and floodwalls are barriers that hold back floodwaters.
levee is constructed of compacted soil and requires more land area.
are built of manmade materials, such as concrete and masonry.
structures may completely surround the building or may tie into high ground at
each end. If openings are left for the driveway and/or sidewalk, closures must
be installed to seal these access points prior to a flood.
Because levees and floodwalls are located away from
the structure or area to be protected, they provide flood protection without
altering the building.
Although levees and
floodwalls can be built to any height, they are usually limited to four feet
for floodwalls and six feet for levees (due to cost, aesthetics, access, water
pressure, and space).
The structure should be
built at least one foot higher than the anticipated flood depth (freeboard
No matter how high the
barrier is, it can always be overtopped by a larger flood, which would cause as
much damage as if no protection were provided (or more).
In areas with high
velocity flow, erosion protection may be necessary to protect an earthen levee
or prevent undermining of a floodwall.
Flash flooding precludes the use of
closures that require human intervention to install.
If flooding lasts more than 3 to 4 days,
seepage is more likely to pose problems.
levee or floodwall is not feasible if it would impede flow or block natural
drainage in amanner that results in damage to surrounding property.
horizontal space is required for levees; floodwalls are generally more
appropriate for small sites.
underlying soil must support the levee or floodwall and resist seepage of water
under the structure.
house with a basement can still experience flood damage even if a levee or
floodwater protects the structure from surface water.
soil can exert hydrostatic pressure on basement walls, causing them to crack,
buckle, or event collapse.
to the structure can be enabled by providing a means of crossing over a levee
or floodwall, such as a ramp or stairway.
If this is not feasible, it may be
necessary to design openings at driveways, sidewalks, or other entrances and a
mechanism for closing all such openings.
that do not require human intervention are preferable. If a closure requires
manual installation, the effectiveness of the flood protection system depends
on the availability of a capable person who is aware of the flood threat and
has sufficient time to install closures and make certain they are properly
rounded outlines of an earthen levee can be shaped to blend into the natural
can be designed as attractive features by incorporating them into the landscape
design and utilizing decorative bricks or blocks (although this will generally
increase the cost).
A levee or floodwall cannot be used to
bring a substantially damaged or substantially improved structure into
compliance with current floodplain development standards.
on the availability of suitable local soil, levees may be less expensive than
other flood proofing options.
if suitable fill material is not locally available, the expense of transporting
proper material to the site can be significant.
cost of floodwalls is usually greater than that of levees.
To be effective, a levee must be
constructed with compacted, impervious soils.
The practice of piling stream sediment
on the bank does not provide flood protection.
The embankment slopes
must be gentle (usually a ratio of one vertical to two or three horizontal) to
provide adequate stability and minimize erosion.
The levee‟s widthtimes itswillheight. thus
Floodwalls are generally constructed of
solid concrete (alone or in combination with masonry).
must be designed to withstand water pressure without overturning or
Mechanisms for closing
access openings in a levee or floodwall include automated systems (usually
expensive) or manually operated flood gates, stop logs, or panels. There are
often hinges or sliding mechanisms for installation.
the closure is not permanently attached, it must be stored in a readily
Any sewers or drain
pipes passing through or under a floodwall or levee require closure valves to
prevent backup and flooding inside the building and protected area.
Rain, snow melt, and
seepage water must be removed from the protected side of a levee or floodwall
using drains (with flap valves to prevent backflow during a flood) and a sump
An emergency power
source for the electric sump pump enables operation during a power outage.
enables identification and repair of problems while they are still minor.
Levees should be
checked for signs of erosion, settlement, loss of vegetation, animal burrows,
Inspect floodwalls for cracking,
spelling, or scour.
Routine maintenance is
needed to make sure that sump pumps, valves, drain pipes, and closures operate
Advantages and Disadvantages of Levees and
and floodwalls can protect a building and the surrounding area from inundation
without significant changes to the structure if the design flood level is not
is no pressure from floodwater to cause structural damage to the building.
barriers are usually less expensive than elevating or relocating the structure.
do not have to leave the structure during construction.
technique cannot be used to bring a substantially damaged or improved structure
into compliance with floodplain development standards.
violate floodplain development standards, particularly in floodway locations,
by causing obstructed flow or in increased flood heights.
or overtopping of a levee or floodwall results in as much damage as if there
was no protection (or more).
restrict access to the structure. If human intervention is required for
closures, there must be adequate warning time.
buildings with basements, hydrostatic pressure from groundwater may still cause
drainage can be affected, possibly creating water problems for others.
drainage must be provided.
require considerable land area.
reduction in flood insurance premiums.
ü Do not eliminate the need to evacuate during floods.