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Floodwaysi for this study were computed on the basis of equal convey- ance reduption from each side of the flood plain, except where such equal redpction would be prevented by high bluffs. Under no circum- stance iSI thE~ floodway encroached into the stream channel itself. The resul~s of these computations are tabulated at selected cross sections ~or each stream segment for which a floodway is computed (Table 4). As shown on the Floodway Map (Exhibit 2), the floodway boundaries were dete~mined at cross sections; between cross sections, the boundarie~s were interpolated. In cases where the floodway and 100- year flood boundaries coincide, only the floodway boundary has been shown. , , The area ;between the floodway and the boundary of the lOa-year flood is itermed the floodway fringe. The floodway fringe thus encompass~es the portion of the flood plain that could be completely obstructed without increasing the water-surface elevation of the I lOa-year Iflood more than 1.0 foot at any point. Typical relation- ships betiween the floodway fringe and their significance to flood , plain de~elopment are shown in Figure 5. , I. 100-YEAR FLOOD PLAIN )1 I IfLOODWAY FRINGE FLOODWAY FLOODWAY FRINGE STREAM CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FLOODWAY ENCROACHMENT : --r ENCROACHMENT -,- . ,--- . I Dol . -L AREA OFiFLOOD PLAIN THAT COULD BE USED FOR DEVELOPMENT BY RAISING <pROUND -~ -~,,-,^"..... FLOOD ELEVATION BEFORE ENCROACHMENT ON FLOOD PLAIN LINE AB IS THE FLOOD ELEVATION BEFORE ENCROACHMENT. LINE CD IS THE FLOOD ELEVATION AFTER ENCROACHMENT 'SURCHARGE IS NOT TO ~XCEED 1.0 FOOT (FIA REQUIREME~T) OR LESSER AMOUNT IF SPECIFIED BY STATE , ' Figure 5. Floodway Schematic 21 ,,,,-~"- ,"-- -...".;..."------~-~ 1_- ----'~-~~.....-"- ~~~