FLOOD03286

• County: Adams
• Community: Wheat Ridge, Arvada
• Stream Name: Lower Clear Creek
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 10/1/1981
• Prepared For: Adams County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The 100-year peak flows for future developnent conditions 1 isted in Table
III-1 have been used in the prel iminary design of the recommended drainage
improvanents discussed in this report. A h)drological model study by the
Omaha District of the U.S.A.C.E. has shown that short reaches of channeliza-
tion on lower Clear Creek will not significantly change the peak flows down-
strean. However, future developnent in the lower Clear Creek basin may
create pressures to channel ize more reaches of Cl ear Creek. Increased chan-
nel ization and consequent reduction in natural floodpl ain storage could
increase the peak flood discharges on lower Clear Creek by as much as 20%.
This fact should not be overlooked in the future should pressures occur to
channel ize other reaches of Clear Creek be~nd those identified in the
prel iminary design.

111-2

VEGETATION

Vpgetation adjacent to Clear Creek, on sandy and gravelly alluvial soils con-
sists primarily of native grasses, mainly western l'.I1eatgrass, saltgrass, blue
grana, and switchgrass. Trees found along the banks are predominantly cot-
ton\\Oods and willows. This vegetation is 1 argely sustained by the natural
water table and by flooding. The main concern in establ ishing and maintain-
ing grass, shrub, tree, and garden plantings on this soil is wetness. Selec-
tion of water tolerable vegetation is critical for establ ishment.

SOILS

Soils within the Clear Creek Study Area, adjacent to Clear Creek consist pri-
marily of sandy and gravelly alluviun. These alluvial soils are moderate to
rapidly permeable, and are subject to periodic flooding in the spring runoff
months, April through July. The four main soils groups found adjacent to
Clear Creek and its floodplain are Sandy Alluvial Land (SM): Mollie Ustiflu-
vents, sandy-skeletal, 0-3 percent slopes (10S); Alda LOiJTI, 0-2 percent
slopes (3A); and Loany Alluvial Land, gravelly substratun (LV).

Detailed information pertaining to the soils, classifications and character-
istics along Clear Creek was prepared by the U.S. Department of Agriculture,
Soil Conservation Service. The information is contained in Soil Survey of
Adams County, Colorado, October 1974, and Inventory and Evaluation of Soils
for Jefferson County, prepared by the Field Office and Soil Survey staff of
the U.S.D.A. Soil Conservation Service for the Urban Drainage and Flood Con-
trol District, April 4, 1980.