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<br />rI <br /> <br />16 <br /> <br />area, roughness and hydraulic radius. Width of the section is <br /> <br />. <br /> <br />considered in three basic segments, main channel and right and left <br /> <br />. <br /> <br />overbanks. Separate values of roughness are usually selected for each <br /> <br />segment. Area and hydraulic radius are also isolated by segments, with <br /> <br />hydraulic radius determined as the length of the actual water-earth <br /> <br />boundary for each segment. The same basic equation as in the Standard <br /> <br />, <br /> <br />Step Method is used, except that it is modified to allow separate <br /> <br />calculations for each segment of flow. To apply the equation, it is <br /> <br />first necessary to determine discharge in each flow segment. These <br /> <br />sub-discharges are computed from Manning's equation by an iterative <br /> <br />solution of assuming a given .slope and solving for discharges. The next <br /> <br />iteration multiplies the solution from the previous iteration by the <br /> <br />ratio of actual discharge to calculated discharge. After obtaining sub- <br /> <br />discharges, the equation appears as: <br /> <br />. <br /> <br />(V;Qs)2 <br />a2 2gQ + d2 + z2 + aj <br /> <br />(V2Q )j <br />~ + dj + Zj + hf + he <br />2gQ <br /> <br />where V = velocity in a segment <br />s <br /> <br />Qs = discharge in a segment <br /> <br />h = eddy losses <br />e <br /> <br />hf <br /> <br />friction losses, computed from an iterative solution for <br />friction slopes at each section. <br /> <br />Other quantities are as in the Standard Step Method. <br /> <br />Eddy losses are computed as a coefficient times the difference in <br /> <br />. <br /> <br />velocity head between the sections. A negative differential in velocity <br /> <br />head (calculating step-wise upstream) indicates an expansion, so a loss <br /> <br />. <br /> <br />coefficient of 0.50 is used. A coefficient of 0.10 is used for contrac- <br /> <br />tions. <br />