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<br />notes. For each depth (hi)' a distance weighted topwidth Bi is defined <br />producing a table of values that may be used for fitting (using least- <br />squares or a log-log plot) a single equation of the form B = Khm to define <br />the prismatic channel geometry. <br /> <br />For rivers with very steep valley side-walls adjacent to the channel <br />(see Fig. la), an additional parameter (hv) may be specified to indicate the <br />depth at which the channel geometry no longer follows the B = Khm <br />relation. As can be seen in Fig. Ib, this feature allows for a more <br />accurate representation of the true channel-valley shape. <br /> <br />. <br /> <br /> <br />Fig. la. Typical Downstream Cross-Section <br /> <br />1 <br />----, <br /> <br /> <br /> <br />T <br /> <br />hv <br /> <br />Fig. lb. Approximated Prismatic Downstream Cross-Section <br /> <br />2.3 Downstream Routing <br /> <br />. <br /> <br />After the maximum breach outflow and stage have been calculated, it is <br />necessary to route the flow downstream. This routing is achieved by employ- <br />ing dimensionless curves developed using the NWS OAMBRK model. These <br />dimensionless curves are grouped into families (see Appendix la) and have as <br />their X-coordinate the ratio of the downstream distance (from the dam to a <br />selected cross section) to a distance parameter computed using the equations <br />given in Appendix I. The Y-coordinate of the curves used in predicting peak <br />downstream flows is the ratio of. the peak flow at the selected cross section <br />to the computed peak flow at the dam. <br /> <br />5 <br />