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<br />HYDROLOGY <br />Rainfall <br />Rainfall information for the State of Colorado is published <br />by the National Weather Service in a volume titled NOAA Atlas <br />2, Precipitation-Frequency Atlas of the Western United <br />States, Volume 3-Colorado. The publication contains maps <br />giving total rainfall depths for the 2 through 100-year <br />frequencies and the 6-hour and 24-hour durations. For the <br />24-hour duration, the 10-year rainfall total is 1.8 inches, <br />the 25-year total is 2.1 inches and the 100-year total is 2.6 <br />inches. <br />Runoff Volumes <br />• <br />Runoff volumes were computed using equation 10.10 and the <br />procedure outlined in Chapter 10 of the Soil Conservation <br />Service's National Engineering Handbook, Section 4 - <br />Hydrology, dated 1971. Antecedent Moisture Condition - II <br />(AMC) curve numbers (CN) were estimated for the tributary <br />areas of each pond considering the worst case for the land <br />use and ground cover. AMC-II is considered applicable for <br />average conditions and allows for a total rainfall of 1.4 to <br />2.1 inches within the preceeding five days of the storm. <br />Peak Flow Rates <br />Peak rates of runoff for each pond tributary area were <br />calculated for the 10, 25 and 100-year, 24-hour duration <br />precipitation events in accordance with Procedures for <br />Determining Peak Flows. in Colorado, a publication of the Soil <br />Conservation Service dated March, 1980. The tributary areas <br />Leonard Rice Consulting Waler Engineers.lnc. <br />