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iiiuaiuu 1HU 11:1J FAS W W WEEELER f~Ij011 <br /> <br /> <br />observed peaking patterns on the daily records for the streans shown <br />in Table 1. It should be realized, however, that the peak rates of <br />snowmelt runoff are very sensitive to spring weather conditions, in <br />particular the daily temperatures, and must be viewed rat~ar objec- <br />tivel~. The critical aspect of the snowmelt runoff is the v~~lume <br />rather than the peak flow. <br />RAINFLOODS <br />Whereas the snowmelt runoff is characterized by large volume but <br />relatively small (and controllable) peak rates of flow, the rainflood <br />is generally just the opposite. After initial abstraction and infil- <br />tration, high intensity rainfloods are characterized by high peak flows <br />but small volume when compared to the snowmelt runoff. <br />For this analysis, rainfloods with 50, 100, 200 and 500 year <br />recurrence intervals were determined as were the average annual and <br />Probable Maximum (PM) rainfloods. <br />Precipitation <br />The precipitation for the frequency floods (average annual, 50, <br />100, 200 and 500 year events) was derived using procedures contained in <br />NOAH Atlas 2, Precipitation - FrrauP~r_v Atlas o; the Westerr,llnited <br />States. The PM precipitation was derived using Hydrometeoroingical <br />Report No. 49, Proha6le Maximum Precipitation Estimates, Colorado River <br />and Great Basin Drainages, prepared by the National Weather Se:rviee. <br />The estimated precipitation values are as follows: <br />Flood Event <br />gverage Annual <br />50-year <br />100-year <br />200-year <br />500-year <br />Probable Maximum <br />Six Hour Precipitation <br />0..90 inches <br />1.88 inches <br />2.05 incfies <br />2.30 inches <br />2.55 inches <br />8.80 inches in two hours <br />_8_ 024?53 <br />W.4I. WHEELER <br />RECEIVED TIME NOV, 9, 11~i1RM PRINT TIME NOV. 9. 11~17RM <br />