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I I I I I I I I I I I 1 1 I I I I I I the basin divide. The drainage basin in the upper portion of the Sampson Gulch study reach is rolling to hilly with some sandstone outcroppings and many Ponderosa pine trees interspersed with native grasses. The stream channel is deeply cut in some areas with nearly vertical banks of up to ten feet. Low density residential development is the primary land use in the upper portion of the basin. The lower part of the basin is presently undeveloped but is projected to experience substantial development with future construction of the E-470 Tollway which will cross Sampson Gulch just above the confluence with Piney Creek. There is a mining operation on one of the major north tributaries. The channel slope varies from 1.0% to 1.5% in this part of the study reach. Rangeland grasses and forage crops are the primary types of vegetation in this are,a with some willows and cottonwoods along the stream channel. FLOOD HISTORY Large flows have occurred on streams in the Piney Creek basin as evidenced by the extent of erosion of many bank areas along the tributaries included in this study as well as the main channel. The magnitude and frequency of occurrence of these flood events is not well documented however due to the sparse population in the basin, the few road crossings, and the limited number of structures near the channels. Some general comments regarding flooding which has occurred in nearby areas have been recorded in a previous floodplain report prepared for the UD&FCD and Arapahoe County in 1976 and are summarized here. Historic information on floods on Piney Creek was obtained through conversations with local residents, research of the historic files of the Denver Post, Rocky Mountain News, the Denver Public Library and various U.S. Geological Survey publications. Since no stream gauging stations exist on piney Creek or any of its tributaries no official records of peak discharges are available. The USGS, however, estimated the peak flow on piney Creek which occurred in June of 1965 to be approximately 14,100 cfs. That would have been over 1.5 times the estimated peak for the 100-year event. That is consistent with the magnitude of flooding which occurred on several streams throughout the Cherry Creek and South Platte River basins in 1965. HYDROLOGIC ANALYSIS Hydrologic analyses were completed for portions of the Piney Creek basin for use in this Flood Hazard Area Delineation report. These new CUHP analyses were completed for the tributaries in order to supplement discharges available for the main channel of Piney Creek from the 1975 report, "Flood Hazard Area Delineation, Piney Creek, Cottonwood Creek, Lone Tree Creek, and Murphy Creek". 5