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<br />Ii( <br /> <br />1 aD-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 FLOODWAY <br /> <br /> <br />AREA OF FLOOD PLAIN THAT COULD <br />BE USED FOR DEVELOPMENT BY <br />RAISING GROUND <br /> <br />L'NE AB '5 THE FLOOD ELEVATION BEFORE ENCROACHMENT. <br />LINE CD 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 3. Floodway Schematic <br /> <br />It should be noted that -the floodway for Cement Creek downstream of <br />cross section 306 was determined using the flow confined to the <br />creek only (980 cubic feet per second). A floodway through the <br />shallow flooding area south of cross section 306 into the Animas <br />River is not recommended because the area is developed and floodwater <br />will be less than 1.0 foot in depth. It should also be noted that <br />channel improvement is required downstream of the breakout point if <br />the community chooses to encroach the creek at the breakout point. <br />An encroachment will increase floodflow downstream frqrn 980 to 1640 <br />cubic feet per second. The channel improvement is to ensure that <br />the encroachment will not cause the water-surface elevation of the <br />IOO-year flood to use 1.0 foot more than the existing condition. <br /> <br />5.0 INSURANCE APPLICATION <br /> <br />In order to establish actuarial insurance rates, the Federal Insurance <br />Administration has developed a process to transform the data from the <br />engineering study into flood insurance criteria. This process includes <br />the determination of reaches, Flood Hazard Factors, and flood insurance <br />zone designations for each flooding source studied in detail affecting <br />the Town of Silverton and the designated unincorporated areas of San Juan <br />County. <br /> <br />] 7 <br />