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tNuvemco Monogram Mine SWMP <br />o Slope= 0.001 ft/ft <br />• The Mannings Coefficient is 0.040 which is for rough rock. This will result in the <br />greatest depth over the outlet. <br />Using the above in the Haestad Methods, Inc computer program F1owMaster and solving <br />for the depth of water, it was determined that the depth would be 0.27 feet. As the outlet <br />silts in, the coefficient will be reduced and the depth will be less. Output for this <br />calculation is attached. The resulting velocity across the outlet is 1.46 feet per second <br />(fps). <br />RIPRAP DESIGN <br />The next step was to size the riprap for the detention pond outlet and the channel <br />downstream where it enters the existing natural channel. The slope of the channel was <br />calculated using the contours shown on Map T-2. The slope of the channel was <br />calculated between each 2-foot contour line from elevation 6300 to 6292 feet. The <br />results are shown below. <br />LENGTH SLOPE CHANNEL VELOCITY <br />ELEVATION ( feet) (feet/feet) SHAPE (fps) <br />6300 <br />6298 <br />13.7 0.146 Trapezoidal <br />36.4 0.055 Trapezoidal 2.51 <br />6296 <br />25.1 0.080 Trapezoidal 2.82 <br />6294 <br />61.9 0.032 Vee 2.96 <br />6292 <br />* - Not computed, upstream of detention pond outlet <br />The riprap will be designed for the channel section from Elevation 6296 to 6294 which is <br />the steepest section. The riprap will use stone from on-site. <br />Using the equation <br />W = 0.0002 V6 SG/(SG-2)3 sin -3 (r-a) <br />W = minimum rock mass (size or weight) <br />V = velocity to which bank is exposed <br />SG = specific gravity of rock <br />r = 70° (for randomly place rubble, a constant) <br />a = outside slope face angle with horizontal, DEGREES <br />4