Water storage and gravity for urban sustainability and ... - TRC Solutions

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Polenghi-Gross et al | http://dx.doi.org/10.5942/jawwa.2014.106.0151 Peer-Reviewed

Water storage and gravity for urban sustainability and climate readiness ISABELLA POLENGHI-GROSS,1 STACY A. SABOL,2 STEVEN R. RITCHIE,3 AND MICHAEL R. NORTON4 1AMEC,

Oakland, Calif. Solutions, San Francisco, Calif. 3San Francisco Public Utilities Commission, Calif. 4AMEC, Bristol, UK 2TRC

The water sector is facing significant challenges worldwide as a result of climate change. Drinking water utilities need to incorporate climate considerations into long-term planning and management; they need to become climate ready. Aging water infrastructure, high costs for maintenance and treatment, increasingly stringent environmental regulations, and inadequate funding are all obstacles to achieving water utilities’ goals. Two effective features of a sustainable drinking water supply are water storage and elevation.

Water storage enhances water supply sustainability, and elevation enables the earth’s gravity to drive water and produce hydroelectric power naturally and inexpensively. This article reviews a case study of a successful century-old water system characterized by a large reservoir for storing high-quality mountain water and by gravitydriven water transmission; the focus is on the Hetch Hetchy Regional Water System in California, with a comparison with similar reservoirs in the United States and Europe.

Keywords: water storage, gravity, climate readiness, urban sustainability, water–energy nexus, Hetch Hetchy A drought emergency was officially declared in California in January 2014. The previous year was the driest year for San Francisco since local rainfall data was first recorded in 1849; 2013 saw only 5.59 in. of rain compared with an annual average of approximately 23.65 in. (Henson, 2014). Drought is but one of the many challenges we face worldwide as a result of climate change. The temporal and spatial distribution of water resources is changing and affecting the supply of water, and higher temperatures and lower soil moisture are affecting the demand for water. With population growth compounding these problems, drinking water utilities and other water users have no choice but to become climate ready, an emerging concept that involves incorporating climate considerations into long-term utility planning and management (USEPA, 2012). However, an aging water infrastructure, high maintenance and treatment costs, increasingly stringent environmental regulations, and inadequate funding are all obstacles to water utilities achieving their goals. Two effective features of a sustainable drinking water supply are water storage and elevation. Water storage enhances water supply sustainability: with an increasing variability in rainfall and temperature, water can be stored and be reliably available when and where it is needed. Water driven by gravity from a high elevation can produce hydroelectric power naturally (i.e., with no other energy source) and inexpensively, especially compared with energy that is fossil-fuel-based, which is expensive. This article reviews a case study of a successful water system— the Hetch Hetchy Regional Water System. Its primary source is JOURNAL AWWA

in California’s Yosemite National Park, and it is characterized by a large reservoir for storing high-quality mountain water, gravitydriven transmission, and hydroelectricity production. The Hetch Hetchy system supplies 85% of the drinking water to the 2.6 million people living in the San Francisco Bay Area through 167 mi of gravity pipelines and tunnels; it also generates approximately 1.7 billion kW·h of electricity per year. Its infrastructure, built primarily between 1914 and 1933 in an area vulnerable to major earthquakes, is one of the most extraordinary examples of a visionary engineering system conceived to supply water and power to future generations. The system has shown great resilience and has helped San Francisco to be better prepared to face climate-change challenges. Featuring high storage capacity and high-elevation gravity to drive water from mountain to tap, this “old yet modern” system guarantees a low-cost, reliable source of water and energy with minimal environmental impact. The analysis of the Hetch Hetchy system and a discussion of similar reservoirs in the United States and Europe reveal that these examples of centuryold systems, though considered vital infrastructure in their time, can be viewed with hindsight as visionary models of green design and climate readiness.

THE CHALLENGE The challenge of meeting the direct water demand of 9.5 billion people and all of their indirect demand associated with energy and food needs by 2050 will lie in balancing and allocating our

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available water resources. The challenge is made more complex when we consider the range of possible effects of unmitigated climate change on both water availability and water demand. Population. Although the world’s population-growth rate has almost halved from a peak of 2% in 1963, it has nonetheless doubled from 3.5 billion between 1970 and now. Increases in population and strong economic growth result in raised living standards for both developed nations and developing nations that seek the lifestyle of the developed nations. As living standards rise, water footprints grow. As a result, 7 billion people currently withdraw approximately 3.6 billion acre-ft of freshwater for domestic, industrial, and agricultural uses (2030 Water Resources Group, 2009). The world’s population is predicted to reach more than 9.5 billion by 2050, after which there could be a slight decline, but an upper bound could still be in excess of 30 billion by 2300 (United Nations, 2004). Currently, more than half the world’s population lives in urban settings, and this proportion will rise to two-thirds later in this century. The sustainability of these urban habitats is coming under stress. Water supply to cities will play a pivotal role in urban sustainability and climate readiness. Water resources: supply and demand. It is estimated that the world’s renewable water resource, defined as the volume of water that reaches the oceans from our rivers, is approximately 34 billion acre-ft per year (FAO, 2014). However, there are vast amounts of water resources that, for all practical purposes, are not accessible as a result of their remoteness (e.g., Canada, Greenland, and Russia) or localized skewed distribution (e.g., the Amazon River). It has been estimated that only approximately 9.5 billion acre-ft per year of the world’s renewable water resource is available (University of Michigan, 2006). Currently we withdraw approximately 3.6 billion acre-ft per year of our global renewable water resource to meet our water demand (2030 Water Resources Group, 2009). In the last 50 years, water withdrawals have almost tripled. The demand for water is estimated to be approximately 5.5 billion acre-ft per year by 2030. It is postulated, however, that we will not be able to supply that demand if we continue to generate new supply at historic rates, even if we make improvements in domestic, agricultural, and industrial water use efficiency (2030 Water Resources Group, 2009). In any case, it can be argued that even now we are reaching the limits of available resources for supply, especially if we wish to leave enough water in our rivers to maintain their aquatic ecosystems, which in turn are a valuable ecosystem service. Effects of climate change. Much research has been, and continues to be, carried out on the projected effects of climate change on renewable water resources and water demand. The evidence is strong that the effects are already present and are set to intensify. Very broadly, predictions are for higher rainfall and runoff in the higher latitudes, and lower rainfall and runoff in the tropical and middle to lower latitudes (Intergovernmental Panel on Climate Change, 2013). The volume of water stored in glaciers will decrease, thereby reducing meltwater runoff. Higher temperatures will worsen water pollution problems in rivers and lakes and will increase evaporation from open water bodies and JOURNAL AWWA

soil. More intense rainfall events will result in increasing occurrences of flooding in urban areas and from rivers. Average temperature increases in urban settings will be higher than the global average, resulting in an approximately 72% increase in global demand for air conditioning (Sivak, 2013).

THE ROLE OF WATER STORAGE AND GRAVITY IN URBAN SUSTAINABILITY Managers of urban water utilities already face the current challenges of aging water infrastructure, high maintenance and treatment costs, and increasingly stringent environmental regulations. Most are also facing the future challenges of population growth in their supply area, increased water demand, and the effects of climate change. Proactive climate-ready actions will help water sector utilities become more resilient. New approaches to climate readiness. Water management in urban settings has seen many new developments in thinking in recent years, such as the International Water Association’s (IWA’s) Cities of the Future initiative and the ambitious ecocity concepts that led to the planning of Dongtan in China and Masdar City in Abu Dhabi. The ecocity concept was proposed by Register (1987) and later defined by Novotny and Novotny (2011) as “a city or part thereof that balances social, economic and environmental factors (triple bottom line) to achieve sustainable development.” The evolving aim is to move from urban systems that are historically heavy users of nonrenewable resources and generators of wastes to systems that focus on renewable resources and recycling of wastes. Water is at the center of the emerging concepts of urban sustainability. Most managers of urban water utilities and wastewater utilities have been implementing measures that are loosely termed “demand management” or “water conservation.” Such measures include reducing leakage in water distribution systems and introducing recycling of treated wastewater. Utilities also have encouraged their customers to install household appliances that use less water and to harvest rainwater for nonpotable uses. Utilities want to minimize the costs of their primary water supply, so they will increasingly seek water from sources that are less expensive to secure and that offer resilience to the effects of climate change and weather extremes. Water–energy nexus. The picture becomes more complex as we enter the so-called water–energy nexus. Water has an energy footprint, derived from its treatment, transmission, and distribution, as well as from its collection and treatment as wastewater. Typical energy consumption values range from 2,000 kW·h/mil gal for a 400-ft-deep groundwater abstraction to 9,200 kW·h/mil gal for raw water transfer to southern California. Water treatment uses from 10 kW·h/mil gal for high-quality groundwater to 15,000 kW·h/mil gal for seawater desalination. Wastewater treatment uses an average of 2,500 kW·h/mil gal treated (World Economic Forum, 2009). In California, an estimated 19% of the state’s electricity use and 32% of all natural gas consumption are related to water (Cooley & Donnelly, 2013). Similarly, energy has a water footprint, derived from consumption of water to generate energy, such as evaporation from hydroelectric reservoirs and abstraction of cooling water


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for thermal power stations. Typical consumption varies from 190 gal/MW·h for natural-gas-fueled, combined-cycle power stations to 720 gal/MW·h for nuclear power stations (World Economic Forum, 2009). Urban sustainability: What does it mean? There are a number of manifestations of the concept of urban sustainability, including One Planet Living, the IWA’s Cities of the Future, and ecocities. The World Wildlife Fund (WWF International and BioRegional, 2008) developed its One Planet Living principles, as shown in Table 1. The 10 principles provide a framework to examine the sustainability challenges and develop action plans to live and work within a fair share of the earth’s resources. Urban sustainability is related to the ecocity concept, whereby an ecocity is a city that powers itself with renewable sources of energy, creates the smallest possible ecological footprint, and produces the lowest quantity of pollution possible. It also uses land efficiently and recycles or converts waste to energy. If such practices are adapted, overall contribution of the city to climate change will be minimal and below the resiliency threshold. The IWA’s Cities of the Future concept features the central role of water management in the planning of infrastructure and services. The approach proposes that a partnership of urban planners, the water sector, and other sectors can meet sustainability and livability objectives set by the community (Binney et al, 2010). The IWA has also proposed a framework for setting and developing strategy and for measuring progress. This is schematically illustrated in Figure 1. Another concept whose objectives mesh with urban sustainability is that of urban metabolism, a term used to describe the processes of transformation of energy and resources within an urban community. Urban metabolism is a mass-balance concept that relates inputs into a city (materials, chemicals, water, energy, and food) to the outputs (Novotny & Novotny, 2011). We can conceptualize the objectives as minimizing nonrenewable resource consumption and maximizing recycling of waste, thereby minimizing net polluting outputs (Rogers, 1998; Figure 2). Two of the fundamental inputs into the urban metabolism are water and energy. Urban sustainability will be enhanced through maximizing the renewable nature of these inputs and minimizing

TABLE 1

their mutual footprints; the water cycle shown in Figure 3 illustrates the process through which our planet’s water continuously renews itself. Our challenge is to ensure that our demand for water on a local temporal and spatial basis can be sustained. When available, both water storage and gravity can help guarantee a sustainable water supply. The role of water storage and gravity. Storage of runoff from rainfall and snowmelt has for centuries been the system of technology applied to balancing supply and demand. As will be illustrated, this has been achieved by capturing water at higher elevations, where rainfall and snowmelt are generally higher, and in deep valleys, which are relatively easily dammed. This stored water feeds the urban metabolism with its renewable water resource. Gravity is a force of acceleration, or more scientifically, the attraction that results from the interaction of bodies of mass; in this case, it is the attraction between the body of water at rest in the upland reservoir and the mass of the earth lying below it. Therefore, when available, drinking water systems that use water from reservoirs at high elevations can provide a great contribution toward sustainability. In effect, a reservoir has a stored energy that transmits the water to the urban metabolism without the need for any external energy source. In many such systems, the stored energy is considerably more than is needed for the transmission of the water; the excess is thus a potential source of energy (with the help of turbines) to feed the urban metabolism. Compare this type of system with the following types: those that depend on pumping water from deep aquifers (some of which are not renewed); those that abstract turbid water from lowland rivers; and those that desalinize seawater. (water storage + gravity) → lowers urban metabolism → urban sustainability

Several existing examples of freshwater reservoirs with gravitydriven water transmission systems that follow this sustainable model are described in the next section. These systems were generally constructed in the early 20th century, and today they serve as both engineering marvels and visionary examples of sustainability for the future.

The 10 “One Planet” principles Principle

Description

Zero carbon

Making buildings more energy-efficient and delivering all energy with renewable technologies

Zero waste

Reducing waste, reusing where possible, and ultimately sending zero waste to landfills

Sustainable transport

Encouraging low-carbon modes of transport to reduce emissions, reducing the need to travel

Sustainable material

Using sustainable, healthy products, with low embodied energy, sourced locally, made from renewable or waste resources

Local and sustainable food

Choosing low-impact, local, seasonal, and organic diets and reducing food waste

Sustainable water

Using water more efficiently in buildings and in the products we buy; tackling local flooding and water course pollution

Land use and wildlife

Protecting and restoring biodiversity and natural habitats through appropriate land use and integration into the built environment

Culture and heritage

Reviving local identity and wisdom; supporting and participating in the arts

Equity and local economy

Creating bioregional economies that support fair employment, inclusive communities, and international fair trade

Health and happiness

Encouraging active, sociable, meaningful lives to promote good health and wellbeing

Source: WWF & BioRegional, 2008

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FIGURE 1

A vision for the cities of the future

FIGURE 2

Urban metabolism

Adapted from Rogers, 1998

Based on Binney et al, 2010

FIGURE 3

The water cycle

Source: US Geological Survey, 2013

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HETCH HETCHY RESERVOIR, YOSEMITE, CALIF.

its water enters the eastern end of Hetch Hetchy Reservoir. At O’Shaughnessy Dam, which impounds the Tuolumne River, the The Hetch Hetchy Regional Water System with its primary water is diverted through Canyon Power Tunnel to the Kirksource in Yosemite National Park in California (USA) provides wood Powerhouse. Water that is not diverted continues downdrinking water to 2.6 million people living in the San Francisco stream in the Tuolumne River channel. The middle portion of Bay Area, including the counties of San Francisco, San Mateo, the watershed from Hetch Hetchy Reservoir to Don Pedro Santa Clara, and Alameda, and satisfies 85% of their total water Reservoir is characterized by deep canyons and forested terrain. supply needs; the remaining 15% comes from two local waterThe river exits the Sierra Nevada foothills near the town of La sheds—the Alameda Creek and Peninsula (SFPUC, 2013a). On Grange, and flows through a gently sloping alluvial valley that average, 222 mgd of clean water originating from Sierra Nevada twoTuolumne column River figureWatershed width 44 pica or 7.25 inches is incised into Pleistocene alluvial fans. snowmelt come through the Upper The Tuolumne River also provides an excellent habitat for and flow into the 360,360-acre-ft (117.4-bil-gal) reservoir of many species of wildlife, including bald eagles, spotted owls, Hetch Hetchy, generating 400 MW of hydroelectric power prairie falcons, and Chinook salmon, as well as supporting a wild (SFPUC, 2013b). The water then enters the aqueduct system and, trout fishery. over approximately three days, flows by gravity through 167 mi Water transmission system. Hetch Hetchy Reservoir is one of of pipelines all the way to Bay Area reservoirs Remove (Figure 4).this Theinformation eight reservoirs of the San Francisco Regional Water System. It is delivered water from Hetch Hetchy Reservoir is so clean and located at an elevation of 3,783 ft within Yosemite National Park, pristine that it does not require any filtration. approximately 65 mi northeast from the city of Merced in CaliTuolumne River Watershed. The Tuolumne River originates at an fornia. The reservoir, formed by O’Shaughnessy Dam, has a elevation of approximately 13,000 ft above Tuolumne Meadows, one column figure width on-line 20 picas capacity of 117 bil gal (360,000 acre-ft) and holds approximately in the central Sierra Nevada, at the confluence of streams descendor 3.5 inches 25% of the total San Francisco overall storage capacity. It is 8 mi ing from the slopes of Mt. Lyell and Mt. Dana, the tallest peak long, has a surface area of 1,972 acres, and a maximum water in Yosemite National Park. The river flows nearly 150 mi down depth of 312 ft. to the San Joaquin River in the Central Valley, approximately 10 Construction work in the Hetch Hetchy Valley started just mi west of Modesto. It is the largest tributary of the San Joaquin after President Wilson signed the Raker Act in December 1913, River and, together with its tributaries, drains an area of 1,960 granting rights of way to San Francisco to develop the reservoir. sq mi on the western slope of the Sierra Nevada. The project was opposed by some environmentalists, including At higher elevations, the Upper Tuolumne River Watershed, Sierra Club founder John Muir, but the need for a more reliable which is located entirely within Yosemite National Park, is comwater supply—clearly demonstrated during the devastating fires posed primarily of granitic bedrock that was scoured by glaciers. after the 1906 earthquake—prevailed, and the reservoir was built As a result, the watershed is characterized by mountainous terbetween 1919 and 1923, and O’Shaughnessy Dam was comrain, patchy forests, and a variety of steep canyons and mountain pleted to its current height of 430 ft in 1938. From Hetch Hetchy meadows. At an elevation of approximately 4,000 feet, part of

FIGURE 4

San Francisco water supply system

Source: San Francisco Public Utilities Commission

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Reservoir the water flows through two hydroelectric powerhouses and for 167 mi within the water transmission system all the way to the greater Bay Area, entirely by gravity. Hetch Hetchy is owned by the City and County of San Francisco and has been operated and maintained by the San Francisco Public Utilities Commission (SFPUC, 2013c) since 1932. The reservoir’s primary purpose is to supply drinking water to the San Francisco Bay Area and electric power to municipal facilities in San Francisco. Water quality. Thanks to the elevation and snowmelt source, the granitic nature of its upstream watershed, and the park protection programs for the Yosemite Wilderness (swimming and boating in the reservoir are prohibited and fishing is only permitted from the lake shore), the water collected in Hetch Hetchy Reservoir is of such exceptionally good quality that it consistently meets or exceeds federal and state standards for safe drinking water. The turbidity of Hetch Hetchy water is measured every four hours. The monthly average turbidity value documented in 2012 was less than 0.5 ntu, which is significantly lower than the Maximum Contaminant Level of 5 ntu (SFPUC, 2013a). As a result, SFPUC was granted a “filtration avoidance” status for the Hetch Hetchy water source by the US Environmental Protection Agency. Hetch Hetchy water is treated for corrosion control at Rock River by the addition of lime. It undergoes stringent disinfection treatment processes and is continuously and extensively monitored to check its bacteriological quality. In the summer of 2011, the SFPUC began using ultraviolet (UV) light as an additional disinfection step. The new Tesla Treatment Facility uses stateof-the-art UV treatment equipment to provide advanced disinfection for the Hetch Hetchy supply in the Regional Water System to protect the water supply from the Cryptosporidium parasite (SFPUC, 2013a). The benefits of UV treatment are that it requires minimal contact time to disinfect, it is cost-effective compared with other advanced technologies, it leaves no chemical disinfection by-products, and it is highly effective for waterborne parasites. Renewable dependable electricity. Hydropower in the Hetch Hetchy Valley was first produced in 1918 when the Early Intake Powerhouse was built to provide electricity to run the equipment and lighting for nighttime construction of the reservoir and dam. The Hetch Hetchy Power System currently consists of three hydroelectric powerhouses: the Moccasin and the Kirkwood Powerhouses, which rely on gravity-driven water flowing downhill from the Hetch Hetchy Reservoir, and the Holm Powerhouse, which relies on gravity-driven water flowing downhill from Cherry Reservoir. The combined total hydroelectric output for these facilities is more than 400 MW. On average, the Hetch Hetchy Power System produces 1.7 billion kW·h of clean hydroelectric energy each year (i.e., the equivalent annual power usage of 350,000 homes), generating approximately $40 million in annual revenue. Approximately 65% of the electricity generated by Hetch Hetchy Power is used to provide electric service to San Francisco’s municipal customers (including the airport, the municipal transportation, the Port of San Francisco, hospitals, streetlights, and the SFPUC’s Water and Wastewater Enterprises). Surplus electricity is sold to Central Valley irrigation districts JOURNAL AWWA

(Turlock and Modesto) and other public agencies or is transferred to the power grid. The hydroelectric system provides carbon-free electricity to city agencies at low rates and helps fund local renewable-energy projects. Climate-change considerations. San Francisco, like many other cities, is facing multiple challenges, such as the following: • Population growth—San Francisco population in 2010 was 805,235 and it is projected to increase by 35% to 1,085,641 by 2040 (One Bay Area, 2013). • Reduction in the average annual snowpack as a consequence of the snowline rising (i.e., less snow at low elevations) and snowmelt runoff occurring earlier in the year. By 2050, scientists project a loss of at least 25% of the Sierra snowpack (California Department of Water Resources, 2014). • Sea level rise and increase in saltwater intrusion—historical records show that sea level in San Francisco Bay has risen approximately 7 in. during the past 100 years (California Environmental Protection Agency, 2006). By 2050, sea level is predicted to rise from 11 to 19 in. above the 2000 level, and from 30 to 55 in. by 2100 (Cayan et al, 2012). Rising sea levels will lead to saltwater intrusion into wetlands and waterways, as well as coastal erosion, flooding, and increased storm surges. • Higher temperatures and changing precipitation will lead to more droughts. A drought emergency was officially declared in California in January 2014. San Francisco experienced a new record in calendar year 2013: the driest year in almost 165 years of recorded local rainfall measurements, with only 5.59 in. of rain compared with an annual average of approximately 23.65 in. (Henson, 2014). • Long-term changes in watershed vegetation and increased incidence of wildfires could affect water quality. Wildfires are burning through twice as many acres per year on average in the United States as they were 40 years ago, and this number could double again in the next 30 years (Kramer, 2013). Because of its proximity to Yosemite, the August 2013 Rim Fire in the Sierra Nevada, one of the largest fires in California’s history, could easily have had an adverse effect on Hetch Hetchy water quality; fortunately, however, there has been no effect on either water quality or water delivery operations (SFPUC, 2013d). Thanks to its high storage capacity and gravity-driven water transmission from mountain to tap, the San Francisco Regional Water System has shown great resilience and has helped the city to be better prepared to face climate-change challenges and waterscarcity issues, guaranteeing low-cost, reliable, high-quality water and energy with minimal environmental impact. The SFPUC is also undertaking several actions to enhance the ability of the San Francisco water system to meet the service goals for water quality, seismic reliability, delivery reliability, and water supply, and to reduce its reliance on fossil fuels. The following projects are being implemented or designed: • Implementation of a $4.6 billion Water System Improvement Program (Labonte, 2013), a project to improve the system’s reliability that includes a large conservation program to save and recycle water • Construction of green infrastructure elements around the city to optimize water use and minimize waste


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• Diversification of the city’s water sources to the maximum extent possible (including groundwater extraction from local aquifers)

OTHER EXAMPLES OF SUCCESSFUL CENTURY-OLD WATER SYSTEMS In addition to the San Francisco Regional Water System, other examples exist of sustainable water supply systems (Table 2). The authors selected four examples of systems with sustainable features from around the world (three in the United States and one in the United Kingdom) because they satisfy these five important criteria: • They supply exceptional-quality water that in most cases does not require filtration. • They deliver water almost completely by gravity. • They have large storage capacity. • They generate hydroelectric energy. • They were built about 100 years ago to provide water to major cities. Despite the fact that these dammed systems were often regarded by opponents as damaging the environment, a century later they are still operational and have proved to be a valuable legacy for future generations because they provide clean, inexpensive, and reliable water to important cities. These systems, which currently operate with small carbon and water footprints and are expected to continue working successfully, serve as excellent examples of sustainable systems that could be built by cities in preparation for climate change. New York City Water Supply System. The New York City Water Supply System, operated and maintained by the New York City Department of Environmental Protection (NYCDEP), provides approximately 1.1 bil gal of drinking water to 9 million people living in New York City and in the four upstate counties of Westchester, Putnam, Orange, and Ulster; the system satisfies 100%

TABLE 2

of their total water demand. The New York City Watershed consists of two interconnected reservoir systems: the Catskill/ Delaware Watershed, west of the Hudson River, and the Croton Watershed, east of the Hudson River (Figure 5). All together, the system consists of 19 reservoirs and three controlled lakes in the Catskill Mountains and the Hudson River Valley, north and northwest of New York City, and has a total storage capacity of 580 bil gal. Water is delivered almost entirely by gravity (95%) through a total of 295 mi of aqueducts and tunnels within the system (Garigliano, 2013). It is one of the largest gravity-fed, unfiltered water supply systems in the world. The Catskill Water Supply System, completed in 1927, and the Delaware Water Supply System, completed in 1964, together provide approximately 90% of New York City’s water supply. Drinking water from the Catskill/Delaware system is of high quality and is delivered to consumers unfiltered. The Croton Water Supply System provides approximately 10% of New York’s water supply. The Old Croton Aqueduct, which was completed in 1842, was largely replaced by the New Croton Aqueduct, which was built in 1890. Drinking water from the Croton system has been of high quality for many years; however, even though it meets all of the existing health-based water quality regulations, its high water turbidity often violates the aesthetic standards for color. As a result, the Croton water supply will begin to be filtered when the testing of the filtration process at the newly constructed Croton Water Filtration Plant is completed, which is expected to be in the spring of 2015 (Bosh, 2014). Currently four hydroelectric plants within the system generate hydropower: two operated by the NYCDEP at the ends of the East Delaware (20 MW) and Neversink Tunnels (25 MW) discharging into the Rondout Reservoir; one operated by the New York Power Authority at the head of the Catskill Aqueduct at Ashokan Reservoir (4.2 MW); and one operated by Brookfield Power at the end of the West Delaware Tunnel entering Rondout

Key features of the reviewed water supply systems

Water Supply System Reservoir

City Served

River Feeding the Reservoir

People Gravity Water Storage Served Unfiltered Aqueducts Hydropower Capacity millions Water mi MW acre-ft

Water Delivered mgd, % of total water need

Construction Years

Hetch Hetchy Reservoir

San Francisco (Calif.)

Tuolumne River

2.6

Yes

167

400

360,360

222, 85%

1914–1938

Castkill/Delaware and Croton Reservoirs

New York City (N.Y.)

Delaware River Croton River

9

Yes

295

57.2

1,779,952

1,100, 100%

1842 (Croton) 1927 (Catskill)

Quabbin (Q) and Wachusset (W) Reservoirs

Boston (Mass.)

Swift River (Q) Nashua, Quinapoxet, Stillwater Rivers (W)

2.3

Yes

100

8

1,264,380 (Q) 199,477 (W)

200, 65%

1926–1946 (Q) 1897–1908 (W)

Chester Morse Lake and Masonry Pool

Seattle (Wash.)

Cedar River

1.3

Yes

30

30

52,171

75, 60%

1901

Elan Valley Reservoirs

Birmingham (United Kingdom)

Elan River Claerwen River

1.3

No

73

4.2

76,722

95

1904–1952

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FIGURE 5

New York City water supply system

Source: www.nyc.gov/dep

Reservoir (8 MW). The overall combined hydropower produced by the system is 57.2 MW. NYCDEP is pursuing federal licensing to install three new hydroelectric plants at the bases of Cannonsville, Pepacton, and Neversink Reservoirs with planned capacity of 14.08, 1.7, and 0.94 MW, respectively (Garigliano, 2013). The Boston Water Supply System. Water for Greater Boston is supplied by the Quabbin and the Wachusett Reservoirs, which are maintained by the Massachusetts Water Resources Authority (MWRA). The two reservoirs, located in central Massachusetts, 65 and 35 mi west of Boston, respectively (Figure 6), currently supply approximately 200 mgd of wholesale water to 2.3 million people, satisfying 65% of their water demand. Some MWRA customer communities have their own supplies, which include both surface and groundwater, accounting for another 70 mgd (Estes-Smargiassi, 2014). The system supplying water to Boston is one of the most abundant and high-quality water supplies in the world. The Quabbin Reservoir was completed in 1946 and has a capacity of 412 bil gal. Its capacity is large enough to hold a four-year supply of water (MWRA, 2013a). The Wachusett reservoir was completed in 1908 and has an aggregate capacity of 65 bil gal. The Boston Water Supply System consists of more than 100 mi of JOURNAL AWWA

aqueducts and tunnels that transport water entirely by gravity to points of distribution within the MWRA service area. The reliable yield of the Quabbin and the Wachusett Reservoirs is 300 mgd on a long-term annual average basis, based on the extreme multiyear drought of the 1960s. Climate change analyses of the MWRA water supply indicate that because of the large reservoir storage volume compared with the watershed area, the safe yield is predicted to increase in the future. This increase, coupled with the decreasing trend of the MWRA system water demand (from approximately 340 mgd in 1980 to around 200 mgd in 2013 [MWRA, 2013b]) means that MWRA will have water available to supply both its existing customers and to help neighboring communities whose supplies either are stressed or are stressing the environment (Estes-Smargiassi, 2014). Hydropower is generated at four locations within the MWRA system: the hydroelectric facilities at Deer Island, Oakdale, Cosgrove, and Loring Road. The overall combined hydropower capacity of these facilities is more than 8 MW for production of approximately 23 million kW·h of electricity per year, with projected annual savings and revenues of more than $1.8 million (MWRA, 2012). The Seattle Water Supply System. The Cedar River Watershed, located 35 mi southeast of Seattle (Figure 7), provides approximately 75 mgd of drinking water to 1.3 million people living in the greater Seattle area, satisfying 60% of their total water demand; the Tolt River Watershed, located in the foothills of the Cascade Range in eastern King County, supplies the remaining 40%. The 90,638-acre Cedar River Watershed feeds two reservoirs—Chester Morse Lake and Masonry Pool—with snowmelt and rain. All together, the system, which is owned and operated by the City of Seattle, has a total storage capacity of 17 bil gal and delivers its water almost entirely by gravity flow from high in the foothills to the city, along 30 mi of large-diameter pipe aqueducts and tunnels (Hilmoe, 2014). Similar to San Francisco, the rapid population growth in the late 1800s and the devastating Great Seattle Fire of June 6, 1889, prompted the establishment of an improved municipal water system. The Cedar River Watershed has been in use as the main water supply since 1901. Masonry Dam, which impounds the previously natural Cedar Lake and forms Chester Morse Lake, was completed in 1914 and diverts the water to the hydroelectric power plant at Cedar Falls. Typically the plant produces approximately 17 MW of electricity, but it has the capacity to generate up to 30 MW. At the Landsburg Diversion Dam, at the westernmost boundary of the watershed, 22% of the Cedar River’s annual flow is diverted from the river and sent to Lake Youngs. The water is screened, disinfected by chlorination, fluoridated, ozonated, exposed to UV light, and supplemented with lime to maintain its high quality. Cedar River water is tested daily and meets or exceeds all federal standards for drinking water. The rest of the water (78%) continues past Landsburg down the Cedar River and supports a diverse ecosystem, including salmon habitats (Hilmoe, 2014). Elan Valley Reservoirs System (United Kingdom). The Elan Valley Reservoirs in Mid Wales represent another example of a visionary


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century-old water supply system. Today the system delivers 95 mgd of water to 1.3 million people in Birmingham. The Elan system consists of four main manmade lakes created from damming the Elan and Claerwen Rivers (Figure 8). All together the system has a capacity of approximately 25 bil gal (Bradford, 2012) and generates 4.2 MW of hydroelectric power; its

FIGURE 6

water, all driven by gravity, maintains a flow of less than 2 mph to reach Birmingham in a day and a half. Built in the pristine mountains of Mid Wales during the Industrial Revolution at the end of the 19th century, the system was designed to provide clean water, which at that time was in short supply; major epidemics of waterborne diseases, including typhoid

Boston water supply system

Source: Massachusetts Water Resources Authority

FIGURE 7

Seattle water supply system

FIGURE 8

The Elan Valley reservoir system (UK)

Modified from www.rhayader.co.uk/images/uploads/elan-valley-map.gif Source: Seattle Public Utilities

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and cholera, were affecting an otherwise rapidly growing population. The Elan and Claerwen Valleys offered a number of features suitable for metropolitan water supply: great water storage potential resulting from high average annual rainfalls, narrow downstream valleys that were ideal for building dams, impermeable bedrock to prevent water seepage, and high elevation to enable gravity-driven water transmission. The dams were built in two phases: The Elan Valley dams were completed at the beginning of the 20th century, but because of the first and second world wars, the Claerwen Dam was not completed until nearly 50 years later. In 1904, King Edward VII and Queen Alexandra opened the Elan dams, and water started flowing along 73 mi of pipeline to Birmingham. The Claerwen Dam was officially opened by Queen Elizabeth II in 1952. Unlike the systems described earlier, water from the Elan Valley Reservoir System is filtered to meet UK and European Union drinking water quality requirements at times of higher raw-water turbidity.

CONCLUSIONS Nearly a century ago, visionary engineers, construction workers, and politicians conceived of, designed, and built extraordinary municipal water systems. Many of these systems stand today as engineering marvels, featuring high-elevation locations, large storage capacity, pristine water quality, and gravity-driven water transmission from mountain to city. These old-yet-modern systems guarantee low-cost, reliable sources of clean water and energy with arguably minimal environmental impact when compared with their environmental benefits. Although it is true that some dams associated with these reservoirs have come under public scrutiny because of effects on the environment, many of the adverse effects have been managed or overcome by modernized design criteria and environmental legislation. What has not been fully appreciated is how these systems have provided enduring solutions to some of the challenges faced by modern-day urban populations, including accelerated population growth, climate change, limited water resources, and other urban sustainability issues. At the time these systems were built, their original designers could not have conceived of the magnitude or severity of these modern-day challenges. Water industry professionals are constantly having to convince the rate-paying public of the need to maintain these systems and understand the inherent costs associated with their maintenance. This article offers support to those professionals. Further, the article promotes concepts to help the public appreciate the vital role that these systems play not only in ensuring a sustainable water supply, but also in meeting the challenges associated with urban sustainability.

ABOUT THE AUTHORS Isabella Polenghi-Gross (to whom correspondence should be addressed) is a senior environmental scientist at AMEC Environment & Infrastructure, Inc., 180 Grand Ave., Oakland, CA 94612; [email protected]. She earned her doctoral degree at Ca’ Foscari, University of Venice, in JOURNAL AWWA

Italy. Polenghi-Gross has 15 years of environmental consulting experience. She has been working with Michael Norton (co-author) on water scarcity issues and on sustainability practices and adaptation strategies for drinking water utilities and water agencies to address climate change impacts on water resources. Stacy A. Sabol is California unit leader, environmental/remediation at TRC Solutions in San Francisco, Calif. Steven R. Ritchie is assistant general manager of the water enterprise at San Francisco Public Utilities Commission. Michael R. Norton is director of municipal water at AMEC in Bristol, UK.

PEER REVIEW Date of submission: 05/12/2014 Date of acceptance: 08/01/2014

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