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<br />envelope curves of maximum flooding in these basins, and demonstrate that flood variability in <br />the high plains in eastern Colorado is a function of local topographic relief (fig, 4). <br /> <br />Maximum paleofloods from rainfall in Cherry Creek range from about 30,000 f13/S near <br />Franktown to about 74,000 f13/s near Cherry Creek Reservoir, Maximum paleofloods in Box <br />Elder Creek range from about 9,000 f13/s near Elizabeth to about 8,700 f13/S near Watkins <br />(1-70). The envelope curve of maximum flooding for Box Elder Creek basin (fig, 4) probably <br />is lower than for Cherry Creek basin and "other" Palmer Divide streams (fig. 4) because the <br />headwaters of Box Elder Creek or Running Creek (fig, 1) originate more than 5 miles north of <br />the Palmer Divide, which has an elevation more than 7,600 fI near the headwaters of Box Elder <br />Creek basin, In addition, the basin is elongated (fig, 1) and soils and streambeds have high- <br />infiltration rates, therefore, is much less susceptible to extreme rainfall and flooding, <br /> <br />The lack of substantial flooding in Cherry and Box Elder Creek basins is consistent with rainfall <br />maxima (fig, 1), paleoflood estimates (fig, 4), streamflow-gaging station data (figs, 6 and 7), <br />and rainfall-runoff modeling results (figs, 8 and 9), The lack of substantial rainstorms and <br />flood evidence in Cherry and Box Elder Creek basins probably is explained by several factors, <br /> <br />First, localized relief within the general area of the Palmer Divide and other smaller <br />topographic features in eastern Colorado have a major effect on the location of maximum <br />rainfall (fig, 1), Maximum rainfall is located very near the ridge of the Palmer Divide and <br />extends only a few miles north and south of the Divide, The primary sources of flooding in <br />Cherry Creek basin in 1965 and for the largest paleofloods were Newlin and Piney Creeks (fig, <br />1). Moist air that flows north in East Plum Creek basin appears to be forced over the Plum and <br />Cherry Creek basin divide (relief over 300 ft) between Castle Rock and Sedalia where East <br />Plum Creek Iurns sharply westward (fig, 1), Localized relief appears to produce locally heavy <br />rainfall runoff in the headwaters of Newlin Creek; paleofloods for these basins are substantially <br />larger than other nearby basins without substantial topographic relief, The source of flooding <br />in Piney Creek (e.g" 1965) probably is moderately depleted Gulf moist-air flow over Bijou <br />and Kiowa Creeks and the Palmer Divide (fig, 1), <br /> <br />Second, elevations above 7,700 ft along the Palmer Divide in the headwaters of north-draining <br />basins (Cherry and Box Elder Creek basins) appear to substantially deplete the available <br />moisture for producing extremely large rainfall amounts, which may be similar to the <br />topographic control (about 7,500 f1) of limiting extreme rainfall-flooding in the Colorado <br />foothills (Jarrett and Costa, 1988; Jarrett, 1990, in review a; Pitlick, 1994; Jarrett and <br />Way thomas, in press; Jarrett and others, in review), Downwind areas from the 7,700 fI ridge <br />on the Palmer Divide have received much greater rainfall and flooding on the upslope <br />(southerly-draining) Palmer Divide streams; these include Jimmy Camp, Black Squirrel, Big <br />Sandy Creeks, and other streams (fig, 4; "other PO streams"), Although Bijou Creek is a <br />northerly-flowing stream, its greatest topographic relief is oriented normal to a southeasterly <br />flow of Gulf air, In addition, because so much of the upper Bijou Creek basin is near the crest <br />of the Palmer Divide, it would be more susceptible to large localized rainstorms (fig. 1); Bijou <br />Creek has had the largest floods in Colorado (Matthai, 1969). <br /> <br />Isolated cells of maximum rainfall also are associated with buttes (e,g" Dawson, Raspberry <br />Mountain), which have several hundred feet of relief, such as those located north of the Divide <br /> <br />11 <br />