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area and flow eastward to Great Western Reservoir. Woman Creek heads in the study area, draining the south side of the Rocky Flats Plant site, and flows eastward into Standley Lake. The Upper Big Dry Creek basin heads near the mouth of Coal Creek Canyon and follows a course south of the Rocky Flats Plant site to Standley Lake. Coal Creek and Rock Creek flow northward out of the study area with Rock Creek draining its northern part. RAINFALL/RUNOFF PARAMETERS Each of the drainage basins evaluated in the Master Plan was analyzed for factors affecting the rainfall-runoff relationship. Six ditches convey water through the study area. The South Boulder Diversion Canal carries water southward from South Boulder Creek (north of the study area) along the western boundary of the plant to Ralston Reservoir. The South Boulder Diversion Canal carries Denver water supply. Last Chance Ditch, Upper Church Ditch, McKay Ditch, and Kinnear Ditch tap and divert water from Coal Creek. The Last Chance Ditch delivers water to Rocky Flats Lake and Standley Lake. Outflow from Rocky Flats Lake is transported by Smart Ditch No.1 to two natural ponds (D-1 and D-2) in the southeast corner of the Buffer Zone. The Upper Church Ditch supplies water to Upper Church Lake and Great Western Reservoir, McKay Ditch supplies water to Great Western Reservoir, and Kinnear Ditch supplies water to Standley Lake. Mower Ditch taps Woman Creek in the eastern portion of the plant site and supplies Mower Reservoir east of Indiana Street. The analysis included review of past reports for Rocky Flats, field inspections, study of United States Geological Survey (USGS) topographic mapping and detailed mapping. Comparisons were made with earlier findings made by UDFCD consultants. Test computer runs were made of the parameters to determine if resulting hydrographs would be similar to the approved hydrographs for Standley Lake and Great Western Reservoir. They were found to be similar. The relationship between rainfall and the resulting runoff is dependent upon many factors related to topographic, geologic, soil and physical characteristics of the drainage basin. The following factors were utilized in the computer model: . Basin Area - The area of land which collects rainfall and contributes to the runoff flow at a particular design point (basin outlet). The following portions of this section describe the topography, rainfall/runoff parameters, drainage basin descriptions, major drainage basin designations, soils, geology and groundwater of the study area. . Basin Length - The distance from the upstream end of the basin to the downstream design point (basin outlet). . Lea - The distance from the centroid of the basin area to the design point (basin outlet). TOPOGRAPHY Geomorphologically and topographically, the most important single impact on Rocky Flats is Coal Creek. Coal Creek flood flows created the Rocky Flats alluvial deposit on which the Rocky Flats Plant is located. Coal Creek also separates the plant site hydrologically from the foothills, limiting the drainage basins to extending only a short distance westward. Basin Slope - The average slope of the basin from the design point (basin outlet) to the upstream divide. . Impervious Existing - The percent of land in the drainage basin for which infiltration of water will not typically be significant under existing site conditions (e.g., paved parking lots and roadways). Rocky Flats topography is characterized as a broad alluvial fan west of the plant site, and west of Highway No. 93. Through the plant site, erosional forces have incised drainage swales which run from west to east. While the alluvial fan surface has a general slope from west to east of 2.5 percent, the drainages slope at up to 5.5 percent which results in significant topographic relief to the east near Indiana Street. . Impervious Developed - Same as directly above, except under future developed site conditions (year 2015).