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<br />provided that hazardous velocities are not produced. <br /> <br />Steep slopes and numerous obstructions along the riverine <br />flood plains in Trinidad cause unstable flow and hazard- <br />ous velocities. Therefore, no encroachment within the <br />100-year flood boundaries is considered feasible on the <br />tributaries; and on the Purgatoire River, encroachment <br />is indicated only on the left bank, as shown on the <br />Floodway Map, Exhibit 2. The fringe areas shown above <br />and below the Pinon Canyon confluence are relatively <br />isolated from main-stem flow; their exclusion from the <br />floodway does not alter the water-surface elevation. <br />Table 1 summarizes the dimensions of the floodways at <br />selected cross sections. <br /> <br />. <br /> <br />The area between the floodway and the boundary of the <br />100-year flood is termed the floodway fringe. The <br />floodway fringe thus encompasses the portion of the <br />flood plain that could be completely obstructed without <br />increasing the water-surface elevation of the 100-year <br />flood more than 1 foot at any point. Typical relation- <br />ships between the floodway and the floodway fringe and <br />their significance to flood plain development are shown <br />in Figure 5. <br /> <br />I ( <br /> <br />100-YEAR FLOOD PLAIN <br /> <br />.1 <br /> <br />FLOODWAY <br />FRINGE <br /> <br /> <br />FLOODWAY <br /> <br />FLOODWAY <br />FRINGE <br /> <br />STREAM <br />CHANNEL <br /> <br />FLOOD ELEVATION WHEN <br />CONFINED WITHIN FLOOOWAY <br /> <br /> <br />AREA OF FLOOD PLAIN THAT COULD <br />BE useD FOR DEVELOPMENT BY <br />RAISING GROUND <br /> <br /> <br />D <br /> <br />FLOOD ELEVATION <br />BEFORE ENCROACHMENT <br />ON FLOOD PLAIN <br /> <br />LINE AS IS THE FLOOD ELEVATION BEFORE ENCROACHMENT. <br />LINE CO IS THE FLOOD ELEVATION AfTER ENCROACHMENT. <br />.SURCHARGE IS NOT TO EXCEED 1.0 FOOT (FIA REQUIREMENT) OR LESSER AMOUNT IF SPECIFIED BY STATE. <br /> <br />Figure 5. <br /> <br />Floodway Schematic <br /> <br />11 <br />