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roughness. The following discussion of this method is very general. For specifics, the reader is referred to the discussion of gradually varied flow in Chow (1959). Given the discharge, the elevation of the bed and distance between cross sections, and an assumed value for Manning's n, the computations follow this general sequence. 1. Starting at the downstream-most cross section, a water surface elevation is assumed or given. For the next section upstream, an eTevation is assumed; this elevation will be verified or rejected on the basis of subsequent calculations. Z._ The depth of flow is computed for the corresponding water surface elevations. 3. The cross-sectional area is determined from the channel dimen- sions and assumed water surface elevation. 4. The mean velocity is calculated, using the continuity equation for the known discharge and cross-sectional area. 5. The velocity head (V2/2g) is calculated, and the total head determined by addition to the starting water surface eleva- ti on-. A separate set of calculations is then made using the Manning equation: 6. The hydraulic. radius is determined for the cross 'section, using the above assumed-water surface elevation. 7. The energy slope between adjacent cross sections is determined by: Se =. n2 V2 ? Cg) 2..22-R4 where, n = the assumed value for Manning's n V = the mean velocity calculated in step 4 above R = the hydraulic radius from step 6 above. 8. The friction loss between the two adjacent cross sections is found by multiplying the average energy slope by the distance between stations. 9. This friction loss is added to the computed total head at the first station, to give the total energy head at the next upstream station. If the value obtained does not agree closely with that found in step 5, a new water surface eleva- tion is assumed and the process repeated until agreement is obtained. ?3