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<br />Soils of the region exhibit characteristics that are directly related to their physiographic
<br />position, The highest of three physiographic positions, semiarid, mountains and foothills, is
<br />comprised of rock outcrop and deep (greater than 40 inches to bedrock) to moderately deep
<br />(20 to 40 inches to bedrock) soils formed by material derived from acid igneous rock or hard
<br />sedimentary rock, The lesser extensive soils formed through the erosion and weathering of
<br />acid igneous rock are 35- to 60-percent cobble with a loamy matrix, while more extensive
<br />soils formed with material derived from sedimentary rock generally are loamy with O. to
<br />25.percent gravel. The lowest of the physiographic positions, semiarid to arid plains, has
<br />deep to shallow soils that form in eolian and alluvial deposits as well as material derived from
<br />clayey shales, Deep soils forming eolian and alluvial deposits are well-drained, sandy to
<br />clayey, and are usually lacking in rock (gravel or cobble) fragments, while shallow soils
<br />formed with materials derived from shale are clayey, lacking in significant gravel, and are
<br />well-drained. The intermediate physiographic position, semiarid foothills and plains, is
<br />dominated by soils derived from hard sedimentary rock, but also has a few soils formed in
<br />alluvium and from interbedded sandstone and shale, Soils formed with material derived from
<br />hard sedimentary rock are sandy or loamy, well-drained, and have less than lO-percent gravel
<br />(Reference 7),
<br />
<br />Generally, the mountain and foothill areas have high coefficients of runoff, steep stream
<br />gradients, and narrow floodplains, High-plains areas generally have a lower coefficient of
<br />runoff, gradual elevation changes, and relatively broad streambeds and floodplains,
<br />
<br />Within the region, precipitation varies considerably because of elevations, major wind
<br />currents, and local geographic features, Winter storms, typically from the northwest, tend
<br />to lose their moisture on the western side of the Rocky Mountains, The major precipitation
<br />is due to late spring snows influenced by southeasterly winds on upslopes and from summer
<br />thunderstorms, Pikes Peak produces a "rain shadow" which causes a semiarid zone to the
<br />east. Annual precipitation varies from a low of 8 inches to a high of 20 inches in the higher
<br />elevations. Normal annual precipitation for Colorado Springs is 13,2 inches. with the normal
<br />maximum monthly amount of 2.4 inches occurring in July (Reference 8),
<br />
<br />2,3 Principal Flood Problems
<br />
<br />Most of the flood-producing storms in the study area occur from May through August. The
<br />most severe storms occur in late spring or early fall when polar air intrusions are more
<br />intense, Isolated summer thunderstorms are frequently severe, but limited in areal extent.
<br />Available records do not indicate that snowmelt has contributed significantly to flood
<br />occurrences in the study area, Floods are characterized by high peak flows, moderate
<br />volumes, and short durations,
<br />
<br />Available flood history for El Paso County is almost exclusively concerned with the larger
<br />aspects of flooding on Fountain or Monument Creeks in the urbanized areas, Major flooding
<br />probably included simultaneous flooding on the smaller streams as well. References to the
<br />smaller streams appeared only rarely in newspaper accounts until recently, Specific
<br />information on the intensity, duration, and magnitude of the storms and flood effects is
<br />generally lacking,
<br />
<br />The May 1935 flood is the largest recorded flood: 55,000 cubic feet per second (cfs) on
<br />Fountain Creek above the confluence with Jimmy Camp Creek (Reference 9), This storm,
<br />which was concentrated chiefly over the Kettle Creek basin, also caused the largest known
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