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i~ Steamboat Springs, Colorado, during the 1954 water year. This hydrograph illustrates that <br /> spring runoff is the principal contributor to streamf low (April, May, and June). <br /> Runoff generated by infrequent summer thunderstorms has only a minimal influence. The <br /> relatively constant baseflow depicted in Figure 7-11 (July through March) is maintained by <br />groundwater discharge to the Yampa River, <br />Figure 7-12 depicts a histogram of annual discharges measured for the Yampa River at <br />Steamboat Springs, Colorado from 1914 through 1957. Compared to other gaged streams <br />within the Yampa River Basin that course through more avid watersheds, the annual <br />variability in discharge at this site is less pronounced, largely due to less variation in <br />annual precipitation (dominated by snowfall) in the drainage basin above Steamboat <br />Springs. <br />lorns et. al. (1965b) contains flow duration tables including data for the Yampa River at <br />Steamboat Springs, Colorado. The tables indicate that 90 percent of the time, discharge <br />equals or exceeds 73 cfs, and that flows equal to or greater than 140 cfs occur 50 percent <br />of the time. The mean discharge for the Yampa River at this location is 472 cfs. The <br />® flow duration curve constructed from these tables for the Yampa River at Steamboat Springs <br />is typical of snowmelt-type streams. <br />Regional Surface Water Quality. The geologic units and soils over which runoff water <br />flaws greatly influences the chemical quality of the surface water. In the Green Division <br />of the Upper Colorado River Basin, and more proximate, within the Yampa River Basin, this <br />statement has been supported by lorns et. al, 11965b). <br />The Yampa River Basin, into which Dry and Sage Creeks flow, originates in the Park Range <br />Mountains which are principally composed of igneous {Tertiary volcanics) and metamorphic <br />(Precambrian) rocks. The lower altitude, interior portions of this basin are chiefly <br />underlain by marine and continental rocks (Williams Fork Formation, Mancos Shale) and <br />predominantly continental rocks (Dakota Sandstone, Morrison Formation). The marine and <br />continental rocks and the predominantly continental rocks have the greatest potenti al `or <br />influencing water chemistry through solution of readily available minerals. <br />According to data presented in lorns et. al, (1965b), a[ times of lii gh flow generated <br />l~ largely by snowmelt runoff from the upland areas (underlain by igneaus and metamorphic <br />rocks), the water is of [he calcium bicarbonate cype. During law flow, the water features <br />'.7 <br />