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e "I'... EM 1110-2-1416 15 Oct 93 -- ,. L 0 U . N "' , C ,. . .' 11.2..:1.41..."'. - .. e . 0Mr0R0 COIO'IITEll "'-"" ttCXtnt SAtQ10H cotfIUTED P'\.OU Figura 5-2. Discharge hydrograph at tha oakford gaga at tha mouth of the Sangmon Rlvar . F determine. For bed slopes from 2 to 5 feet per mile, the need for unsteady flow analysis may depend upon the study objectives. Large inflows from tributaries or back- water from a receiving stream may require the applica- tion of unsteady flow. Flow reversals may occur under such conditions, rendering hydrologic routing useless. For slopes greater than 5 feet per mile, steady flow analysis is usually adequate if the discharge is correct , . . e C. Full networks. For full networks, where the flow divides and recombines, unsteady flow analysis should always be considered for subcritical flow. Unless the problem is simple, steady flow analysis cannot directly compute the flow distribution. For supercritical flow, contemporary unsteady flow models cannot determine the split of flow. Records of current speeds and directions at different points in a flooded valley and rates of inunda- tion of floodplains help determine whether a one-dimensional approach to a simulation is adequate (see Chapters 4 and 6). 5-4. Geometry The geomeby of the reach can be determined from topo- graphic maps, surveyed profiles and cross sections, onsite inspection, and aerial mapping. a. Costs. The influence of errors in reach geomeby on predicted stages can be estimated based on regression equations given in "Accuracy of Computed Water Sur- face Profiles" (U.S. Army Corps of Engineers 1986). Profile errors can also be investigated in a simplified, though representative, reach by modifying its geomeby in accord with the possible error and noting the effect on predicted discharges and stages. The costs associated ~