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• <br />• <br />Table U 13 -16 Ditch 7.18.2011.xlsx <br />• <br />Annual Rainfall 19.9 inches <br />Snowfall 68.8 inches <br />Average Temp High 62.7 inches <br />Average Temp Low 29.9 inches <br />Rain fall low May <br />Rain fall high August <br />Pan Evaporation 37.8 inches <br />Peak Flow (Type II Storm -Steep Slope >16% slope <br />Figure D -2) <br />NRCS Runoff Curve Number 58 <br />Reference <br />Drainage Area 20 acres max <br />Table -U -15 <br />Rolling Dip Outslope 6% <br />Typical May Day Road Ditch <br />Stormwater Hydraulics Analysis <br />May Day Idaho Mine Complex <br />Durango, Colorado <br />Soil Conservation Service, Soil Conservation Naltion Engineering Handbook, Section 4- Hydrology NEH -4. <br />Drainage Flow <br />Area CFS /inch Velocity <br />Return Period Rainfall Duration Rainfall Amount Runoff (acres) Runoff Peak flow (fps) <br />2 24 1.25 0.00 20 25 0.0 <br />10 24 2.7 0.18 20 25 4.5 5.1 See Ditch Design Calculations <br />25 24 3.5 0.45 20 25 11.3 8.5 <br />100 24 3.78 0.58 20 25 14.5 8.8 <br />U.S. Department of Commerce, 1961, Technical Paper 40- Rainfall Frequency Atlas of the United States for Durations from 30 minutes to 24 hours <br />and Return Periods fromm 1 to 100 years. Washington , D.C. <br />Wilkes, S. Glade and Erke C. King, 1975, Procedures forDetermining Peak Flows in Colorado, Incorporateds and Supplements Technica Release No. 55 <br />Uraban Hydrology for Small Water <br />