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Technical Revision 90-06 <br />DRAINAGE AND SEDIMENT CONTROL PLAN <br />DESIGN CRITERIA AND METHODOLOGY <br />Drainage and sediment control structures for Mine No. 3 have been designed in compliance <br />with Rule 4.05 using standard engineering design practices. The design methodology utilized <br />is consistent with the engineering practices outlined in the publications entitled: "Procedures <br />for Determining Peak Flows in Colorado", USDA-Soil Conservation Service Technical Release <br />No. 55, and "Predicting Rainfall Erosion Losses", USDA-Soil Conservation Service Handbook <br />No. 537. The design calculations for the drainage and sediment control structures are <br />presented at the end of this section, following the description of the methodology. <br />HYDROLOGY <br />Rainfall <br />Rainfall depths for the project area were determined from the National Weather Service <br />publication; "NOAA Atlas 2, Precipitation-Frequency Atlas of the Western United States, <br />M Volume 3-Colorado". Rainfall depths for the design events specified by Rule 4.05 are as <br />follows: <br />~ 10-year, 24-hour storm event, 1.8 inches <br />~ 25-year, 25-hour storm event, 2.1 inches <br />~ 100-year, 24-hour storm event, 2.7 inches <br />Runoff <br />The amount of runoff resulting from the respective design storm events was determined by <br />utilizing the standard Soil conservation Service (SCS- method outlined in Technical Release <br />No. 55: <br />~ The contributing drainage area was delineated on a 1 " = 200' topographic map <br />M <br />TR 90-06 Exhibit 3 - 5 Revised 11 /16/90 <br />