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FLOOD10493
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Last modified
1/29/2010 10:12:11 AM
Creation date
10/29/2007 12:01:00 PM
Metadata
Fields
Template:
Floodplain Documents
County
Adams
Arapahoe
Community
Aurora
Stream Name
Upper Box Elder Creek
Basin
South Platte
Title
Upper Box Elder Creek Outfall Systems Planning Study - Alternative Evaluation Report
Date
12/1/1994
Prepared For
Aurora, Arapahoe County, Adams County, UDFCD
Prepared By
CH2M Hill
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br /> <br />which have high <br /> <br />soils, <br /> <br />channel of Box Elder Creek consists primarily of type A <br />infIltration characteristics. <br /> <br />Section 2.0 <br />A _11..,. n....co","';...,.f;nn <br />.l"11. I\l;CI ....,1\1;.,,,,1. 1.1' "..v.... <br /> <br />C4-......:I.., <br />.:I,"UUJ <br /> <br />Water Resources <br /> <br />Surface <br /> <br />2.3 <br /> <br />Topography and Physiography <br /> <br />Stream Characteristics <br /> <br />Two main north-flowing streams exist in the study area. These are Box Elder Creek and <br />Coyote Run, a major left bank tributary to Box Elder Creek. In addition, 89 separate <br />major drainageways flow to these two creeks. All of the creeks in the study area are <br />ephemeral, flowing intennittently in response to significant rainfall or snowmelt events or <br />high groundwater inflow. <br /> <br />2.3.1 <br /> <br />2.1 <br /> <br />Box Elder Creek is located east of metropolitan Denver in the rolling plains area adjacent <br />to Colorado's Front Range. The Box Elder Creek watershed is extremely long and <br />narrow. The watershed extends approximately 100 miles from its headwaters at the <br />Monument Divide in EI Paso County to the confluence with the South Platte River near <br />Kuner, Colorado. The watershed is generally 3 to 5 miles wide over the entire length of <br />the creek. <br /> <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />I <br /> <br />The mainstem Box Elder Creek channel is wide and shallow, with a sandy bottom and flat <br />side slopes. Box Elder Creek exhibits a meandering channel pattern over most of its <br />length in the study area; however, one significant reach of channel has a markedly <br />straight, braided form. This reach extends from approximately 2 miles upstream of 1-70 <br />to 3 miles downstream. <br /> <br />Local residents have attested that this straight reach has a high capacity to infIltrate base <br />flows. One resident located 4 miles upstream of 1-70 mentioned that water flowed by his <br />property for more than 2 months during the summer of 1993, including one runoff event <br />that produced a flow depth of 2 to 3 feet, but none of the flow reportedly reached 1-70. <br />The straight, braided form of this reach is most likely the result of aggradation processes <br />that occur when sediment-laden flows infiltrate in this reach, leaving sediments to <br />accumulate in fans on the channel bottom. <br /> <br />The Upper Box Elder Creek study area is shown in Figure 2-1. The study area is located <br />in the far southeastern portion of the UDFCD boundary. The upstream study limit <br />coincides with the ArapahoelElbert County line and the downstream study limit is located <br />at the south boundary of the Denver International Airport, approximately 4.5 miles north <br />of 1-70. The study area is approximately 75 square miles in area. Of this, the Coyote <br />Run watershed comprises approximately 29 square miles, and the Box Elder Creek <br />watershed comprises approximately 46 square miles. The study area is under the <br />jurisdiction of Arapahoe County, Adams County, and the City of Aurora. The area under <br />Aurora's jurisdiction is located generally in the vicinity of 1-70. <br /> <br />I <br />I <br /> <br />The portion of the Box Elder Creek watershed that is upstream of the study area is <br />indicated in Figure 2-1. This upstrecull watershed is located in Elbert and El Paso <br />Counties and is approximately 127 square miles in area. Box Elder Creek is identified as <br />Running Creek in this portion of the watershed. <br /> <br />also <br /> <br />I <br />I <br />I <br /> <br />Although infiltration along Box Elder Creek appears to be significant during base flows <br />and small runoff events, it is not expected to have much of an impact on peak discharges <br />during infrequent, large flood events. Therefore, stream losses were assumed to be <br />negligible during the flood events modelled in this study. <br /> <br />Coyote Run and the smaller tributaries generally exhibit a meandering channel form and <br />are vegetated with grasses and occasional shrubs and trees. These tributaries generally <br />have more pronounced side slopes than the Box Elder Creek channel, which tends to be <br />broad and flat. <br /> <br />The highest point in the watershed on the Monument Divide in EI Paso County is <br />7440 feet above mean sea level (MSL). The lowest point in the study area, at the north <br />study limit, is at elevation 5390 MSL. Watershed topography shifts from steep, relatively <br />rugged terrain in the upper portion of the watershed to moderate rolling terrain in the <br />lower portion of the study area. The transitional zone from steep to moderate terrain is <br />located about 2 to 3 miles south of 1-70. The alluvial floodplain area of Box Elder Creek <br />is broad and flat in the lower portion of the study area. <br /> <br />Box Elder Creek has an average channel gradient of 0.5 percent through the study area, <br />dropping 535 feet over a distance of 21 miles. Coyote Run and the smaller tributaries <br />have generally steeper gradients, ranging as high as 2.9 percent. <br /> <br />2.2 Soils <br /> <br />Hydrologic soil types within the watershed study area are shown in Appendix A. <br />Hydrologic soil types were identified based on soil surveys produced by the U.S. Soil <br />Conservation Service for Adams (SCS, 1974) and Arapahoe Counties (SCS, 1971). <br /> <br />2.3.2 Reservoirs <br /> <br />There are no reservoirs within the study area, other than a number of small farm ponds. <br />A detention dam was constructed between 1938 and 1941 near the Town of Elizabeth to <br />help control flooding in the town (WRC, 1979). This dam was reportedly enlarged in <br /> <br />2-1 <br /> <br />Hydrologic soil types B and C are predominant in the watershed. Type B soils have <br />moderate infIltrations rates and type C soils have lower infiltration potential. The main <br /> <br />DENl00lS184.wPS <br /> <br />I <br />I <br />I <br />I <br /> <br />I <br />I <br />I <br />I <br />
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