More photos of the plant and dam.

Sewalls Falls Dam

In 1657 this land of 500 acres was surveyed and laid out under right granted to Massachusetts Governor John Endicott. In 1668, the land was conveyed to John Hull, a wealthy mintmaster from Massachusetts. Upon his death, the property was willed to his daughter Hanna, wife of Samuel Sewall, a judge in the days of witchcraft. Legend has it that this land was the favorite abode of Indian Chief Passaconaway.
The area was also used to launch logs from the mast yard into the Merrimack River to float downstream to be used for the construction of Royal Navy vessels.
The Sewalls Falls site was also the site of the longest rock crib dam in the world. Constructed in 1894, the dam was 633 feet of timbers and hand packed stones. On April 7, 1984 pressure from spring floodwaters breached the dam.
Much of the hydroelectric canal and gates still exist. It is planned that the site will be redeveloped with a historic museum giving the history of the dam and hydroelectric power in New Hampshire and further providing a wildlife area for all to enjoy. The State of New Hampshire Fish and Game Department is developing fishing piers and canoe access points near the hydroelectric plant.
The dam was constructed as part of a plan of a major industrial and residential development (the first in Concord) that was not completed.

In 1835 an attempt was made by the “Sewall’s Falls Locks and Canal Corporation” to. utilize another water-power for manufacturing purposes. Already, some ten years before, a sawmill had been erected by Ebenezer Eastman, Simeon Virgin, and Jeremiah Shepard on the east side of the river, about midway between the place of the modern dam and Sewall’s Falls bridge, and by them was used for sawing all kinds of lumber until it was destroyed by fire in 1837.  The new enterprise contemplated the construction of a dam at Sewall’s Falls, whence a canal was to be excavated terminating near Federal bridge in the village of East Concord, the site of the contemplated cotton mills. The works were begun, but never finished, and the enterprise was given up, “with heavy loss to the corporation,”  and with not a little disappointment to many who had grounded upon its anticipated success high hopes, especially for the growth and improvement of the east village, and generally for the consequent advancement of the town. At the same time, however, just above on the Contoocook, where, for some years, miscellaneous manufacturing had been carried on, the property of the chartered Contoocook Manufacturing Company came into the possession of Freeman and Francis Fisher, of Boston, by whom were commenced operations, destined to a better issue than were those at the falls of the Merrimack, just below, and for whom a precinct of the town was long to bear the name of Fisherville.

 Historical Background
Timber crib dams are typically built across streams to generate waterpower. Part of the flow is diverted into a power canal, whereas excess water flows over the top of squared timber cribbing which forms the spillway.    Large stones are packed inside the cribbing to make the dam strong enough to withstand the impact of floods and ice rafting. Sometimes these dams are straight, and sometimes they are slightly convex upstream. Often an inclined plane (or “apron”) is constructed upstream of the dam so that the force of the water cannot undermine the structure, and a second inclined plane is needed on the downstream side so as to break the fall of the water. When a timber dam is especially important or is meant to be particularly long-lasting, then the abutments that anchor the ends of the dam to its riverbanks are built of solid masonry.    This prevents leakage around the ends of the dam. Another possibility is that sturdy sheet-piles may be driven into the bottom of the river to help anchor the dam.
While some of the longest timber crib dams were constructed across rivers in the western United States, easily the longest such dam in the east was built at a falls on the Merrimack River in Concord, New Hampshire.    Known as the “Sewall’s Falls Dam” and positioned at the eastern end of Second Street in Concord, this was formerly a popular fishing site for the Penacook Indians (a tribe of the Western Abenaki) and the site of a European trading post in the 1650s.  Later, Judge Samuel Sewall purchased land in the vicinity of the falls, giving the site its name, and then the first white settlers arrived here in 1726.
Much later, in 1833, the New Hampshire Legislature granted a charter to the Proprietors of Sewall’s Falls Locks and Canal, “empowering them to build a canal from the head of Sewall’s Falls to the mouth of Mill Brook, a distance of about two miles.” This was to have been a transportation canal, and the adjoining property was to have been developed for mill sites.    The company partially dug the canal but finally gave up and lost about $80,000. It was the first of several companies to incorporate for the purpose of developing the Falls, but each failed.
The next effort was made in 1871, when the New Hampshire Legislature granted a charter to the Sewall’s Falls Transmitting Power Company, whose purpose was “to develop the water-privilege and to transmit power to the city of Concord by a vague scheme for compressing air.”  Their intent was to erect a dam, they were capitalized with $500,000, but they never began construction.
The next company to contemplate a dam at Sewall’s Falls was the Sewall’s Falls Land & Water Power Company. They incorporated in 1881, acquired title to the water privilege, and purchased land on both sides of the Merrimack River.
An assessment of the falls was conducted that year by Ray T. Cile, C.E., who concluded that, the total fall in a distance of about one mile and a half is found to be 19 3/4 feet, thus furnishing ample power for all the manufactories that would ever be located there. The width of the river at the point where the dam would probably be built is such as to require a dam 350 feet in length. The cut granite already on the ground in the abutments built by the old canal company is sufficient to build more than half of a dam of this length.    The deepest cut that would have to be made eastern section is approximately 50 feet. The first apron and second apron of the spillway are clearly visible, although in poor condition, and much of the steel nosing (1/4″ thick x 24″ x 42″) is still present which protected the timbers from ice flows.    Remains of the cofferdam–which channeled water toward the power canal–are still visible in front of (north of) the western section of the spillway, and a couple of “deadmen” (logs used as an anchor for guy ropes) are still positioned north of the spillway. At the present time the top of the spillway is approximately 15 feet above the current water line in the Merrimack River.    Only the dam’s east and west abutments–rising 14 feet above the crest of the dam–are as sturdy as ever, and both abutments are flanked on the south with piles of granite quarry waste (rip-rap).

A few days later the Concord Land & Water Power Company was, in fact, delivering power to the City of Concord.
Floods in 1895 and 1896 caused extensive damage to the middle and lower aprons of the dam, and in 1896 the cribs were repaired and the surfaces were replanked with Georgia pine.” It was not long, though, before the company ran into financial problems, went into receivership, and then on July 1, 1901, the Concord Electric Company was organized to take over the operation. After that time the dam, canal, and powerhouse were maintained in their original form, except that the canal was widened and the dam strengthened.    As noted by R.G. Knowlton, “When the Concord Electric Company first started operations in 1901, it is believed that there were 22 employees and only 222 customers …,” but “In 1905 the plant at Sewalls Falls was expanded and.the capacity of its generators was doubled from 1000 to 2000 KW.”  This expansion is described in the following passage:
The new installation consists of two units, each consisting of 3–55″ bronze runners of the Francis type, mounted on a vertical shaft and hung on a step bearing. The machines are of the Escher-Wyss type built by the Allis Chalmers Company, American representatives of the EscherWyss Co.    The gates are of wicket pattern, controlled by Escher-Wyss mechanical governors, also built by The Allis Chalmers Company. The generators, which are direct connected to the vertical shaft wheels, are of 500 k.w., 3-phase, 60 cycle, 2,000 volt, 100 r.p.m., revolving field type.    Excitation is furnished by one 75 h.p., 3-phase, 2,600 volt induction motor, direct connected to a 45 k.w., 125 volt, compound wound D.C. generator. The exciter unit runs at 680 r.p.m.
Soon afterward, a new building was erected in 1908 containing a steam engine (a steam relay plant) for standby service when the waterpower was shut down.
After these beginnings, the history of the dam and canal at Sewalls Falls was one of periodic maintenance, typically in the late summer of each year when the river level was at its lowest. Repairs during the 1930s had to be especially extensive because of flooding in 1936 and a hurricane in 1938. On March 20, 1936 “the Merrimack River reached an all-time record of 16.8 feet above the crest at Sewalls Falls”, and the wing walls of the dam had to be sandbagged. And then on September 21, 1938, a hurricane caused the river to crest some 13.9 feet above the dam. There were repairs to the dam in 1933 that involved the removal and replacement of approximately 208 of the volume of the timber crib and rock filling. The five wooden gates of the headgate structure were also replaced in 1933.16
Finally, at the end of the 1966 power year, generation at the hydro plant was suspended because it had become cheaper for the Concord Electric Company to purchase power from the Public Service Company of New Hampshire, which was
burning fossil fuel. Then, in 1969, Concord Electric turned over its operating license for the dam to the Federal Power Commission, and the State of New Hampshire purchased the dam for $1.00. Concord Electric gave the State $10,000 with which to cover future repair costs for the dam; but the money was deposited in the State’s General Fund, the annual maintenance work on the dam ceased, and the dam was allowed to deteriorate to the point that many individual timbers washed out, weakening the structure.
The final blow came during the night of April 7-8, 1984 when a 100-foot-long section of the dam gave way after several days of heavy rain, and the Merrimack River has been rushing through the breach in the dam ever since.    The silt that had been deposited north of the dam has all washed through, much of the timber cribbing has washed out, and with the river level radically lowered, the exposed spillway.of the dam is an imposing sight.

Description of the Dam Site
The original drawings of the Sewall’s Falls dam and canal were prepared by a civil engineer, E.F. Smith of Philadelphia; the canal was built under the direction of Daniel Ulrich; while the powerhouse was designed by Eugene F. Carpenter. The dam itself was constructed by William H. Ward of Lowell, Massachusetts, and was intended to develop 5000 horsepower. Work on the dam and canal began in August of 1892, and the company ran a track to the dam site in order to supply construction materials.    They also set up a temporary arclighting plant so that the work could be continued around the clock, and what may be the remains of this plant can now be found several hundred feet to the west of the dam site, where a foundation and the remains of a steam boiler have been located.
The people of Concord were fully aware of the importance of what was being built. In the Concord Evening Monitor of August 8, 1893 this was described as “the finest dam in New England,” spanning 497 feet between abutments and with a height of 22 feet.    The approximate cost of the dam was $125,000, and it was predicted to last for at least 40 years. The paper also noted that “Nine times so far the work has been baptized in blood, six of the victims being employed on the dam and three being lumbermen”.

Slightly later, on September 29, 1893, the Concord Evening Monitor reported that, at the Bridge street powerhouse of the Concord Land & Water Power Company this afternoon at 2 o’clock, was made the first practical demonstration of the use of the triphase current system of electric power distribution in the United States, and in fact the first on the American continent.
It would thus appear that they were quite unaware of the generation of three phase current in Redlands, California, just 22 days earlier.    Still, if the coffer dam had not washed out in October of 1892, Sewall’s Falls would probably have had priority over Redlands by several months.

The Dam
The dam was built in three stages, each about 20 feet wide, with the lowest step being downstream. The top of each step was covered with heavy planks spiked down to the timbers in the cribs, and the spaces inside the cribs were hand-packed with stones.    The abutments and wing-walls were made with squared granite blocks laid in cement. The spillway was constructed with 12″ x 12″ longitudinal timbers, hemlock and fir, and 10″ x 10″ cross ties fastened with bolts. “About 1,500,000 feet of timber and 20,000 cubic yards of rubble stone were used in the spillway, and 5,0003 cubic yards of hammered granite were used for the abutments and head gates”.

The Head gate Structure
The head gate structure, utilizing five gates with masonry piers between them, is located west of the west granite abutment.    Each of the five brick arch conduits has a timber gate approximately 10′ wide and 11’5″ high. The head gate structure is made of granite blocks, and the hoisting equipment for the gates was operated by a rack and pinion system, powered by electricity.    The gatehouse that housed this equipment is now gone, having been burned by vandals.    The canal that begins at the head gates runs for a distance of 1280 feet, and water in the canal ran through a 50-foot waste weir (trash rack) at the southern end of the canal into short pen stocks and then to the turbines in the two brick powerhouses. The canal is 60 feet wide and 13 feet deep at its center, and it has an L-shape–it bends sharply in the middle. The sides of the canal are “formed of wooden cribs buried in earth embankments, with vertical sheet-piling spiked to the canal faces of the crib”.  After water passed through this channel and through the powerhouses, it then was carried by a tail race channel, approximately 200 feet long, back to the river.

Powerhouse No. 2
In the original powerhouse (No. 2 Station), there were five wheel-cases with draft tubes, four of which had a pair of wheels (turbines). This first powerhouse utilized Rodney Hunt turbines.    The water wheels were in the basement of the powerhouse, and belting extended upward through the operating floor to the shafting. There were four 3-phase generators made by General Electric, rated at 225 kilowatts each and operating at 2,300 volts and 50 cycles.    (The current “alternated” 100 times/second so there were 50 cycles/second.) There were two Edison bi-polar dynamos used as exciters, and five Thompson-Houston arc-light dynamos. Transmission lines were carried across the river, through East Concord, and then south to the city of Concord.

Powerhouse No. 1
A second powerhouse (No. 1 Station) was built in 1905, and it became completely operational in 1907. The turbines in No. 1 Station were built by the Allis-Chalmers Company (two Allis-Chalmers triplex turbines of 900 horsepower each).  All generating equipment was finally removed from the powerhouses when they were decommissioned in the mid-1960s. Both powerhouses are presently used as storage space by the New Hampshire Water Resources Board, and wooden flooring overlies the penstocks and draft tubes which are still intact.

Wooden Spillway
When the wooden spillway washed out in 1984, it split the dam into two sections, and the span of the western section is approximately 250 feet, while the eastern section is approximately 50 feet. The first apron and second apron of the spillway are clearly visible, although in poor condition, and much of the steel nosing (1/4″ thick x 24″ x 42″) is still present which protected the timbers from ice flows.    Remains of the cofferdam–which channeled water toward the power canal–are still visible in front of (north of) the western section of the spillway, and a couple of “deadmen” (logs used as an anchor for guy ropes) are still positioned north of the spillway. At the present time the top of the spillway is approximately 15 feet above the current water line in the Merrimack River.    Only the dam’s east and west abutments–rising 14 feet above the crest of the dam–are as sturdy as ever, and both abutments are flanked on the south with piles of granite quarry waste (rip-rap).