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thereby increasing the lOO-year flood hazard. For any channel modification or fill in the sheet flow areas, a detailed review of the improvement should be undertaken to determine the effects downstream. The results of these computations were tabulated at selected cross sections for each stream segment for which a floodway was computed (Table 2). As shown on the Flood Boundary and Floodway Map (Exhibit 2), the floodway widths were determined at cross sections; between cross sections, the boundaries were interpolated. In cases where the boundaries of the floodway and the lOO-year flood are either close together or collinear, only the floodway boundary has been shown. The area between the floodway and the boundary of the lOO-year flood is termed the floodway fringe. The floodway fringe thus encompasses the portion of the flood plain that could be completely obstructed without increasing the water-surface elevation of the lOO-year flood more than 1.0 foot at any point. Typical relation- ships between the floodway and the floodway fringe and their signif- icance to flood plain development are shown in Figure 2. I- 100-YEAR FLOOD PLAIN -, F LOODWA Y FRINGE F LOODWA Y FLOODWAY FRINGE STREAM CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FlOOOWAY AREA OF FLOOD PLAIN THAT COULD BE l''1E[) FOR DEVELOPMENT BY RAISING GAlJUND ENCROACHMENT ,- o SlIRCHARC,( . F LoaD ELEVATION BEFORE ENCROACHMENT ON FLOOD PLAIN LINE AB IS THE FLOOD E:.!...EVAT10N BEFO~E ENCROACHfllENT LINE CD 15 THE I-LOOD ELEVATION AFTER ENCROACHM2NT .SURCHARGE IS NOTTO EXCEED 1 0 "'.OOT (FEMA REGUIREMENT) OR LES~~ER AMOUNT IF SPECIFIED BY STATE, Figure 2. Floodway Schematic 17