Flowing water creates energy that can be captured and turned into electricity. This process is called hydroelectric power or hydropower.
The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. But hydroelectric power doesn't necessarily require a large dam. Some hydroelectric power plants just use a small canal to channel the river water through a turbine.
Holyoke Gas & Electric (HG&E) in Massachusetts owns the Holyoke Hydroelectric Project. The 43.8 megawatt (MW) FERC Project #2004 is located on the Connecticut River in Hampden, Hampshire, and Franklin counties, Massachusetts. The southwest end of the Project’s dam is located in the City of Holyoke and the northeast end of the dam is located in the Town of South Hadley, with the majority of the Project’s structures and all of the generating facilities located in the City of Holyoke.
The 30 feet (ft) high, 985 ft. long masonry and concrete dam is located at a physiographic feature know as Hadley Falls. Here the elevation of the riverbed drops approximately 50 ft over a short distance, making the site ideally suited for hydropower usage. The dam is topped by five 3.5 ft high inflatable rubber bladder sections which impound a 2,290 acre reservoir with a normal maximum surface elevation of 100.6 ft National Geodetic Vertical Datum (NGVD).
A 25 ft wide bascule gate is located at the southwest end of the dam between the spillway and the intake for the Hadley Falls Station. Hadley Falls Station (30 MW), located on the impoundment at the southwest end of the dam, is the largest of the hydroelectric generating stations included in the Project (43.8 MW total). The Project has a three-level canal system with a 6,000 cubic feet per second (cfs) hydraulic design capacity, which extends through the lower areas of the city and provides water for industrial use and hydropower generation.
The Holyoke Canal System begins with the canal gatehouse structure located between the intake for the Hadley Falls Station and the west shore. The gatehouse discharges into the First Level Canal (about 6,500 ft long) and from there the flow is routed through the Second and Third Level Canals and then back to the Connecticut River. The Holyoke Canal System was listed in the National Register of Historic Places in 1980.
The Connecticut River is the longest river in New England, originating 2,625 ft above sea level in the Fourth Connecticut Lake and accumulating water from several major tributaries as it flows south at a slope of about 6 ft per mile, making the Hadley Falls drop particularly powerful for hydro-power. The waterway serves as the boundary between New Hampshire and Vermont, then runs through Massachusetts and Connecticut before emptying into Long Island Sound, over 400 miles from its source.
Located 86 river miles upstream of the Long Island Sound, the dam at Hadley Falls, known as the Holyoke Dam, is the first barrier that anadromous fish encounter during their upstream spawning migration. An area of about 8,309 square miles is drained by the river at the Holyoke Dam. Flows in the Connecticut River at the Project average about 17,000 cubic feet per second but seasonal extremes range from more than 80,000 cfs in spring to less than 5,000 cfs in late summer.