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<br />any discrepancies on the base map. To aid in the establishment of flood
<br />elevations, Larimer County has established permanent bcnch~arks in the
<br />
<br />field. Table 1 lists these benchmarks and related information.
<br />
<br />rheloca-
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<br />tions of the bencbmarks are appropriately labeled On Plates 2 through 10.
<br />
<br />l'loodways
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<br />Encroachment on flood plains, auch aa artificial fill, reduces the
<br />flood-carrying capacity and increases flood heights, thus increasing flood
<br />hazards in areaa beyond the encroachment itself. One aspect of flood-plain
<br />management involves balancing the economic gain from flood-plsin develop-
<br />ment against the resulting increase in flood hazard. For purposes of the
<br />National FLood Insurance Frogram, the concept of a floodwsy is used as a
<br />tool to assist local cowaunities in this aspect of flood-plain mana~ement.
<br />Under this concept, the area of the lOO-year flood i5 divided into a
<br />floodwsy and a floodway fringe. The floodway is the channel of a stream,
<br />plua anv adjacent flood-plain areas, that must be kept free of encroachment
<br />in order that the 100-year flood be carried without substantial increases
<br />in flood heiehts. As minimum standards, the Federal Insurance Administra-
<br />tion limits such increases in flood heights to 1.0 foot, provided that
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<br />hazardou" velocities are not produced.
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<br />Larimer County has an ordinance
<br />
<br />which limits the increase in flood heights to 0,5 foot above the pre-
<br />floodwsy elevation for the plains portion of the county; therefore, a
<br />floodway having nO mor~ th~n ~ O.~-f~~t ~~rcharg~ has been ~eline~t~d in
<br />this study.
<br />
<br />The floodway in this atudy was computed on the basis of equal convey-
<br />ance reduction for each side of the flood plain. The results of these
<br />computations are tabulated at selected cross sections for each stream
<br />segment for which a floodway is computed (Table 6).
<br />
<br />The area between the floodvay and the boundary of the lOO-year flood
<br />is termed the flood'..aj' fringc. The floodvay frinl;e 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 O.S
<br />feat at any point. Typi<:sl relationships b.,twccn the. floodway and the
<br />floodvay fringe and their significance to flood-plain development arc sho~~
<br />in Fig. 1.
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<br />RE:\OURCE: CON\UlT~NT\ INC
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