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The recurrence interval, or return period, may be computed from the equation T 1 P(C) (3) For the regional regression analysis, 15 gaging stations located in the drainage basins of North Fork South Platte River, Bear Creek, Clear Creek, Upper St. Vrain Creek, and Upper Big Thompson River were selected. These stations were selected so that peak flows are not significantly affected by diversions and/or regulations and lengths of record are at least 15 years. Among the 15 stations, the drainage areas range from 14.4 to 575 square miles and the mean watershed elevations range from 8,800 to 11,140 feet. The average length of record is 43 years. From the recorded streamflow charts, the annual peak flows of rain floods and snowmelt floods were determined for each gaging statione For each individual station, the mean, standard deviation (and hence the coefficient of variation), and skew were computed from the annual flood series for each type of flood event. Regres- sions of the means, coefficients of variation, and skews on drainage areas and mean watershed elevations were then carried out for the 15 stations in the region. Final regression equations, or regional relationships, thus obtained are as follows: 0.627 log A MR MS 1.271 (4) 0.443 log A 1.751 (5) When: R Rainfall events S Snowmelt events M Mean of the logarithms of annual floods A Drainage area (in square miles). For any ungaged site in the region with a given drainage area, the regional relationships, equations (4) and (5), may be used to compute M in the flood-frequency relationship for each type of event by equation (1). The Colorado Urban Hydrograph Procedure (CUHP) (Reference 6) was used to estimate the 10-, 50-, and 100-year flood discharges for the study reaches of Mount Vernon Creek and Bear Creek Tributary 10