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EM 1110-2.1416 15 Oct 93 taSSDS:PP% AXVeR . { T .. e ... % . I . N .. . .. .. .. . T .. .:we rI!it 1tAR..N"R: .x.H..;JUI... .,M>> ~ OCT HJY ~ .."" -~ I1EtPKtS CI8S STAOe: I1I!Jftt:a ci::lttP\n1!D STMI! Figure 5-5. Reproduction of Stage et Memphis from Stage. Routed from Cairo, 220 Mlle. Upstream stage hydrograph. This difference could have been cor- rected by adjusting the n values, but the error would have become apparent as an inconsistency when verifying against other events. Figure 5.7 shows the correct simu- lation which includes the ungaged inflow. (2) The estimation of ungaged inflow is difficult because of the wide variation in spatial rainfall patterns. Two methods are proposed: estimating runoff using drainage area ratios applied 10 gaged watersheds in the vicinity and use of a rainfall-runoff model. Drainage area ratios work well for large events when the rainfall is relatively uniformly distributed spatially. For smaller events, which cause small peaks in low flow, the method is less appropriate. A hydrologic model is preferable, but 5-8 it may be an additional stody step to develop and main- tain, and requires precipitation data. Small, often unnamed, tributaries may be lumped together and entered uniformly as a single hydrograph which is distributed along a portion of the stream. Generally, the distribution is according to floodplain distance. Uniform lateral inflow is for the convenience of the modeler. (3) Lateral inflow from a gaged tributary or from a large ungaged tributary is usually entered at a point. For streams with a flat bed slope a tributary inflow causes a disruption in the stage profile, as shown in Figure 5-8 by the correspondence between flow and stage discontinu- ities. Locating point inflows, even for ungaged areas, . . . .. . e