FLOOD02514

• County: Statewide
• Community: Nationwide
• Basin: Statewide
• Title: Design Guidelines for Flood Damage Reduction
• Date: 10/1/1981
• Prepared By: FEMA
• Floodplain - Doc Type: Educational/Technical/Reference Information

Sediment traps, installed at
storm sewer inlets, belp
prevent sediment deposits
and maintain the steady
drainage of storm water.

Flooding causes tbe huild-
up of exterior water
pressure, which must be
equalized to avoid major
structural damage to
buildings located in
flood-prone areas.

64

decrease the velocity of storm water runoff and to release
water at controlled points and rates of flow. Lines and ac-
cess points need to be sized and distributed to accommo-
date the runoff likely to be associated with the site and
not cause backup of water and the resulting overspill of
flash flooding The capacity of the storm sewer system can
be impaired by sediment deposits within the systems; to
avert this problem, drain inlets should be designed with
sediment traps and filters.

BuDdiIl, Desiau 'Iechm.ques
In the design of buildings that must be located in a flood
hazard area, several problems should be addressed in re-
ducing the threat of flood damage. These include:
. Entrance of water through building openings
. Damage to building finishes and contents
. Seepage through walls, floors, and foundations
. Water pressure on foundations, walls, and floor slabs
. Back-up of water through sewer systems
. Access to and from buildings during floods.
To deal with these problems adequately the designer
can incorporate a variety of flood damage reduction tech-
niques in building design These techniques interact with
site design features and, as with site design, the tech-
niques used for any given project will vary with indi-
vidual circumstances, needs, and resources.
Floodproofing. The term floodproofing is used here
to describe any method of making buildings resistant to
flood damage Floodproofing strategies are particularly
appropriate where moderate flooding (ie, low flood
stage, low velocities and short duration) is likely, or where
buildings' uses require riverine or coastal locations. The
principal approach to achieving this objective is to protect
buildings from water by keeping their interiors dry dur-
ing flooding This can involve raising buildings above
flood levels or Waterproofing the portions of the building
that are below flood levels.
Keeping flood water out of buildings requires special
structural support During flooding water entering the
building serves to equalize water pressure that builds up
on the exterior. If this equalization is eliminated by water-
proofing then the building is likely to collapse. If a strat-
egy is adopted that keeps water ou~ then the building
must also be made structurally capable of withstanding
these exterior water pressures.
The "dry" floodproofing approach, as described
above, is the most common and widely applicable way to
protect buildings and their contents from flood damage.
An alternative that can be used in some situations is "wet"
floodproofing, which involves purposely allowing water
to flow into a building when flood levels rise, thereby
equalizing water pressures and avoiding major structural