the east which forced the flow to curve around and flow from the southeast. In <br />addition, the minor tributary of Sylvester Gulch empties into the major valley immediately <br />upstream from the monitoring site. Drainage from Sylvester Gulch flows due north, and as it <br />merges with the drainage through the major valley itself, lends a south-southeasterly component to <br />the flow. <br /> <br />Between 8:00 a.m. and 4:00 p.m., three wind regimes were present. During the earlier part of this <br />period, drainage flows continued. Because the minor drainage component from Sylvester Gulch, <br />which most likely ceases almost immediately after sunrise, was not present, the flow exhibited <br />more of an east-southeast behavior. The light drainage through the main valley ceased about 10:00 <br />a.m. After a short transition period, upslope flows began to dominate. <br /> <br />These upslope flows continued until about 4:00 p.m. The period from 4:00 p.m. to 8:00 p.m. was <br />another period of transition. During this time, upslope flows decreased and downslope flows <br />became dominant. By 8:00 p.m., the drainage flow pattern was once again well established.