<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
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