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<br />Accumulated point precipitation values at S-minute, <br />lS-minute, I-hour, 2-hour, 3-hour, and 6-hour time increments <br />were obtained from the NOAA Atlas 2 for the 10-, SO-, 100-, <br />and SOO-year flood frequencies. The SOO-year accumulated <br />point precipitation values were determined by extrapolating <br />the 2-, S-, 10-, SO-, and 100-year values. Values for all <br />frequencies were adjusted for depth-area durations prior to <br />application in the HEC-l. The maximum 6-hour point rainfall <br />values and adjusted rainfall values are presented in Table 2. <br />Adjusted rainfall values were reduced by S percent for the <br />lower region and 17 percent for the upper region based on <br />elliptical shaped storms with major to minor axis ratio of 2.S <br />and areal coverage of 3S square miles for the lower region and <br />4S0 square miles for the upper region. The residual <br />precipitation over the upper region was based on the areal <br />adjusted rainfall for the upper region, reduced to account for <br />the greater intensities at the storm center which was centered <br />over the lower region. This additional adjustment reduced the <br />upper region areal adjusted rainfall by less than 2 percent. <br />Hypothetical storm distribution for each frequency is listed <br />in Table 3. <br /> <br /> TABLE 2 <br /> 6-HOUR ACCUMULATED RAINFALL VALUES <br /> RALSTON CREEK BAS~N <br /> UPPER REGION LOWER REGION <br /> Areal Areal <br /> Point Adjusted Point Adjusted <br />Frequency Rainfall Rainfall Rainfall Rainfall <br />(years) (inches) (inches) (inches) ( inches) <br />10 2.2 2.0 2.3 2.2 <br />SO 2.8 2.3 3.0 2.8 <br />100 3.3 2.7 3.6 3.4 <br />SOO 4.9 4.0 S.O 4.7 <br /> <br />S <br />