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<br />5 <br /> <br />4. Sediment-Transport Function: <br /> <br />The bed-load transport rate, % in vol ume per unit wi dth, is computed <br />from the Meyer-Peter and Muller formula (Meyer-Peter and Muller, 1948): <br /> <br />where <br /> <br />_ 12.85 ( )1.5 <br />qb - - TO - T C <br />,tp Y s <br />= bed shear stress <br />= critical shear stress = 0.047 <br /> <br />.... (2-5) <br /> <br />T <br />o <br />TC <br />P = density of water <br />y s = specific weight <br />y = specific weight <br />ds = median sediment <br /> <br />(y - y)d <br />s s <br /> <br />of sediment <br />of water <br />particle <br /> <br />size <br /> <br />The suspended-load transport rate, qs in volume per unit width, is given by <br />the Einstein formula (Einstein, 1950): <br /> <br />where <br /> <br />qb Gw-1 <br />qs = Tf6 w ((V/u*) + 2.5) 11 + 2.5 12) <br />. (I-G) <br /> <br />....(2-6) <br /> <br />G = depth of bed layer divided by sediment diameter <br />u = shear velocity <br />* <br />V = mean flow velocity <br />11 & 12 = Einstein's integrals <br />w = Rouse Number = particle fall velocity/(0.4u*) <br /> <br />The combined bed-material transport rates are further corrected for the fine- <br />sediment concentration using Colby's empirical relationships (Colby, 1957). <br />Duri ng the sedi ment- rout i ng phase. armori ng effect and bed-materi a 1 <br />composition changes are considered. In determining the armored layer, a <br />functional relationship between mean flow velocity and median sediment size, <br />whi ch determi nes the si ze of sediment that will not move, was fi rst deri ved <br />using Shields' criterion. The channel is assumed to be armored when a layer <br />of nonmoving sediment that is twice as thick as the smallest size of moving <br />sediment particles is established. <br />