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IElnI.ONE In lieu of reconstructing the flood control reservoir and dam at this location, the U.S. Army Corps of Engineers (USACE) constructed the Cherry Creek Reservoir. Cherry Creek Reservoir is located immediately downstream of the study reach and the Cherry Creek Dam is located approximately 5.1 miles downstream of Arapahoe Road. Construction of the Cherry Creek Dam was completed in 1953 and water storage began in 1957. The dam was built by the USACE to provide flood control for Denver and attendant recreational use. The reservoir continues ownership and operation under the USACE. The reservoir and land surrounding it was leased to the Cherry Creek Recreation Area in 1957. The 3,915-acre park continues to receive extensive recreational use. The reservoir is currently operated at a normal conservation pool elevation of 5,550 feet, with a storage capacity of 13,266 acre-feet, and a surface area of 850 acres. The Cherry Creek Dam is an earth fill structure with a partial cutoff trench into bedrock. The depth of the alluvium exceeds the cutoff at two locations by over 50 feet. These zones allow groundwater to flow beneath the dam and to continue to provide baseflow in Cherry Creek downstream of the dam. The reservoir also creates a backwater effect for the Cherry Creek models. 1.2.3 Diversions Water from Cherry Creek has been used extensively through either direct diversion or through pumping of alluvial wells. Historically, the primary use was agriculture. However, due to the limited availability of water and the increasing urbanization in the watershed, many of the senior irrigation rights have been converted to municipal use. Presently, most of the Cherry Creek water rights are for municipal purposes and are diverted through alluvial wells (Halepaska and Associates, 2000). 1.3 SOIL CHARACTERISTICS Soils within the watershed were identified from Soil Survey information for Arapahoe County obtained from the Soil Conservation Service (SCS, 1997) and supplemented by geographic information system (GIS) soils data obtained from the U.S. Department of Agriculture (USDA)-SCS State Soil Geographic Data (STATSGO) database. Soils within the watershed are typified by Hydrologic Soil Group Type B and C. However, several areas of rock outcropping exist in the Upper Watershed. 1.4 WATERSHED IMPERVIOUSNESS The percent watershed imperviousness used in the study for both existing and future land use conditions was based on land use mapping available for the project area. The land use conditions for existing and future conditions were obtained from Trust for Public Lands, as compiled and reviewed from the local sponsors. 1.5 VEGETATION The vegetation in the study area consists of a mix of shrub land, prairie grassland, and riparian vegetation communities with some wetlands throughout. These communities are commouly dominated by Gambel's oak, blue grama, buffalograss, big bluestem, needle and thread, cottonwood, and willow. INTRODuenON The streambanks and floodplains along the corridor are generally fairly vegetated. Some reaches are seen heavily vegetated particularly along the Cottonwood subdivision. While there are tall standing trees (mostly cottonwoods) along the creek, most vegetation is relatively short and should not cause significant increase in bed resistance to flow during high flows. I I I I I I J I I I I I I I I I I . I 1.6 DEVELOPMENT IN THE FLOODPLAIN Development in the Cherry Creek floodplain within the study reach has been relatively moderate. The most common form of development was historically associated with fannsteads and an agricultural area. However, recent residential development has occurred in close proximity to the Cherry Creek floodplain. Several bridges have been constructed or modified to encroach on the floodplain in the last 30 years. At present, the more congested development associated with urban areas remains external to the floodplain being located essentially on the hills and rolling countryside adjacent to the stream valley. ' 1-2