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<br />DRAINAGE CRITERIA MANUAL <br /> <br />RAINFALL <br /> <br />. <br /> <br />3. DESIGN STORM DISTRIBUTION FOR CUHP <br /> <br />3.1 Temporal Distribution <br />The 1982 version of the CUHP (see RUNOFF) was designed to be used with <br />THE NOAA I-hour ra infa 11 depths provi ded under 2.1. To obta i n a temora 1 <br />distribution for a design storm in the Denver region, the I-hour depth is <br />transferred into a 2-hour design storm by multiplying the I-hour depth(s) by <br />the percentages for each time increment given in Table 3-1. The resultant <br />design storm(s) may then be used with the 1982 version of the CUHP. <br /> <br />3.2 Example: Develop a 2-Hour Design Storm <br />Develop a 2-hour, lO-year design storm using the I-hour, 10-year depth of <br />1.6 inches from Example in 2.3. Set up a working table (Table 3-2) with <br />columns for "Time", "Percent of I-hour Rainfall", and "Incremental Rainfall". <br />Take the "Percent of I-Hour NOAA Rainfall Atlas Depth" for the 10-year case <br />from Table 3-1 and enter in the second column of Table 3-2. For each time <br />increment multiply the 1.60-inch I-hour depth by the value in the second <br />. column. After dividing the answer by 100 and rounding off to two decimal <br />places enter the result in the third column under "Incremental Rainfall". The <br />third column then is the 5-minute incremental tabulation of the 10-year design <br />rainfall. <br />You will note that the total of all the incremental depths for the first <br />hour does not agree with the I-hour depth of 1.60-inches from Example in <br />Section 3.2. Do not be alarmed. The temporal distribution was cal ibrated to <br />work with the CUHP procedure and the fi rst hour of the des i gn storm is not <br />intended to be the same as the I-hour depth obtained from the NOAA Atlas. <br />Nevertheless, the NOAA Atlas value is "imbeded" in the most intense portion of <br />the 2-hour design storm. <br /> <br />. <br /> <br />5-1-84 <br />