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(References 7 and 8, respectively). The 100-year flood discharges on Lefthand Creek and St. Vrain Creek are 4,250 cfs and 10,200 cfs, respectively. The 500-year flood discharges for these two streams equal the discharges for the standard project floods as published in the Flood Plain Information reports (References 7 and 8). These relationships are based on a log-pearson Type III analysis of peak runoff data recorded at gages on St. Vrain Creek near Lyons and near Platteville, Colorado (Reference 13). The years of record vary from 79 years at the Lyons gage to 47 years at the platteville gage. i Discharge-frequency relationships for Dry Creek NO. 1 and Spring Gulch were computed using the COE HEC-l Flood Hydrograph package (Reference 14). Synthetic flood hydrographs computed by this method reflect the effects of characteristics of the basin: pre- cipitation, ground cover, slope, drainage area, and other physical characteristics of the drainage basin. Where available, hydro- logic data were compared with other studies completed in the area (References 15 and 16). The effects of detention storage near State Highway 66 and at Long Peak Dam on spring Gulch were studied (Reference 15) and found to be insignificant for the magnitude of the floods considered in this study. That portion of the spring Gulch Basin located north and east of Terry Lake is considered to be contained completely by Terry Lake. The major portion of the Dry Creek No. 1 Basin is located outside the limits of the study area. Runoff from this area contributing to peak discharges within the study reach is limited by the Colo- rado and Southern Railroad, which diverts most of the upstream runoff north to St. Vrain Creek. Rainfall data for the synthetic hydrologic analysis were taken from a rainfall/runof'f information report (Reference 17). The discharges computed using the HEC-l program were verified using the plains Region equations developed by the USGS (Reference 18) . Peak discharges were also verified by the U.S. Soil Conservation Service (SCS) runoff prediction method (Reference 19). , Discharges for the 500-year floods of all streams were checked by straight-line extrapolation of frequencies previously determined using the procedure of the USGS (References 9 and 10), and com- pared to the COE Standard project Flood data when available. The hydrologic analyses for this study were revised to include information presented in flood plain information reports for Left- hand Creek, Dry Creek No.1, and St. vrain Creek (References 1-4), Peak discharge-drainage area relationships for Dry Creek NO, 1, St. Vrain Creek, Lefthand Creek, and spring Gulch are shown in Table 1. 13