In my last post, Down
by the Water, I noted that my office looks onto the Merrimack River and the
upstream Amoskeag dam and the hydroelectricity power plant that has been in
operation for ninety years. In this post, I take a closer look at this power
plant, which I had an opportunity to tour, as well as its sister upstream plants
in Hooksett and at Garvin Falls.
In the process of learning more about the operation of the Amoskeag Dam and the hydro plant, I was fortunate enough to be given a tour of the operations by the experienced hydro team at PSNH. The photographs below were taken during this tour. My tour of the facility was fascinating. I got a great view of the dam from the powerhouse side and was able to view the power plant from the inside.
In the process of learning more about the operation of the Amoskeag Dam and the hydro plant, I was fortunate enough to be given a tour of the operations by the experienced hydro team at PSNH. The photographs below were taken during this tour. My tour of the facility was fascinating. I got a great view of the dam from the powerhouse side and was able to view the power plant from the inside.
The power plant is home to three 1920s vintage turbine and
generator sets, which continue to work perfectly today and are so well designed
and maintained that replacement is not warranted. As an engineer, I was very
impressed to see these 90+-year old units still operating and generating
electricity. The hydro industry is rather unique in the electricity generation
business, in that many of the operations rely on old, well-designed equipment,
which, in some cases, are 100 years old. This is a testament to past engineers
who designed these units without the use of calculators, spreadsheets, or
computer-aided design and drawing tools.
Photo: PSNH Flckr Photostream
The Amoskeag Power Plant has a long history. The project was started by the Amoskeag Manufacturing Company, the textile manufacturing company established on the banks of the Merrimack River and which led to the founding of Manchester. The Amoskeag Mill was at one time the largest cotton textile plant in the world. At its peak, the mill was powered by thirty water turbines, twelve steam engines, and five steam turbines. In 1918, a decision was made to completely dam the Merrimack at the Amoskeag Falls and to install a hydroelectric generating station. This was placed into operation in 1924.
During my research I was excited to uncover the photograph below
from the PSNH Shoebox website, which is a
collection of old PSNH-related photographs. This shows one of the turbines being readied for
installation in the Amoskeag powerhouse in the 1920s. It is still in operation
today.
Photo: PSNH Shoebox
After World War I, business became difficult for the Amoskeag
Manufacturing Company because the US was in recession. Furthermore, the
proliferation of electrical generating operations throughout the US, and
especially down south, meant that cotton did not need to be transported north
to be milled and woven. High costs, aging equipment, and labor unrest
eventually led to the bankruptcy of the Amoskeag Manufacturing Company and the
sale of the hydro operations to PSNH in 1936.
The Amoskeag Dam spans the Merrimack River so that the river
flow can be harnessed and fed through the three turbines at the Amoskeag
Powerhouse (see photograph below). The average annual river flow is some 4000
cubic feet per second (cu. ft/sec) (equivalent to 1.8 million gallons per hour).
At full power, the maximum combined water flow through the turbines is 5000 cu. ft/sec. This means during average
river flows of 4000 cu. ft/sec, all the water, except for a 280 cu. ft/sec habitat bypass, is directed through the turbines
and there is no overflow over the top of the dam. My photographs of the water
overtopping of the Amoskeag Dam were taken during the tour. Because the river
flow that day was very low (~ 2000 cu. ft/sec), I was surprised to see
overtopping. It turned out that the Amoskeag power house was down for
maintenance because the transformers were being replaced so there was no river
flow going through turbines and the full river flow, except for the bypass, was consequently all
spilling over the top of the dam.
I was also fortunate to be taken down to the lower levels of
the powerhouse, where I walked to the other side of the dam through a service
tunnel inside the dam wall that runs along its entire length. On emerging on
the other side, I got a closer look at the inflatable gate that is used to
control the height of the water in the dam.
Photo: PSNH Flckr Photostream
The Amoskeag dam is just one of three hydro plants operated by PSNH on a fairly short stretch of the Merrimack river, so I decided to take myself to the river* and drive upstream to visit the other two. About 7 miles above the Amoskeag dam, there is a small single turbine 1.6 MW hydro plant on the Hooksett dam; a further 5 miles upstream is the much larger Garvin Falls Dam, which hosts four turbines in two powerhouses which have a combined capacity of 12.1 MW. The PSNH Merrimack coal-fired power plant, which uses the Merrimack River as a cooling water source, lies between these two dams. It is clear that, even today, the mighty Merrimack has an enormously important role to play in energy generation in New Hampshire. Below are some photographs from my upstream excursion.
Much of this post has been touristy in nature with
descriptions of power plants, tours and lots of pictures but in the next post I will dig
deeper into the technical information, such as river flows and electricity generation,
associated with these hydro operations. My visits and research for these posts
has given me a better understanding of the operation and importance of these
hydroelectric facilities as well as a much better appreciation for the engineering design and construction
skills of those old time engineers.
Until next time, remember to turn off the lights when you leave
the room.
Mike
Mooiman
Franklin Pierce
University
mooimanm@franklinpierce.edu
(*Take Me to the River – The fabulous and heavily covered Al
Green tune. The definitive cover is by the Talking Heads. Here it is from one
the best concert movies ever made – “Stop Making Sense”. Turn up the volume and
enjoy Take Me to River.)
Hii great reading your blog
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