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- II II tl II II II II II II II II II II II II II II II II Lower Big Dry Creek Hydrologic Study channelized and of uniform width and depth. Some areas of embedded cobble are present in areas where bridges cross the stream (Aquatics Associates 1999b). Previous studies (W'WE 2000) have indicated that erosion of the streambed (i.e., vertical erosion) is minor in this segment; however, banlc erosion is common on the outside bends of stream meanders. Overall, the streambed slopes from Standley Lake to the confluence with the South Platte River are relatively mild, less than 0.35 percent, with the exception of slopes ranging from 0.5 to 2.0 percent from just below the dam to approximately 1 04th Avenue. The natural channel slope is affected by several grade control structures that exist along the creek such as bridges, diversion structures, and riprap weirs (WWE 2000). The stream has a concave profile from Standley Lake to approximately 1 04th Avenue, indicating that the stream has downcut over time. This would be expected because of the construction and long-term placement of the dam creating Standley Lake. From 104th AVI:::nue to 128th Avenue, the slope remains fairly constant at approximately 0.34 percent. From 128th Avenue to just above the confluence with the South Platte, the slope also remains relatively constant at 0.24 to 0.21 percent. The slope decreases to 0.12 percent just prior to the confluence (WWE 2000). 3.4 Extent of Current Development and Urban Growth Boundaries Municipal and unineorporated county areas within the watershed boundaries inc:1ude unincorporated Jefferson County (over half of which is Rocky Flats), Westminster, unincorporated Weld County, unincorporated Adams County, the City and County of Broomfield, Thornton, Arvada, and Northglenn, as shown in Figures 2 and 3. Very minor portions of Superior and Federal Heights make up the remainder. Rapid urbanization is occurring along the 1-25, E-470 and U.S. 36 corridors, particularly in northeastern Broomfield and northern Thornton. Historically agricultural areas continue to change to residential, commercial and indm;tria1 uses. The Denver Regional Council of Governments (DRCOG) reports that the middle reaches of the Big Dry Watershed are blanketed by plans for urban growth over the next 25 years (DRCOG 2005). 971-179.092 June 2005 Page 16 Wright Water Engineers, Inc.