2012-06-20_PERMIT FILE - C2010089 (89)

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f high terraces sdlacent to larger stream• in the nnrtheaatern Montana study even. Along the Yellowstone and Missouri Rivers, somewhat higher terraces exhibit eubirri- gited vegetative characteristics. Such characteristics are exhibited on nearly all small tributary etreemo in regions of wheat farming, producing a network of small alluvial valley floors in the headwaters. It appears then that subirrigation of desirable agricultural forage any occur in • slightly larger area in northeastern Montana than in the area of southeastern Montana studied by Maids sod vlea. Alluvial valley floors in the northeastern Montana study leo own by Schmidt to exhibit the following additional characteristic 1' o ..se in southeastern Montana: (1) • substantial percentage of ; o seat grow- ing areas are in marsh areas which presently receive e • ` ( Ler flow from nearby fields; (2) a substantial percentage of valley f •Y'Lit slight to severe salinity problems; and (3) larger portions of valley f1 u e covered, as well as underlain, by thicker, poorly sorted alluvial valley gray s. This last factor can ,preclude production of sufficient grass for hay production and wildlife usage if the gravel deposit outcrops so as to limit the near - surface water retention capacity and provide poor plant grovth medium characteristics. Sowever, the gravels may remain highly productive aquifers and can be important as areas of recharge to downstream alluvial valley floors. In northeastern Montana, Schmidt found that wheat farmers viewed the drainage areas, including alluvial valley floors, as obstacles to development. This appears to be true also in North Dakota. Over the past ten years the amount of land utilised for wheat has grout While hayed lands have decreased (in northeastern Montana). How - ever, ranchers in Dawson County, Montana, interviewed by Schmidt indicated that the amount of land used for hay production will probably increase in response to higher hay prices and recent lower wheat prices. Thus the amount of alluvial valley floor land used for hay production say also increase in the near future. These types of changes show that assessments of land use in an area suet be conducted over several years and supplemented by interviews with farmers and ranchers if the agricultural role of the valleys is to be determined. In any one year, an alluvial valley floor soy be used only for unimproved rangeland, wildlife habitat and water drainage. Of course, regardless of land use, the physical or natural characteristics of eubirii- gated alluvial valley floors probably remain. Methods Used to Identify Alluvial Valley Floors This reconnaissance review of alluvial valley floors in existing and proposed surface coal sine areas in the interior western United States was performed utilis- ing aerial imagery, reconnaissance field work of other agencies, and limited field investigations by the authors. Data from a wide variety of sources were used to develop the conclusions and hypotheses that follow. A tabulation of the locations (i.e., township, range, and section) of lease tracts for existing and proposed surface coal sines in the interior western United States was provided by the 0. 5. Bureau of Mines, Intermountain Field Operations Center, Denver, Colorado. Since • field review of the ninety -two identified sine sites was not possible due to time and budgetary constraints, color and color in- frared aerial imagery were obtained for the majority of nine sites. U. S. Ceolo- '•gical Survey topographic saps, generally at • scale of 1:24,000, were also obtained when available. The aerial imagery facilitated the assessment of relative heights of stream terraces, widths of lowland areas, and vigor and general types of vegeta tion. The topographic saps served is base naps and permitted more accurate identi- fication of elevations and location of land unit boundaries. It should be noted that the mine sites considered in this analysis of alluvial ♦alley floors include only those situ scheduled to be in production in the next OCT 3 0 1981 $