Hydro Hall of Fame: Celebrating 100 Years at Ninety-Nine Islands

Duke Energy’s 18-MW Ninety-Nine Islands hydroelectric facility has provided a reliable source of clean, renewable power to the Piedmont Carolinas for 100 years and is positioned to continue operating well into the future. Ninety-Nine Islands is one of the 2010 inductees into the Hydro Hall of Fame.

The 18-MW Ninety-Nine Islands hydro station, near Blacksburg, S.C., was commissioned in 1910 and thus celebrated 100 years of service on May 27, 2010. At the time it was built, this project was part of Southern Power Company’s rapidly growing generation portfolio, joining three other hydro stations on the Catawba River – 6.6-MW Catawba Hydro (completed in 1904), 24-MW Great Falls Hydro (completed in 1907), and 28-MW Rocky Creek Hydro (completed in 1909).

The roots of Duke Energy Corporation can be traced to this early interconnected network of hydro stations that brought a newfound economical and reliable source of electricity to the Carolinas. This fledgling collection of hydro stations would provide the “spark” that would drive economic growth and spur a transformation in this sleepy rural region of the South.

Duke Energy and Ninety-Nine Islands early history

In 1905, James B. Duke, Benjamin N. Duke, Dr. Gill Wylie, and W.S. Lee launched Southern Power, the primary predecessor that eventually grew to become Duke Energy. Their initial focus was to meet the growing need for electricity in mills and factories, thus spurring industrial growth in the Carolinas’ textile industries. Prior to this time, most generating plants were rather isolated and served a single nearby mill, factory, or city.

However, this group of men had a larger vision for a series of generating plants, interconnected by high-voltage transmission lines that would form a single combined system. This vision would include the nation’s first comprehensive development of an entire river, the Catawba, which ultimately would provide power from 13 hydro stations on 11 reservoirs. Not only would this be a means to provide more reliable electric service, but it would allow a more integrated and efficient use of multiple hydropower resources.

Construction of the 18-MW Ninety-Nine Islands hydroelectric project was completed in 1910. The resulting reservoir covered about 885 acres, with about 14 miles of shoreline.

By 1909, the vision of an interconnected system also was taking shape as Southern Power placed into service the industry’s first double-circuit, 100-kilovolt line stretching 190 miles from Great Falls, S.C., to Durham, N.C. Additionally, the company soon established linkages with other utility companies and gained national recognition for creating a pioneering “system of systems.”1

The 18-MW Ninety-Nine Islands powerhouse has undergone significant rehabilitation but still retains much of its historical integrity.

Among the earliest chosen hydroelectric sites was a location known as Ninety-Nine Islands on the Broad River. This site had been associated with industrial developments long before the hydro project was planned. King’s Creek, which drains into the Broad River immediately downstream of the facility, was the location of an iron manufacturing plant from about 1815 until the late 1860s. Having already thoroughly scoured the Carolinas to find the best hydroelectric sites, Southern Power engineers considered the Ninety-Nine Islands site to be one of the best prospects.

So, in early 1906, bankrolled by the Duke brothers’ tobacco fortune, the company set out to acquire the land and riparian rights necessary for construction of the project. A year later, Southern Power had title to all the necessary land and began construction of a railroad track to the site, as well as offices, warehouses, and housing for the construction crews.

By April 1907, Southern Power was aggressively developing and building multiple projects simultaneously. Even before the plant at Great Falls was completed, Southern Power was in the midst of building another hydro plant at Rocky Creek on the Catawba River, as well as beginning the Ninety-Nine Islands project. An economic downturn in late 1907 forced work at Ninety-Nine Islands to cease temporarily as Southern Power focused its resources on completing the construction of Rocky Creek Hydro. In 1908, the company resumed its efforts at Ninety-Nine Islands, contracting with B.H. Hardaway Company to built this new facility.

Construction of the facility began with the installation of a cofferdam upstream of the dam site between Stroup Island and the eastern bank of the Broad River. A second cofferdam was constructed downstream of the dam site. Granite for the Ninety-Nine Islands Dam was quarried from the Broad River and forms the core of the 891-foot-long, 86-foot-high cyclopean concrete dam. In the early 1900s, cyclopean concrete was a common construction technique in which large stones, many weighing more than several hundred pounds, are placed and embedded in the concrete as it is deposited.

When the project became operational in 1910, the reservoir covered about 885 acres with about 14 miles of shoreline. The six generating units contained Allis-Chalmers horizontal back-to-back Francis turbines with a total generating capacity of 18 MW. The powerhouse itself contained two sections: the generator bay and a transformer house. The generator operating floor rests on a masonry base with six arches above the tailrace and features many decorative elements, including multi-light and butterfly windows, a narrow clerestory, and a slate roof. The transformer house is a two-story steel frame structure clad in red brick that houses the transformers, control room, choke coils, and other electrical equipment.

Preparing for the next 100 years

By the late 1990s, the turbine-generating units and many other auxiliary components at Ninety-Nine Islands had deteriorated with age and were in need of a major rehabilitation effort. In addition, heavy transport of silt and debris, common to the Broad River basin, increasingly was creating intake blockage problems for the generating units after high water situations.

As part of Duke Energy’s overall system-wide upgrade program, known as HydroVision, a comprehensive upgrade plan was initiated in 1996. The goal was to extend the life of the Ninety-Nine Islands facility for at least another 40 years. Extensive reviews were conducted to assess all civil, electrical, and mechanical rehabilitation needs. As results were received, appropriate adjustments had to be made to the scope of the work in order to maintain alignment with the economic business case for the project.

First, analysis for extreme high water conditions showed that dam remediation would be required to increase the factor of safety for preventing dam sliding during a Probable Maximum Flood (PMF) event. To meet these modern Federal Energy Regulatory Commission (FERC) guidelines, a series of 48 post-tensioned anchors were installed to tie down the spillway and bulkheads during work in 2004 and 2005.

Next, to facilitate extensive civil rehabilitation work in the forebay at Ninety-Nine Islands, an eight-month station outage was scheduled in 2006. This complete station shutdown provided additional safety for dive teams and personnel working from barges while also maximizing productivity of construction teams and equipment. Work performed during this outage included:

– Replacing the old timber head gates with new steel head gates containing integral pad gates;

– Installing a drag rake trash removal system to work in concert with new trashracks and a new log boom to help keep the forebay clear of trash and debris accumulation;

– Installing a new 25-ton powerhouse crane and realigning the crane rails in preparation for unit upgrades;

– Upgrading Units 1 and 3 through installation of new turbine-generator equipment, replacement of wearing rings, and complete overhauling of the turbine operating mechanisms;

– Rehabilitating Units 2 and 4, including overhauls of the gate cases; and

– Upgrading station auxiliary systems, including compressed air, service water, bearing oil, and governor oil systems.

As part of the electrical scope review, protective relaying and hardwired control systems installed during a 1989 electrical upgrade were deemed viable for continued long-term service. However, significant upgrades to generator excitation, direct current power systems, and controls for supporting remote operation were needed to remain consistent with Duke Energy’s HydroVision program objectives and equipment standards. All of these upgrades were completed in 2006 and early 2007.

Granite quarried from the Broad River formed the core of the 891-foot-long Ninety-Nine Islands Dam.

In spite of the installation of numerous new components, electronic controls, and auxiliary equipment, Ninety-Nine Islands retains much of its historic integrity. Operationally required upgrades throughout the history of the station have resulted in numerous changes to the architectural features, but these changes have not diminished the integrity of the facility’s historic setting or the role that Ninety-Nine Islands played in the development of the region. As a result, the South Carolina State Historic Preservation Office determined in 2001 that the Ninety-Nine Islands Project was eligible for inclusion in the National Register of Historic Places.

Finally, as a result of the upgrade efforts, in October 2007, FERC certified the Ninety-Nine Islands incremental generation as being eligible for production tax credits. Duke Energy requested the certification based on increased efficiency from upgrades to the turbine-generators that were completed in March 2007. FERC’s order certified a historical average annual generation baseline of 68.8 gigawatt-hours (GWh), anticipated generation with improvements of 74.668 GWh, and incremental generation of 5.868 GWh. FERC certified the percentage of generation due to improvements as 8.53 percent.

Back to the future

A look ahead shows that the Ninety-Nine Islands project also is going to be extremely important as the station begins its second century of service. In addition to continuing as a clean, renewable source of generation, the reservoir is expected to serve as a principal cooling water source in support of the proposed 2,234-MW Lee Nuclear Station just upstream from the dam.

For more than 100 years, Ninety-Nine Islands has played an important role in the development of the Carolinas. With recent upgrades and a planned nuclear station on the horizon, Ninety-Nine Islands is clearly positioned to remain an important, viable renewable energy and water resource well into the 21st century.

Jennifer Huff is senior environmental resource manager and Greg Lewis, PE, is technical manager with Duke Energy. Huff supports hydro project relicensing and historic preservation, and Lewis provides technical direction and upgrade support across Duke’s fleet of 30 hydro stations.



  1. Durden, Robert F., Electrifying the Piedmont Carolinas, Carolina Academic Press, Durham, N.C., 2001.


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Hydro Hall of Fame: Taking Holtwood Next into the Century

PPL’s 108-MW Holtwood plant celebrates 100 years of operation on the Susquehanna River in Pennsylvania. The plant is being expanded through the addition of a second powerhouse that, in combination with the existing facility, will enable PPL to provide “green” power for generations to come. Holtwood is one of this year’s inductees into the Hydro Hall of Fame.

For 100 years, the 108-MW Holtwood hydroelectric plant has generated clean, renewable energy for businesses and residents in south central Pennsylvania. This facility, now owned by PPL Holtwood, uses the power of the water held back by a 55-foot-high dam across the Susquehanna River between Lancaster and York counties.

The plant began operating in 1910 and has operated continuously for the intervening 100 years. An expansion currently under way will more than double the capacity of the project and allow PPL Generation to extend the life of this historic facility. The expansion is scheduled to be complete in the spring of 2013.

Building Holtwood

McCall’s Ferry Power Co., organized in 1905, built the Holtwood facility. The company broke ground in October 1905 for a 55-foot-high dam that would span nearly half a mile across the Susquehanna River. At the peak of construction, more than 2,500 men were working around the clock to complete construction of the dam. However, in late 1907 the company defaulted on the bonds due to an economic crisis, and Knickerbocker Trust Co. in New York initiated foreclosure. With the project nearly 80 percent complete, the company had to secure alternate financing.

The board of directors contacted John E. Aldred, a New England financier, entrepreneur, and hydroelectric industry pioneer. Aldred was president of Shawinigan Falls Power Co. in Canada; was president of Consolidated Gas, Electric Light and Power Company in Baltimore; and provided financing for the Italian hydroelectric industry. Aldred agreed to be named receiver of McCall’s Ferry Power and thus took possession of the unfinished powerhouse, partially completed dam, railroad yard, construction shops, and village that provided homes for the laborers building the project.

To secure financing to complete the project, Aldred turned to two Canadians — Sir Herbert S. Holt, president of Montreal Light, Heat & Power Company, and Edward R. Wood, vice president of Toronto Securities. Because of the tenuous financial markets in the U.S., the financing was obtained from Canada and Scotland. The company was reorganized as Pennsylvania Water & Power Company.

Aldred then named the plant and the surrounding community Holtwood in honor of the two Canadians. Aldred himself is memorialized by Lake Aldred, the 2,400-acre lake formed by the dam that provides opportunities for boating, fishing, and other public recreation.

Pennsylvania Water & Power began generating electricity at Holtwood in October 1910, with full-scale commercial operation beginning a year later. The last of the plant’s ten units began operating in March 1924.

The 108-MW Holtwood plant in south central Pennsylvania began generating electricity in 1910 to power the growing city of Baltimore, about 50 miles southwest.

When all ten units are operating, the plant has a capacity of about 108 MW. Two smaller units are used to generate direct current electricity for station use. At the time it was completed, much of the electricity generated by Holtwood was used to power the growing city of Baltimore, about 50 miles southwest of the plant.

Pioneering spirit

The Holtwood facility served as a pioneering location for both individual hydroelectric plants and the industry as a whole.

For example, at the time of its completion, Holtwood Dam was the second longest dam in the U.S. and the third longest in the world. The dam is 2,392 feet long.

The 125-MW expansion (simulation in the foreground) of the existing 108-MW Holtwood facility, currently under construction, will allow owner PPL Generation to continue its long tradition of service and benefit to the central Pennsylvania region.

The hydroelectric plant was built to house a hydraulic testing laboratory. This laboratory, which was constructed in 1930, went on to produce several technology breakthroughs used by hydroelectric generating facilities throughout the world. For example, model hydraulic turbines for the 380-MW Safe Harbor, 134-MW Santee-Cooper, and 6,809-MW Grand Coulee projects were tested at the Holtwood plant, according to archives compiled for Holtwood’s 75th anniversary in 1985.

The generators and turbines used for the Holtwood plant weigh 200 tons combined. When the Holtwood units first began operating, this weight exerted tremendous pressure on the roller thrust bearings supporting the machines. The bearings wore out at a high rate, lasting only two or three months. Engineers at the plant experimented with several solutions, including a water-lubricated thrust bearing. That bearing also failed within a couple of months.

In 1912, plant personnel installed a new style thrust bearing on Unit 5 for a test trial. The new bearing, developed by Albert Kingsbury, was able to support the weight of the generator and turbine using sliding film bearing technology. After the successful trial run, Kingsbury bearings were installed on all of the units at Holtwood. Units 1 through 7 were retrofitted between 1912 and 1914. Kingsbury bearings were included in the installation of Units 8 (1914) and 9 and 10 (1924). This type of bearing later became standard equipment not only for hydro plants but for propellers of large ships, steam turbines, and other rotating equipment.

In 1987, the thrust bearing installed on Unit 5 was designated as the 21st International Historic Engineering Landmark by the American Society of Mechanical Engineers. It is still running with all the original parts and has an estimated life of more than 1,000 years based on wear rates.

Holtwood also was the launching pad of the pump-turbine, which could be used as a turbine during peak hours of demand and reversed to pump water back uphill for reuse in generation. The pump-turbine concept was never used at Holtwood. However, the principle has been applied at pumped-storage hydroelectric power plants throughout the world.

Another source of power

The Susquehanna River drains 27,500 square miles — an area larger than Delaware, Massachusetts, New Jersey, and Vermont combined.

In the mid-19th and early 20th centuries, much of the Susquehanna River basin included active anthracite coal mines that provided much of the energy for America’s growing economy. Some of the anthracite eventually ended up in the river as a by-product of coal mining and cleaning operations. This coal would settle to the bottom of the river, especially at dams such as Holtwood and Safe Harbor.

From the time the dam was built in 1910, Pennsylvania Power & Water had been dredging the coal out of Lake Aldred to ensure the buildup would not impede the flow of water at the dam. The company began selling this coal in the 1920s, but the rapid growth of industry at that time created an increased demand for electricity. This was the impetus for installation of an anthracite coal-fired steam electric station at Holtwood.

Unit 5 in the 108-MW Holtwood powerhouse contains a sliding film thrust bearing that was designated as the 21st International Historic Engineering Landmark by the American Society of Mechanical Engineers. The bearing has an estimated life of more than 1,000 years based on wear rates.

The new power plant — adjacent to the Holtwood hydroelectric project — went on line in 1925 with two 15-MW turbine-generator units. A third 80-MW steam electric unit was added in June 1955. All the coal-fired units were fueled with coal dredged from the river, a total of nearly 500,000 tons per year.

Dredging operations ended in 1972 after Hurricane Agnes brought significant flooding and damage to the river basin. The two original steam units were retired in 1972. The company continued to run the third, larger unit, using purchased coal, until it was retired in 1999.

Beginning a new era

In 1955, Pennsylvania Power & Light (PP&L) announced it was purchasing Pennsylvania Water & Power. As part of the transaction, the Allentown-based PP&L acquired Holtwood and one-third of the Safe Harbor station, upriver from Holtwood. This acquisition helped bolster the company’s plan to expand its generation assets.

In 1994, PP&L formed a holding company called PP&L Resources. It was a parent to the regulated electric utility and to a new, unregulated subsidiary called Power Markets Development Company. PP&L formed the latter company to invest in power projects in the U.S. and overseas.

In 2000, PP&L changed its name to PPL Corporation to better reflect operations and strategy that reaches far beyond Pennsylvania. The company now operates hydroelectric plants in Pennsylvania and Montana as part of a fleet with more than 11,000 MW of generating capacity utilizing a diversity of fuels.

At this time, Power Markets Development Company became PPL Global. Thus, PPL has operations on two continents. The company delivers energy to about 4 million customers in the U.S. and the United Kingdom.

PPL Corporation has four major business lines:

— PPL Generation, the parent company of PPL Holtwood, is a deregulated business line that operates the company’s fleet of power plants in the U.S.;

— PPL EnergyPlus sells wholesale electricity to other utilities, municipalities, energy marketers, and large customers. It also procures the fuel for PPL power plants. PPL EnergyPlus sells electricity to PPL’s regulated business in Pennsylvania;

— PPL Electric Utilities delivers electricity and award-winning service to 1.4 million customers in 29 counties of central and eastern Pennsylvania; and

— PPL Global owns and operates locally regulated electricity distribution companies in England and Wales.

Combined, these companies serve about 2.6 million customers.

Environmental commitment

All of PPL’s business lines are committed to providing energy responsibly, in a manner that balances the needs of the communities in which the company operates, the environment, and shareowners and customers. That commitment to environmental stewardship and community involvement are evident at Holtwood.

Over the years, PPL has made numerous investments to preserve and protect the environment in the area surrounding the Holtwood dam and hydroelectric plant. Without question, the most visible preservation project is the fish lifts.

The Holtwood fish lifts are part of a multi-million-dollar project to enable migrating American shad to continue their annual spring journey up the Susquehanna River to spawn. Like salmon, shad spend most of their lives in saltwater but spawn in fresh water. With the completion of the lifts at the Holtwood and Safe Harbor dams in 1997, more than 200 miles of the Susquehanna River and tributaries are open to American shad and other migratory fish.

The Holtwood facility acts like an elevator, carrying the silvery fish over the dam and channeling them into the river, where they continue their upstream migration to spawning areas in the Susquehanna River watershed. The Holtwood facility contains two hoppers to accommodate the flow of the river and the layout of the dam and powerhouse, making this the largest operating elevator-style fish lift in the U.S. Lifts are operated during the spring migration season. They are capable of lifting tens of thousands of fish over the dam each season.

In 2001, Holtwood’s fish lifts transported more than 100,000 American shad and other fish upstream. It was the largest spawning run in more than a century, according to the U.S. Fish and Wildlife Service.

American shad have been called the “poor man’s salmon.” Native Americans harvested shad during the annual spring spawning runs and taught colonists how to catch shad to feed their families. Dried shad have been credited with saving George Washington’s troops from starvation when they camped along the Schuylkill River at Valley Forge. By the 1800s, shad became one of the most commercially valuable fish in Pennsylvania, Maryland, the District of Columbia, and Virginia. By the early 1900s, water pollution, over-fishing, and construction of dams in the lower Susquehanna River had depleted shad populations.

Shad spend most of their lives along the Atlantic seaboard from Labrador to Florida. Rising spring temperatures prompt shad to leave the ocean and return to their natal rivers. The migration season usually begins in late April and ends in mid-June. Males arrive at spawning grounds first, followed by egg-laden females. A female releases 100,000 to 600,000 eggs, or roe, into the water to be fertilized by several males.

The young hatch in four to 12 days. Fry, or juvenile shad, spend their first summer in freshwater. Young shad serve as a food source for other fish, such as smallmouth bass, bluefish, and striped bass. By autumn, the shad swim to the ocean, where the cycle is completed.

In addition to the fish lifts, PPL manages the Holtwood Environmental Preserve. This preserve provides lakeside recreational opportunities and facilities for camping, hiking, picnicking, boating, sightseeing, fishing, and hunting on more than 5,000 acres on both shores of the lower Susquehanna River in Lancaster and York Counties.

The environmental preserve also is home to four nesting pairs of bald eagles, the symbol of our country and a species once on the brink of extinction, and the Shenk’s Ferry Wildflower Preserve, one of the most impressive wildflower areas in the eastern U.S. PPL takes pride in preserving the glen as a wildflower sanctuary.

The Holtwood hydroelectric plant and environmental preserve demonstrate the successful combination of power generation, recreation, environmental education, and land management.

Preparing for the future

As Holtwood enters its second century of power generation, PPL has begun work on one of the most significant hydroelectric expansions in the U.S.

This major improvement at the Holtwood plant is part of PPL’s commitment to make sound financial investments while increasing the proportion of non-fossil-fuel resources in its generation portfolio. About 40 percent of the electricity PPL generates annually comes from nuclear, hydroelectric, and renewable sources that do not emit carbon dioxide to the atmosphere.

PPL is adding two new units that together will provide 125 MW of low-impact, renewable, and environmentally friendly electric generating capacity, in a new powerhouse adjacent to the existing 100-year-old Holtwood hydroelectric plant. Work on this expansion began in December 2009.

The Holtwood expansion project will create more than 200 “green energy” construction jobs and provides for additional jobs for key contractors and suppliers. One example is the nearby Voith Hydro manufacturing plant in York, Pa., which is producing the turbines for the project.

Investment tax credits that are part of the federal government’s economic stimulus package made the $434 million Holtwood expansion project feasible. These stimulus funds help to offset the economic factors that caused the company to withdraw its original application for the project in 2008 after the economic downturn.1

Additional benefits of the project are improved recreational opportunities and improved passage for migratory fish along the Susquehanna River and its tributaries. PPL will conduct extensive in-river rock excavation to create additional passage routes for American shad, replace wooden flashboards on Holtwood Dam with new inflatable rubber dam segments, and construct a new low-height barrier dam across the river immediately below the dam. The inflatable dam is expected to stabilize lake levels, improve recreational boating, and enhance flow control for migratory fish. The barrier dam is expected to stabilize river habitat downstream from Holtwood Dam and direct American shad to the fish passage facility.

When the expansion is completed in the spring of 2013, the new hydroelectric turbines at Holtwood will more than double the plant’s capacity to generate electricity from a renewable resource and continue the long tradition of service and benefit to the central Pennsylvania region.


  1. Ingram, Elizabeth A., “Using Stimulus Funds to Advance Hydro Development,” Hydro Review, Volume 29, No. 3, April 2010, pages 18-30.

Chris Porse, P.E., MBA, is the plant manager for PPL’s Holtwood hydroelectric plant.


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