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Table 5,--Caloulated synthetio hydrograph for the estimated 25-year peak disoharge on an 8,25-square-mile basin Constants2 Synthetic hydrograph 3 Dimensionless Time Di scharge con- Time Discharge hyd rograph I constant stantQ', in (txT' ) (qxQ'), Time Discharge T', in cubic feet per in in cubic unit, unit, minutes second per flow minutes feet per t q unit second second 0 0 3.24 65,8 0 0 3 5.6 3.24 65,8 10 368 5 13 3.24 65.8 16 855 7 25 3.24 65.8 23 1,640 10 49 3.24 65.8 32 3,220 11 57 3,24 65.8 36 3,750 12 60 3.24 65,8 39 3,950 13 59 3,24 65.8 42 3,880 14 55 3.24 65,8 45 3,620 18 38 3.24 65,8 58 2,500 23 23 3.24 65,8 75 1,510 30 12 3.24 65.8 97 790 40 5.2 3.24 65.8 130 342 50 2.0 3.24 65.8 162 132 60 .5 3,24 65.8 194 33 70 0 3,24 65.8 227 0 IModified from Craig (1970), 2Based on an estimated 25-year peak discharge of 3,950 ft3/s and flood volumes of 285 acre-ft (see text), the time and discharge constants are cal- culated as follows: Q Q' = ~ = 3,950 = 65 8 ft3/s per discharge unit, and 60 60 ' T' = 0.748V - 0.748 (285) = 3,24 min per time unit. Q' - 65,8 3Synthetic hydrograph shown in figure 7. Sufficient data were not available for split-sample testing in this analysis and, consequently, there is uncertainty associated with these statistical measures of reliability. As an indication of the prediction accuracy of equations 15 and 19, table 9 and figure 6 compare the observed and the estimated lOO-year flood dis- charges for 28 stations within and adjacent to the Arkansas River basin in Colorado which were not used in this analysis. Six of these stations are partially urbanized basins located in the Denver-Boulder metropolitan area. All of the remaining nonstudy stations have watersheds similar to those studied, and are 27 -_._.~~