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North Decline Final Reclamation <br />Powderhorn Coal Company <br />• Riprap Size Aeguirements for North Decline Drainage Channel <br />SECTION 1 <br />Riprap Size = 12" <br />Slope = 0.075 <br />Discharge = 470 cfs <br />Manning's n = 0.0395 x ds tib = 0.0395 x 1t~6 = 0.0395 <br />At n = 0.0395, V = 10.84 fps (from F1pMp.STER program) <br />Drainage Criteria Manual rock size requirements: <br />VSO.n = 5.8 <br />dsn . (Ss_1) . <br />where: V = velocity in feet/sec <br />S = channel slope in feet/foot <br />SS = specific gravity of rock <br />dsu = riprap site <br />assume: SS = 2.5 <br />dso = ((10.84 x 0.075o.t~) / ((2.5-1)0.66 x 5.8))Z <br />-' dso = 0.85' = 10.2" <br />• therefore, 12" rock is acceptable <br />6ECTION 2 <br />Riprap Size = 6" <br />Slope = 0.025 <br />Discharge = 470 cfs <br />Manning's n = 0.0395 x dsot/6 = 0.0395 x O.St~6 = 0.0352 <br />At n = 0.0352, V = 8.26 fps (from F1,pMASTER program) <br />dso = ( (8.26 x 0.025.77) / ( (2.5-1)0'66 x 5.8) )Z <br />dso = 0.34' = 4.1" <br />therefore, 6" rock is acceptable <br />.. • <br />(New 2-26-92) <br />NDEC - 13 <br />