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I I I I I I I I I I 291'i II-13 The May 1894 storm was undoubtedly of major magnitude. Moreover, the maximizing factor of 2,25, which is somewhat high for a major storm, raised the level of the maximized storm to somewhere near the lower limit of the confidence band for the 24 to 48-hour PMP, as indicated by comparison of line E with lines F and G in Table 11-2. It was stated earlier that the 24-hour rainfall was most for deriving the project design flood, value (7.9) of the May 1894 storm (line The ratio of the maximized important 24-hour E, Table 11-2) to the 24-hour PMP value of 8.7, obtained from transposing and maximizing the June 1964 storm (line A), is 0.91. This ratio applied to the PMP values of line A yielded the values shown on line C. Hourly values for the various subbasins can be obtained by multiplying the values of Table 11-3 by 0.91. I I I I I I The values of line C in Table 11-2 are definitely below the general level of PMP for the project basin but apparently approximate the bottom limit of the confidence band. Nevertheless, the combination of the, design storm of line C with the most critical snowmelt flood conditions should yield a reasonable and safe design flood, The snowmelt criteria given on pages 53 to 64 of the Chatfield repor~/ are applicable to the project basin, A comparison of the design storm of line C with a 1948 ' 9/ estimate- follows: Duration (hour s) 6 12 18 24 1948 design storm 2.5 4.2 5.2 5.8 Line C design storm 3.0 5.3 6.8 7.9 Increase (percent) 20 '26 31 36 ~/ u.s. Weather Bureau, "Probab:e Maximum Precipitation over South Platte River, Colorado, and Minnesota River, Minnesota", Hydromet Report 44. 1969. I I '}j "Final-Type Spillway Design Flood Study, Narrows Damsite, South Platte Subbasin, Colorado", memo dated February 5, 1948, by R. 1. Brasaemle and D. L. Miller, Flood Hydrology Section, Bureau of Reclamation. I DAIVIIES e. MOORE