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<br />6 <br /> <br />5. Numerical Scheme: <br /> <br />HEC2SR fi rst runs the HEC-2 program to sol ve (2-3) and (2-4) by the <br />standard, iterative-step method. The computational procedure is as follows: <br /> <br />(1) Assume a water-surface elevation, Y2' at section 2. <br />(2) Based on the assumed value of Y2' determine the corresponding total <br />conveyance and velocity head. <br />(3) Compute Sf and compute he from (2-4). <br />(4) Check the equality of (2-3) with the computed value using the <br />assumed Y2. <br />(5) Adjust Y2 if the error in step (4) is significant, repeat steps 1 <br />through 5 until the values agree to within 0.01 ft. <br /> <br />After the HEC-2 computation, the bed-material discharge, which considers both <br />sediment avail abil ity and transport capacity, is estimated for each <br />computational reach. The channel aggradation/degradation corresponding to the <br />difference between the sediment inflow and outflow is also determined for each <br />reach. This sediment-volume change is distributed uniformly along the <br />reach. The change in elevation at each cross-section vertical is determined <br />by a weighting factor based on flow conveyances in adjacent lateral <br />subsections. This technique is also used in KUWASER (see Section II-B) <br /> <br />6. Data Requirement: <br /> <br />HEC2SR requires the following input data: <br />(1) Data on channel geometry in HEC-2 format. <br />(2) Information on subreaches which are divided according to hydraulic <br />and sediment-transport characteristics. including number of cross <br />sections, reach length, number of tributaries, surface and subsurface <br />sediment-size distributions, and potential armor layer. <br />(3) Watershed data. including channel-geometry representation and <br />sediment-size distribution; this can be neglected if the sediment <br />inflow from the lateral tributaries is neglected and/or the upstream <br />reach does not connect to the upland watershed area. <br />