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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 0- 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 <br /> <br />10 <br />