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<br />28 <br /> <br />T = critical shear stress for erosion <br />ce <br />T cd = critical shea r stress for deposition <br />Cb = sediment concentration in bed layer <br />Cmax = maximum concentration in bed layer <br /> <br />5. Numerical Scheme: <br /> <br />The Link-Node Hydrodynamic model fi rst sol ves (2-37) and (2-39), which <br />yield the depth-averaged mass-velocity component, u , and flow depth. The <br />(l <br />depth-averaged sediment-particle velocity, <U >, then is calculated from (2- <br />s <br />44). The convective-diffusion equation, (2-38), is next solved using the <br />finite-element method with isoparametric, quadrilateral elements. Time <br />marching is effected by a two-point implicit scheme. At each time step, the <br />model provides the average sediment concentration at every computational node <br />point and the cross-section bed profile. Note that (2-45) and (2-46) are used <br />to determine the source/sink term, S, in (2-38). <br /> <br />6. Data Requirements: <br />SEDIMENT-4H requires the following input data: <br /> <br />(1) Number of cross sections. <br />(2) Initial cross-section geometries of all cross sections. <br />(3) Manning's n at each cross section. <br />(4) Downstream stage hydrograph. <br />(5) Bed-material characteristics: median size, fall velocity, <br />critical shear stress, maximum permissible concentration in bed <br />layer, bed-strata data, and initial suspended-sediment <br />concentration. <br />(6) Diffusion coefficient in the longitudinal direction. <br />(7) Upstream sediment boundary condition: suspended-sediment <br />concentration specified as a function of time. <br /> <br />7. Model Limitations and Applicability: <br /> <br />SEDIMENT-4H considers only a single sediment-particle size. Suspended- <br />sediment particles are assumed to be convected at the local water-flow <br />