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<br />17 <br /> <br />qsi = qsbi + qssLi + qssMi + qssUi <br /> <br />.... (2-22) <br /> <br />where <br />qsi = <br />qsbi = <br />qssLi = <br />qssMi = <br />qssUi = <br /> <br />bed-material discharge for the i-th fraction of bed sediment <br />bed-load discharge for the i-th fraction of the bed sediment <br />suspended-load discharge in lower zone <br />suspended-load discharge in middle zone <br />suspended-load discharge in upper zone <br /> <br />Detailed procedures for computation <br />by Toffaleti (1966). <br /> <br />of q bi' q Li' q M" and q U' are given <br />s ss SS 1 SS 1 <br /> <br />5. Numerical Scheme: <br /> <br />HEC-6 first solves the one-dimensional energy and continuity equations, <br />(2-20) and (2-18), using an iterative, standard step-backwater method, to <br />obtain basic hydraulic parameters such as depth, width, and slope at each <br />section which are necessary to compute the sediment-transport capacity. <br />Friction loss is calculated from Manning's equation with specified n values. <br />A functional relationship between Manning's n and water discharge or flow <br />stage can be used if available. Expansion and contraction losses are <br />calculated using loss coefficients. The potential sediment-transport <br />capacities at all cross sections are computed next, using one of the five <br />optional sediment-transport functions. Note that the sediment discharge at <br />the upstream boundary must be related to the water discharge by a rating table <br />for different sediment-si ze fractions. COII1lutations of sediment-transport <br />capacity begi n at the upstream boundary and move reach by reach to the <br />downstream boundary. Equation (2-19) is then solved using an explicit, <br />finite-difference scheme: <br /> <br />-(GR - GL) B(Yp'- Yp) <br />0.5 ( XL + XR) + lit = 0 <br /> <br />.... (2-23) <br /> <br />or <br /> <br />llt <br />Yp' = Yp + 'O'3B (GR- GL )/(XL + XR) <br /> <br />.... (2-24) <br />