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<br />. <br /> <br /> <br />COLORADO STATEWIDE <br />DRAINAGE AND FLOODPLAIN MANAGEMENT CRITERIA MANUAL <br /> <br />Step 4: Plot the time-intensity-frequency curve for the 100-year storm for <br />Rocky Subdivision. (See Figure CH5-F116). <br /> <br />Application: The time-intensity-frequency curve is used to determine the <br />rainfall intensities used in the Rational Method of detennining runoff <br />described in Chapter 5, Section 2.0. <br /> <br />1.7.3 EXAMPLE 3: CUHP STORM DISTRIBUTION <br /> <br />Problem: <br /> <br />Develop a 100-year rainfall distribution to be used with CUHP model for a 17 <br />square mile drainage basin. <br /> <br />100-year, 1-hr rainfall depth = 2.20 inches <br />100-year, 3-hr rainfall depth = 2.75 inches <br /> <br />Solution: <br /> <br />. <br /> <br />Step 1: Since the drainage basin is less than 20 square miles but greater <br />than 10 square miles, a three-hour stonn distribution should be. used <br />with CUHP. First, a two-hour temporal distribution should be <br />developed by multiplying the 100-year, 1-hour rainfall value of 2.2 <br />inches by the incremental distribution percentages from Table CH5- <br />T103. <br /> <br />Step 2: Calculate incremental rainfall depths for the period between 125 and <br />180 minutes by evenly distributing the rainfall depth difference <br />between the 100-year, 3-hour rainfall depth of 2.75 inches and the 2- <br />hour total precipitation. <br /> <br />Step 3: Apply the depth-area reduction factors from Table CH5- T104 to the <br />calculated incremental rainfall depths for the entire storm duration. <br /> <br />Results of the above three steps are shown in Table CH5-T105. <br /> <br />. <br /> <br />CHAPTER 5 <br />HYDROLOGY <br /> <br />SECTION 1.0 <br />RAINFALL <br /> <br />AUGUST 2002 <br /> <br />RAINFALL <br /> <br />CH5-111 <br />