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I I I I I I I I I I I I I I I I I I I II. STUDY AREA DESCRIPTION Direct Flow Area 0054 is situated predominantly in T 67 N, R 2 W, of the 6th Prime Meridian, between Grange Hall Creek and Brantner Gulch. It is a west bank tributary to the South Platte River. From its origin in the hills along the west bank of the Platte River, the basin slopes to the east and consists of several short tributary channels which either combine or flow directly into the South Platte River. Drainag-e Basin Characteristics The 0054 drainage basin, as shown in figures II-l and II-2, is triangular in shape, approximately 2.l miles along the South Platte River and 2.8 miles from the South Platte to the westernmost point of the drainage basin boundary. It drains approximately 4.3 square miles. Approximately 610 acres of the basin are within the City of Thornton and 2,l40 acres are in Adams County. The basin is also intersected by Riverdale Road, the Lower Clear Creek Canal and Colorado Agricultural Canal, all of which including Holly Street, are directly impacted by the drainage patterns within the basin. The development status of Direct Flow Area 0054 has been classified as "C" by the Denver Regional Council of Governments (DRCOG) in their 1971 Project REUSE, meaning the basin has undergone partial development and has been evaluated to have a moderate to low probability of future development. As it stands now, however, the basin west of Holly Street in Thornton is expected to experience nearly total development as single family residential communities. East of Holly Street, the land use is still rural residential and agricultural and this status is not expected to change. For the purposes of developing runoff hydro graphs, the land use patterns show on the "Future Land Use" map, figure II-3, were assumed. Study Reach Description From the Platte River westward to Riverdale Road, there are three tributaries which drain DF A 0054 and run roughly parallel to each other. The southern and longest tributary basin, 0054-1, rises at an elevation of 5,270 feet above mean sea level and falls about 240 feet in its 2.4 mile course. The northern most tributary, 0054-3, has two main branches that merge below Riverdale Road to a common drainage swale that continues to the South Platte River. The basin of the middle tributary, 0054-2, is bounded by the basins of 0054-l to the south and 0054-3 to the north, and is the smallest of the three. All three tributaries have been included in the Flood Hazard Area Delineation analysis, but only 0054-l has been included in the Phase 'A" study. For the purposes of this study, the 0054-l channel has been divided into four reaches: Reach 1 Confluence with the South Platte River to Riverdale Road, Adams County Riverdale Road to Holly Street, Adams County Holly Street to East 112th Avenue, City of Thornton East 112th Avenue to the Upstream Study Limits, City of Thornton Reach 2 Reach 3 Reach 4 II-I