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<br />Small areas within the flood boundaries may lie above the flood elevations, <br />and, therefore, not be subject to flooding; owing to lack of detailed <br />topographical information or to limitations of the map scale, such areas are <br />not shown. In cases where the 100-year and the 500-year flood boundaries <br />are close together, only the 100-year boundary has been shown. <br /> <br />4.2 <br /> <br />Floodways <br /> <br />~ <br /> <br />Encroachment on flood plains, such as artificial fill, reduces the flood- <br />carrying capacity and increases flood heights, thus increasing flood hazard in <br />areas beyond the encroachment itself. One aspect of flood plain <br />management involves balancing the economic gain from flood plain <br />development against the resulting increase in flood hazard. For purposes of <br />the Flood Insurance Program, the concept of a floodway is used as a tool to <br />assist local communities in this aspect of flood plain management. Under <br />this concept, the area of the 100-year flood is divided into a floodway and a <br />flood way fringe. The floodway is the channel of a stream, plus any adjacent <br />flood plain areas, that must be kept free of encroachment in order that the <br />100-year flood be carried without substantial increases in flood heights. As <br />minimum standards, the Federal Insurance Administration limits such <br />increases in flood heights to 1.0 foot, provided that hazardous velocities are <br />not produced. Currently, the State of Colorado does not have a stricter <br />requirement. <br /> <br />~~ <br /> <br />The 'floodway recommended for the San Miguel River, Fan Creek, and <br />Leopard Creek was computed on the basis of equal conveyance reduction <br />from each side of the flood plain. The results of these computations are <br />tabulated at cross sections for each stream segment for which a flood way is <br />computed (Table 3). At some cross sections, floodway boundaries were <br />delineated at the river banks. The flood way for Cornet Creek is not <br />recommended because of the absence of a stable, defined channel in the <br />alluvial fan. Portions of floodway for the San Miguel River lie within the <br />Town of Sawpit. <br /> <br />-. <br /> <br />As shown on the Floodway Map (Exhibit 2), the floodway boundaries were <br />determined at cross sections; between cross sections, the boundaries were <br />in terpola ted. <br /> <br />The area between the floodwayand the boundary of the 100-year flood is <br />termed the floodway fringe. The flood way fringe thus encompasses the <br />portion of the flood plain that could be completely obstructed without <br />increasing the water-surface elevation of the 100-year flood more than 1.0 <br />foot at any point. Typical relationships between the floodway and the <br />floodway fringe and their significance to flood plain development are shown <br />in Figure 2. <br /> <br />13 <br /> <br /> <br />~...~~~~~~:f~:;_--,:: <br />