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The City of Fort Collins has a floodway criteria which limits increases in flood heights to 0.5 foot for all water courses except Dry Creek, therefore a floodway based upon a O.S-foot rise was computed and delineated for Spring Creek and the Cache La Poudre River while Dry Creek was based on a 1.0-foot rise. The floodway for this study was computed on the basis of equal conveyance reduction from each side of the flood plain. The results of these computations are tabulated at selected cross sections for each stream segment for which a floodway is computed (Table 2). As shown on the Flood Boundary and Floodway /lap (Exhibit 2). the floodway boundaries were determined at cross sections; between cross sections. the boundaries were interpolated. In cases where the floodway and lOO-year flood boundaries are close together. 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 lOO-year flood more than 0.5 foot at any point. Typical relationships between the floodway and the floodway fringe and their significance to flood plain development are shown in Figure 2. \- 100-YEAR FLOOD PLAIN ) I F LOODWA Y FRINGE fLOOOWAY FLQODWAY FRINGE STREAM CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FLOODWAY AREA OF FLOOD PLAIN THAT COULD BE USED FOR DEVELOPMENT BY AAISING GROUND FLOOD ELEVATION BEFORE ENCROACHMENT ON FLOOD PLAIN LINE AB IS THE FLOOD ELEVATION BEFORE ENCROACHMENT. LINE CD IS THE FLOOO ELEVATION AFTER ENCROACHMENT. .SURCHARGE IS NOTTO EXCEeD 1.0 FOOT OR LESSER AMOUNT IF SPECIFIED BY STATE. Figure 2. Floodway Schematic 10