Environmental Engineering Reference
In-Depth Information
Building dams
can reduce the threat of flooding by
storing water in a reservoir and releasing it gradually.
Dams have a number of advantages and disadvan-
tages (Figure 11-8). Another way to reduce flooding is
to
preserve existing wetlands
and
restore degraded wet-
lands
to enhance the natural flood control provided by
floodplains.
We can also
identify and manage floodplains
to re-
move people from flood-prone areas. This
prevention
or
precautionary
approach is based on thousands of
years of experience that can be summed up very sim-
ply:
Sooner or later the river (or the ocean) always wins.
On a personal level, we can use the precautionary
approach to
think carefully about where we live.
Many
poor people live in flood-prone areas because they
have nowhere else to go. Most people, however, can
choose not to live in areas especially subject to flood-
ing (or to water shortages caused by climate and in-
creased population and economic development; see
Figure 11-5).
11-5 WATER POLLUTION: TYPES,
EFFECTS, AND SOURCES
Science: Major Types and Effects
of Water Pollutants
Infectious bacteria, inorganic and organic chemicals,
and excess heat pollute water.
Water pollution
is any chemical, biological, or physical
change in water quality that harms living organisms or
makes water unsuitable for desired uses. Table 11-1
lists the major classes of water pollutants along with
their major human sources and their harmful effects.
Study this table carefully.
Table 11-1
Science: Major Categories of Water Pollutants
I
NFECTIOUS
A
GENTS
Examples:
Bacteria, viruses,
protozoa, and parasitic
worms
Major Human Sources:
Human and animal wastes
Harmful Effects:
Disease
Major Human Sources:
Surface runoff, industrial
effluents, and household
cleansers
Harmful Effects:
Can
(1) make fresh water unusable
for drinking or irrigation,
(2) cause skin cancers and
crippling spinal and neck
damage (F
-
), (3) damage the
nervous system, liver, and kid-
neys (Pb and As), (4) harm fish
and other aquatic life, (5) lower
crop yields, and (6) accelerate
corrosion of metals exposed to
such water.
(NO
3
-
), phosphate (PO
4
3-
),
and ammonium (NH
4
+
) ions
Major Human Sources:
Sewage, manure, and runoff
of agricultural and urban
fertilizers
Harmful Effects:
Can cause
excessive growth of algae and
other aquatic plants, which
die, decay, deplete water of
dissolved oxygen, and kill fish.
Drinking water with excessive
levels of nitrates lowers the
oxygen-carrying capacity of
the blood and can kill unborn
children and infants (“blue-
baby syndrome”).
uranium, cesium, and
thorium
Major Human Sources:
Nuclear and coal-burning
power plants, mining and
processing of uranium and
other ores, nuclear weapons
production, natural sources
Harmful Effects:
Genetic
mutations, miscarriages,
birth defects, and certain
cancers
O
XYGEN
-D
EMANDING
W
ASTES
Examples:
Organic
waste such as animal
manure and plant debris that
can be decomposed by
aerobic (oxygen-requiring)
bacteria
Major Human Sources:
Sewage, animal feedlots, pa-
per mills, and food processing
facilities
Harmful Effects:
Large popu-
lations of bacteria decompos-
ing these wastes can degrade
water quality by depleting wa-
ter of dissolved oxygen. This
causes fish and other forms of
oxygen-consuming aquatic life
to die.
H
EAT
(T
HERMAL
P
OLLUTION
)
Examples:
Excessive heat
Major Human Sources:
Water cooling of electric
power plants and some types
of industrial plants. Almost
half of all water withdrawn in
the United States each year is
for cooling electric power
plants.
Harmful Effects:
Lowers
dissolved oxygen levels and
makes aquatic organisms
more vulnerable to disease,
parasites, and toxic chemi-
cals. When a power plant
first opens or shuts down
for repair, fish and other
organisms adapted to a
particular temperature range
can be killed by the abrupt
change in water tempera-
ture—known as
thermal
shock.
O
RGANIC
C
HEMICALS
Examples:
Oil, gasoline, plas-
tics, pesticides, cleaning sol-
vents, detergents
Major Human Sources:
In-
dustrial effluents, household
cleansers, surface runoff from
farms and yards
Harmful Effects:
Can
(1) threaten human health by
causing nervous system
damage (some pesticides),
reproductive disorders (some
solvents), and some cancers
(gasoline, oil, and some sol-
vents) and (2) harm fish and
wildlife.
S
EDIMENT
Examples:
Soil, silt
Major Human Sources:
Land
erosion
Harmful Effects:
Can
(1) cloud water and reduce
photosynthesis, (2) disrupt
aquatic food webs, (3) carry
pesticides, bacteria, and
other harmful substances,
(4) settle out and destroy coral
reefs and feeding and spawn-
ing grounds of fish, and
(5) clog and fill lakes, artificial
reservoirs, stream channels,
and harbors.
I
NORGANIC
C
HEMICALS
Examples:
Water-soluble
(1) acids, (2) compounds of
toxic metals such as lead (Pb),
arsenic (As), and selenium
(Se), and (3) salts such as
sodium chloride (NaCl) in
ocean water and fluorides (F
-
)
found in some soils
P
LANT
N
UTRIENTS
Examples:
Water-soluble
compounds containing nitrate
R
ADIOACTIVE
M
ATERIALS
Examples:
Radioactive
isotopes of iodine, radon,
