Source: WATER DISTRIBUTION SYSTEMS HANDBOOK
CHAPTER 1
INTRODUCTION Larry Larr y W.Mays W.Mays Department of Civil and Environmental Environmental Engineering Arizona State University University Tempe, AZ
1.1 BACKGROUND The cornerstone of any healthy population is access to safe drinking water water.. The goal of the United Nations International Drinking Water Water Supply and Sanitation Decade from 1981 to 1990 was safe drinking water for all. A substantial effort was made by the United Nations to provide drinking water and sanitation services to populations lacking those services. Unfortunately,, the population growth in developing countries almost entirely wiped out the Unfortunately gains. In fact, nearly as many people lack those services today as they did at the beginning of the 1980s (Gleick, 1993). Table 1.1 lists the developing countries needs for urban and rural water supplies and sanitation. Four-fifths of the world’s population and approximately 100 percent of the population of developing countries are covered by this table. Also refer to Gleick (1998). Because of the importance of safe drinking water for the needs of society and for industrial growth, considerable emphasis recently has been given to the condition of the infrastructure. Large Large capital expenditures will be needed to t o bring the concerned systems to higher levels of serviceability and to lend vigor to U.S. industry and help it remain competitive in the world economy. economy. One of the most vital services to industrial growth is an adequate water supply system—without it, industry cannot survive. The lack of adequate water supply systems is due to both the deterioration of aging water supplies in older urbanized areas and to the nonexistence of water supply systems in many areas that are undergoing rapid urbanization, such as in the southwestern United States, In other words, methods for evaluation of the nation’s water supply services need to consider not only rehabilitation of existing urban water supply systems but also the future development developm ent of new water supply systems to serve expanding population centers. Both the adaptation adaptatio n of existing technologies and the development of new innovative innovative technologies will be required to improve the efficiency and cost-effectiveness of future and existing water supply systems and facilities necessary for industrial growth. An Environmental Protection Agency (EPA) survey (Clark et al., 1982) of previous water supply projects concluded that the distribution facilities in water supply systems will 1.1
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Source: WATER DISTRIBUTION SYSTEMS HANDBOOK
CHAPTER 1
INTRODUCTION Larry Larr y W.Mays W.Mays Department of Civil and Environmental Environmental Engineering Arizona State University University Tempe, AZ
1.1 BACKGROUND The cornerstone of any healthy population is access to safe drinking water water.. The goal of the United Nations International Drinking Water Water Supply and Sanitation Decade from 1981 to 1990 was safe drinking water for all. A substantial effort was made by the United Nations to provide drinking water and sanitation services to populations lacking those services. Unfortunately,, the population growth in developing countries almost entirely wiped out the Unfortunately gains. In fact, nearly as many people lack those services today as they did at the beginning of the 1980s (Gleick, 1993). Table 1.1 lists the developing countries needs for urban and rural water supplies and sanitation. Four-fifths of the world’s population and approximately 100 percent of the population of developing countries are covered by this table. Also refer to Gleick (1998). Because of the importance of safe drinking water for the needs of society and for industrial growth, considerable emphasis recently has been given to the condition of the infrastructure. Large Large capital expenditures will be needed to t o bring the concerned systems to higher levels of serviceability and to lend vigor to U.S. industry and help it remain competitive in the world economy. economy. One of the most vital services to industrial growth is an adequate water supply system—without it, industry cannot survive. The lack of adequate water supply systems is due to both the deterioration of aging water supplies in older urbanized areas and to the nonexistence of water supply systems in many areas that are undergoing rapid urbanization, such as in the southwestern United States, In other words, methods for evaluation of the nation’s water supply services need to consider not only rehabilitation of existing urban water supply systems but also the future development developm ent of new water supply systems to serve expanding population centers. Both the adaptation adaptatio n of existing technologies and the development of new innovative innovative technologies will be required to improve the efficiency and cost-effectiveness of future and existing water supply systems and facilities necessary for industrial growth. An Environmental Protection Agency (EPA) survey (Clark et al., 1982) of previous water supply projects concluded that the distribution facilities in water supply systems will 1.1
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INTRODUCTION
1.2
Chapter One
TABLE 1.1 Developing Country Needs for Urban and Rural Water Supply and Sanitation, 1990 and 2000
Source: From Gleick (1993).
These data present the drinking water and sanitation service needs in developing countries only and use United Nations population estimates for 2000. The level of service is typically defined by the World Meteorological Organization. As used here by the World Health Organization (WHO), safe drinking water includes treated surface water and untreated water from protected springs, boreholes, and wells. The WHO defines access to safe drinking water in urban areas as piped water to housing units or to public standpipes within 200 m. In rural areas, reasonable access implies that fetching water does not take up a disproportionate part of the day.
account for the largest cost item in future maintenance budgets. The aging, deteriorating systems in many areas raise tremendous maintenance decision-making problems, which are further complicated by the expansion of existing systems. Deterioration of the water distribution systems in many areas has translated into a high proportion of unaccounted-for water caused by leakage. Not only does this amount to loss of a valuable resource; it also raises concerns about safe drinking water because of possible contamination from cracked pipes. The reliability of the existing aging systems is continually decreasing (Mays, 1989). Only recently have municipalities been willing or able to finance rehabilitation of deteriorating pipelines, and needed maintenance and replacement of system components is still being deferred until a catastrophe occurs or the magnitude of leakage justifies the expense of repair. Water main failures have been extensive in many cities. As a result of governmental regulations and consumer-oriented expectations, a major concern now is the transport and fate of dissolved substances in water distribution systems. The passage passag e of the Safe Drinking Drin king Water Water Act in 1974 and its it s Amendment Amendmentss in 1986 (SDWAA) (SDWAA) changed the manner in which water is treated and delivered in the United States. The EPA EPA is required to establish maximum contaminant level (MCL) goals for each contaminant that may have an adverse effect on the health of persons. These goals are set to the values at which no known or expected adverse effects on health can occur occur.. By allowing a margin of safety (Clark, 1987), previous regulatory concerns were focused on water as it left the treatment plant before entering the distribution system (Clark, 1987), disregarding the variations in water quality which occurred in the water distribution systems. To understand better where we are and where we may be going, it is sometimes wise to look at where we have been. This is particularly true in water management, where understanding the lessons of the history of water management may provide clues to
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INTRODUCTION
Introduction
1.3
solving some of the present-day and future problems. The next section is devoted to the aspects of the historical development of water distribution systems.
1.2 HISTORICAL 1.2 HISTORICAL ASPECTS A SPECTS OF O F WATER DISTRIBUTI DIST RIBUTION ON
1.2.1 Ancient Urban Water Supplies Humans have spent most of their history as hunters and food gatherers. Only in the last 9000–10,000 years have human beings discovered how to raise crops and tame animals. This agricultural revolution probably took place first in the hills to the north of presentday Iraq and Syria. From there, the agricultural revolution spread to the Nile and Indus Valleys. Valleys. During the time of this agricultural breakthrough, people began to live in permanent villages instead of leading a wandering existence. About 6000–7000 years ago, farming villages of the Near and Middle East became cities. The first successful efforts to control the flow of water were made in Mesopotamia and Egypt. Remains of these prehistoric irrigation canals still exist. Table 1.2 from Crouch (1993) presents a chronology of water knowledge. Crouch (1993) pointed out, traditional water knowledge relied on geological and meteorological observation plus social consensus and administrativ administrativee organization, particularly among the ancient Greeks. Knossos, approximately 5 km from Herakleion, the modern capital of Crete, was one of the most ancient and unique cities of the Aegean Sea area and of Europe. Knossos was first inhabited shortly after 6000 B.C., and within 3000 years it had became the largest Neolithic (Neolithic Age, ca. 5700–28 B.C.) settlement in the Aegean. During the Bronze Age (ca. 2800–1100 B.C.), the Minoan civilization developed and reached its culmination as the first Greek cultural miracle of the Aegean world. During the neopalatial period (1700–1400
TABLE 1.2 Chronology of Water Knowledge
Crouch (1993). * Indicates an element discovered, probably forgotten, and rediscovered later. ? Indicates an educated guess. Source:
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INTRODUCTION
1.4
Chapter One
B.C.), Knossos was at the height of its splendor. The city occupied an area of 75,000– 125,000 m2 and had an estimated population on the order of tens of thousands of inhabitants. The water supply system at Knossos was most interesting. An aqueduct supplied water through tubular conduits from the Knunavoi and Archanes regions and branched out to supply the city and the t he palace. Figure 1.1 shows the type of pressure conduits used within the palace for water distribution. Unfortunately Unfortunately,, around 1450 B.C. the Mycenean palace was destroyed by an earthquake and fire, as were all the palatial cities of Crete. The Acropolis Acropolis in Athens, Greece, has been a focus of settlement starting in the earliest times. Not only its defensive capabilities, but also its water supply made it the logical location for groups who domiaated the region. The location of the Acropolis on an outcropping of rock, the naturally occurring water, water, and the ability of the location to save the rain and spring water resulted in a number of diverse water sources, including cisterns, wells, and springs. Figure 1.2 shows the shaft of one archaic water holder at the site of the Acropolis. Anatolia, also called Asia Minor, which is part of the present-day Republic of Turkey, Turkey, has been the crossroads of many civilizations during the last 10,000 years. In this region, there are many remains of ancient water supply systems dating back to the Hittite period (2000–200 B.C.), including pipes, canals, tunnels, inverted siphons, aqueducts, reservoirs, cisterns, and dams. An example of one ancient city ci ty with a well-developed water supply system is Ephesus Eph esus in Anatolia, Turkey, which was founded during the 10th century B.C. as an Ionian city surrounding the Artemis temple. During the 6th century B.C., Ephesus was reestablished at the present site, where it further developed during the Roman period. period . Water Water for the great fountain, built during 4–14 A.D., was diverted by a small dam at Marnss and was conveyed to the city by a 6-km-long system consisting of one larger and two smaller clay pipe lines. Figure 1.3 shows the types of clay pipes used at Ephesus for water distribution purposes.
FIGURE 1.1 Water distribution pipe at Knossos, Crete. (Photograph by L.W.Mays).
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INTRODUCTION
Introduction
1.5
FIGURE 1.2 Shaft of water holder at the Acropolis at Athens, Greece. (Photograph by L.W L.W.Mays). .Mays).
FIGURE 1.3 (A, B) Water distribution pipe in Ephesus, Turkey. Turkey. (Photographs by L.W.Mays)
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INTRODUCTION
1.6
Chapter One
Baths were unique in ancient cities, such as the Skolacctica baths in Ephesus that had a salon and central heating. These baths had a hot bath (caldarium), a warm bath (tepidarium), a cold bath (frigidarium), and a dressing room (apodyterium). The first building of this bath, which was constructed in the 2nd century A.D., had three floors. A woman named Skolacticia modified the bath in the 4th century A.D., making it appealing to hundreds of people. There were public rooms and private rooms and those who wished could stay for many days. Hot water was provided using a furnace and a large boiler to heat the water. Perge, located in Anatolia, is another ancient city that had a unique urban water infrastructure. Figure 1.4 illustrates the majestic fountain (Nymphaion), which consisted of a wide basin and a richly decorated architectural facade. Because of the architecture and statues of this fountain, it was one of Perge’s most magnificent edifices. A water channel (shown in Fig. 1.4) ran along the middle, dividing each street and bringing life and coolness to the city. The baths of Perge were magnificent. As As in other ancient cities in Anatolia, three separate baths existed (caldarium, tepidarium, and frigidarium). The early Romans devoted much of their time to useful public works projects, building boats, harbor works, aqueducts, temples, forums, town halls, arenas, baths, and sewers sewers.. The prosperous bourgeois of early Rome typically had a dozen-room house, with a square hole in the roof to let rain in and a cistern beneath the roof to store the water. The Romans built many aqueducts; however, however, they were not the first. King Sennacherio built aqueducts, as did both the Phoenicians and the Hellenes. The Romans and Hellenes needed extensive aqueduct systems for their fountains, baths, and gardens. They also realized that water transported from springs was better for their health than river water and did not need to be lifted to street level as did river water. water. Roman aqueducts were built on elev elevated ated structures to
FIGURE 1.4 Majestic fountain (Nymphaion) at Perge, Anatolia, Turkey. (Photogtaph by L.W.Mays).
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INTRODUCTION
Introduction
1.7
provide the needed slope for water flow. flow. Knowledge of pipe making—using bronze, lead, wood, tile, and concrete—was in its infancy, and the difficulty of making pipes was a hindrance. Most Roman piping was made of lead, and even the Romans recognized that water transported by lead pipes was a health hazard. The water source for a typical water supply system of a Roman city was a spring or a dug well, usually with a bucket elevator to raise the water. If the well water was clear and of sufficient quantity, quantit y, it was conveyed to the city by aqueduct. aque duct. Also, water from several sources was collected in a reservoir reservoir,, then conveyed by aqueduct or pressure conduit to a distributing reservoir (castellum). Three pipes conveyed the water—one to pools and fountains, the second to the public baths, and the third to private houses for revenue to maintain the aqueducts (Rouse and Ince, 1957). Figure 1.5 illustrates the major aqueducts of ancient Rome. Figure 1.6 shows the Roman aqueduct at Segovia, Spain, which is probably one of the most interesting Roman remains in the world. This aqueduct, built during the second half of the 1st century A.D. or the early years of the 2nd century A.D., has a maximum height of 28.9 m. Water flow in the Roman aqueducts was basically by gravity. Water flowed through an enclosed conduit (specus or rivus), which was typically underground, from the source to a terminus or distribution tanks (castellum). Aqueducts above above ground were built on a raised embankment (substructio) or on an arcade or bridge. Settling tanks (piscinae) were located along the aqueducts to remove sediments and foreign matter. Subsidiary lines (vamus) were built at some locations along the aqueduct to supply additional water. Also, subsidiary or branch lines (ramus) were used. At distribution points, water was delivered through pipes (fistulae) made of either tile or lead. These pipes were connected to the castellum by a fitting or nozzle (calix) and were usually placed below the ground level along major streets. Refer to Evans (1994), Frontius (1973), Garbrecht (1982), Robbins (1946), and Van Deman (1934) for additional reading on the water supply of the city of Rome and other locations in the Roman Empire. The following quote from Vitruvius’s Vitruvius’s treatise on architecture, as translated by Morgan (1914), describes how the aqueduct castellern worked (as presented in Evans, 1994): When it [the water] has reached the city, build a reservoir with a distribution tank in three compartments compartmen ts connected with a reservoir to receive the water, and let the reservoir have three pipes, one for each of the connecting tanks, so that when the water runs over from the tanks at the ends, it may run into the one between them. From this central tank, pipes will be laid to all the basins and fountains; from the second tank, to baths, so that they yield an annual income to the state; and from the third, to private houses, so that water for public use will not run short; for people will be unable to divert it if they have only their own supplies from headquarters. This is the reason why I have made these divisions, and in order that individuals who take water into their houses may by their taxes help to maintain the conducting of the water by the contractors. It is interesting that Vitrivius’s treatise is frequently in conflict with what the actual practice was in the Roman world (Evans, 1994). According to Evans (1994), the remains of distribution tanks (castella) that survive at Pompeii and Nines indicate that the tanks distributed water according to geography as opposed to use. The pipes from the castellum, located along the main streets, carried water to designated neighborhoods, with branched pipes supplying both public basins and private homes, (Richardson, 1988). The Greco-Roman city of Pompeii is located on the Bay of Naples, south-southeast of Mt. Vesuvius in Italy. Sources of water for Pompeii included wells, cisterns, and other reservoirs, and a long-distance water supply line (Crouch, 1993). According to Richardson
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INTRODUCTION
1.8
Chapter One
FIGURE 1.5 Aqueducts in ancient Rome. (A) Termini of the major aqueducts. (Evans, 1994) (B) The area of Spes Vetus showing the courses of the major aqueducts entering the city above ground. (From R.Lanciani, Forma Urbis Romae, as presented in Evans) (1994).
(1988), there were no springs within the city of Pompeii. The water table was tapped within Pompeii using wells as deep as 38 m below the surface (Maiuri, 1931). A long-distance water supply line from the hills to the east and northeast also supplied the city. Figure 1.7 illustrates the water distribution system of Pompeii (ca. 79 A.D.). The fall of the Roman Empire extended over a 1000-year transition period called the Dark Ages. Ages. During this period, the concepts of science related to water resources probably retrogressed. retrogresse d. After the fall of the Roman Empire, water sanitation and public health declined in Europe. Historical accounts tell of incredibly unsanitary conditions—polluted water, human and animal wastes in the streets, and water thrown out of windows onto passersby. passersby. Various epidemics ravaged Europe. During the same period, Islamic cultures, on the periphery of Europe, had religiously mandated high levels of personal hygiene, along with highly developed water supplies and adequate sanitation systems.
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INTRODUCTION
Introduction
1.9
FIGURE 1.6 Roman aqueduct in Segovia, Spain. (Photograph by L.W L.W.Mays). .Mays).
FIGURE 1.7 Plan showing all the known water system elements of Pompeii. (From Crouch 1993).
1.2.2 Status of Water Water Distribution Systems in the 19th Century Treatise on Hydraulic and Water-Supply Water-Supply Engineering In J.T.Fannings’s work, A Practical Treatise (1890), the following quote is presented in the preface:
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INTRODUCTION
1.10
Chapter One
There is at present no sanitary subject of more general interest, or attracting more general attention, than that relating to the abundance and wholesomeness of domestic water supplies. Each citizen of a densely populated municipality must of necessity be personally interested in either its physiological or its financial bearing, or in both. Each closely settled town and city must give the subject earnest consideration early in its existence, At the close of the year 1875, fifty of the chief cities of the American Union had provided themselves with public water supplies at an aggregate cost of not less than ninety-five million dollars, and two hundred and fifty lesser cities and towns were also provided with liberal public water supplies at an aggregate cost of not less than fifty-five million dollars. The amount of capital annually invested in newly inaugurated water-works is already a large sum, and is increasing, yet the entire American American literature relating to water-supply engineering exists, as yet, almost wholly in reports upon individual works, usually few of those especially in pamphlet form, and accessible each to but comparatively comparativ ely few of those especially interested in the subject. Fanning (1890): discussed the use of wood pipes, the bored and Wychoff’s Wychoff’s patent pipes also. Bored Pipes. The wooden pipes used to replace the leaden pipes, in London, that were destroyed by the great fire, three-quarters of a century ago, reached a total length exceeding four hundred miles. These pipes were bored with a peculiar coreauger, that cut them out in nests, so that small pipes were made from cores of larger pipes. The earliest water-mains laid in America were chiefly of bored logs, and recent excavations in the older towns and cities have often uncovered the old cedar, pitchpine, or chestnut pipe-logs that had many years before been laid by a single, or a few associated citizens, for a neighborhood supply of water. Bored pine logs, with conical faucet and spigot ends, and with faucet ends strengthened by wrought bands, were laid in Philadelphia as early as 1797. Detroit had at one time one hundred and thirty miles of small wood water pipes in her streets. Wyckoff’s Patent pipe. pip e. A patent wood woo d pipe, manufactured manufact ured at Bay City Cit y, Michigan, has recently been laid in several western towns and cities, and has developed an unusual strength for wood pipes. Its chief peculiarities are, a spiral banding of hoopiron, to increase its resistance to pressure and water-ram; a coating of asphaltum, to preserve the exterior of the shell; and a special form of thimble-joint. Figures 1.8 to 1.13 present some of the various water distribution components presented in Fanning (1890).
1.2.3 Persp Perspectives ectives on Water Water Distribution Mains in the United States In the United States, the construction of water supply systems dates back to 1754, when the system for the Moravian settlement of Bethehem, Pennsylvania, was built (American Public Works Association, 1976). This system consisted of spring water forced by a pump through bored logs. Philadelphia was also developing a water supply system during this same period. The water supply system included horse-driven pumps, as this was before the steam engine.
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INTRODUCTION
Introduction
1.11
FIGURE 1.8 Tank stand pipe, South Abington Water Works, Massachusetts. (From Fanning, 1890).
FIGURE 1.9 Fairmount pumping machinery, Philadelphia. (From Fanning, 1890).
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INTRODUCTION
1.12
Chapter One
FIGURE 1.10 Nagle’s geared pumping engine, front elevation—sectional through the center of pump. (From Fanning, 1890).
The following perspective on water mains is extracted from the Report to Congress of the Comptroller General of the United States (1980): Most water distribution mains in our older cites are made of cast iron, an extremely long-lasting material. Many American cities have cast iron mains over 100 years old which are still providing satisfactory service. No industry standard exists for replacing cast iron mains based on age alone. Ordinarily, breaks and leaks in mains are repaired, and large sections are replaced only if the mains are badly deteriorated or too small. A new form of cast, called ductile iron, has come into general use in recent years. This product has been almost failure free, a good sign for the future. Reduced carrying capacity caused by tuberculation—the products of internal corrosion—occurs in many older cast iron mains but can often be remedied by in-place cleaning and cement mortar lining, a less costly solution than replacement. Deterioration caused by external corrosion does not appear to be a major factor.
Water Distribution Mains in Older Cities Cast iron has been the material most used for water distribution mains in older cities since its introduction in the United States in the early 1800s. Current estimates of the total number of miles of distribution mains, or of cast iron mains, are not available. A survey done in the late 1960s by the Cast Iron Pipe Research Association (now called the Ductile Iron Pipe Research Association) reported that in the 100 largest cities, about 90 percent (87,000 miles) of water mains 4 inches and larger
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INTRODUCTION
Introduction
1.13
FIGURE 1.11 Stop-valves (A) Flowers stop-valve (Flowers Brothers, Detroit). ( B) Coffin’s stop-valve (Courtesy of Boston Machine Co., Boston) (From Fanning, 1890).
were cast iron. Twenty-eight of the cities reported having cast iron mains 100 years old or older. Based on this survey, this association estimated that the United States had over 400,000 miles of cast iron water mains in 1970. In Boston, 99 percent of the distribution system is cast and ductile iron; in Washington, D.C., 95 percent; and in New Orleans, 69 percent.
Early developments America’s first piped water supply was in Boston in 1652 when water was brought from springs and wells to near what is now the restored Quincy Market area. In about 1746, the first piped supply for an entire community was built in what is now Schaefferstown, Pennsylvania. In both instances, the water was stored in wooden
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INTRODUCTION
1.14
Chapter One
FIGURE 1.12 Lowry’s flush hydrant (Courtesy of Boston Machine Co., Boston) (From Fanning, 1890).
FIGURE 1.13 Check-valve. (From Fanning, 1890).
tanks from which citizens filled buckets. Early systems used wooden pipes and the force of gravity to move water from higher to lower elevations. Water systems as we know them today began when steam-driven pumps were first used in 1764 to move water uphill in Bethlehem, Pennsylvania.
Development of cast iron pipe The first cast iron water main in the United States was laid in Philadelphia in 1817. Even that early in United States history, a cast iron main in Versailles, France,
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INTRODUCTION
Introduction
1.15
was already 153 years old. This main, laid in 1664, is still in use after more than three centuries. Like most manufactured items, cast iron pipe has undergone a number of changes and improvements over the years. Early iron pipe was statically cast in horizontal sand molds. By the late 1800s, most pipe was cast vertically in static sand molds—often called pit casting. Some pipe made by both methods had portions of the pipe wall thinner than others because the mandrel around which the iron was poured to form the pipe bore shifted. While many cities have such “thick and thin” pipe still in use today, it does not withstand stress as well as more recently manufactured pipe. In 1908, AWWA published the first standards for vertical pit casting. The formula for wall thickness considered internal pressures and included an arbitrary factor to provide for stresses which were unknown or could not be satisfactorily calculated. Static casting continued until about 1921 when the centrifugal casting method came into use. This method, using either sand or metal molds, continues in use today. Centrifugal casting, combined with increased knowledge of metallurgy, produced a pipe with considerably more tensile strength than pit cast pipe. However, some of the early centrifugally cast pipe had very thin walls and broke easily. In 1948, a metallurgically different cast iron pipe, having the favorable characteristics of both steel and cast iron, was invented. Called ductile iron, it is less brittle than its predecessors, collectively called gray iron, and has superior strength, flexibility, and impact resistance. National standards for this pipe were first published in 1965. In the last 3 or 4 years, virtually all cast iron pipe produced has been ductile iron. Boston started using ductile iron in 1968 and has used it exclusively since 1970. At the end of 1979, at least 73 miles, or 7 percent, of the system was ductile iron. New Orleans and Washington have only small amounts of ductile iron mains. Because cast iron has been so long lasting, older cities may have mains of each type. Louisville, for example, had some mains from every year since 1862 still in service at the end of 1976. Boston had some mains that were installed in 1853, and officials estimated that about 20 percent of the system was installed before 1900. About half of the cast iron mains in New Orleans were installed between 1904 and 1908 and most of the remainder from 1909 to 1950. Washington’s present system went into service in the late 1800s, and most of the original mains remain.
Ways of joining cast iron pipes Methods of joining pipes have also changed over the years. Until about 1935, the common joint for cast iron pipe was the “bell and spigot.” The straight (spigot) was inserted in the larger (bell) end, and the space between was caulked with lead. If the pipe moved, the lead worked loose. In an 1851 report, the city of Boston noted an improved bell with a groove cast in it which would fill with lead to better hold the joint. From about 1920 until about 1955, some cities used a sulphur compound in place of lead. This material was cheaper and easier to use. Some water company officials stated, however, that it produced an extremely rigid joint which contributed to cast iron main breaks. Also about 1920, a bolted mechanical joint, developed for the natural gas industry, was first used for water mains. The next development was a rubber ring gasket which was used in place of the lead or sulpher caulking on bell and spigot pipe. Since 1955, new cast or ductile iron pipe has been installed with a rubber gasket that fits in a groove in the bell. This method produces a watertight joint with a good deal of flexibility.
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INTRODUCTION
1.16
Chapter One
1.2.4 Early Pipe Flow Computational Methods In Fanning’s A Practical Treatise on Hydraulic and Water-Supply Engineering (1980), the pipe flow formulas in Table 1.3 were compared. This book did not cover the flow in any type of pipe system, even in a simple branching system or a parallel pipe system. Le Conte (1926) and King et al. (1941) discussed branching pipes connecting three reservoirs and pipes in series and parallel. The book Water Supply Engineering, by Babbitt and Doland (1939), stated, “A method of successive approximations has recently (1936) been developed by Prof. Hardy Cross which makes it possible to analyze rather complicated systems with the simple equipment of pencil, paper and slide rule.” The authors then quoted the following method of solution from Cross (1936): (a) Assume any distribution of flow. (b) Compute in each pipe the loss of head, h=rQn. With due attention to sign (direction of potential drop), compute the total head loss around each elementary closed circuit, ⌺h=⌺rQn. (c) Compute also in each such closed circuit the sum of the quantities R=nrQn-1without referencet sign. (d) Set up in each circuit a counterbalancing flow to balance the head in that circuit (⌺rQn.=0) equal to
(e) Compute the revised flows and repeat the procedure. Continue to any desired precision. In applying the method, it is recommended that successive computations of the circuits be put on identical diagrams of the system. In office practice such diagrams will usually be white prints. Write in each elementary circuit the value ⌺ R, and outside the circuit write first (above) the value ⌺h for flow in a clockwise direction around the circuit. On the right of these figures put an arrow pointing to the large figure. This arrow will show correctly the direction of counter flow in the circuit.
1.3 MODERN WATER DISTRIBUTION SYSTEMS
1.3.1 The Overall Systems Water utilities construct, operate, and maintain water supply systems. The basic function of these water utilities is to obtain water from a source, treat the water to an acceptable quality, and deliver the desired quantity of water to the appropriate place at the appropriate time. The analysis of a water utility is often devoted to the evaluation of one or more of the six major functional components of the utility: source development, raw water transmission, raw water storage, treatment, finished water storage, and finished water distribution as well as associated subcomponents. Because of their interaction, finished water storage is usually evaluated in conjunction with finished water distribution and raw water storage is usually evaluated in conjunction with the source. Figure 1.14 illustrates the six functional components of a water utility.
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INTRODUCTION
Introduction
1.17
TABLE 1.3 Results Given by Various Formulas for Flow of Water in Smooth Pipes, under Pressure, Compared Data.- To find the velocity, given Head, H =100 feet; Diameter, d=1 foot; and Lengths, l, respectively as follows:
Source: Fanning
(1890).
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INTRODUCTION
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Chapter One
FIGURE 1.14 Functional components of a water utility. (Cullinane, 1989).
Urban water distribution is composed of three major components: distribution piping, distribution storage, and pumping stations. These components can be further divided into subcomponents, which can in turn be divided into sub-subcomponents. For example, the pumping station component consists of structural, electrical, piping, and pumping unit subcomponents. The pumping unit can be further divided into subsubcomponents: pump, driver, controls, power transmission, Mid piping and valves. The exact definition of components, subcomponents, and sub-subcomponents is somewhat fluid and depends on the level of detail of the required analysis and, to a somewhat greater extent, the level of detail of available data. In fact, the concept compenent-subcomponentsubsubcomponent merely defines a hierarchy of building blocks used to construct the urban water distribution system. Figure 1.15 summarizes the relationship between components and subcomponents. 1. Subsub-components. Subsubcomponents represent the basic building blocks of systems. Individual sub-subcomponents may be common to a number of subcomponents within the water distribution system. Seven sub-subcomponents can be readily identified for analysis: pipes, valves, pumps, drivers, power transmission units, controls, and storage tanks. 2. Subcomponents. Subcomponents representing the basic building blocks for components are composed of one or more sub-subcomponents integrated into a common operational element. For example, the pumping unit subcomponent is composed of pipes, valves, pump, driver, power transmission, and control sub-subcomponents. Three subcomponents can be used to evaluate the reliability of the urban water distribution systems: pumping units, pipe links, and storage tanks. 3. Components. Components represent the largest functional elements in an urban water distribution system, Components are composed of one or more subcomponents.
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INTRODUCTION
Introduction
1.19
. ) 9 8 9 1 , e n a n i l l u C ( m e t s y s n o i t u b i r t s i d r e t a w a r o f s t n e n o p m o c b u s b u s d n a , s t n e n o p m o c b u s , s t n e n o p m o c f o p i h s n o i t a l e r l a c i h c r a r e i H 5 1 . 1 E R U G I F
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Chapter One
These include distribution piping, distribution storage, and pumping stations. Distribution piping is either branched as shown in Fig. 1.16, or looped, as shown in Fig, 1.17, or is a combination of branched, and looped. A typical pumping station is shown in Fig. 1.18. A typical elevated storage tank installation is shown in Fig. 1.19. A representation of distribution system in a pipe network model is illustrated in Fig. 1.17. A typical water distribution model display is illustrated in Fig. 1.20.
1.3.2 System Components Pipe sections or links are the most abundant elements in the network. These sections are constant in diameter and may contain fittings and other appurtenances, such as valves, storage facilities, and pumps. Pipes are manufactured in different sizes and are composed of di fferent materials, such as steel, cast or ductile iron, reinforced or prestressed concrete, asbestos cement, polyvinyl chloride, polyethylene, and fiberglass. The American Water Works Association publishes standards for pipe constraction, installation, and performance in the C-series standards (continually updated). Pipes are the largest capital investment in a distribution system. Figure 1.21 shows a steel pipeline that is coated with polyethylene tape and lined by cement mortar once in place. Figure 1.22 shows a steel pipeline that is tape coated and epoxy lined. Figure 1.23 shows a prestressed concrete cylinder pipe (PCCP). A node refers to either end of a pipe. Two categories of nodes are junction nodes and fixed-grade nodes. Nodes where the inflow or the outflow is known are referred to as junction nodes. These nodes have lumped demand, which may vary with time. Nodes to which a reservoir is attached are referred to as fixed-grade nodes. These nodes can take the form of tanks or large constant-pressure mains. Control valves regulate the flow or pressure in water distribution systems. If conditions exist for flow reversal, the valve will close and no flow will pass. The most common type of control valve is the pressure-reducing (pressure-regulating) valve (PRV), which is placed at pressure zone boundaries to reduce pressure. The PRV maintains a constant pressure at the downstream side of the valve for all flows with a pressure lower than the upstream head.
FIGURE 1.16 Typical branched distribution system.
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INTRODUCTION
Introduction
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FIGURE 1.17 Typical water distribution map (from Pennsylvania American Water Company).
FIGURE 1.18 Schematic of a typical water distribution system pumping station.
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INTRODUCTION
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Chapter One
FIGURE 1.19 Typical elevated storage tank installation. (Cullinane, 1989).
FIGURE 1.20 Typical water distribution model display (from T.Walski).
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INTRODUCTION
Introduction
1.23
FIGURE 1.21 Steel pipeline, 81 in diameter, Seattle, Washington. Polyethylene tape coated, to be cement mortar lined in place. (Courtesy of Northwest Pipe Company).
FIGURE 1.22 Steel pipeline, 72 in diameter, tape coated and epoxy lined. (Courtesy of Northwest Pipe Company).
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Source: WATER DISTRIBUTION SYSTEMS HANDBOOK
CHAPTER 1
INTRODUCTION Larry Larr y W.Mays W.Mays Department of Civil and Environmental Environmental Engineering Arizona State University University Tempe, AZ
1.1 BACKGROUND The cornerstone of any healthy population is access to safe drinking water water.. The goal of the United Nations International Drinking Water Water Supply and Sanitation Decade from 1981 to 1990 was safe drinking water for all. A substantial effort was made by the United Nations to provide drinking water and sanitation services to populations lacking those services. Unfortunately,, the population growth in developing countries almost entirely wiped out the Unfortunately gains. In fact, nearly as many people lack those services today as they did at the beginning of the 1980s (Gleick, 1993). Table 1.1 lists the developing countries needs for urban and rural water supplies and sanitation. Four-fifths of the world’s population and approximately 100 percent of the population of developing countries are covered by this table. Also refer to Gleick (1998). Because of the importance of safe drinking water for the needs of society and for industrial growth, considerable emphasis recently has been given to the condition of the infrastructure. Large Large capital expenditures will be needed to t o bring the concerned systems to higher levels of serviceability and to lend vigor to U.S. industry and help it remain competitive in the world economy. economy. One of the most vital services to industrial growth is an adequate water supply system—without it, industry cannot survive. The lack of adequate water supply systems is due to both the deterioration of aging water supplies in older urbanized areas and to the nonexistence of water supply systems in many areas that are undergoing rapid urbanization, such as in the southwestern United States, In other words, methods for evaluation of the nation’s water supply services need to consider not only rehabilitation of existing urban water supply systems but also the future development developm ent of new water supply systems to serve expanding population centers. Both the adaptation adaptatio n of existing technologies and the development of new innovative innovative technologies will be required to improve the efficiency and cost-effectiveness of future and existing water supply systems and facilities necessary for industrial growth. An Environmental Protection Agency (EPA) survey (Clark et al., 1982) of previous water supply projects concluded that the distribution facilities in water supply systems will 1.1
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