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channel and the floodway boundary is the 100-year flood boundary. For Bear and Mount Vernon Creeks, the encroachment is limited by the velocity criterion rather than the criterion that permits a I-foot rise in energy grade line or water-surface elevation. The data presented in the Floodway Data table represents the computed water-surface elevations. The floodways presented in this study were computed on the basis of equal conveyance reduction from each side of the flood plain. The results of these computations were tabulated at selected cross sections for each stream segment for which a floodway was computed (Table 3). 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 100-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 100-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 100-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 6. I- 100-YEAR FLOOD PLAIN -I FLOODWAY FRINGE FLOODWAY FLOODWAY FRINGE STRIiAM CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FLQODWAY AREA OF FLOOD PLAIN THAT COULD BE USED FOR DEVELOPMENT BY RAISING GROUND ..,7 FLOOD ELEVATION BEFORE ENCROACHMENT ON FLOOD PLAIN LINE AB IS THE FLOOD ELEVATION BEFORE ENCROACHMENT. LINE CO IS THE FLOOD ELEVATION AFTER ENCROACHMENT. .SURCHARGE IS NOT TO EXCEeD 1.0 FOOT (FEMA REQUIREMENT) OR LESSER AMOUNT IF SPECIFIED BY STATE. Figure 6. Floodway Schematic 16