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4. EFFECTIVE FLOW OPTIONS A series of program capabilities are available to restrict flow to the effective flow areas of cross sections. Amono these capabilities are options to simulate sediment deposition, to confine flows to leveed channels, to block out road fills and bridge decks, and to analyze flood plain encroachments. These program options are illustrated in Figure 3 below. """',,,. '~.!i.!:'.... ....:-~.: z o I- .0: > UJ ..J UJ LEGENC: 6 Channel Bank SIalians o G R Cata Paints STATION INEFFECTIVE AREAS: ] I FLOW BELOW BANK ELEVATIONS t*Jt~ FLOOC PLAIN ENCROACHMENT ~ SEDIMENT DEPOSITION _ BRIDGE DECK Figure 3. Types of Effective Flow Options Sediment deposition may be specified by variable ELSED on the X3 card. The specified elevation (ELSED) is extended horizontally across the cross section and the area below this elevation is not considered by the program to carry flow. Cross sections with low overbank areas or levees, require special consideration in computing water surface profiles because of possible overflow into areas outside the main channel. Normally the computations are based on the assumption that all area below the water surface elevation is effective in passing the discharge. However, if the water surface eleva- tion at a particular cross section is less than the top of levee elevations, and if the water cannot enter or leave the overbanks upstream of that cross section, then the flow areas in these overbanks should not be used in the computations. Variable IEARA on the X3 card and the bank stations coded in fields three and four on the Xl card are used for this condition. By setting IEARA equal to ten the program will consider only flow confined by the levees, 17