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II II II II 1m' il im m m m II II il il II I- II II II Lower Big Dry Creek Hydrologic Study Figure 6 delineates the land areas covered by several key planning studies, confirming that practically all of the watershed upstream of the Weld County line has undergone planning. For example, the Rocky Flats report (WWE 1992) covers the watershed area from its headwaters to just below Great Western Reservoir and Standley Lake; the Muller (1989) study area reaches from this point to the Baseline Road (Weld County line); the Kiowa (1999) study area covers Broomfield and viciniity; and the WWE (1989b) study covers the tributaries north of Big Dry Creek from 144th to the Weld County line. Portions of the Greenhorne and O'Mara study that were not updated by Kiowa (1999) include the Gay Reservoir and West Lake sub-basins. The watershed area north atld east of the Weld County line has not been studied in detail and remains primarily farm land. Highlights of key studiles are presented below, from upstream to downstream. It should be noted that some of these studies are now 10-15 years old and that much of the planned development at the time of these reports has been completed. At the time this study was conducted, an update to the northern area tributaries plan in the Adams County, Thornton, Broomfield and Westminster areas was being initiated, with contractor selection slated for July 2005 (personal Communication with John Doerfer, UDFCD, 2005). The Rocky Flats Master Drainage Plan is not discussed here beeause of its location upstream of Standley Lake and the designation of the site as a wildlife refugl~ with very little impervious area expected to be remaining in the future. 5.3.1 Biq Dry Creek. Adams County and Tributaries Master Drainaqe Plan The purpose of the Big Dry Creek, Adams County and Tributaries Master Drainage Plan (Muller 1989) was to present a comprehensive plan for the development of a drainage outfall system for a 31-square-mile area located primarily in Westminster and unincorporated Adams County. The principal objectives were to propose solutions to existing drainage problems in developed areas and prevent the creation of drainage problems in areas of future development. Key approaches to achieving the study goals recommended in the plan included regional detention, improved channel conveyance, and floodplain preservation and regulation. The study area was divided into six study basins: Standley Lake Basin, Walnut Creek Basin, Hy1ands Hills Basin, Airport Creek Basin, Cozy Comer Basin, and the Lake Erie Basin. Key aspects of this plan are summarized below. 971-179.092 June 2005 Wright Water Engineers, Inc. Page 33