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<br />incorporating urbanization effects into rainfall estimates, the existence of this increase <br />should be recognized where the study watershed falls within the sphere of urban <br />influence. Measured rainfall data could be used to supplement the generalized data <br />which, along with conservative selection of loss rates, could account for some of the <br />urbanization effects on rainfall. Sensitivity tests using increased rainfall amounts could <br />be performed to evaluate this approach. <br /> <br />6.3. HYPOTHETICAL STORM CALCULATION WITHIN HEC-1. Once <br />the individual is familiar with the derivation of hypothetical storms, the potential exists <br />to perform many of the calculations with HEC-1. The current version of the computer <br />program can develop the SPS and PMS for areas east of the 1 05th meridian, with the <br />user-supplied point rainfall index and shape factor. The latest version of HEC-1 <br />incorporates procedures for the development of annual-series hypothetical-frequency <br />storms for the user-supplied point rainfall depth-duration array. Adjustments for <br />depth, area, and annual series are made automatically, incremental depths are <br />determined, and the entire storm pattern is arranged within the program. <br /> <br />FURTHER SUGGESTED READING <br /> <br />Technical Memorandum NWS HYDRO-35, 1977. "Five to 60 Minute Precipitation <br />Frequency for the Eastern and Central U.S." <br /> <br />NWS TP 40, 1961. "Rainfall Frequency Atlas of the United States, 30-minute to 24- <br />hour Durations, 1 to 100 Year Return Periods." <br /> <br />NWS TP 49, 1964. "Two to Ten Day Precipitation for Return Periods of 2 to 100 <br />Years in the Contiguous United States." <br /> <br />NOAA Atlas 2, 1973. "Precipitation Frequency Atlas of the Western United States," <br />Volumes 1-13. <br /> <br />EM 1110-2-1411, "Standard Project Flood Determination," revised March 1965. SPS <br />procedures for the eastern and central U.s. East of 1050 longitude and for basins less <br />than 1000 square miles. <br /> <br />HMR 33 "Seasonal Variation of Probable Maximum Precipitation (PMPI, East of the <br />105th Meridian for Areas 10 to 1000 Square Miles and Durations of 6 to 48 hours, <br />"1956. Applies to areas east of the Rockies. <br /> <br />7-22 <br />