WSP09166

• File Number: 5960
• Description: Flood Protection Section - Miscellaneous Publications
• State: CO
• Basin: Statewide
• Date: 9/1/1981
• Author: FEMA
• Title: Multi-Government Management of Floodplains in Small Watersheds - Federal Emergency Management Agency
• Water Supply Pro - Doc Type: Report/Study

0011G4

A more troublesome use of flood-
plains has been human habitation. Peo-
ple farming on floodplains must live near
their source of livelihood. This means
that if no higher ground is available,
people must dwell in the floodplain.
Homes are often elevated on stilts to
protect against moderate flooding, but
occasional catastrophic floods continue
to inflict great loss of life and property
in heavily populated floodplains, espe-
cially in the monsoon regions of North-
ern India, China, and Southeast Asia.

The United States now has an esti-
mated 6.4 million dwelling units in
coastal and riverine flood hazard areas
(Fig. 7). These are mostly unrelated to
any productive use of the floodplain but
have been so located out of ignorance or
unconcern about the flood hazard or be-
cause flood-prone sites may be relatively
cheap. Loss of life is relatively rare in
U.S. floods today due to improved
warning and evacuation systems as com-
pared with a few decades ago. But dis-
ruption of communities, loss of personal
property, and psychological harm are
widespread results of flooding in resi-
dential neighborhoods.
Industry is another frequent occupant
of floodplains. Industrial development of
sites adjoining water was promoted dur-
ing the 19th century by the doctrine of
"riparian rights" which grants special
privileges to owners of land adjoining a
stream, lake, or coastline. Riparian own-
ership involves a right of access to water
for navigation, including the right to
build docks and wharves. Riparian own-
ers may withdraw water for manufactur-
ing or other needs, may impound water
to yield energy, or may (subject to re-
cent water pollution laws) dispose of
wastes cheaply through outfalls to the
common water body. The northeastern
region of the U.S. is still characterized
today by old mill towns with factories
along with homes and businesses concen-
trated in low-lying areas next to streams
and rivers. Many communities like
Wilkes-Barre, Pennsylvania, have been
repeatedly damaged by floods but con-
tinue to rebuild. In a few cases like Win-
sted, Connecticut, or Rapid City, South
Dakota, damaged structures have been
removed and their sites returned to the
river as open floodplain.
Electrification freed industry from de-
pendence upon mechanical water power,

but many other factors have combined
to encourage continued industrial and
related development in floodplains. Ac-
cess to navigation and shipping facilities
is an important need. floodplains have
always heen regarded as convenient and
level routes for railroads and highways
and as sites for airports. These in turn
have promoted economic development
of adjacent land which, as in the case of
Jackson, Mississippi, sometimes proves
to be highly vulnerable to flooding (See
Case Study 1 below). Many communities
have deliberately used their redevelop-
ment and zoning powers to encourage
growth on remaining open floodplains,
viewing them as vacant land ripe for new
construction and thereby adding to their
local tax base (and often to the flood
problems of their neighbors).
Federal investment in highways, sew-
ers, waterlines, shore stabilization works,
and flood control measures have indi-
rectly promoted further development on
floodplains throughout the U.S. Execu-
tive Order 11988 issued by President
Carter on May 24, 1977, requires federal
agencies to "avoid direct or indirect sup-
port of floodplain development wherever
there is a practicable alternative." Some
progress has been made towards incor-
porating flood considerations into
agency decision-making.

,
,
.

t
.i

;

C. Costs of floods

Human use of floodplains for the vari-
ous purposes listed above usually entails
interference with natural conditions. The
water itself may be diverted, impounded,
and altered in chemistry, appearance,
smell, and temperature. Land next to
water becomes valuable for the location
of human activities associated with river-
ine resources: agriculture, wharves and
warehouses, power generating plants,
recreation facilities, sewage treatment
plants, etc. According to a study of 26
U.S. cities by the U.S. Geological Survey
in 1974, the average proportion of their
floodplain areas devoted to their de-
velopment was 52%.
The inevitable result of human en-
croachment has been frequent and
mounting flood losses. During the 19th
centur;', flood disasters in the U. S. were
confined to relatively limited areas and
unusual circumstances. Failure of an
earthen dam during a heavy thunder-

10