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I I I I I I I I I I I I I I I I I I I STUDY AREA DESCRIPTION This Flood Hazard Area Del ineation study includes the following streams in Douglas and Arapahoe Counties: Happy Canyon Creek Badger Gulch Newlin Gulch Baldwin Gulch Sulphur Gulch Tallman Gulch Northern Douglas County and southern Arapahoe County have developed as residential areas. Business and industrial activities in Denver support much of their working population. The result has been extensive residential growth and a loss of agricultural land use. For the purpose of this study, the drainage basins are considered to be fully developed consistent with existing land use and the land use plans of Arapahoe and Douglas Counties. The cl imate of the study area is of the high inland continental type, as modified by the Rocky Mountains immediately to the west and Palmer Lake Divide to the south. Precipitation is 1 ight, with an annual average from 15 to 18 inches. There is substantial variation in the totals for individual years because a large part of the yearly total is from summer thunderstorms. Happy Canyon Creek originates in the Daniels Park area and flows north- easterly through Douglas County into Arapahoe County, joining Cherry Creek about 1.5 miles north of the county line. The study includes the length of the stream from Interstate 25 to Cherry Creek, approximately 6.3 miles. From 1-25 to Grandview Estates, the area is zoned residential and relatively undeveloped, North of Grandview Estates to the county line, the area is zoned for commercial development. From the county line to Cherry Creek, little or no development exists in what is an agricultural area and east of Jordan Road, the flood plain of Cherry Creek. The streams, which are tributaries to Cherry Creek, are intermittent flowing streams and all originate in northern Douglas County, Only Happy Canyon Creek extends into Arapahoe County before its confluence with Cherry Creek. Badger Gulch joins Happy Canyon Creek at the south limits of Grandview Estates. The study area includes a length upstream from the confluence of 1.6 miles through residentially zoned land. Temperatures in the area range from a high of slightly more than 100oF. to minimum lows of approximately -350F. Mean annual air temperature is 470F. and mean summer air temperature is 660F. Approximately 3.4 miles of Newlin Gulch are studied upstream from Cherry Creek to the Urban Drainage and Flood Control District jurisdictional limit. The area is zoned for residential development with few existing buildings. Within the study area there are three basic soil types. Loamy and sandy soils exist on the flood plains and terraces. Terrain in these areas is nearly level to gently sloping and vegetation is mainly grass, with a few trees, Adjacent to the drainageways, the terrain is gently sloping to moderately steep with sandy and gravelly soils on the uplands. Vegetation is mainly grass with some gambel oak, mountain-mohogany and ponderosa pine. Most of the remaining area is gently sloping to moder- ately steep, with loamy soils on the uplands. Baldwin Gulch flows westerly to Cherry Creek passing between the Ponderosa Hills and Homestead Hills developments. A detention dam and reservoir east of Pine Drive controls flood flows downstream to Cherry Creek. Approx- imately 3.6 miles of Baldwin Gulch are studied. The Sulphur Gulch drainage area is immediately south of the Baldwin Gulch drainage and similarly, it flows westerly, passing immediately south of the Town of Parker. Tallman Gulch, flowing north, has its confluence 2