Volume2 10/6/04 10:08 AM Page 1 U•X•L ENCYCLOPEDIA OF water science Volume2 10/6/04 10:08 AM Page 3 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 water_fm 10/20/04 10:54 AM Page iv U•X•L Encyclopedia of Water Science K. Lee Lerner and Brenda Wilmoth Lerner, Editors Project Editor Imaging and Multimedia Manufacturing Lawrence W. Baker Lezlie Light, Kelly A. Quin, Dan Rita Wimberley Newell Editorial Charles B. Montney Product Design Jennifer Wahi Permissions Denise Buckley, Shalice Shah- Composition Caldwell, Ann Taylor Evi Seoud ©2005 by U•X•L. U•X•L is an imprint or information storage retrieval sys- Cover photographs reproduced of Thomson Gale, a division of tems—without the written permis- courtesy of Photodisc by Getty Thomson Learning, Inc. sion of the publisher. Images (volume 1, sailboats), courtesy of Digital Vision Ltd. (volume 2, U•X•L® is a registered trademark For permission to use material pump), and by permission of Corbis, used herein under license. Thomson from this product, submit your photograph by Lester Lefkowitz (vol- Learning™ is a trademark used here- request via Web at http://www.gale- ume 3, Hoover Dam). in under license. edit.com/permissions, or you may download our Permissions Request While every effort has been made to For more information, contact: form and submit your request by fax ensure the reliability of the informa- Thomson Gale or mail to: tion presented in this publication, 27500 Drake Rd. Thomson Gale does not guarantee Farmington Hills, MI 48331-3535 Permissions Department the accuracy of data contained here- Or you can visit our Internet site at Thomson Gale in. Thomson Gale accepts no pay- http://www.gale.com. 27500 Drake Rd. ment for listing; and inclusion in the ALL RIGHTS RESERVED Farmington Hills, MI 48331-3535 publication of any organization, No part of this work covered by the Permissions Hotline: agency, institution, publication, serv- copyright hereon may be reproduced 248-699-8006 or 800-877-4253, ext. ice, or individual does not imply or used in any form or by any 8006 endorsement by the editors or pub- means—graphic, electronic, or Fax: 248-699-8074 or 800-762-4058 lisher. Errors brought to the attention mechanical, including photocopying, of the publisher and verified to the recording, taping, Web distribution, satisfaction of the publisher will be corrected in future editions. 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 This title is also available as an e-book. ISBN 0-7876-9398-7 (set) Contact your Thomson Gale sales representative for ordering information. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 water_ch07 10/20/04 10:49 AM Page 199 S Chapter 7 Science and Technology S Aqueducts SAqueducts 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 water_ch07 10/20/04 10:49 AM Page 200 WORDS TO KNOW order to keep water for use by people clean, aqueducts that sup- plied people with water featured covered channels or pipes. SCistern: A man-made reser- The first aqueduct made of stone-covered waterways was built voir for storing water, usually underground. by the Assyrians around 690 B.C.E. Centuries later, Roman aqueduct builders perfected the closed channel design, building SIrrigation: Water channeled thousands of miles (kilometers) of stone aqueducts throughout to lands for growing crops. the Roman Empire. STerra cotta: Ceramic materi- Ancient aqueducts were carefully planned before they were als made from baked clay used constructed. Water flowed through the channels by the force of in Ancient Rome for aqueduct pipes, dishes, and some tools. 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 water_ch07 10/20/04 10:49 AM Page 201 S Roman Aqueducts 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 Built by the ancient Romans, the three tiered Pont used for storing water. From the cisterns, water du Gard aqueduct spans the Gard River in France. was carried to public fountains or private © Archivo Iconografico, S.A./Corbis. Reproduced by permission. homes by a system of lead or terra-cotta pipes. Sometimes water was carried directly from the The Romans were the greatest aqueduct aqueduct conduits to public baths or pools. However, taking water directly from the aque- builders of the ancient world. In fact, when one ducts was usually illegal. Only the emperor and mentions the word aqueduct, most people very wealthy citizens were permitted to con- think of the beautiful, ancient, arched aque- struct special conduits that took water directly duct bridges throughout southern Europe that from the aqueduct to their private residences. were built by the Romans. However, these aqueduct bridges or spans were only a small The aqueducts were one of Rome’s most fraction of the Roman aqueduct system. For prized possessions. The army guarded the example, of the aqueducts that served the city water system and almost one hundred engi- of Rome, only 30 miles (48 kilometers) out of neers supervised maintenance and repairs.