PERMFILE106580 - Laserfiche WebLink

Home Browse Search

Included below is a discussion of wind patterns at the original Seneca Mine located east of Hayden. This discussion is an excerpt from a report entitled "Analysis of the Meteorological and Air Quality Data for the Seneca Mine, January 1978 -December 1978", submitted to Peabody by Western Scientific Services, Inc., Roy M. Barnes. "There are two preferred wind directions at the Seneca Mine site from which the wind blows 80 percent of the time. This is induced by the local topography, i. e., the north-south oriented valley as shown in Map 1. During the night as the earth's surface cools by radiation, the lowest level of air also cools. As rt becomes denser than the upper level air, it uncouples from the upper level synoptic wind regimes whose patterns are controlled by broad scale pressure fields. This cool air layer, due to its increased density, will flow downhill or down valley at the Seneca Mine which is represented by southerly wind directions. A majordy of the nights during the year show this drainage flow as a preferred wind direction. The other wind direction commonly exhibited at the Seneca Mine is up valley flow or winds from the north-northwest. The predominant wind direction in the annual data set for neutral stability conditions which are typical of synoptic events (Figure SC) is north-northwest. Historical data from the Hayden power plant located to the west of the Seneca Mine valley, indicated the predominant synoptic wind direction to be westerly at the surface due to the terrain effects of the Yampa River valley. Thus, the terrain effects tend to channel the prevailing synoptic west and southwest winds to parallel the east-west orientation of the Yampa River valley. As the winds enter the north end • of the Seneca Mine from the Yampa River valley, they are forced to the south or up the valley, resulting in winds Trom the north-northwest. This explains how prevailing upper level west or south-west synoptic winds become northerly at the surface in the Seneca Mine valley. Thus, the winds on a typical day at the Seneca Mine site are controlled by two tagors, the extent to which the cool air layer builds during the night, and the intensity of the synoptic wind fields. As the night progresses, the drainage winds from the south develop unless the synoptic winds are strong enough to counteract the cooling effects. The valley drainage winds will persist until affer sunrise when the valley surface begins to heat. In the summer, the drainage flow will break down sooner than in the winter due to the more direct angle of the sunlight and greater amount of surface heating. It is possible in the winter to never heat up enough to break the diurnal temperature inversion, resulting in light variable winds throughout the day which would otherwise have been stronger and relatively constant as the valley winds linked up with the synoptic regime. In the summer, the synoptic weather patterns are much weaker than during the winter, allowing the sudace of the valley and the valley air to heat up considerably. This hot air is buoyant and rises, frequently resulting in up valley flow from the north. This is analogous to the nighttime drainage flow, but has more variability in the winds since the rising air may go up the valley sides rather than being restricted to only down valley flow. The duration and intensity of the unstable convective activity is controlled by the amount of heating required to break the inversion in the morning. Usually by 1800 MST, the sun angle becomes too low to continue heating and by sunset, the stable drainage winds start to form". • 4