[Figure 8-801]
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Flood Control: Standards for Fencing/Walls
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Fence/Wall Type
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Uses of Fencing/Walls Permitted
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AE Zones
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Floodway
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A
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Yes
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Yes
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B
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Yes
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Yes, with limited cross fencing
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C
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Design specifications required
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Design specifications required
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D
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Yes, if elevated
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Review of design required
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E
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Yes, if elevated
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No
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F
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Review of design required
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No
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Fence/Wall Types:
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A.
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"Open" barbed, or barbless, wire. For floodplain management
purposes, barbed and/or barbless wire will be considered "open" if
there is no more than one horizontal strand per foot of height and
no more than one vertical wire, or post, every six feet.
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B.
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"Open" pipe, or rail, fencing (e.g., corrals). For floodplain
management purposes, pipe/rail fencing will be considered "open" if
the horizontal pipes/rails occupy less than 10% of the area fenced
and vertical posts are spaced not less than eight feet from each other.
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C.
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Breakaway/collapsible fencing.
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D.
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Other wire, pipe, or rail type fencing (e.g., field, chicken
wire, etc.) which does not meet the "open" requirements described
above.
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E.
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Chain-link fencing.
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F.
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Continuous Fencing or Masonry Walls. For floodplain management
purposes, "continuous fencing" shall be solid panels, and/or components
which create a solid panel, which do not meet the criteria of "open"
(above).
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* Individual horizontal wire strands can be placed below the
flood height, provided they are spaced no closer than six inches apart.
Individual vertical wire strands can be placed below the flood height,
provided that they are spaced not closer than six feet apart. For
wire, pipe, or rail fencing that does not meet the "open" requirements,
and for wood or masonry walls/fences, the bottom of the wall/fence
must be elevated to or above the elevation of the water during the
one-percent flood event. Wood and masonry fencing/walls do not need
to be elevated if they provide enough openings at their bases to allow
the free flow of floodwaters without increasing the depth of water
at all. Said openings' dimensions shall be equivalent to one square
inch per one square foot of area enclosed. In the case that an area
is not "enclosed" by said fencing/wall, openings shall be required
to be one square inch for each square foot of lot area, exclusive
of structures.
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Example 8. Post-FIRM building — substantial improvement.
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Substantial improvements made to a post-FIRM structure must
meet the requirements of the current ordinances. Figure 8-9 shows
a lateral addition made after a map revision took place and the BFE
was increased.
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Figure 8-9. Substantial Improvements to post-FIRM buildings
must be elevated above the new BFE. Nonresidential buildings may be
floodproofed.
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Example 5. Vertical addition — residential.
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When the proposed substantial improvement is a full or partial
second floor, the entire structure must be elevated (Figure 8-6).
In this instance, the existing building provides the foundation for
the addition. Failure of the existing building would result in failure
of the addition, too.
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