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I I I I I I I I I I I I I I I I I I I 2.3 Surface Water Resources 2.3.1 Stream Characteristics Two main north-flowing streams exist in the study area. These are Box Elder Creek and Coyote Run, a major left bank tributary to Box Elder Creek. In addition, 89 separate major drainageways flow to these two creeks. All of the creeks in the study area flow only intermittently, in response to significant rainfall or snowmelt events or high groundwater inflow. The main stem Box Elder Creek channel is wide and shallow, with a sandy bottom and flat side slopes. Box Elder Creek exhibits a meandering channel pattern over most of its length in the study area; however, one significant reach of channel has a markedly straight, braided form. This reach extends from approximately 2 miles upstream ofI-70 to 3 miles downstream. Local residents have attested that this straight reach has a high capacity to infiltrate surface flows. One resident located 4 miles upstream of 1-70 mentioned that water flowed by his property for more than 2 months during the summer of 1993, including one high-flow event that overtopped channel banks, but none of the flow ever reached 1-70. The straight, braided form of this reach is most likely the result of aggradation processes that occur when sediment laden flows infIltrate in this reach, leaving sediments to accumulate in fans on the channel bottom. Coyote Run and the smaller tributaries generally exhibit a meandering channel form, are vegetated with grasses and occasional shrubs and trees, and have more pronounced side slopes than the Box Elder Creek channel. Box Elder Creek has an average channel gradient of 0.5 percent through the study area, dropping 535 feet over a distance of 21 miles. Coyote Run and the smaller tributaries have generally steeper gradients, ranging as high as 2.9 percent. 2.3.2 Reservoirs There are no reservoirs within the study area, other than a number of small farm ponds. A detention dam was constructed between 1938 and 1941 near the Town of Elizabeth to help control flooding in the town (WRC, 1979). This dam was reportedly enlarged in 1976 by the U.S. Soil Conservation Service. The location of this facility is not readily apparent on current 1:50,000 scale U.S. Geological Survey (USGS) mapping of Elbert County. Bootleg Reservoir, a State jurisdictional dam owned by the Henrylyn Irrigation District, is located in Adams County, approximately 12 miles downstream of the study area. This dam was breached in the early 1980's because of safety concerns by the State Engineer's DENlOOlSl84.WPS 2-2