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<br />ATTACHMENT 1 <br />To establish the critical flow velocity, the following procedure <br />should be followed. Shields relation will provide the velocity at <br />which a particle of a given size will be at incipient motion. <br />Assuming the boundary is completely rough, the Shields relation <br />becomes <br />T <br />0.047 = c <br />IYS-Y Ds <br />where Ys = 165.4 lb/ft3 and Y = 62.4 lb/ft3, rc is the critical <br />shear stress in Ib/ft2 and Ds is particle size diameter in feet. <br />Solving for rc <br />s = 4.84 D <br />c s <br />For particle sizes equal to 1, 2.5, and 3.5 inches, the critical shear <br />stress becomes <br />tc = 0.4 1D/ft2 for Ds = 1" <br />rc = 1.0 lb/ft2 for Ds = 2.5" <br />is = 1.4 lb/ft2 for Ds = 3.5" <br />The resistance formula <br />f = BZT, <br />V p <br />where f is the Darcy-Weisbach friction factor, r is the bed shear <br />stress, V is the velocity and p is the density, can be solved for <br />V as <br />1/2 <br />V = (8 P} <br /> <br />