FLOOD08796 - Laserfiche WebLink

Home Browse Search

Discharge magnitudes for floods analyzed in detailed study of the South platte River and Horse Creek were based on statistical analyses of the previously mentioned stream gaging records, as explained in U.s. Water Resources Council Bulletin 17 (Reference 15). Discharge-probability relationships for the upstream and down- stream study limits were developed using data from the gaging stations below Cheesman Lake and at South Platte, respectively. Peak discharge-drainage area relationships for the streams studied by detailed methods are shown in Table 1. Hydrologic information for the streams studied by approximate methods was obtained from various sources. Existing UDFeD reports were used directly for Badger Gulch, Big Dry Creek, Cottonwood Creek, Dad Clark Gulch, Happy Canyon Creek, Marcy Gulch, McMurdo Gulch, and Piney Creek (References 16-21). A drainage area versus discharge curve was developed using UD&FCD information for Happy Canyon Creek Tributary, Jordan Road Tributary, KOA Tributary, New- lin Gulch, South Newlin Gulch, and Oak Gulch. A procedure devel- oped by the SCS was used for the 6400 Tributaries (Reference 22), the Computer Model SWWM was used for Tributary A (Reference 23), and the SCS TR-20 computer program was used to develop hydrologic information for Glade Gulch and Section 34 Tributary (Reference 12). Technical Manual No. 1 (Reference 13) was used for all other approx- imate-study reaches. 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the ele- vations of floods of the selected recurrence intervals. The water-surface profiles for the 10-, 50-, 100-, and 500-year floods were developed using the SCS WSP-2 computer program (Refer- ence 24) for Plum Creek; the portions of East Plum Creek through the Towns of Larkspur, Castle Rock. and Sedalia; West Plum Creek; Indian Creek; Hangmans Gulch; the portion of Sellers Gulch through Castle Rock; Unnamed Tributary to Sellers Gulch; Sulphur Creek; Happy Canyon Creek; Newlin Gulch; Baldwin Gulch; Sulphur Gulch; Tallman Gulch; Bayou Gulch; South Platte River; Horse Creek; and West Creek. These profiles and elevations were compared with historic floods and the flood stages then determined. The water-surface profiles for 10-, 50-, 100-, and SOD-year floods on the portions of East Plum Creek between Larkspur and Castle Rock and between Castle Rock and Sedalia and the portion of Sellers Gulch upstream of Castle Rock were developed using the COE HEC-2 step- backwater computer program (Reference 25). 19