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

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natural balance of the beach and dune system
Impervious Surfaces. Nonporous surfaces contribute
to the volume and velocity of water runof~ adding to the
level of flood waters and increasing the chance of flash
flooding This is especially important on steep slopes and
in the urban environmen~ where a large proportion of
the surface has already been covered by buildings, streets,
and parking areas.
Site design should maximize the preservation of
open space and vegetation and avoid large continuous ex-
panses of impervious surfaces. Large parking areas should
be punctuated with planting Streets, walkways, and park-
ing areas should be constructed of porous paving mate-
rials wherever possible Gravel, for instance, is highly
porous, and bricks and flagstones can allow infiltration
between joints. When soil conditions vary on the site,
buildings should be located on the less porous soils, leav-
ing areas with better filtration as open space
Water Stomge. Water storage can be either temporary
or permanen~ depending on local ground water supplies,
geology. and climate. Temporary storage can take a variety
of forms, including the preservation of natural surface de-
pressions in the landscape Such "dry pond" storage helps
to detain water after a storm, with gradual drainage, per-
colation, and evaporation to reduce the volume and veloc-
ity of runoff This technique also helps replenish ground
water supplies and can boost property values by increas-
ing the site amenity and providing recreation space
Temporary water storage can also be designed into
parking areas by creating depressions in paved surfaces
tha~ in combination with drainage channels, allow grad-
ual runoff. In some situations large expanses of flat roof

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Large expanses of nonpor-
ous surfaces, such as those
used for parking lots, in-
crease runoff. Parking
areas should be designed to
minimize impervious sur-
faces, using vegeta#on to
maintain or improve natu-
L _ _ _ _ _ _ _ _ _ _ _ _ _. _ _ _ -1 ral drainage characteristics.

Dunes should not be cut by
site-development structures.
Access to beacbes can be
provided by catwalks,
stairs, and ramps that pr0-
tect the fragile composi#on
of the dune system.

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