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1. Four-Mile Creek's Hydrology: Frequency discharges were computed by regional analysis of seven stream gages in the Arkansas River Basin and four in the Platte River Basin. These gaged stations have twenty or more years of reliable data and record peak flows unaffected by regulation or diversion (with some exception on Four-Mile Creek's gage). Omitted from the study were gages at locations above 8000-foot or below 4000-foot elevation, urban gages, gage with upstream regulation, gages with less than twenty years of record, and gages located on streams with topographic features markedly dissimilar to those of the Four-Mile watershed. Table 1 shows the seven selected gages from the Arkansas River Basin and the four selected gages from the Platte River Basin, as well as the drainage area of each gaged basin, and the number of years of recorded annual peak data. The drainage areas for the selected stream gages vary from 86.6 to 1320 sq. miles and the gage elevations are from 4100 feet to 6910 feet. GAGE LOCATION wlS Years of Sta. AREA Record Ave. (Sa. Mi.) Skew 06700500 Goose Creek above Cheesman Lake 86.6 58 0.05 06707000 North Fork South Platte River 479 72 0.05 06709500 Plum Creek near Louviers 302 41 0.05 06710500 Bear Creek at Morrison 164 81 0.05 07096500 Four-Mile Creek near Canvon Citv 434 26 0.36 07106000 Fountain Creek near Fountain, CO 681 23 0,11 07119500 Aoishaoa River near Fowler. CO 1125 57 0,00 07121500 Timoas Creek at Swink. CO 496 28 0,00 07122400 Crooked Arrovo near Swink. CO 108 24 0.00 07124500 puraatoire River at Trinidad. CO 795 69 0.00 07126000 Purgatoire River near Alfalfa, CO 1320 22 0,00 Table 1 - Regional Analysis of U,S. Geological Survey's Stream Gages The linear equations for Four-Mile Creek's discharges are: Corr. Coefficent Q(10) = 10[1.419327*Log(A) - 0.095560] 0.91 Q(25) = 10 [1. 390321*Log (A) + 0.186880] 0.88 Q(50) = 10 [1. 363207*Log(A) + 0.394743] 0.84 Q(100) = 10 [1. 334726*Log(A) + 0.594275] 0,80 Q (500) = 10 [l,260348*Log(A) + 1,048243] 0.68 Where watershed area A = 434 sq. miles GAGE ID lO-Yr 25-Yr FREQUENCY FLOW (cfs) 50-Yr lOO-Yr 500-Yr (*) 07096500 4,445 7,142 9,777 13,019 23,572 (*) Q(500) = 23,200 cfs (by graph) is recommended for use. 8