The year 1928 was pivotal in the history of the Connecticut River in northeast Vermont and New Hampshire. The free-flowing nature of the Connecticut River along Fifteen Mile Falls was forever altered, resulting in change to the geography and ecology of the river.
The Comerford Dam project in East Barnet was the first to begin and it came at a pivotal time. The employment of 3,400 workers and construction costs of $32 million (more than $400 million in today's dollars) provided a major economic stimulus to the communities surrounding the site and the national economy.
The dedication ceremony to mark the official opening of Comerford Dam took place on Sept. 30, 1930. It marked the end of two years of intense construction. President Herbert Hoover touched a golden key at the White House at 10:30 a.m., sending an electrical impulse over a special 700-mile circuit and starting the first big water wheel. Leaders in the world of business, finance, engineering, journalism and public service from four states, gathered in the spacious generator room to witness the ceremony. They were made aware of President Hoover’s action when a big globe flashed red and the sound of rushing water filled the enormous structure. One after another, the four big generators began to turn, impelled by the force of falling water from the new eight-mile lake above the dam. In less than seven minutes, the whole plant hummed with life, and electricity from New England’s largest power giant was speeding across the new transmission lines to the Tewksbury, Mass. Substation, 126 miles away. The president of New England Power Association, Frank D. Comerford, for whom the dam is named, presided over the ceremonies.
Prior to 1928, the river was in its natural form. Although there were fording points and bridges that had been built spanning the river, it remained open. For many years, it had been utilized as a major artery of transportation by Native Americans and early settlers. It was utilized for the great log drives from 1870 to 1915. Logs were floated down river from headwaters near Quebec to saw mills in Connecticut and Massachusetts. The drives provided lumber, crucial in building several New England cities during the 19th century. As villages, towns and cities developed along the river, the water power it provided was used to power pre-revolutionary mills and later manufacturing plants. Small water wheels were connected directly to the machines through a system of belts and flywheels. These mills and factories needed to be located along the shore to utilize the water power.
The development of electric generators and high-tension transmission lines would revolutionize the manufacturing process. Industrial centers grew in locations distant from water power sources. Hydro installations and transmission systems provided advantages over local power facilities because they were cheaper and more reliable.
By the mid-1880s, towns and cities across America were vying to be the first in their area to be electrified. The ability to send electricity at a high voltage, and reduce it at the receiving end, would help make this happen. Key inventions related to the production and transmission of electricity were largely in place by 1925, which paved the way for the development of hydroelectric generating plants along the Connecticut River.
Fifteen Mile Falls
The falls were a portion of the Connecticut River extending from Gilman, in southern Essex County, to the mouth of the Passumpsic River, in Caledonia County, wherein the river falls 320 feet over a distance of about 20 miles. Over centuries, in pre-glacial days, the river wore out a gorge 40 to 100 feet deep. The result was a gentle gradient of 10 feet per mile. This section of “white water” where the river cascaded down over boulders and ledges had been the subject of study over an extended period of time. Careful investigation of the geology at chosen sites determined the feasibility of hydroelectric installations. It was also determined that plentiful supplies of sand and rock for concrete materials were conveniently located at the proposed Lower Dam (Comerford) project site and that there were ample deposits for the earth dam construction found at each of the Fifteen Mile Falls project locations.
A master plan was created to develop the Fifteen Mile Falls by building three dams.
Unlike the contemporary efforts to erect wind turbines along ridgelines and build the Northern Pass, the Fifteen Mile Falls development encountered relatively little opposition prior to starting the Comerford project in August of 1928. Building of the dams would forever alter the free-flowing nature of the Connecticut River, along the Fifteen Mile Falls, resulting in a change to the ecology of the river wildlife. Mulligans Lower Pitch — a notorious set of rapids which began near Cushman's bridge and continued down to the nine islands where the Passumpsic River flows into the Connecticut — would be lost forever. In addition, building the dams required the flooding of farmland and the creation of large reservoirs that would provide a combined capacity of over 91 billion gallons of water. The combined area of these two lakes would be slightly larger than that of Lake Sunapee. While these man-made lakes would provide new resources and benefits, they would alter the natural topography of the proposed construction sites. The quarrying of stone and the removal of sand and soil during construction would have an environmental impact and the creation of high tension transmission lines would create aesthetic and environmental changes. Despite this, the proposal was widely supported since businesses and residents were anxious to receive the benefit of electricity.
Once land acquisition had been completed by the New England Power Company, creating the infrastructure to facilitate the building of the Comerford project was a major undertaking. The New England Power Construction Company provided design engineers and the Connecticut River Development Company would handle the construction work in collaboration with Fraser-Brace Engineering Company, Inc., which furnished part of the construction equipment and personnel. The first step of the program was the building of four miles of railroad connecting the Comerford site and the rock quarry above it with the Canadian Pacific Railway at Inwood Station in East Barnet. The completion of the railroad was essential for the transportation of supplies, construction equipment and components. During the first five months following the construction of the spur line to the construction site, 330 cars of freight were hauled over this line.
A quarry at the Comerford site provided rock needed for concrete production. A large crushing plant was built about a mile away. It consisted of a large motor-driven “jaw crusher” and three smaller motor-driven crushers. Over 350,000 cubic yards of crushed rock and 200,000 cubic yards of sand were used for concrete production. All of the sand was obtained on site from a 14-acre sand pit that had been cleared and “stripped,” leaving a beautiful swimming pond for later generations of New England power employees and their families.
A huge concrete mixing plant, consisting of four mixers was built on site. This plant was capable of producing 2,500 to 3,000 cubic yards of concrete in 24 hours. Many guy derricks were erected to facilitate handling and pouring of concrete. These derricks were over 100 feet high and could be operated with great speed and efficiency. A “bucket” containing two cubic yards of concrete could be lifted from a railroad car, swung by a guy derrick over a form and emptied.
A construction “camp” was built to accommodate about 75 percent of the 1,500 to 1,700 workers, the number employed varied depending on the seasonal labor demand. At its peak, over 3,400 men were employed, both on and off site. Generally, 1,300 men worked the day shift from 7 a.m. to 6 p.m. with one hour off and 300 men worked the night shift. About 50 percent of the laborers came from Vermont and New Hampshire, with 35 percent from other New England states and New York. The labor force included professionals, skilled tradesmen, a wide variety of specialists and laborers. Sixteen bunkhouses were built to accommodate the laborers. About 30 cottages were constructed for members of the staff, foremen and their families. The company maintained a general store nearby for the convenience of the employees. Two large dining halls, one seating 516 and the other 336, were built. A “staff house” was built with a small library. Fire and police protection was available. A hospital located on the construction site was under the management of a doctor and a staff of experienced nurses. Ambulances were available to provide for the evacuation of emergency cases. A theatre was built to provide a recreational outlet for the workers and was used for church services each Sunday. Sports teams were organized to provide recreational.
The first step in the construction of the Comerford project required the creation of a channel to divert the river around the construction site. This was achieved by excavating a diversion channel, 500 feet long and 40 feet deep, through ledge on the Vermont side of the river. It was necessary to excavate some 60,000 cubic yards of rock. The base of the concrete dam was poured across this channel, with two openings left in the dam through which the entire river flowed during construction. Heavy gates were constructed on the upstream side of these openings, which were closed once the dam was completed allowing the reservoir to fill. When completed, the dam required 2,300 cubic yards of concrete to seal the channel. A concrete retaining wall extends 500 feet upstream and 395 feet downstream from the center of the dam. During construction, “coffer-dams” were formed by placing a series of timber “cribs” around the area in the river that were filled with earth and rock strengthening them to withstand the pressure of the water. The water was then pumped from this enclosure, leaving the river bed dry for constructions purposes. This allowed work to be carried on many feet below the surface of the water surrounding the coffer-dam without fear of an accident. This was done in order to place the foundations of the dam on the solid rock of the river bed.
The dam consists of a concrete structure 1,300 feet long, and a earth dam 750 feet long on the New Hampshire side of the river. The concrete section rests on solid rock. The earth section of the dam required over 400,000 cubic yards of material and is anchored to the a massive concrete retaining wall, the largest ever built in the United States at the time. The wall is 900 feet long and contains 90,000 cubic yards of concrete.
The “intake” section of the dam, through which the water passes from the reservoir to the power house below, extends across the river from the retaining wall and is provided with racks equipped with mechanical rakes for trash removal. The water then passes into the turbines through four steel plate penstocks that are 19 feet in diameter. The four penstocks are 150 feet long and each of them weighs 190 tons.
The power house is constructed with a steel frame and enclosed by brick. The power house is 236 feet long and 99 feet wide. Two 115-ton electric cranes are mounted at the ceiling level and can be conveyed along the length of the powerhouse. The generator room contains the four vertical water wheels that produce approximately 200,000 horsepower. The substructure below the powerhouse was constructed 35 feet below the river bed to provide for the draft tubes through which the water passes after leaving the turbines.
The switchboard room that operates the plant is located in a gallery upstream above the generator room. An elevator provides access to the power house and a large open shaft provides access for lowering equipment and materials with a large overhead crane located in the service building above the dam. The dam was designed to be self-sufficient for maintenance purposes. There is a fully equipped machine shop, a blacksmith and welding shop, located in the service building.
A, 850-foot-long spillway, located on the Vermont side of the dam, augments the release of excess water during periods of high water.
The transformers are located on the deck at the top of the dam, next to the service building. The electrical energy is generated at 13,800 volts. The transformers step up the voltage to 66,000 for local distribution and 220,000 volts for long distance transmission.
Following the completion of construction, individuals were hired as operators, linemen, maintenance men and administrators. These individuals comprised a workforce of between 50 to 60 employees. As a result of automation and changes to maintenance, the number of workers presently employed at the Fifteen Mile Falls dams has been substantially reduced. Compared to the early construction period, these dams today are sleeping giants. In 2005, the hydroelectric dams on the Connecticut and Deerfield rivers were purchased from US Gen New England, a subsidiary of Pacific Gas & Electric, to TransCanada Corporation for $550 million. The 13-station network purchased by TransCanada included the 15-Mile Falls hydro project. In April of 2017, the same 13 hydroelectric stations on the Connecticut and Deerfield Rivers was purchased from TransCanada by Great River Hydro a, a subsidiary of Boston Arclight Capital Partners for $1.07 billion.