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<br />Nuvemco Monogram Mine SWMP <br />50-YR 1.8 2.75 <br />100-YR 2.0 3.0 <br />This information was entered into UD-RainZone v 1.01 a, Z-2 to calculate the Rainfall <br />Intensity-Duration-Frequency Table for Zone Two in the State of Colorado that is <br />attached. <br />Time of Concentration <br />In order to use this information it is necessary to calculate the Time of Concentration, or <br />duration for the study area. The time of concentration used to determine the average <br />intensity of rainfall, is equivalent to the amount of time needed for runoff to travel from <br />the most remote point of the basin to the design point. <br />For the study area, this distance is only approximately 209' using the previously <br />described AutoCAD drawing, Map T-2. There are various methods available to compute <br />the time of concentration. Various publications recommend minimum times from 5 <br />minutes in urban areas to 10 minutes in rural areas. Using the Kirpich formula and the <br />sdsu tc calculator, the time of concentration for the small study area is only 1.33 minutes. <br />See attached printout. For this study a time of concentration of 5 minutes will be used. <br />Using a time of concentration of 5 minutes, the rainfall intensity for a 100-yr 24-hr storm <br />is 5.22 inches/hour. See the attached printout. <br />Area <br />See the above section for discussion and calculations. <br />Q <br />Using all of the above and inputting it into the Rational formula Q = CiA where <br />Q = peak discharge, cfs <br />C = Rational Method runoff coefficient =0.95 <br />i = rainfall intensity, inches/hour = 5.22 inches/hour <br />A = Area, acres = 0.68 acres <br />Q = 3.507 cfs <br />See attached printout from sdsu.edu. <br />DETENTION POND OUTLET <br />The peak discharge computed above of 3.5 cfs will be used to size the detention pond <br />outlet as shown on Map T-2. The following assumptions were made in sizing the outlet: <br />• The outlet is trapezoidal with <br />o A bottom width of 8.00 feet; <br />o The side slopes are 3H:1 V