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<br />DRAINAGE CRITERIA MANUAL <br /> <br />RAINFALL <br /> <br />. <br /> <br />1. GEN ERAL <br /> <br />The Urban Storm Drainage Criteria Manual (US&DCM) that was originally <br />published in 1969 contained rainfall depth-duration-frequency maps for the 2-, <br />10-, and 100-year recurrence frequencies. A detailed set of guidelines were <br />given on how to use the depth-duration-frequency maps to develop desi gn <br />rainstorms and time-intensity-frequency curves for any location within the <br />Urban Drainage and Flood Control District. In 1973 the National Oceanic and <br />Atmospheric Administration (NOAA) published Rainfall Depth-Duration-Frequency <br />Atlas for Colorado (39). This document was based on a longer period of record <br />and a large number of gages within Colorado. Unfortunately the maps in USDCM <br />and NOAA Atlas did not agree with each other. <br />Since 1977 the Urban Drainage and Flood Control District (UDFCD) has <br />studied the rainfall and runoff relationships in the Denver Metropolitan Area. <br />As part of this effort, rainfall depth-frequency distribution was investigated <br />for a 73-year period at the Denver raingage. Inconsistencies between the <br />rainfall frequency distribution obt~ined using a long term data record and the <br />. rainfall depth-frequency-duration maps in the USDCM were discovered and <br />reported (40). Further investigations indicated that the NOAA Atlas maps, <br />although not perfect, were more in line with the rainfall frequency <br />distribution of the long term record. <br />As the 1982 versi on of the CUHP was being developed (see RUNOFF) it <br />became apparent that the information in the NOAA Atlas could be converted to a <br />family of design rainstorms by distributing these design storms in a manner <br />that yi el ded reasonable peak runoff recurrence frequency di stributions. For <br />the above stated reasons and to use rainfall information consistent with the <br />informati on bei ng used by the State of Colorado, it was concl uded that the <br />NOAA Atlas rainfall information should also be used within the UDFCD. <br /> <br />. <br /> <br />5-1-84 <br />