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<br />Flood boundaries are indicated on the Flood Insurance Rate Map <br />(Panel 0001). On this map, the 10D-year flood boundary corresponds <br />to the boundary of areas of special flood hazards (Zones AI, A2, and <br />A3), and the SOD-year flood boundary corresponds to the 'boundary of <br />areas of moderate flood hazards (Zone B) , <br /> <br />Small areas within the flood boundaries may lie above the flood <br />elevations and, therefore, not be subject to flooding; owing to <br />limitations of the map scale, such areas are not shwon. <br /> <br />4.2 Floodways <br /> <br />Encroachment on flood plains, such as artificial fill, reduces the <br />flood-carrying capacity and increases flood heights, thus increasing <br />flood hazards in areas beyond the encroachment itself. One aspect <br />of flood plain management involves balancing the economic gain from <br />flood plain development againstithe resulting increase in flood <br />hazard. For purposes of the Flood Insurance Program, the concept of <br />a floodway is used as a tool to assist local communities in this <br />aspect of flood plain management. Under this concept, the area of <br />the 100-year flood is divided into a floodway and a floodway fringe. <br />The f100dway is the channel of a stream, plus any adjacent flood <br />plain areas, that must be kept free of encroachment in order that <br />the 100-year flood be carried without substantial increases in flood <br />heights. As minimum standards,. the Federal Insurance Administration <br />limits sucn increases in flood heights to 1.0 foot, provided that <br />hazardous velocities are not produced. <br /> <br />In Greenwood Village, at the recommendation of the city, a floodway <br />having no more than an O.S-footsurcharge has been delineated for <br />this study. The floodway for this study was computed on the basis <br />of equal conveyance reduction from each side of the flood plain. <br />The results of these computations are tabulated at selected cross <br />sections for each stream segment for each stream segment for which a <br />floodway is computed (Table 2)., As shown on the Floodway Map <br />(Exhibit 2), the f100dway boundaries were determined at cross sections; <br />between cross sections, the bo~daries were interpolated. <br /> <br />The area between the f100dway and the boundary of the 100-year flood <br />is termed the floodway fringe. The floodway fringe thus encompasses <br />the portion of the flood plain that could be completely obstructed <br />without increasing the water-surface elevation of the 100-year flood <br />more than 0.5 foot at any point; Typical relationships between the <br />floodway and the floodway fringe and their significance to flood <br />plain development are shown in Figure 2. <br /> <br />8 <br />