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COLORADO <br /> Division of Water Resources <br /> Department of Natural Resources <br /> Table 1 Sizing Guidelines for Livestock Water Tanks and Erosion Control Dams <br /> Minimum Recommended Minimum Recommended <br /> Bottom Width'(Feet) Bottom Width'(Feet) <br /> Drainage Area (Acres)' Low Intensity Rainfall Zone' High Intensity Rainfall Zone' <br /> 175 8 8 <br /> 225 8 10 <br /> 275 8 12 <br /> 325 8 15 <br /> 375 10 17 <br /> 425 11 19 <br /> 475 12 21 <br /> 525 13 24 <br /> 575 15 26 <br /> 625 16 28 <br /> 675 17 30 <br /> 725 19 33 <br /> 775 20 35 <br /> 825 21 37 <br /> 875 22 39 <br /> 925 24 42 <br /> 975 25 44 <br /> 1025 26 46 <br /> 1075 28 48 <br /> 1125 29 51 <br /> 1175 30 53 <br /> 1225 31 55 <br /> 1275 33 57 <br /> 1325 34 59 <br /> 1375 35 62 <br /> 1425 37 64 <br /> 1475 38 66 <br /> 'Minimum recommended bottom width for drainage areas less than 175 acres is 8 feet <br /> 2Refer to map of rainfall intensity zones <br /> 3USGS StreamStats(https://streamstats.usgs.gov/ss)can be used to estimate drainage area if unknown (note: 1 square mile equals 640 <br /> acres. <br /> Crest Elevation <br /> Freeboard <br /> 3 ft (min) / �Sideslope 2:1 (min) <br /> for earthen channels <br /> Bottom Width <br /> Spillway Section <br />