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<br />I <br />I <br />I <br />1 <br />I <br />I <br />I <br />I <br />I <br />1 <br />I <br />1 <br />1 <br />1 <br />I <br />I <br />1 <br />I <br />1 <br /> <br />Complex (Dennison Elementary, Fletcher Miller, Creighton Junior High, plus <br />the Jefferson County stadium) as well as the Federal Center is in open space <br />or grass cover condition, and thusly does not produce high peak runoff values. <br />C. Topographic and Geophysical Features <br />The McIntyre Gulch basin has a west to east aspect with the high point <br />of the basin on the eastern edge of Green Mountain at approximately elevation <br />6700. The thalweg elevation of McIntyre Gulch at the confluence with Lakewood <br />Gulch is approximately elevation 5400 feet. The total length of the basin is <br />approximately 6 miles or an average drop of 216 feet per mile. Actually, <br />the Green Mountain area down to approximately Union Blvd. slopes approximately <br />400 feet per mile, and the remainder of the drainageway has an average slope <br />of 85 feet per mile (1.6%). <br />The flank of Green Mountain is relatively steep, and the storm flows <br />are carried eastward off the mountain in narrow steep ravines. While the <br />upper portion of the mountain is currently and can be expected to remain <br />in open space, the flow velocities are very high, and the water will carry <br />considerable sediment. The erosion process is quite active depending <br />primarily upon frequency of significant rainfall, but also has been aggra- <br />vated by the removal of the natural vegetative cover on the steep slopes. <br />The soils of the basin are derived from the underlying shales, sand- <br />stones, and conglomerates of the Dawson Arkose. Green Mountain is comprised <br />of more resistant members of the upper part of the Dawson, including some <br />andesitic material and volcanic tuff. The soils are generally a calcarious <br />clay loam of relatively low permeability. Along the banks of the drainageway, <br />coarser layers of predominantly sand and small gravel are found on an <br />intermittent basis. <br /> <br />D. Land Use <br />The present land use in the McIntyre Gulch study area is comprised <br />of single family residential, the large school complex, the Federal Center, <br />some commercial along Union Blvd. and Alameda Parkway, a small amount of <br />multi-family area, and open space. The current area of open space, lawns, <br />pastures, parks, and undeveloped property results in a perviousness of <br />approximately 69 percent of the total basin. The upper portion of the basin <br />has approximately 75 percent perviousness at this time, while the portion of <br />the Federal Center within the McIntyre basin has 46 percent perviousness at <br />this time. <br />The projected future land use for the McIntyre Gulch basin has been <br />determined from the existing development, current zoning and land use <br />planning as provided by the Lakewood Planning staff. The future development <br />as currently defined would produce a pervious percentage of 53 percent. <br />The planning study currently underway for the Federal Center was <br />utilized to establish the open space or impervious area breakdown for the <br />Center. The hydrology for the basin was determined assuming the Federal <br />Center will develop fully per the master plan, but will incorporate runoff <br />control measures to limit runoff peak flow to approximately the same levels <br />as occur with the present level of development. <br /> <br />4 <br />