[PDF]Encyclopedia of Water Science Vol 2

U*X*L ENCYCLOPEDIA OF



U«X«L ENCYCLOPEDIA OF



water science



Volume 2
Economics and Uses



K. Lee Lerner and Brenda Wilmoth Lerner, Editors

Lawrence W. Baker, Project Editor



U-X-L

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U»X»L Encyclopedia of Water Science

K. Lee Lerner and Brenda Wilmoth Lerner, Editors



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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA

UXL encyclopedia of water science / K. Lee Lerner and Brenda Wilmoth Lerner, editors ;
Lawrence W. Baker, project editor,
p. cm.

Includes bibliographical references and index.

ISBN 0-7876-7617-9 (set : hardcover : alk. paper) — ISBN 0-7876-7673-X (v. 1 : hard-
cover : alk. paper) — ISBN 0-7876-7674-8 (v. 2 : hardcover : alk. paper) — ISBN 0-
7876-7675-6 (v. 3 : hardcover : alk. paper)

1. Water — Encyclopedias, Juvenile. 2. Hydrology — Encyclopedias, Juvenile. I. Lerner, K.
Lee. II. Lerner, Brenda Wilmoth. III. Baker, Lawrence W.

GB662.3.U95 2005

553.7— dc22 2004021651



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Chapter 7

Science and Technology



4 Aqueducts
Aqueducts are man-made conduits constructed to carry
water. The term aqueduct comes from words meaning "to lead
water" in Latin, the language of the Romans who were the first
builders of large aqueducts. Aqueducts carry water from natu-
ral sources, such as springs, into cities and towns for public use.



The first aqueducts

Wells, rivers, lakes, and streams are the oldest sources of
water. In the ancient world however, rivers and lakes were also
sometimes used as places to dispose of sewage and trash. Water
from rivers that flowed though several villages often carried dis-
ease-causing organisms. Aqueducts provided a way for a plen-
tiful supply of clean water to be piped into cities.

The earliest aqueducts were also used to transport water for
irrigation (watering crops). Aqueducts were used in ancient
India, Persia, Assyria, and Egypt as early as 700 b.c.e. The
Romans, however, are regarded as the most famous ancient
aqueduct builders. Between 312 b.c.e. and 230 C.E., the most
complex and efficient ancient system of aqueducts was built to
supply the city of Rome with water. Outside of the capital city
of Rome, the Romans built aqueducts throughout their large
empire. Ruins of ancient aqueducts can still be seen in Italy,
Greece, North Africa, Spain, and France.



How ancient aqueducts functioned

Ancient aqueducts used tunnels and channels (passages for
water to flow) to transport water. The earliest irrigation aque-
ducts were simple canals and ditches dug into the ground. In



199



WORDS TO KNOW

Cistern: A man-made reser-
voir for storing water, usually
underground.

Irrigation: Water channeled
to lands for growing crops.

Terra cotta: Ceramic materi-
als made from baked clay used
in Ancient Rome for aqueduct
pipes, dishes, and some tools.



order to keep water for use by people clean, aqueducts that sup-
plied people with water featured covered channels or pipes.
The first aqueduct made of stone-covered waterways was built
by the Assyrians around 690 b.c.e. Centuries later, Roman
aqueduct builders perfected the closed channel design, building
thousands of miles (kilometers) of stone aqueducts throughout
the Roman Empire.

Ancient aqueducts were carefully planned before they were
constructed. Water flowed through the channels by the force of
gravity alone. The rate of flow (how many gallons could flow
through the conduit in a day) was determined by the force of
the spring that fed the aqueduct. Aqueduct channels were con-
structed with a gradual slope (angle) so that water from the
source could flow downhill to its destination. There were no
pumps that could move water up a hill or slope. Thus, when
crossing hilly terrain, aqueducts were built on stone bridges
and in tunnels. Pipes made of stone or a type of baked clay
called terra cotta carried water through carved out tunnels.
Aqueduct bridges (or elevated spans) were required to with-
stand the heavy weight of water. Spectacular Roman aqueduct
bridges featuring several stories (or tiers) of strong arches can
still be seen today. Some are still in use!

After the aqueducts entered the city, water flowed into pub-
lic cisterns (large pools or wells that store water) or flowed
from public fountains. In Rome, some citizens had water from
the aqueducts piped directly to their homes. Wastewater was
carried by sewer systems that emptied into outlying streams
that normally did not feed into the aqueduct.

Like modern water supply systems, ancient aqueducts
required constant maintenance. Where aqueducts ran under-
ground, shafts (tunnels) were built to provide access to the
aqueduct for repairs. Chalk and other minerals built up in the
conduits and required regular cleaning. Wars, earthquakes,
storms, and floods sometimes damaged whole sections of aque-
ducts. Fixing aqueducts was an expensive undertaking and
required the work of strong laborers and skilled engineers.



Innovations in aqueduct technology

After the fall of the Roman Empire in the fifth century, aque-
duct building ceased in Europe. For centuries, the scientific
knowledge necessary to build aqueducts, aqueduct bridges, and
sewers was lost. Rome and some other cities continued to use
their ancient aqueducts. However, during the Middle Ages
(500-1500 c.e.), people mostly used wells and rivers as a source



200



U*X«L Encyclopedia of Water Science





Roman Aqueducts




Built by the ancient Romans, the three tiered Pont
du Gard aqueduct spans the Gard River in France.
© Archivo Iconografico, S.A./Corbis. Reproduced by
permission.

The Romans were the greatest aqueduct
builders of the ancient world. In fact, when one
mentions the word aqueduct, most people
think of the beautiful, ancient, arched aque-
duct bridges throughout southern Europe that
were built by the Romans. However, these
aqueduct bridges or spans were only a small
fraction of the Roman aqueduct system. For
example, of the aqueducts that served the city
of Rome, only 30 miles (48 kilometers) out of
nearly 300 (483 kilometers) miles of aque-
ducts crossed valley and hills on arched
bridges.



The aqueduct system that served Rome was
the largest and most complex in the ancient
world. Until the late 1800s, it remained unsur-
passed in terms of both distance and the
amount of water carried. Over a period of 500
years, (from 312 b.c.e. to 230 c.e.), 11 aque-
ducts were built to serve the city of Rome. The
longest aqueduct brought water from a spring
over 59 miles (95 kilometers) away into the
heart of the city.

When water from the aqueduct reached the
city, it was carried to cisterns that were built on
high ground. Cisterns are large, deep pools
used for storing water. From the cisterns, water
was carried to public fountains or private
homes by a system of lead or terra-cotta pipes.
Sometimes water was carried directly from the
aqueduct conduits to public baths or pools.
However, taking water directly from the aque-
ducts was usually illegal. Only the emperor and
very wealthy citizens were permitted to con-
struct special conduits that took water directly
from the aqueduct to their private residences.

The aqueducts were one of Rome's most
prized possessions. The army guarded the
water system and almost one hundred engi-
neers supervised maintenance and repairs.
Over two hundred towns in the Roman Empire
also had their own water systems featuring
:|ueduct:



of water. During the Renaissance (1300s-1600s), a renewed
interest in classical architecture and engineering led scholars of
the day to rediscover how ancient water systems worked and
how aqueducts were constructed.

In the 1600s, aqueducts were once again included in public
water systems. In France, a system of pumps moved water from
a river to an aqueduct system that began on the crest (high
point) of a nearby hill. An aqueduct spanning 38 miles (61 kilo-
meters) carried water into the city of London, England. The



Aqueducts



201



An aqueduct and canal near
Bakersfield, California. © Yann
Arthus-Bertrand/Corbis.
Reproduced by permission.



Chadwell River to London aqueduct flowed over 200 small
bridges.

In the eighteenth and nineteenth centuries, innovations such
the steam pump permitted water to be pressurized. Pressurized
water is water that is mixed with air or steam that, with the help
of a pump, can be moved forcefully through pipes and conduits.
This allowed water systems to move water over any terrain.
Aqueducts and water pipe systems carried water over greater
distances with the aid of pressurized water. Pressurization also
created a need for stronger pipes. Instead of terra-cotta, pipes
were made of metals or concrete.

Between the 1830s and 1900, the growing city of New York
constructed several aqueducts to bring spring and river water
into the city from sources over 120 miles (193 kilometers) away.
These aqueducts incorporated new and old aqueduct technolo-
gy. They employed pumps and deep underground pipe systems,
but the Old Croton aqueduct, in use until 1955, also featured a
Roman-like aqueduct bridge. Today, the three major aqueduct
systems that serve New York City deliver nearly 1.8 billion gal-
lons (approximately 6.8 billion liters) of water per day.



202



U*X«L Encyclopedia of Water Science



Aqueducts today

Aqueducts remain an important and efficient means of deliv-
ering clean water to cities. Today's aqueducts are longer and
able to carry more water than ancient aqueducts. Pumps and
pressurized water flow permit aqueducts to flow up a slope.
Improved pipe materials allows today's aqueducts to be com-
pletely hidden deep underground. The largest modern aque-
duct system in the world has been under construction since the
1960s. When finished, the aqueduct will carry water 600 miles
(966 kilometers) through the state of California, from the
northern part of the state south to the Mexican border.

Adrienne Wilmoth Lerner

For More Information

Books

Hodge, A. Trevor. "Roman Aqueducts and Water Supply."
London: Gerald Duckworth & Co., 2002.

Websites

"Aqueducts." British Waterways. http://www.britishwaterways.
co.uk/responsibilities/heritage/aqueducts.html (accessed on
August 24, 2004).

"Roman Aqueducts." InfoRoma. http://www.inforoma.it/
feature.php?lookup=aqueduct (accessed on August 24,
2004).

"The Water Science Picture Gallery — Aqueducts Move Water."
United States Geological Survey, http://ga.water.usgs.gov/
edu/aqueductl.html (accessed on August 24, 2004).



Dams and Reservoirs

Dams are structures that restrict the flow of water in a river
or stream. Both streams and rivers are bodies of flowing surface
water driven by gravity that drain water from the continents.
Once a body of flowing surface water has been slowed or
stopped, a reservoir or lake collects behind the dam. Dams and
reservoirs exist in nature, and man-made water control struc-
tures are patterned after examples in the natural word. Many
lakes are held back by rock dams created by geologic events
such as volcanic eruptions, landslides or the upward force of
Earth that creates mountains. Humans and beavers alike have



Dams and Reservoirs



203



WORDS TO KNOW:

Aqueduct: A channel or
conduit, usually resembling a
bridge, that carries water on
land or over a valley, from a
higher point to a lower one.

Channel: Man-made water-
courses designed to carry
goods or water.

Gorge: A deep, narrow ravine,
often with a river or stream run-
ning through it.

Graded profile: The con-
stant slope or slanting contour
of the land that a river creates
by sedimentation and erosion
as it flows to the sea.

Hydrologic potential: Poten-
tial energy in water stored in
reservoirs above the elevation
of a river downstream.

Reservoir: A lake, usually
man-made by damming a river,
where water is stored for later
use by the community.

Weir: A low dam built across
a stream or any flowing body of
water, usually with rocks, to
raise its level or divert its flow.



discovered how to modify their natural environment to suit
their needs by constructing dams and creating artificial lakes.

Dams are classified into four main types: gravity embank-
ment, buttress, and arch.

• Gravity dams: Gravity dams are massive earth, masonry
(brick or stone work), rock fill, or concrete structures that
hold back river water with their own weight. They are usu-
ally triangular with their point in a narrow gorge (deep
ravine). The Grand Dixence dam in the Swiss Alps is the
world's tallest gravity dam.

• Embankment dams: Embankment dams are wide areas of
compacted earth or rock fill with a concrete or masonry
core that contains a reservoir, while allowing for some sat-
uration and shifting of the earth around the dam, and of the
dam within the earth.

• Buttress dams: Buttress dams have supports that reinforce
the walls of the dam and can be curved or straight.
Buttresses on large modern dams, such as the Itaipu dam in
Brazil, are often constructed as a series of arches and are
made of concrete reinforced with steel.

• Arch dams: Arch dams are curved dams that depend on the
strength of the arch design to hold back water. Like gravi-
ty dams, they are most suited to narrow, V-shaped river val-
leys with solid rock to anchor the structure. Arch dams,
however, can be much thinner than gravity dams and use
less concrete.

Dams in history

Humans have used dams to trap and store fresh water in
reservoirs for more than 5,000 years. Although water is ulti-
mately a plentiful, renewable resource on Earth (Earth is after
all "the water planet"), fresh water is scarce or only seasonally
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