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Watershed Management for Potable Water Supply: Assessing the New York City Strategy (2000)

Chapter: 2 The New York City Water Supply System

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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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2
The New York City Water Supply System

New York City between the 1840s and the 1960s developed the largest and, some would argue, the best urban water supply system in the world in terms of quality, reliability, and innovative management. The 1997 Memorandum of Agreement (MOA) reflects a new era of creative management in response to the dual realities posed by (1) the need to comply with the federal Safe Drinking Water Act (SDWA) and (2) the unavailability of new sources to augment or replace existing supplies. This chapter sketches the historical evolution of the New York City water system in relation to socioeconomic growth of the city during the nineteenth and early twentieth centuries. It then describes the basic physical elements of the system as it exists today, together with the biophysical geography of the Catskill/Delaware headwaters from which 90 percent of the City's water is derived. This chapter thus provides the background and context essential to the detailed examination of the MOA that follows in later chapters.

BRIEF HISTORY OF THE NEW YORK CITY WATER SUPPLY

At the dawn of the nineteenth century, American cities were few in number, small in size, and coastal in location. Infrastructure inherited from the colonial period was primitive even by the standards of a half century later: streets were crooked and unpaved, public buildings were spartan, street lighting was rare, waste collection was practically unknown, and water supplies were totally inadequate. With immigration, industrialization, and the growth of an urban middle class, the population of towns began to swell in the early decades of the century. New York City in particular grew from 60,000 to 200,000 between 1800 and 1830. This rapid growth in population was accompanied by a succession of

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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epidemics, vaguely understood to be related to impure water, as well as frequent outbreaks of fires that could scarcely be contained with available water supplies.

New York City was surrounded by tidal, brackish water with no immediate access to fresh water streams. Residents depended initially upon wells or rainwater cisterns for their water needs. The water table aquifer on which it depended was easily contaminated with surface wastes. Wells close to the shore became brackish because of saltwater intrusion. And with limited surface recharge of local groundwater, the reliable yield of springs and wells was insufficient. Rainwater cisterns added little to the general supply. Adding further to water demand was the patenting of the flush toilet in 1819, which greatly increased water consumption per capita as waterborne sewerage gradually replaced on-site privies and night soil collection (Weidner, 1974, p. 55).

During the early nineteenth century, the provision of urban water supply was regarded as a private rather than a public function (Blake, 1956). New York, Boston, Baltimore, and several small towns relied initially on enfranchised private companies in preference to assuming the burden directly. An exception was Philadelphia, where recurrent outbreaks of yellow fever at the turn of the nineteenth century prompted a more aggressive municipal response. In 1801, Philadelphia constructed at public expense a pumping plant on the Schuylkill River powered by two steam engines. This project was designed and promoted by the noted engineer Benjamin Latrobe. It marked both a technological and an institutional breakthrough, namely in the use of the steam engine to pump water and the use of public taxation to establish a municipal water supply (Blake, 1956). In the case of Boston, the Jamaica Pond Aqueduct Company was chartered in 1796 to bring water to that city through a series of hollow log pipes.

In New York City, the Manhattan Water Company was chartered in 1799 with an exclusive franchise to supply the city with water. It constructed a reservoir in lower Manhattan to supply 400 families from local groundwater.

But this water proved both scarce and bad; the company, neglecting the ostensible purpose of its organization, soon turned its attention almost exclusively to banking affairs and thus lost the confidence of the community, and it was not long before the new works voted a failure. (Booth, 1860)

In 1811, a plan for the future expansion of New York was prepared by a special commission established by the state legislature. The "Commissioners' Plan" projected future streets marching miles into the countryside of upper Manhattan as far as "155th Street." The plan was an accurate forecast of the spatial growth of the city. The opening of the Erie Canal in 1825, which connected the Hudson River with the Great Lakes, established the City's economic preeminence in the nation and contributed to its rapid population growth and prosperity. Local water sources were hopelessly inadequate to serve this rapid rate of growth in terms of quantity, quality, and pressure. Various schemes were

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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debated fruitlessly, with many in favor of a nearby diversion from the Bronx River just outside the city limits. This source, however, could not meet the prospective needs of the expanding city for long (Blake, 1956).

Damming the Croton River

The solution of the New York City water crisis ultimately required a synthesis of innovation in technology, in public administration, and in civic responsibility previously unknown in urban history. These factors, in conjunction with growing public desperation and fear, contributed to a municipal achievement that still today is the envy of other cities worldwide. In particular, public action to establish a water supply could no longer be debated or delayed after the city was wracked by fires in 1828 and 1835 and by cholera in 1832. The City retained an engineer, Colonel DeWitt Clinton, Jr., to study the water crisis and propose a solution. He predicted that Manhattan would reach a population of 1 million by 1890 (which proved to be late by 12 years). To meet the crisis, he proposed tapping the Croton River 40 miles north of the city to obtain a reliable supply of 20 million gallons per day (mgd) of pure upland water, a project of stunning simplicity in concept but daunting in terms of cost and engineering challenge. The elevation of a Croton River reservoir at 200 ft above sea level would permit the water to flow by gravity through an aqueduct to be constructed with enough "head" to serve the needs of taller buildings and fire fighting in the city (Weidner, 1974, pp. 28–31). To reach far beyond the city limits would ensure (at the time) that water would be relatively pure and that private landowners would be powerless to object to the diversion of local stream water to the city. The project also attracted the interest of civic leaders and politicians in both city and state government. (The federal government had no role in the project whatsoever.)

The Croton River project required the construction of storage and conveyance facilities unprecedented since the Roman Empire. With the total cost estimated at several million dollars, the project was considered too large and too important for private enterprise. Accordingly, the City of New York, under authority from the state legislature, undertook to plan and execute the Croton River project directly. A water commission was quickly appointed, financing was approved by the City's voters in 1835, and construction began in 1837 (Blake, 1956).

The project involved five major structural elements: (1) a masonry dam 50 ft high and 270 ft long impounding a reservoir with a surface area of 440 acres and a storage capacity of 600 million gallons, (2) a 40-mile covered masonry aqueduct with a cross section of seven by eight ft, (3) a 1,450-ft-long "high bridge" to convey the aqueduct across the Harlem River into Manhattan, (4) a 35-acre receiving reservoir located within the future site of Central Park, and (5) a four-acre, masonry-walled distributing reservoir located on the present site of the New York Public Library at Fifth Avenue and 42nd Street. The first Croton River

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Croton Dam. Source: The Hudson (Lossing, 1866. © 1866 by H.B. Nims & Co.).

water arrived in Manhattan on July 4, 1842, an event celebrated with church bells, cannon, and a five-mile-long parade. The event was both a technological and an institutional threshold: the City of New York had arrived of age (Weidner, 1974, pp. 45–46; Platt, 1996, p. 187). Within a decade, the City could celebrate another milestone—the opening of Central Park—which contained the key receiving reservoir for the Croton system. A map of the current Croton water supply watershed is given in Figure 2-1.

Evolving Public Health Laws

During this time, two important public health laws relating to drinking water safety were being developed in New York State that would make continued expansion of the New York City water supply possible. First, the New York Metropolitan Health Act was adopted by the New York State legislature in 1866 as the first major American public health law. It was directly inspired by the findings of English sanitary reformer James Chadwick, whose 1842 "Report of

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-1 The Croton water supply system. Courtesy of the NYC DEP.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

the Poor Law Commissioners Concerning the Sanitary Condition of the Labouring Population of Great Britain'' prompted a parallel investigation in New York City by John Griscom in 1845. These reports began to convince the informed public that the incidence of infectious disease such as cholera and typhoid was closely related to the purity and abundance of the water supply.

The second important piece of legislation was the New York State Public Health Law of 1905. This statute allowed the city to regulate land use in the upstate watershed region to protect City drinking water (Article 11). The law also gave New York City the authority to acquire land through eminent domain, and it authorized the State Department of Health to promulgate rules and regulations to protect the City's drinking water (Nolan, 1993, p. 534).

Expanding the Water Supply

As the population of New York City crossed the one million threshold in the 1870s, the City began to address the need to expand the Croton system. A new Croton aqueduct was opened in 1892, and a massive new Croton River Dam that entirely submerged the old dam was completed in 1905. With the construction of several smaller dams by 1911, the present-day Croton River system was in place, providing a potential maximum supply of 336 mgd (which exceeds the entire supply available to metropolitan Boston today).

But even this expanded Croton system would be insufficient to keep pace with the City's tremendous growth. In 1898, Greater New York with a population of 3.5 million was formed through the consolidation of Manhattan, the Bronx, Queens, Brooklyn, and Staten Island. New York water engineers in the early decades of the twentieth century began to look further afield, to sources in the Catskill Mountains beyond the Hudson River. Between 1907 and 1929, the City acquired water rights and constructed the Schoharie and Ashokan reservoirs in the Catskill Mountains. A new 92-mile Catskill aqueduct conveyed water from Ashokan to the City, crossing under the Hudson River by means of an "inverted siphon" 3,000 ft long and 1,100 ft below sea level (Weidner, 1974, p. 161). The Catskill system also included the Construction of the Kensico and Hillview reservoirs just north of the City, City Tunnel No. 1, and the terminal Silver Lake Reservoir on Staten Island.

This feat was repeated in the 1940s when the City reached out to the headwaters of the Delaware River over 100 miles away. Unlike the Catskill reservoirs, which tapped streams entirely within New York State, the Delaware is an interstate river basin. The proposed diversion of substantial quantities of water from the headwaters to New York City aroused opposition from the downstream states of New Jersey and Pennsylvania, where many communities draw on the Delaware River for their own water supplies. Under the U.S. Constitution, disputes between states may be taken directly to the U.S. Supreme Court. Ultimately, New York City's Delaware River diversion was authorized up to a maxi-

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-2 The Catskill/Delaware water supply system. Courtesy of the NYC DEP.

mum limit by the Court in decisions in 1931 and 1953. The 105-mile Delaware River Aqueduct was the world's longest continuous aqueduct tunnel (Weidner, 1974, p. 300). It meets the Catskill Aqueduct at Kensico Reservoir east of the Hudson River, which it crosses via a deep inverted siphon. Today, the combined systems (Croton, Catskill, and Delaware) are capable of supplying New York City with about 1.3 billion gallons per day, of which approximately 40 percent is derived from the Catskill system, 50 percent from the Delaware System, and 10 percent from the Croton System. A map of the Catskill/Delaware watershed is presented in Figure 2-2. Figure 2-3 shows both the Croton and Catskill/Delaware systems. A chronology of important water supply events is found in Table 2-1.

Both New York City and metropolitan Boston followed roughly similar strategies of water supply development between the 1840s and the 1960s, impounding hinterland sources of water to be conducted via gravity flow to the user region. But the two systems differ markedly in terms of their institutional organization. New York City itself established and continues today to operate its water supply system, even in upstate New York. By contrast, Boston conveyed its system in 1895 to a newly created regional entity, the Metropolitan Water District, which in turn was absorbed into a state agency—the Metropolitan District Commission, established in 1919. The latter completed the 400-billion-

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-3 New York City water supply. Courtesy of the NYC DEP.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-1 Chronology of the New York City Population, Water Supply, and Related Events

NYC Pop.

Year

Event

60,000

1800

 

 

1811

Commissioners Plan for New York City—future growth envisioned

 

1819

Albert Giblin patents the silent valveless wastewater preventor (flush toilet) in Great Britain

 

1825

Erie Canal opened

200,000

1830

 

 

1832

Cholera epidemic strikes New York City and other cities

 

1834

NYC Board of Water Commissioners established by state legislature

 

1835

Great Fire burns much of New York City

 

1837

Croton River Dam and 41-mile aqueduct begun

 

1842

First water reaches New York City from Croton River—celebrations

 

1858

Central Park opened—including reservoir

 

1866

New York State Metropolitan Health Act

1 million

1878

 

 

1893

Completion of New Croton River aqueduct

 

1898

Consolidation of "Greater New York City"—five boroughs

3.5 million

1905

State Legislature gives New York City power to regulate upstate watershed land

4.6 million

1911

New Croton River system completed—10 percent of present New York City system

 

1925

Interstate compact re Delaware River allocation—only ratified by New York

 

1927

Catskill Mountain system completed—40 percent of present New York City system

 

1931

New Jersey v. New York (283 U. S. 336)

 

 

New York City is authorized to withdraw up to 440 mgd from Delaware River headwaters

7.5 million

1936

Delaware River system begun

 

1953

New Jersey v. New York (347 U. S. 995)—NYC authorized to divert up to 800 mgd from the Delaware headwaters subject to maintaining minimum downstream flows. River Master appointed.

 

 

New York City Watershed Regulations published

7.7 million

1961

Delaware River Basin Interstate Compact adopted (four states and U. S.)—Delaware River Basin Commission established

 

1964

Delaware River system completed—50 percent of present New York City system

 

1964–65

Northeast Drought

7.9 million

1970

 

7.3 million

1990

 

 

1997

Watershed Management Agreement signed

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

gallon Quabbin Reservoir, 70 miles west of Boston, during the 1940s. In 1985, responsibility for distributing water to metropolitan Boston was reassigned to a new regional agency, the Massachusetts Water Resources Authority. Thus, while New York City has retained control over its system, and has encountered much anti-City hostility in its source regions, the metropolitan Boston system has long been administered by agencies serving a region containing half the state's population and therefore has gained broader political support in its efforts to protect its water supplies. As both systems follow parallel tracks in seeking to avoid filtration under the SDWA in the 1990s, this contrast in administrative structure may prove to be significant. In particular, the metropolitan Boston system has employed new state laws to promote watershed management in the source areas, while New York City has had to engage in lengthy and delicate negotiations with upstate interests to achieve the set of commitments that underlie the landmark MOA.

It is worth noting that the New York/Boston model of interbasin diversion from distant, upland sources influenced many other American and foreign cities in their own quests for pure water. Sometimes long-distance diversions are not required, as with some Great Lakes cities that enjoy ample water at their doorsteps. Western cities such as Los Angeles, San Francisco, Denver, and Phoenix have aggressively pursued scarce water wherever it could be found, developing whatever technical and institutional measures that were necessary to procure it. In some cases, such as the Owens Valley project of Los Angeles, the legal means were questionable and the technical execution was flawed, as demonstrated in the collapse of the St. Francis Dam in 1905 (Reisner, 1993). But the basic premise behind these western water wars was the same as that which motivated the early New York and Boston projects: employ modern technology and political power to ensure an abundant and inexpensive supply of pure water to the urban populace (Platt, 1996, p. 188).

Future Demands on the New York City Water Supply System

Average daily demand served by the New York City water supply system declined from 1,547 mgd in 1990 to 1,449 mgd in 1995 (Hazen and Sawyer/Camp Dresser & McKee, 1997, p. 11). Although the latter figure is still higher than the system's estimated safe yield of 1,290 mgd, clearly the City's demand management program is paying off. Continued expansion of metering and the installation of water-saving plumbing devices to date have caused the average daily demand to continue to fall since 1995 (Warne, 1999a). Box 2-1 discusses the history of New York City's demand management activities.

Water demand management, which has proven to be effective in both the New York and Boston water systems, is nevertheless vulnerable to being counteracted by increasing numbers of water users. Future increases in users, and therefore in demand on the system, could arise from population growth within the

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

BOX 2-1
Demand Management in New York City

By the late 1980s, the New York City water supply system was called upon to meet an average demand of 1,400–1,450 mgd for the City proper plus an additional 120 mgd provided to eligible suburban communities. With a dependable safe yield from the total New York City water system estimated at about 1,300 mgd, the system was technically deficient. But further augmentation through development of new sources was infeasible. New out-of-basin transfers from upstate rivers including the Delaware are likely to be blocked by legal action. New York City has a seldom-used pumping station on the Hudson River upstream from the salt front, but it would face environmental challenges if the station were to be used on more than an emergency basis. Groundwater underlying Long Island theoretically could supply additional water, but this would be opposed by communities already relying on that source (Platt and Morrill, 1997).

Until the 1980s, water usage in New York City remained almost completely unmetered, which of course discouraged water conservation by households and other users. This nonsustainable situation was addressed in a Universal Water Metering program announced by the mayor in 1986. More than 600,000 meters have been installed at a cost of $350 million. When metering is complete, New York City will be able to monitor the use of water and employ pricing as a strategy to limit both waste and increases in demand.

In 1991, the City launched a pilot water conservation program to stem rising demand. The program offered free leak detection and installation of water-saving plumbing devices such as low-flow showerheads and faucets, aerators, toilet tank displacement bags, and low-flow toilets. These services were provided to 10,000 homes with 1–3 families citywide (Nechamen et al., 1995). Starting in 1993, a larger scale water conservation program conducted leak detection for some 8,000 homes with 1–3 families and 80,000 apartments. The City provided an expanded range of water-saving showerheads and toilet devices, new outreach and public education, and energy conservation in cooperation with the electrical utility Consolidated Edison. The City has developed an audit of leakage as a basis for estimated long-term benefits from subsidized water conservation measures. By 1995, in-city average demand had dropped to about 1,300 mgd. Much greater savings are anticipated from continuation of leak detection and plumbing retrofit efforts. It is anticipated that one-third of the City's residential toilets will be replaced with 1.6-gallon-per-flush units by 1998.

New York's Environmental Conservation Law (ECL), Sec 15-0105, has long declared that "the Waters of the State be conserved." A newer law (ECL, Sec. 15-0314) mandates the use of water-saving plumbing fixtures in all new construction or replacements of existing fixtures, including limits of 3 gallons per minute for sink faucets and showerheads and 1.6 gallons per flush for toilets. The State expects that this requirement will save over 500 mgd statewide (Nechamen et al., 1995).

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

present service area (New York City and certain suburbs in Westchester County) as well as from expanding the service area to include new communities. (For purposes of this discussion, it is assumed that water use per capita will continue to be steady or will decline in the future.)

The likelihood of a significant increase in population in the present service area is slight. During the 1970s, New York City lost 900,000 inhabitants, declining from 7.9 million in 1970 to 7.0 million in 1980. With the improvement in the City's economy and the influx of new migrants from abroad, the City's population in 1990 stood at 7.3 million. Although further small increases may occur, New York City is not expected to regain its former population of nearly 8 million. Since the water system served that level of usership prior to demand management measures and through most climatic perturbations, there is no reason to foresee any problem with meeting the expected demand of the City itself. Nor is it likely that the existing suburban user communities, which in 1995 averaged 123 mgd in demand, will significantly increase in population or water usage. These are mostly older communities that are largely built out. Although some intensification of residential development may occur through the replacement of single family homes with higher-density development, the net effect on the City's water system should not be significant.

A more likely source of future increase in demand on the New York City system would arise from the expansion of its service area to include communities and population currently served by other sources. This could occur in the event that present sources become contaminated or become insufficient to meet the needs of areas within potential reach of the City's distribution system (with installation of necessary connectors). Three possible areas of future shortfalls may be envisioned: (1) Long Island, especially Nassau County, (2) portions of Westchester or Putnam counties within reach of the city's aqueducts, and (3) northern New Jersey. The committee has not conducted any research on the likelihood of water failures in any of these regions, but it is aware of perennial concerns about possible contamination of the deeper aquifers that are the sole sources of water for Long Island. Moreover, all three of the identified regions may be expected to experience further population growth over the next two decades which, even without contamination of present sources, may pose the need for at least supplementary augmentation from the New York City system.

To the extent that the City's system is serving a smaller population now than it did three decades ago, it may be viewed by surrounding jurisdictions as a logical source of future water supply. Ironically, this perception may be enhanced by the City's success in lowering average per capita demand through its conservation measures (see Box 2-1).

The addition of further communities to the New York City system would be a political decision, very likely involving many stakeholders at the federal, state,

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

and local levels. The outcome of a request by a water-deficient jurisdiction cannot be predicted. However, if public health is threatened, emergency connections may well be established that could remain in place indefinitely, leading to de facto permanent dependence on the New York City system, at least in times of drought. The committee is not aware of how the issue of future connections to the City system may have been addressed in legislation or other policy statements to date. However, if the issue remains unaddressed, the relevant parties should take whatever steps may be necessary to protect existing user sources against contamination and against rising demand in order to minimize the potential for future demands on the New York City system.

DESCRIPTION OF THE NEW YORK CITY WATER SUPPLY SYSTEM

The water supply system for New York City is under the jurisdiction of the New York City Department of Environmental Protection (NYC DEP). Drinking water delivered to the city from upstate watersheds is impounded in the Croton, Catskill, and Delaware systems (see Figures 2-1, 2-2, and 2-3). The three watersheds contain 19 reservoirs and three controlled lakes with a total available storage capacity of about 558 billion gallons. During periods of normal rainfall, the total of the average yield for the three systems is estimated at 2,400 mgd (Hazen and Sawyer/Camp Dresser & McKee, 1997). The three water systems are interconnected at multiple locations to enhance flexibility and allow the exchange of water between systems. During periods of severe drought, Hudson River water can be used to augment the water supply by 100 mgd.

Water is delivered by gravity from the reservoirs of the Croton, Catskill, and Delaware watersheds to the City via large aqueducts and two balancing reservoirs. Three tunnels, two of which are deep bedrock tunnels, and two distribution reservoirs are then used to distribute drinking water to consumers. A third deep bedrock tunnel (Tunnel No. 3) has been under construction since 1970 and will supplement the two deep tunnels currently used for Catskill and Delaware water. The flow profile for the Catskill/Delaware system illustrating the changes in elevation as water passes from the Catskill Mountains to the City is shown in Figure 2-4.

A small part of the southeastern section of Queens is supplied by wells in addition to the main city distribution system. These wells, formerly under the operation of the Jamaica Water Supply Company, have been operated by the City since 1987 and supply between 17 and 24 mgd, less than half of the total average daily demand in the service area. A more detailed overview of the entire system is presented below. Table 2-2 lists the hydrological characteristics of each watershed.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-4 Flow profile for the Catskill/Delaware system. Source: Reprinted, with permission, from Hazen and Sawyer/Camp Dresser & McKee (1997). © 1997 by Hazen and Sawyer/Camp Dresser and McKee.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-2 Hydrological Characteristics of the Three New York City Watersheds

Parameter

Croton

Catskill

Delaware

Average percent of total water supply

10

40

50

Safe yielda (mgd)

240

470

580

Available storageb (109 gallons)

86.6

150.6

320.4

Total storagec (109 gallons)

94.6

147.5

325.9

Drainage basin (sq. miles)

375

571

1,010

Permanent population

132,000

36,000

45,000

Population per square mile

352

63

45

a Safe yield refers to the maximum amount of water that can be safely drawn from a watershed during the worst drought in the period of record.

b Available storage is the amount that can be withdrawn from a reservoir through its outlet structure and aqueduct.

c Total storage is the estimated volume between the crest of the spillway and the lowest elevation of the outlet of the reservoir.

Source: Reprinted, with permission, from Hazen and Sawyer/Camp Dresser & McKee (1997). © 1997 by Hazen and Sawyer/Camp Dresser and McKee.

New York City Drinking Water Reservoirs

Croton System

The Croton system normally provides approximately 10 percent to 12 percent of the City's daily water supply and can provide up to 25 percent during drought conditions. The system consists of 12 reservoirs and three controlled lakes on the Croton River, its three branches, and three other tributaries (Figure 2-1). Water from upstream reservoirs flows through natural streams to down-stream reservoirs rather than through aqueducts or tunnels. Water from the terminal New Croton Reservoir is then conveyed through the New Croton aqueduct to the Jerome Park Reservoir in the Bronx.

The Croton watershed is largely within New York, but it includes a small portion of Connecticut. During 1990, permanent and seasonal population of this area was about 132,000, translating into 350 persons per square mile. In 1991, the watershed also contained about 3,000 head of livestock (mostly nondairy). In addition to these population pressures, the quality of the Croton water supply (particularly color and odor) has diminished over the years. Since 1992, NYC DEP has been under an enforceable agreement with the New York State Department of Health to install filtration for the Croton system, although the plant will not be completed until March 1, 2007.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

A limited amount of water can be transferred between the Croton system and the Delaware system via two hydraulic pumping stations and the West Branch reservoir (see Figure 2-5 and the discussion below). In addition, water can be transferred by gravity from the Catskill system into the New Croton aqueduct. These operational possibilities and other factors allow the entire Croton system service area within the city to be supplied by the Catskill/Delaware system if necessary.

Catskill System

The Catskill system was constructed in multiple stages. The Ashokan Reservoir, Catskill aqueduct, Kensico Reservoir, Hillview Reservoir, City Tunnel No. 1, and terminal Silver Lake Reservoir in Staten Island were completed in 1917. Schoharie Reservoir and the Shandaken tunnel were completed in 1927. Seven years later, Tunnel No. 2 from Hillview Reservoir to Brooklyn was completed. Finally, in 1971, Silver Lake Reservoir was replaced with covered tanks.

The Catskill watershed is a sparsely populated area in the central and eastern portions of the Catskill mountains (Figure 2-2). The main tributaries that drain the watershed are the Esopus and Schoharie creeks. The Esopus Creek, a tributary of the Hudson River, is impounded by Ashokan Reservoir, which is divided by a dike into the East and West basins. Schoharie Reservoir, the northernmost basin in the entire system, is fed by Schoharie Creek and other tributaries. Most of the water from the Ashokan and Schoharie watersheds is stored in Ashokan Reservoir, with the balance being stored in Schoharie Reservoir. Water from Schoharie Reservoir is withdrawn through the 18-mile-long Shandaken tunnel to Esopus Creek, where it then flows 15 miles to the Ashokan Reservoir.

Delaware System

The Delaware system was the last of the three systems to be constructed and is furthest from New York City (Figure 2-2). Because of the large number and size of its reservoirs, the Delaware system normally provides 50 percent to 55 percent of the City's daily water supply. Cannonsville Reservoir, Pepacton Reservoir, and Neversink Reservoir collect water from tributaries of the Delaware River. Water from each reservoir travels through individual rock tunnels (West Delaware, East Delaware, and Neversink tunnels) to Rondout Reservoir, where the Delaware aqueduct begins. Rondout Reservoir drains Rondout Creek, a tributary of the Hudson River; however, most of Rondout's water is from the three upstream reservoirs on the branches of the Delaware River.

From Rondout, the Delaware aqueduct is connected to the West Branch Reservoir in the Croton system. Under normal operating conditions, water from the West Branch watershed is transferred to the Delaware system rather than flowing into the Croton system (and this is expected to continue after completion

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-5 Reservoirs, aqueducts, tunnels, and pumping stations east of the Hudson River. Source: Reprinted, with permission, from Hazen and Sawyer/Camp Dresser & McKee (1997). © 1997 by Hazen and Sawyer/Camp Dresser and McKee.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

of the Croton filtration plant). The Delaware aqueduct continues from West Branch to the Kensico Reservoir. The Delaware bypass at West Branch allows water to travel directly from Rondout to Kensico.

Although the Delaware watershed has a lower human population density than the other two watersheds (only 45 persons per square mile), it contains 35,000 head of livestock, most of which are dairy cattle. These agricultural operations can have a significant effect on the water quality of the Delaware supply.

Kensico and Hillview reservoirs, both of which are open, serve as balancing and distribution reservoirs, respectively, for the Catskill and Delaware systems. Either system can bypass the Kensico Reservoir and connect directly into Hillview. Under normal operations, water from both systems is discharged into Kensico Reservoir, thus mixing the two supplies. Water is then conveyed to Hillview Reservoir either through the Delaware aqueduct (which usually bypasses Hillview) or the Catskill aqueduct. Because of the mixing at Kensico, the Kensico and Hillview reservoirs, the sections of the Catskill and Delaware aqueducts between these two reservoirs, and the three City tunnels leaving Hillview Reservoir are referred to collectively as the Catskill/Delaware System.

Chelsea Pumping Station

In times of drought, Hudson River water can be pumped into Shaft 6 of the Delaware Aqueduct from an emergency pumping station at Chelsea. The station was originally constructed in the early 1950s to augment the City water supply prior to completion of the Delaware aqueduct. Although it was dismantled in 1957, it was reconstructed following several drought periods and has subsequently been put into service on three occasions (droughts of 1965–66, 1985, and 1989) (Warne, 1999a). The station is permitted for 100 mgd. Water delivered from the Hudson River is chlorinated prior to entering the Delaware aqueduct, and equipment is in place for coagulation if deemed necessary.

Brooklyn/Queens Aquifer

During the early part of this century, groundwater from the aquifer beneath Brooklyn and Queens provided a significant portion of the City's water supply. However, low water levels and saltwater intrusion have caused the abandonment of all wells except for some that service southeastern Queens. The City is currently investigating the use of renewed groundwater pumping to provide supplemental sources of drinking water.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Water Supply Infrastructure

Aqueducts and Tunnels

The principal reservoirs, aqueducts, tunnels, and pumping stations east of the Hudson River are shown in Figures 2-5 and 2-6. Under normal operating conditions, the Catskill and Delaware aqueducts convey water from the Catskill and Delaware watersheds to Kensico Reservoir, where significant mixing occurs. Monitoring data from NYC DEP have shown that the water quality at the two Kensico effluent locations (DEL 18 and CATLEFF) is similar, except for slightly higher coliform concentrations at DEL 18 (NYC DEP, 1998). Water from both of these effluent locations is conveyed to Hillview Reservoir, where it enters Tunnels No. 1 and 2 for conveyance to the city. Trunk mains convey water from the shafts on Tunnels No. 1 and 2 to the Catskill/Delaware system service area.

Additional flexibility in water delivery between Hillview and the City will be provided by Tunnel No. 3, which is being constructed at a cost of approximately $6 billion. Construction is expected to be complete in 2020. Stage 1 of Tunnel No. 3, completed at a cost of approximately $1 billion, went on-line in July 1998. This 13-mile segment runs from Hillview through the Bronx into Manhattan, under the East River and Roosevelt Island and into Queens. In the future, Tunnel No. 3 also will be connected with Kensico Reservoir directly, allowing water to be delivered from Kensico to the City without passing through Hillview. Operation of City Tunnel No. 3 will allow inspection of Tunnels No. 1 and 2 for the first time since they were put in service in 1917 and 1938, respectively.

Distribution System

The New York City water distribution system consists of a grid network of water mains ranging in size from 6 to 84 inches in diameter. It contains approximately 6,000 miles of pipe, 87,000 mainline valves, and 98,000 fire hydrants. Water pressure is regulated within a range of 35–60 pounds per square inch (psi) at street level; generally, 40 psi is sufficient to supply water to the top of a five-or six-story building. About 95 percent of the total city consumption is normally delivered by gravity.

The distribution system in each borough is divided into three or more zones in accordance with pressure requirements that are determined by local topography. The ground elevation in the City varies from a few feet above sea level, along the waterfront, to 403 ft at Todt Hill in Staten Island. The storage facilities at Hillview and Jerome Park reservoirs and Silver Lake tanks handle the hourly fluctuations in demand for water throughout the City as well as any sudden increase in draft that might arise from fire or other emergencies. With the exception of some communities in the outlying areas of the City, which may experience

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-6 New York City water tunnels. Courtesy of the NYC DEP.

 
Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

low-pressure service in peak hours during summer months, the water distribution system generally provides excellent service. Engineering consultants to the New York City Water Board have judged the distribution system to be in adequate condition, based on criteria such as watermain breaks, pressure tests, flow tests, and leak detection (Warne, 1999b).

Existing Treatment

Table 2-3 shows average water quality conditions in the Catskill/Delaware reservoirs from 1992 to 1996. Because of their high quality, waters from the Croton and Catskill/Delaware systems have historically only been treated with chlorine disinfection, beginning in 1910 for the Croton System and at startup of the Catskill and Delaware systems. Although chlorination has been shown to be effective for killing or inactivating bacteria, viruses, and Giardia, the level of chlorination used by New York City (less than or equal to 2 mg/L free chlorine) is not effective for inactivation of Cryptosporidium oocysts (Liyanage et al., 1997).

Chlorination takes place at multiple locations in the Catskill/Delaware and Croton systems. Croton water is chlorinated at the Croton Lake Gate House to achieve a level of disinfection sufficient to satisfy the Surface Water Treatment Rule (SWTR) in the New Croton aqueduct. Additional chlorine is added at the Jerome Park Reservoir to maintain a residual within the distribution system. Similarly, the Catskill/Delaware system is chlorinated twice prior to the distribution of water into the City. Chlorine is initially added to both the Catskill and Delaware aqueducts as the water leaves Kensico. These chlorine levels are used to determine compliance with the SWTR. Additional chlorine is added to the Catskill aqueduct prior to Hillview downtake chambers to maintain residual levels in the distribution system.

In addition to chlorination, water treatment facilities can also provide alum to increase settling in the reservoirs during periods of high turbidity. Alum is used most frequently for the Catskill system, where it is added to the Catskill aqueduct prior to the Kensico Reservoir. Coagulated solids then settle within Kensico. There is also a facility for adding alum to the Delaware system between West Branch and Kensico. However, this facility has not been used at any time during the last 10 years.

In the 1960s, the City began adding fluoride at the Kensico and Dunwoodie reservoirs for dental health reasons. Sodium hydroxide addition takes place at Hillview Reservoir to assist corrosion control and to neutralize acidity arising from fluoride addition and intermittent alum applications. More recently, orthophosphate facilities have been installed at the Hillview downtake chambers and the Jerome Park Reservoir gate houses. Like sodium hydroxide, orthophosphate also accomplishes corrosion control for the distribution system. Finally, copper sulfate treatment is used on an irregular basis to control algae. Copper sulfate can

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-3 Average Water Quality Conditions in the Catskill/Delaware Reservoirs

Reservoir

pHa

Alkalinitya (mg/L)

Total hardnessa (mg/L CaCO3)

Turbidityb (NTU)

Total organic carbona (mg/L)

Ammoniaa (mg/L)

Ashokan W

6.9

9.68

15.92

4.54

1.7

0.02

Ashokan E

7.0

9.87

16.05

2.09

1.8

0.02

Cannonsville

7.3

14.21

24.77

4.09

2.1

0.021

Neversink

6.4

2.16

8.92

1.58

1.7

0.016

Pepacton

7.2

10.10

18.99

1.69

1.6

0.01

Rondout

7.0

7.94

16.16

1.20

1.7

0.01

Schoharie

7.0

12.81

19.82

8.98

2.2

0.02

Kensicoc

6.9

10.40

18.79

1.05

1.7

0.016

West Branch

7.0

13.50

25.44

1.12

2.0

0.02

a 1986–1998: Whole lake data. Courtesy of the NYC DEP.

b 1993–1996: TMDL Reports (NYC DEP, 1999a–h).

c Kensico Reservoir data best represent the overall quality of the raw water supply prior to treatment.

be added to the system at a large number of locations, both upstream and downstream of the New Croton Reservoir and upstream of Kensico Reservoir. Figure 2-7 illustrates the principal chemical feed locations in both the Croton and Catskill/Delaware systems.

CATSKILL/DELAWARE WATERSHED

The Catskill and Delaware watersheds from which New York City draws the majority of its drinking water encompass an area collectively referred to as the Catskill Mountains. This region, though sparsely populated, has supported a wide variety of enterprises, from agriculture to heavy industry. This section describes the physical attributes of the Catskills, including those that account for New York City's historically excellent water quality. It then describes the evolving land uses within the region that have influenced the quality of New York City drinking water.

Biophysical Setting of the Catskills

As Alf Evers notes in his widely acclaimed 1993 book The Catskills: From Wilderness to Woodstock, the precise regional boundaries of the Catskills are difficult to define. Perhaps the most colorful description can be attributed to an old man who lived in the shadow of Plattekill Mountain. When asked by Evers

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-7 Potential chemical feed locations for the New York City water supply (not all chemicals and feed locations are used on a regular basis). Source: Reprinted, with permission, from Hazen and Sawyer/Camp Dresser & McKee (1997). © 1997 by Hazen and Sawyer/Camp Dresser and McKee.

just where the Catskills began, he replied, ''You keep on going until you get to where there's two stones to every dirt. Then b'Jesus you're there." Native Americans evoked the misty blue appearance of the Catskills in their name, "Onteora," meaning "mountains of the sky." Both are apt descriptions of site, soil, and hydrologic characteristics of the Catskills.

Geology and Soils

The Catskills are an uplifted, maturely dissected portion of the Allegheny Plateau (Isachsen et al., 1991; Titus, 1993). Murdoch and Stoddard (1992) describes the Catskills as an eroded peneplain at the northern end of the Appalachian Plateau, with flat-lying sandstone, shale, and conglomerate bedrock deposited as part of a Devonian Age delta. A wedge-shaped formation, the Catskill

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Escarpment rises steeply (about 1,640 ft) within 5–6 miles of the Hudson River. The highest elevations (3,000–4,200 ft) occur in the Esopus and Schoharie Creek watersheds. From the "High Peaks" area, the plateau tapers to the west into the Delaware Valley and the Finger Lakes region.

Catskill Mountains. Source: The Hudson (Lossing, 1866. © 1866 by H.B. Nims & Co.).

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

During the fall and winter when the deciduous trees are bare, the horizontally bedded sedimentary rock layers are clearly discernible along the Catskill Escarpment when viewed from the Hudson River and from many other vantage points. While hiking through virtually any part of the Catskills, the casual observer will note the horizontal layers and seams in rock outcrops or large boulders. The hydraulic properties and generally horizontal orientation of bedrock largely limit vertical water movement to bedrock fractures. Therefore, most subsurface water flow occurs through the soil mantle.

Most of the Catskills region is blanketed with a thin veneer of glacial till. Rock outcrops and boulder fields are common at higher elevations. Soils on mountaintops, ridgelines, and steep slopes are shallow (˜0.7–4.3 ft) and stony, usually classified as stony sandy loams. The combination of high permeabilities and steep gradients produces rapid rates of lateral subsurface flow and droughty conditions during the growing season (USDA SCS, 1979). In saddles (rounded ridges between two peaks), along lower slopes, and in valley bottoms and floodplains, soils have a larger proportion of fine-textured material (silts and clays) as well as extensive deposits of alluvial sands and gravels. Local landforms and bedrock topography strongly influence the location, spatial extent, and heterogeneity of soils. For example, sand and gravel deposits are prevalent along the steeply incised valleys and relatively narrow floodplains of the Woodland Creek watershed (tributary to the Esopus Creek in the High Peaks region). By contrast, deeper silt loams form broad, flat floodplains along the Beaver Kill, another major tributary entering the Esopus Creek from the east.

Climate and Streamflow

At an approximate latitude and longitude of 42° N and 74–75° W, respectively, the Catskills region is affected by continental and maritime air masses. This results in frontal storms from the west and north, coastal storms from the south (along with an occasional Nor'Easter), and local thunderstorms (Murdoch and Stoddard, 1992; Stoddard and Murdoch, 1991; USDA SCS, 1979). Average annual precipitation is about 47 inches. The average air temperature is –4°C (24°F) in January and 22°C (71°F) in July. Orographic effects1 and differences in land slope and aspect can strongly influence precipitation, air temperature, wind velocity, and relative humidity. Evidence of these microclimatic differences can be found in the species composition and growth form of vegetation, in snow accumulation and melt rates, and in other readily observed ecosystem characteristics.

1  

 Orographic effects refer to increases in precipitation with increasing elevation as air masses flow up and over mountains. This is common in the Catskill/Delaware region as continental air masses move east from the Ohio Valley or maritime air masses move north up the Hudson River valley.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Although highly variable in water equivalent (the total amount of water), spatial extent, and duration, a snowpack typically forms in late November and persists through midwinter thaws until melt occurs in late March and early April. As evidenced by the January 1996 flood, rain-on-snow and snowmelt tend to be the largest and most destructive flow events in the Catskills region. Although precipitation is relatively uniform in temporal distribution, streamflow can vary markedly between dormant and growing seasons, as shown in Figure 2-8(A). In addition to snowmelt events described above, large rain events that occur between leaf-fall and the beginning of snow accumulation can produce very high flows. This occurs when air temperatures and evapotranspiration rates decrease, causing a simultaneous and rapid increase in soil water content, in the extent of saturated source areas, and in streamflow. Finally, large, high-intensity convective storms can produce rapid streamflow response during the growing season or spring (leaf-out) and fall (leaf-fall) transition periods. However, stormflow from large summer thunderstorms is generally less significant than streamflow from snowmelt or dormant season rains. All of these sources contribute to the estimated 2,000 miles (from the U.S. Geological Survey) of watercourses and intermittent streams found in the Catskill/Delaware watershed.

In summary, precipitation is relatively uniform in quantity and timing throughout the year, but total annual streamflow volume is not. The streamflow regimen often is dominated by a few large events. Therefore, vegetative cover, land use, and resulting pathway(s) and rate of flow play an important role in determining how climatic and hydrologic characteristics affect reservoir water quality.

Reservoir Dynamics

Water supply reservoirs have many characteristics that are similar to those of natural lakes. However, there are important differences in spatial and temporal dynamics that influence reservoir productivity2 and water quality (Wetzel, 1990). The drainage basins of reservoirs are consistently much larger relative to the reservoir surface area than is the case for most natural lakes. Thus, reservoirs receive runoff water and associated pollutant loadings from watershed areas that are many (10–200) times larger than those of most natural lakes. In addition, source water for reservoirs is transported mainly via high-order streams, which results in high energy for erosion, large sediment load carrying capacities, and extensive loading of dissolved and particulate contaminants into reservoir water.

2  

 Productivity is defined as the rate of formation of organic matter over some defined period of time, usually a year (never just the "growing season"). Net productivity is the production of new organic matter by photosynthetic organisms, or the acquisition and storage of organic matter by nonphotosynthetic heterotrophic organisms, less losses from respiration and egestion, divided by the time interval.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-8 (A) Streamflow for the Esopus Creek in the Ashokan Watershed, 1995–1998. Source: http:/waterdata.usgs.gov. (B) Water levels in the West Basin of Ashokan Reservoir. Courtesy of the NYC DEP. (A) and (B) show how stream flow volatility is dampened in the reservoir because of the reservoir's large size, selective withdrawals, and the distribution of water between the West and East basins. The crest of the spillway between the West and East basins is 587 ft.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Because reservoir inflows are primarily channelized and often are not intercepted by energy-dispersive buffer zones, runoff inputs are larger, are more directly coupled to precipitation events, and extend much farther into the reservoir per se than is the case for most natural lakes. All of these properties result in high, but irregularly pulsed, pollutant loading to water supply reservoirs.

Within the reservoir itself, the irregular dynamics of inflow and rapid, variable flushing rates can markedly alter environmental conditions for biota. A reservoir can be viewed as a very dynamic lake in which a significant portion of its volume possesses characteristics of a river (Wetzel, 1990). Often the riverine portion of a reservoir functions like a large, turbid river in which turbulence, sediment instability and high turbidity, reduced light availability, and other characteristics preclude extensive photosynthesis, despite high nutrient availability. This reduction in photosynthesis is only partially ameliorated by turbulent, intermittent recirculation of algae into the photic, or light-penetrating, zone. In more lacustrine (lakelike) regions of reservoirs, greater light penetration is possible, the depth of the photic zone increases, and primary productivity increases. Nutrient limitations, so characteristic of natural lakes of low to moderate productivity, can then occur to varying degrees as losses of nutrients exceed loading renewal rates.

Internal loading of nutrients from sediments or deep-water areas of storage, normally low in natural lakes, can be high in reservoirs. Much of the internal nutrient loading in reservoirs is associated with the irregular inflow and withdrawal dynamics, which can disrupt thermal and dissolved oxygen stratification patterns that suppress sedimentary nutrient release and redistribution in more physically stable, natural lakes.

The average depth of the eight primary reservoirs of the Catskill/Delaware system is quite large (approximately 50 ft; Table 2-4). Despite the relatively large storage capacities of the reservoirs, water residence times are variable, between 0.06 to 0.71 years. Residence times of less than a third of a year tend to be relatively unstable and force organisms into rapid growth cycles (Ford, 1990). Pepacton Reservoir's residence time approaches residence times of natural lakes, which can contribute to greater stability, particularly in relation to displacement of nutrients to sediment storage sites.

Withdrawals constitute a removal of maximum storage capacity of approximately 0.0025 percent per day. Although most withdrawals are from surface waters, water can be withdrawn from varying depths within all Catskill/Delaware reservoirs except Schoharie Reservoir. The chosen depth of withdrawal depends on turbidity, dissolved oxygen levels, color, and other water quality parameters (Warne, 1999a).

Wetlands

Wetlands are relatively flat land areas that are partially or wholly flooded throughout the year. Soils in these areas are usually deprived of dissolved oxygen

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-4 Storage Capacities, Drainage Areas, and Residence Times of the Catskill/Delaware Reservoirs

Drainage Basin

Total Storage Capacitya

Drainage Basin Areaa

Mean Depthb

Residence Timec

Average Supply

106 m3

109 gal.

km2

mi2

(ft)

(yr)

(106 gpd)

Catskill System

Schoharie

74.2

19.6

813.3

314.0

44.3

0.10

 

Ashokan—Ed

305.4

80.7

63.5

24.5

41.3

0.31

 

Ashokan—W

178.7

47.2

602.2

232.5

 

0.20

 

Total

558.3

147.5

1,479.0

571.0

 

 

501

Delaware System

Cannonsville

366.1

96.7

1,165.5

450.0

53.5

0.43

 

Pepacton

543.9

143.7

963.5

372.0

69.5

0.71

 

Neversink

134.2

35.5

240.9

93.0

62.0

0.42

 

Rondout

189.4

50.0

246.1

95.0

66.3

0.14

 

Total

1,233.6

325.9

2,616.0

1,010.0

 

 

846

East-of-Hudson

West Branche

38.2

10.1

52.8

20.4

25.9

0.38

 

Kensico

115.8

30.6

34.4

13.3

41.0

0.06

 

a Hazen and Sawyer/Camp Dresser & McKee, 1997.

b Table 2.5 In NYC DEP (1993a).

c From 1999 TMDL reports (NYC DEP, 1999a–h); average of 1992–1996 data. It should be noted that the TMDL reports use "annual residence times" rather than "mean monthly residence time." These different methods for calculating residence time generate different numbers, with the TMDL method generating smaller values.

d East Basin area calculated by subtracting the West Basin area from the total Ashokan drainage basin area (257 sq mi).

e West Branch area is often given as 42.9 sq mi. This value includes areas of Boyd Corners, Lake Gleneida, and Berret's Pond.

and consequently only support the growth of specialized aquatic plants. Much like riparian zones, wetlands often connect upland areas to adjacent waterbodies. Thus, they are critical in the protection of water quality and aquatic habitats and in flood and erosion control. Examples of wetlands include marshes, swamps, ponds, wet meadows, and seasonally flooded floodplains (Tiner, 1997).

Wetlands comprise a small (yet important) proportion of the Catskill/Delaware watershed (Tiner, 1997). They may have organic, mineral, or mixed substrates, and they tend to occur in riparian areas throughout the region. Figure 2-9 shows the general distribution of wetlands and deepwater habitats of greater than ten acres in the Catskill/Delaware watershed. The dominant wetland types

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-9 General distribution of wetlands and deepwater habitats of greater than 12.4 acres in the Catskill/Delaware watershed.  Courtesy of the NYC DEP.

in the Catskill/Delaware region are (1) emergent (commonly called marshes and vegetated with grasses, sedges, cattails, or common reed), (2) scrub-shrub (dominated by woody vegetation less than 20 ft tall, such as speckled alder or willows), and (3) forested (comprised of tree species greater than 20 ft tall such as red maple, eastern hemlock, and associated woody shrubs). Table 2-5 summarizes the types and corresponding areas of wetlands in the Catskill/Delaware region. Detailed discussion of community types, classification methods, and wetland functions can be found in Cowardin et al. (1979), Mitsch and Gosselink (1993), and NRC (1995).

In the Catskill/Delaware watershed, wetlands occur in three landscape positions. First, a small number of relatively large wetlands exist in riparian/floodplain areas, the transition zone between upland and aquatic ecosystems. In these critical landscapes, wetlands reduce flow velocity, trap sediment, assimilate and transform nutrients, and provide valuable and unique habitats. Second, many small wetlands occur in depressional areas in alluvial soils of broad valleys, mainly, if not entirely, in the Cannonsville, Pepacton, and Schoharie watersheds.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-5 Wetland Types and Areas in the Catskill, Delaware, and Croton Watersheds of the New York City Water Supply System (table includes wetlands of less than 10 acres)

Wetland Type

Catskill acres (% of total wetland area)

Delaware acres (% of total wetland area)

Croton acres (% of total wetland area)

Emergent

838

(22%)

1,607

(19%)

750

(5%)

Scrub-Shrub

615

(16%)

769

(9%)

754

(5%)

Shrub/Emergent

169

(4%)

322

(4%)

812

(5%)

Deciduous Forested

894

(23%)

478

(6%)

11,036

(70%)

Evergreen/Mixed Forested

337

(9%)

416

(5%)

158

(1%)

Pond

827

(21%)

1,505

(18%)

2,152

(14%)

Reservoir/Lake/ River shallows and shores

192

(5%)

3,190

(39%)

147

(<1%)

Totals

3,872

(100%)

8,287

(100%)

15,809

(100%)

Watershed area (acres)

365,440

 

648,320

 

247,680

 

Wetland area (%)

1.0

 

1.3

 

6.4

 

 

Source: Tiner (1997).

Finally, wetlands are found in isolated depressions high in the watershed(s). First order perennial streams sometimes originate from these sites, most of which are above the 2,000-ft elevation line and so receive de facto protection from the Catskill State Park and other regulations.

The MOA specifically identifies wetlands for water quality protection, similar to that afforded to reservoirs, major tributaries, and streams. Unlike the U.S. Army Corps of Engineers, which has no minimum acreage requirement for determining its jurisdiction, the MOA protects only those wetlands greater than 12.4 acres in size. This arbitrarily established size limit is not expected to substantially affect water quality in the reservoirs because wetlands smaller than 12.4 acres in the Catskills do not constitute the more important riparian and headwater wetlands discussed above. Rather, they are isolated depressions on agricultural land in the Cannonsville, Pepacton, and Schoharie watersheds (the second type described above) that have an indirect effect on reservoir inflow and quality during the dormant season and have limited or insignificant effects during the growing season. Although depressional wetlands comprise a small fraction of the total watershed area, they can be important nutrient sinks and sediment traps in the subwatersheds of minor tributaries. In addition, they provide critical habitat for a range of plant and animal species. They are most valuable ecologically and economically if kept intact.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
Vegetation

The Catskills landscape is predominantly forested, although the total area of forest varies considerably across the region. The Catskill watershed, which includes the Ashokan and Schoharie reservoirs, also includes the core area of the 335,000-acre Catskill Forest Preserve. The majority of the uplands support mixed-species stands of deciduous trees (red and white oak, beech, yellow, paper, and gray birch, red and sugar maple, and common understory associates). Many stands, especially those on well-drained south aspects, have a dense understory of mountain laurel. Conifers such as eastern hemlock and eastern white pine are more prevalent in valley bottoms and along stream channels at higher elevations. The summits of the highest peaks—Wittenberg, Cornell, and Slide—have remnant stands of balsam fir and red spruce along with small areas of alpine grasses and heath shrubs.

The age and condition of the Catskills forest reflect several centuries of land use and economic change, the most prominent of which are outlined in the following section. Although the forests of the Catskills have been, at various times and for various reasons, repeatedly exploited and ignored, their protective function remains largely intact. Natural regeneration and planted stands have restored the protective litter layer on the forest floor, have increased soil organic matter, and have encouraged colonization by organisms ranging from microbes to small mammals and the proliferation of roots throughout the shallow profile. As a result, wherever forests are present, subsurface (rather than overland) flow has been restored to the watershed. In light of the summary statistics for forest and vacant land, this bodes well for the protection and maintenance of water quality, especially because forests occur on steep slopes and along countless intermittent and ephemeral streams throughout the watershed.

Land Use

Table 2-6 and Figure 2-10 show land use and land cover categories for the Catskill/Delaware watershed. The most significant agricultural land use is centered in valley bottoms of the Delaware watershed. Dairy farming became established in the 1800s when railroads linked the region to lucrative markets in the Hudson Valley and New York City. Post-World War II expansion of dairy farming in western New York and the Midwest intensified competition and led to widespread farm abandonment (evidenced in the vacant land category, abandoned fields not yet classified as forest, in Table 2-6). Residential and commercial development accounts for a relatively small proportion of watershed land use. However, because this development tends to be concentrated in stream valleys, it can have a disproportionately large influence on water quality.

Without active intervention and management, intensive agricultural use (e.g., tilled fields, barnyards, and feedlots) and impervious surfaces associated with

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-6 Land Use in the Catskill/Delaware Watershed by Reservoir Basin (in acres and as percent of total)

Basin

Agriculture

Low-Density Residential

High-Density Residential

Commercial/ Industrial/ Government

Vacant Land

Forests

Other Open Space

Total Acres

Ashokan

54

6,945

6,945

555

2,617

142,975

512

153,873

 

<1%

5%

<1%

<1%

2%

93%

<1%

 

Schoharie

5,975

37,521

748

2,819

25,737

123,760

3,793

200,353

 

3%

19%

<1%

1%

13%

62%

2%

 

Cannonsville

30,523

61,072

751

3,316

37,057

148,256

4,121

285,096

 

11%

21%

<1%

1%

13%

52%

1%

 

Neversink

136

2,376

16

47

1,487

52,955

661

57,678

 

<1%

4%

<1%

<1%

3%

92%

<1%

 

Pepacton

6,960

43,332

622

1,516

23,259

150,957

3,980

230,624

 

3%

19%

<1%

<1%

10%

65%

2%

 

Rondout

1,152

5,157

239

125

2,253

48,614

320

57,862

 

2%

9%

<1%

<1%

4%

84%

1%

 

Totals

44,800

156,403

2,590

8,378

92,410

667,517

13,387

985,486

 

5%

16%

<1%

<1%

9%

68%

1%

 

Note: The low density residential, high density residential, and commercial/industrial/government categories do not correspond with the NYC DEP ''urban" category used in TMDL calculations and the pathogen monitoring studies. NYC DEP's "urban" category is a measure of impervious surfaces, major roadways, commercial, industrial, and high- and medium-density residential areas as derived from LANDSATTM scenes that have a 28.5-m resolution.

Source: NYC DEP, 1993b.

residential and commercial development inevitably generate overland flow. If these areas are connected with the stream channel network, larger quantities of lower quality water reach downstream areas more rapidly than does subsurface flow through native forest. Thus, although nonforest land uses may only comprise single-digit percentages of reservoir watersheds (Table 2-6), they are the principal challenge for mitigation and management.

Land Use History

A chronology of natural resource use in the Catskill Mountains is presented in Table 2-7. A historical review of changes in local economic activities and settlement patterns helps to put into perspective contemporary social and ecological conditions and the cumulative effects they have had on forests, soils, and water resources.

For thousands of years before Hendrick Hudson sailed up the "Great River of Mountaynes" in 1609, Native Americans made limited use of the Catskills. They

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-10 Land cover of the Catskill/Delaware watershed. Note that impervious surfaces ("urban") do not correspond with the residential, commercial, and industrial land use in Table 2-6. Actual impervious cover is a lower percentage of land than the categories used in Table 2-6.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-7 A Chronology of Natural Resource Use in the Catskill Mountain Region, New York

??? ~ 1630

Native American hunting, gathering, and war parties made extensive use of mountain slopes and summits. Farming and seasonal settlements were clustered in and along floodplains of major streams and along the Hudson River.

1609

On a voyage of discovery sponsored by the Dutch East India Company, Hendrick Hudson sails the Half Moon up the "Great River of Mountaynes" [later the North or Mauritius River then, finally, the Hudson River] in search of the Northwest Passage. He claims the region for the Netherlands eleven years before the Mayflower reaches Plymouth.

1610

Active trade with Native Americans, primarily for beaver pelts, begins during Hudson's second voyage.

1624

Dutch settlement proceeds slowly in proximity of the Hudson River, and later the Esopus and Rondout Creeks. In addition to New Amsterdam [now New York City], fur trading posts are established: Wiltwyck [now Kingston] and Fort Nassau [now Albany].

1664

September 8th, Governor Petrus Stuyvesant surrenders New Netherland to a fleet of five English warships. The colony is named New York in honor of the King's brother.

1665

Disease and armed conflicts with white settlers lead to the extirpation of Native Americans from the region.

1700 ~ 1800

Land speculation, namely the 1.5 million acre Hardenbergh Patent, slows the colonization of the Catskills. Not until 1754 is the patent, held by Johannes Hardenbergh and seven partners, divided among their 52 heirs.

~1750–pres.

Agriculture begins in the region. Early subsistence farms evolve into livestock, truck crop, and dairy operations.

1765

Early roads reach the interior. The Plank Road up the Esopus Creek valley [now NYS Route 28] first appears on a map.

1777

October 13th, British troops burn Kingston, the first capital of the State of New York.

1800–1870

Leather tanneries are established near major streams and virgin hemlock (Tsuga canadensis) forests throughout the region. When in peak production raw hides are imported from as far away as South America. Except for small, inaccessible areas, the late successional hemlock forest was destroyed to provide tanbark. Watercourses are fouled with tannery wastes and by deforestation. The native trout fishery is decimated.

1820 ~ 1930

The dense second-growth deciduous forest is repeatedly cut for barrel hoops, mass-produced furniture parts (largely for mail-order catalog companies), and fuelwood (for steamboats and locomotives).

1820 ~1930

Urban dwellers enamored of the writings of Washington Irving (Rip Van Winkle, 1729), James Fenimore Cooper (The Leatherstocking Tales, 1823–1841), and John Burroughs (1837–1921) as well as paintings of the Hudson River School, flock to early mountain houses and boarding establishments.

1830 ~ 1895

Bluestone is quarried throughout the region. Most is hauled to Island Dock on the Rondout Creek near Kingston, then by barge to New York City where it is used for curbs, sidewalks, buildings, and terraces.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

1870–1954

The Ulster & Delaware Railroad extends the New York Central Railroad lines along the Hudson River to the interior of the Catskill region. Improved transportation benefits tourism and agriculture.

1885

The Catskill Forest Preserve is established as "Wild forest, forever" by amendment to the New York State Constitution. Most of the lands are mountaintop and sidehill parcels of second- or third-growth forest, that after being abandoned by owners, revert to state and local governments in lieu of delinquent taxes.

1905

New York State Public Health Law authorizes New York City to secure lands, by eminent domain if necessary, to build reservoirs and infrastructure needed to expand the water supply.

1907–1965

Beginning with the Ashokan Reservoir (Esopus Creek) and ending with the Cannonsville Reservoir, the New York City system encompasses 985,486 acres of watershed land.

1950s

Alpine skiing increases in popularity with the construction of several major ski areas (Belleayre, Highmount, Hunter Mountain, Ski Windham, and others). Deer hunting, trout fishing, hiking, backpacking, camping, and recreational activities increase in popularity. Fall foliage attracts visitors from far and wide.

1960s–present

Forest products industry is reestablished as forest on private lands reach sawtimber size classes. Other forest owners expand the production of maple syrup and sugar.

1970s–present

Improvements in the local and regional highway system and lifestyle changes increase the demand for vacation and second homes.

Adapted from Evers (1993), Stave (1998), and Wilstach (1933).

hunted in deciduous forests along the lower slopes, grew corn, beans, and squash in small floodplain fields, and occasionally moved through the interior hemlock and upper-elevation spruce-fir forests in hunting or war parties. Colonial settlement of the Hudson River Valley by the Dutch and later the British along the lower Esopus, Rondout, and Schoharie creeks loosely encircled the Catskills. Beaver flourished in the numerous headwater streams, and this led to a burgeoning fur trade between Indians and Dutch and English traders. This was the first phase of intensive natural resource use in the region. Trade and other interaction occurred for several decades until fundamental misunderstandings over land transactions led to war and to extirpation of Indians from the region. Indians believed they were giving permission for friendly people to settle amongst them; whites believed they were buying the land in accordance with European norms and traditions (Evers, 1993).

Through an almost unbelievable sequence of events, in 1708 a Kingston merchant, Johannes Hardenbergh, was granted 2 million acres of land, encompassing virtually the entire region (Evers, 1993). This enormous land patent had

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

Workers peeling and piling bark showing the tools neededbarking axes, peeling irons, and a "bob sled" with bark racks to secure the bark for travel to the tannery. Engraving c. 1840s. Collection of the Zadock Pratt Museum. Source: Reprinted, with permission of the Zudock Pratt Museum, from Bare Trees by Patrick Millen (Black Dome Press: 1995).

the effect of forestalling extensive pioneer settlement until the mid-1700s. It also established a precedent for contentious "landlord–tenant" interaction that lingers to this day. The Catskills have been transformed by multiple enterprises, including leather tanning, "cut-and-run" logging, stone quarrying, and subsistence and commercial farming until tourism, the establishment of the Forest Preserve, and finally the New York City water supply system led to the current landscape and community structure (Evers, 1993).

The long and volatile chronology summarized in Table 2-7 reminds us that more changes are, no doubt, in store. The forest continues to mature, farming seems poised to shift from dairy to other crops, and economic and societal changes induce people to seek rural areas as places to live, work, and recreate.

Population Trends in the Watershed Region

One of the reasons the Catskill/Delaware region was tapped for water early in the twentieth century was that it was sparsely populated. There are 40 towns west of the Hudson River with some land in the Catskill/Delaware watershed. An examination of the populations of these communities in the late nineteenth and early twentieth centuries reveals little population growth (Curve A, Figure 2-11). In fact, the town populations actually declined in the initial decades of this century. Although a growth spurt was experienced between 1930 and 1980, since 1980 there has been very little population growth in the region.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-11 Historical (1860–1996) and predicted future (1990–2020) population trends for the Catskill/Delaware watershed region and 40 West-of-Hudson communities.

This analysis, however, can be misleading because less than half the population of the West-of-Hudson watershed towns actually resides within the watershed boundary. In order to determine actual watershed population figures, the 1990 percentages of the town population residing in the watershed (NYC DEP, 1993b) were used to estimate permanent watershed populations since 1860, with results shown as Curve B in Figure 2-11. These estimates demonstrate that the actual Catskill/Delaware watershed population hardly changed between 1860 and 1990. In fact, the 1990 watershed population exceeded the estimated 1860 population by just 235 persons.

Based on these historic trends, future permanent population trends into the year 2020 were estimated assuming three different rates of growth. Average annual growth rates were determined for the periods 1900–1990 (long-term or moderate growth), 1940–1990 (high growth), and 1990–1996 (recent or low growth) using U.S. Census population figures. The corresponding average annual percentage growth rates for the total population of the 40 towns are given in Table 2-8. For the estimated population residing within the watershed boundaries, the three corresponding annual percentage growth rates are somewhat lower, as expected. Population projections based on these alternative growth rates are given in Figure 2-11, Curves C–H. It is clear from the trend lines that the estimated permanent watershed population will change little between now and 2020. If the 1990–1996 growth trend were to continue (Curve H), the permanent population in 2020 would be greater than the 1996 population by 2,500 persons. Figure 2-11 also indicates that growth in the 40 West-of-Hudson communities is likely to come in those areas lying outside the watershed.

The Croton watershed region has experienced significantly more population growth than the Catskill/Delaware watershed. The associated increase in resi-

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

FIGURE 2-12 Historical (1860–1996) and predicted future (1990–2020) permanent population trends for the Kensico and West Branch watershed regions.

dential and commercial construction, the loss of forests, and the increased wastewater demands have seriously degraded the water quality of the Croton watershed reservoirs. Twelve of the 13 reservoirs (including West Branch) are classified as eutrophic. Although the Croton system provides only 10 percent of the City's drinking water during nondrought conditions, almost all of the City's water passes through the Kensico and/or West Branch reservoirs, which reside within the Croton watershed boundaries. Population growth projections for the Croton watershed are likely to reflect conditions within the Kensico and West Branch watersheds that could have a significant impact on water from the Catskill/Delaware watershed.

The historical and future permanent populations residing in these two basins were analyzed by the same method used for the population residing in the Catskill/Delaware watershed. U.S. Census data were used to develop Figure 2-12, which shows that the population living in the Kensico basin has leveled off since about 1970 (Curve A). By contrast, the population residing in the West Branch watershed has grown at higher rates and more continuously than that of the Kensico watershed (Curve B).

Based on historic population trends for each basin (data not shown), three different growth rates were calculated for each, as shown in Table 2-8. These growth rates were applied to estimate future permanent population in the Kensico and West Branch watersheds (Figure 2-12, Curves C–H). Population growth in the Kensico watershed is likely to be relatively moderate into the next century, even under the high growth assumption (2.52 percent per annum), which would raise the population residing in the Kensico basin by about 14,000 between 1996 and 2020. Based on the high growth rate characteristic of 1940–1990 (4.9 percent per year), the West Branch basin population would grow by 83,146 persons,

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

TABLE 2-8 Annual Percentage Growth Rates for Different Regions in the New York City Watershed

Area

1990–1996 Low growth

1900–1990 Moderate growth

1940–1990 High growth

40 West-of-Hudson Towns

0.25

0.38

0.79

Catskill/Delaware Watershed

0.11

0.22

0.49

Kensico Watershed

0.69

1.68

2.52

West Branch Watershed

1.38

3.45

4.90

Adapted from U.S. Census data.

or 200 percent by 2020. These projected population trends underscore the importance of (1) monitoring reservoir water quality, (2) reducing present pollutant loadings via best management practices within the watershed, and (3) preventing future pollutant loading to the Kensico and West Branch reservoirs by restricting certain activities. These will be formidable tasks in the face of future population pressures.

Seasonal residence in the West-of-Hudson region is a factor that was not taken into account in this analysis, partly because estimating this population is difficult. The 1993 environment impact statement (EIS) for the New York City watershed regulations projected that in the absence of regulations, the seasonal population would grow at a rapid rate (NYC DEP, 1993b). It concluded that if the watershed regulations then proposed were adopted, all population growth in the area would be minimal. (The EIS provided no information on how this conclusion was reached.) Unfortunately the analysis in the EIS contains errors, and the EIS relied on a method of estimating seasonal population that yields unreliable results.3

In order to independently assess the role of seasonal population, the committee turned to census data on housing, which support some concern about in-

3  

 To estimate the seasonal population in 2010, the EIS used a census count of vacant houses in 1980 and 1990. The EIS estimated the seasonal population by multiplying the number of vacant houses by the average family size in each township. Using this estimation method for 1980 and 1990, the EIS projected that seasonal population would double between 1990 and 2010 in the West-of-Hudson watershed areas. This procedure is likely to yield exaggerated estimates of seasonal population growth because it does not differentiate between seasonal housing and other vacant housing. For example, areas like Delaware County had the largest number of unoccupied houses and also experienced net population loss during the 1980s. Much of this housing is likely to be vacant, not seasonal housing. In addition, the EIS reported that in 1990 about one-third of all housing units in the West-of-Hudson watershed area were vacant. This appears to be an error resulting in an overestimate of seasonal change in housing. Our review of census figures indicates that about 19 percent of all housing units in the area were vacant in 1990.

Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×

creases in seasonal population in watershed counties west of the Hudson during the 1980s. Between 1980 and 1990, permanent population growth throughout the watershed counties stagnated while the housing stock increased 5 percent, or 0.5 percent annually (which would yield a 10 percent increase in the housing stock if projected to year 2020). This growth in housing in excess of permanent population growth might indicate seasonal home development.

One can also evaluate new housing construction rates and approximate corresponding increases in housing stock. Between 1990 and 1996, the new housing construction rate west of the Hudson dropped by more than half (based on Census Bureau reports of building permits issued), and the rate of growth of the permanent population slightly exceeded that of new construction (0.25 percent compared with 0.20 percent per annum), suggesting little seasonal home development (Department of Commerce, 1990, 1992, 1994, 1996). If the 1990–1996 trend in new construction is projected to 2020, a modest 4 percent increase in the housing stock can be expected. Recent anecdotal accounts of second-home development in some watershed areas west of the Hudson, however, indicate some renewed interest in the area as a seasonal destination (Hall, 1998). In any case, the construction of seasonal homes will result in some growth of part-time residents in the watershed, and attention should be given to the distinctive watershed impacts of such residents.

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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
×
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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Suggested Citation:"2 The New York City Water Supply System." National Research Council. 2000. Watershed Management for Potable Water Supply: Assessing the New York City Strategy. Washington, DC: The National Academies Press. doi: 10.17226/9677.
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In 1997, New York City adopted a mammoth watershed agreement to protect its drinking water and avoid filtration of its large upstate surface water supply. Shortly thereafter, the NRC began an analysis of the agreement's scientific validity.

The resulting book finds New York City's watershed agreement to be a good template for proactive watershed management that, if properly implemented, will maintain high water quality. However, it cautions that the agreement is not a guarantee of permanent filtration avoidance because of changing regulations, uncertainties regarding pollution sources, advances in treatment technologies, and natural variations in watershed conditions.

The book recommends that New York City place its highest priority on pathogenic microorganisms in the watershed and direct its resources toward improving methods for detecting pathogens, understanding pathogen transport and fate, and demonstrating that best management practices will remove pathogens. Other recommendations, which are broadly applicable to surface water supplies across the country, target buffer zones, stormwater management, water quality monitoring, and effluent trading.

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