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Sediment Pond 9, P-9 <br />RIPRAP SIZING - Spillway Channel Across Top of Embankment <br />D50 = Size of Riprap <br />D50 = ((V X S".17)/7.58))"2 <br />D50 = Diameter in feet <br />V = Velocity <br />S = Slope <br />D50 = 0.040 feet 0.482 inches <br />The spillway for sediment pond 9 will be a trapezoidal <br />channel 5.5 feet wide and 0.50 feet deep <br />with a freeboard of 12" for a total depth of 1.500 <br />feet. <br />Considering the fact that the emergency spillway- will <br />probably never have any flow across it, use revegetation <br />as erosion control measure. .4ccordina to Table 4-8, page <br />151 of the Handbook of Steel Drainage & Highway <br />Construction Products, a grass mixture used on a 0-5% slope <br />will resist erosion at velocities in the 3 to 5 fps range. <br />The maximum velocity of the flow through the emergency <br />spillway is 2.95 fps. <br />• POND P-9 VOLUME <br />Drawing D-2-5, No. 1 Mine Seepage Control and Treatment <br />Pond Plan, is the basis for the following pond volume <br />calculations. <br />CONTOUR AREA SF VOLUME VOLUME <br /> Cubic Ft AF <br />4.9 0 <br />6.0 2648 1456 0.033 <br />7.0 3829 3239 0.074 <br />8.0 5011 4420 0.101 <br />9.0 5935 5473 0.126 <br />10.0 6860 6398 0.147 <br />11.0 7650 7255 0.167 <br />11.5 8045 3924 0.090 PRIMARY SPILLWAY INVERT <br /> <br /> 32169 0.74 Volume Sediment Storage & <br /> Water Treatment Storage <br />12.0 8440 4121 0.095 <br />13.0 9271 8856 0.203 <br />13.5 9687 4740 0.109 EMERGENCY SPILLWAY INVERT <br />17716 <br />• TOTAL POND VOLUME 49880 <br />0.41 Volume Available to store <br />the 10-Yr 24-Hr <br />Precipitation Event <br />1.15 <br />P-9-3 New 7-11-91 <br />