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<br />yz <br />w, <br />Wz <br />Qmc1 <br />QmcZ <br />nz <br />n, <br />K, & <br />V'c/w <br /><0.50 <br />0.50 <br />to <br />2.0 <br />>2.0 <br /> <br />_ average depth in the contracted section <br />_ bottom width of the main channel <br />_ bottom width of the contracted section <br />= flow in the approach channel that is transporting <br />sediment <br />= flow in the contracted channel, Often this is <br />Q t l but not always. <br />to Q . <br />- Mannlng n for contracted sectlon <br />- Manning n for main channel <br />Kz = exponents determined below <br /> <br />e <br /> <br />K, <br /> <br />KZ <br /> <br />Moda of Bed Material Transport <br /> <br />0.25 0,59 0,066 mostly contact bed material <br /> discharge <br />1.0 0.64 0,21 some suspended bed material <br /> discharge <br />2.25 0.69 0.37 mostly suspended bed r.laterial <br /> discharge <br /> <br />e - transport factor <br /> <br />V.c '" (gy,s,) 0.5, shear velocity <br /> <br />w '" fall veloc i ty of 050 of bed nater ia1. (See Figure <br />4 .2) <br />g '" gravi~y constant <br /> <br />S1 = slope, en:rgy grade line of nain channel <br /> <br />K, = 6(2+e) <br />7 (3+e) <br />K2 = 6e <br />7(3+e) <br /> <br />Laursen's (9) cle,ar-water contraction scour equation has a <br />much simpler derivation because it does not involve any <br />transport function. It simply recognizes that <br /> <br />where: <br /> <br />'t2 = "C c <br /> <br />'2= average bed shear stress, contracted section, <br /> <br />'c= cri tical bed shear stress, incipiant motion, <br /> <br />12 <br />