The story of how a 22-mile long reach of the Connecticut River was transformed from a wild, free-flowing river with treacherous rapids to a reservoir that serves a hydroelectric generating facility is a fascinating one. Harnessing the power of falling water had, of course, been done for decades along the tributaries of the Connecticut. Grist mills, saw mills, woodworking shops and small machine shops produced goods for their local communities. The power needs of the new manufacturing facilities that were being built along the Connecticut were enormous in comparison. In 1866, a stone-filled wooden crib dam was built at Turners Falls which stood at an elevation of 169.3 feet and created a pool of water behind the dam which could be used to generate electricity. Twenty years later, an enterprising mill owner in Turners Falls was the first to sell electricity generated by the Connecticut River to local residents for their household light fixtures.
In 1905, the wooden crib dam at Turners Falls was replaced with a concrete dam with the same elevation. By 1907, electricity generated in Turners Falls was being transmitted to Amherst. The elevation of the dam was raised to 172.3 feet in 1913 which extended the pool upstream to the French King Gorge. By 1915, flashboards had been added to the dam raising the water level to 179.6 feet and extending the pool to the confluence of the Ashuelot River in the town of Hinsdale, New Hampshire. Power generated in Turners Falls could now be used in the greater Springfield, Massachusetts area. Just ten years later, due to the expansion of transmission facilities and increases in generation efficiency, the Connecticut River at Turners Falls supplied electricity to homes and businesses as far south as Hartford, Connecticut and as far west as Pittsfield, Massachusetts.
In 1942, Western Massachusetts Electric Company (WMECO) was formed following the consolidation of several electric companies. The Federal Power Commission then issued WMECO a license to operate the Turners Falls power generating facility. In 1965, three Connecticut River valley power companies, including WMECO, merged to form Northeast Utilities Service Company (NU). Projected energy deficits and the 1965 power blackout led NU to develop plans to increase generating capacity. One of the projects proposed by NU was the Northfield Mountain Pumped Storage Project.
The Northfield Mountain Pumped Storage Project, completed in 1970, is located about five miles upstream of the Turners Falls dam. During the construction of the Pumped Storage Project, the dam at Turners Falls was once again raised to accommodate a power generating facility, this time to elevation 185.5 feet. A 2,500 acre lower "reservoir", known as the Turners Falls Power Pool, was created behind the dam. The Turners Falls Power Pool is a 22-mile long reach of the Connecticut River between the Turners Falls Dam and the Vernon Dam in Vernon, Vermont.
The concept behind the Pumped Storage Project is simple. This facility only provides power when it is needed; for example, during periods of peak demand. Water is pumped from the lower reservoir (the Connecticut River) to the upper reservoir (elevation 1,000 feet) that is located atop Northfield Mountain. The 300-acre upper reservoir holds 5.5 billion gallons of water. During periods of peak demand, water is released to the lower reservoir via the turbines to generate electricity. The power generating/pumping facility is located completely underground and consists of four 250 thousand kilowatt reversible pump turbines. Each of these turbines can pump a maximum of 22,500 gallons per second of river water up to the upper reservoir. To generate electricity, each turbine can discharge water from the upper reservoir back to the river at a maximum rate of 33,700 gallons per second. Typical water level fluctuations in this reach of the Connecticut River average 3.5 feet per day. Much higher fluctuations, on the order of 9-10.5 feet, may occur over the course of the weekly pump/release cycle.