Laserfiche WebLink
<br />the low sun angle and subsequent shadows at this time of year enhance <br />topographic features. This image also depicts a thin cover of snow. A thin <br />cover of snow can enhance subtle surface features as a result of contrast <br />between snow and shadows. The reverse also can be true, however. Snow may <br />obscure some of the less pronounced topographic features in certain areas. <br />The results of the interpretation procedure are presented on figure 15. <br />Mapped lineaments are superimposed on the Landsat image for February 26, <br />1975, anp faults depicted on available geologic maps have been superimposed <br />on part of the same Landsat image (fig. 15). Only a small percentage of the <br />mapped faults correspond to the lineaments interpreted in this exercise. <br />This is not necessarily indicative of unsatisfactory results, however, <br />because lineaments can be a manifestation of fractures and faults in the form <br />of both subtle topographic and vegetative trends which were not readily <br />discernible during ground-mapping exercises. <br /> <br />The smail scale of satellite imagery allows identification of extended <br />I inear trends but may not be suitable for identification of fault zones that <br />do not have extended surface trends. Conversely, subtle linear trends <br />definable on Landsat images may not be visible to geologists conducting <br />surficial mapping. At the present time, sufficient ground-water data are not <br />availabie in the Yampa River basin for evaluation of the theory that larger <br />yields can be obtained from wells placed along fracture and fault zones. <br />However, many new wells are being drilled in the region which should provide <br />the information necessary for a preliminary evaluation of the correlations <br />between ground-water occurrence and faults or fractures in the near future. <br /> <br />In conclusion, I ineaments were mapped from Landsat imagery using general <br />principles of photographic interpretation. However, ground investigation in <br />the Yampa River basin is required to determine if mapped lineaments are <br />indicative of ground-water occurrence in this area. This method may provide <br />a rapid means of initial ground-water exploration for this and similar <br />regions if the correlations, obtained by other investigations, between faults <br />and fractures and larger yields of ground water hold true. <br /> <br />Mapping Areal Snow-Cover Extent <br /> <br />The melting of mountain snowpack in the spring is the source of greater <br />than 50 percent of the annual streamflow in most areas of the western United <br />States (Committee on Polar Research, 1970; Rooney, 1969). Approximately two- <br />thirds of the total annual streamflow of the Yampa River is supplied by the <br />snowmelt runoff (Steele and others, 1978). Estimation of water equivalent of <br />snow is required for accurate forecasting of water availability derived from <br />the snowpack. This forecasting requires periodic timely information on snow- <br />pack condition and extent. The most COmmon forecast method currently uses <br />water-equivalent values obtained at selected ooints to infer conditions for <br />the remainder of the watershed. Point data may' not be representative of con- <br />ditions for the entire watershed. Recently, investigators have found posi- <br />tive relationships between areal extent of the snowpack and subsequent runoff <br />amounts (Leaf, 1971; Brown and Hannaford, 1975). <br /> <br />30 <br />