FLOOD09627

• County: Statewide
• Basin: Statewide
• Title: National Flood Insurance Program
• Date: 10/1/1990
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

Federal Emergency Management Agency

such additional loading considerations
are imposed. Under no circumstances
will freeboard of less than two feet be
accepted.
OiD For coastal levees, the freeboard
must be established at one foot above
the height of the one percent wave or
the maximum wave runup (whichever
is greater) associated with the 100-
year stillwater surge elevation at the
site.
(iv) Occasionally. exceptions to the
minimum coastal levee freeboard rc-.
quirement described in paragraph
(b)(1)(iiD of this section, may be ap-
proved. Appropriate engineering anal~
yses demonstrating adequate protec-
tion with a lesser freeboard must be
submitted to support a request for
such an exception. The material pre-
sented must evaluate the uncertainty
in the estimated base flood loading
conditions. Particular emphasis must
be placed on the effects of wave attack
and overtopping on the stability of the
levee. Under no circumstances, howev-
er, will a freeboard of less than two
feet above the 100-year stlllwater
surge elevation be accepted.
(2) Closures. All openings must be
provided with closure devices that are
structural parts of the system during
operation and design according" to
sound engineering practice.
(3) Embankment protection. Engi-
neering anal3-'ses must be submitted
that demonstrate that no appreciable
erosion of the levee embankment can
be expected during the base flood, as a
result of either currents or waves, and
that anticipated erosion will not result
in failure of the levee embankment or.
foundation directly or indirectly
through reduction of the seepage path
and sUbsequent lnstablllty. The fac-
tors to be addressed in such analyses
include, but are not limited to: Expect~
ed flow velocities (especially in con-
stricted areas); expected wind and
wave action; ice loading; impact of
debris; slope protection teclmlques;
duration of flooding at various stages
and velocities; embankment and foun-
dation materials; levee alignment,
bends, and transitions; and levee side
slopes.
(4) Embankment and foundation
stability. Engineering analyses that
evaluate levee embankment stablllty

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must be submitted. The analyses pro-
vided shall. evaluate expected seepage
during loading conditions associated
with the base flood and shall demon-
strate that seepage Into or through
the levee foundation and embankment
wlll not Jeopardize embankment or
foundation stablllty. An alternative
analysis demonstrating that the levee
is designed and constructed for stabili-
ty against loading conditions for Case
IV as defined in the U.S. Army Corps
of Engineers <COE) manual. "Design
and Construction of Levees" (EM
1110-2-1913, Chapter 6, Section II),
may be used. The factors that shall be
addressed in the analyses include:
Depth of flooding, duration of flood-
ing, embankment geometry and length
of seepage path at critical loca.tions,
embankment and foundation materi-
als, embankment compaction, penetra-
tions, other design factors affecting
seepage (such as drainage layers). and
other design factors affecting embank.-
ment and foundation stability (such as
berms).
(5) Settlement Engineering analyses
must be submitted that assess the po,
tential and magnitude of future losses
of freeboard as a result of levee settle.
ment and demonstrate that freeboard
will be maintained within the mini-
mum standards set forth in paragraph
(b)(1) of this section. ri'his analysis
must address embankment loads. com-
pressibility of embankment soils, com-
pressibility of foundation soils, age of
the levee system, and construction
compaction methods. In addition, de-
tailed settlement analysis using proce-
"dures such as those described in the
COE manual, "Soil Mechanics
Design-Settlement Analysis" (EM
1100-2-1904) must be submitted.
(6) Interior dra"inage. An analysis
must be submitted that Identifies the
source(s) of such flooding, the extent
of the flooded area, and, If the average
depth Is greater than one foot, the
water-surface elevation(s) of the base
flood. This analysis must be based on
the joint probabllity of Interior and
exterior flooding and the capa.clty of
facUlties (such as drainage lines and
pumps) for evacuating interior flood-
waters.
(7) Other design criteria. In unique
situations, such as those where the

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