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<br />DRAINACE BASINS <br /> <br />Techniques of Happing <br /> <br />, <br /> <br />Drainage basins have been delineate? for a large portion of <br /> <br />the thesis area (Larimer County Planning Office, 1973; Weld County <br /> <br />Planning Office, 1973), and these were in'cluded on the quadrangle <br /> <br />maps. Elsewhere, topographic maps and stereo-air photography were <br /> <br />used to delineate basin boundaries. In areas where the relief is <br /> <br />several times the contour interval, basin boundar,ies can be located <br /> <br />with the maps. In areas of less relief, stereo-air photography was <br /> <br />used to map low drainage' divides. Small channels,' often visible.on <br /> <br />photographs as dark, sinuous bands of grass, trend downhill away <br /> <br />from divides. ,In these areas, furro,ws are often plo,wed with the <br /> <br />same orientation. Irrigation ditches with their constant gradients <br /> <br />provide clues as to the slope of the ,land. <br /> <br />Uncert~~~ties in Basin Boundaries <br /> <br />Although the drainage basins as mapped are generally correct, <br /> <br />there are two factors that can cause local inaccuracies. The first <br /> <br />is that the precision in locating basin boundaries is ~ direct <br /> <br />function of local relief; as topography becomes more flat, precise <br /> <br />location of divides become,s increasingly difficult. In the e.special- <br /> <br />ly flat' portions of the thesis area (north of the Cache la Poudre <br /> <br />River and east of the.Slough) the largest errors in the location of <br /> <br />the divides may be as much as one mile. In the remainde,r of the <br /> <br />area, the largest error probably does not exceed one thousand feet. <br />