Hopkinton Dam, New Hampshire

The Hopkinton Dam, on the Contoocook River, is a control facility in a network of several dams and flood control structures that would be engaged in a major flood event to form a single reservoir, called Hopkinton-Everett Lake. Normally, this lake does not exist. Its formation would only occur to reduce downstream flooding along the Merrimack River. The lake would be more than ten miles long, and would extend from Henniker, in the west, to Interstate 89, near Hopkinton, and south to Everett Dam, in the south. Because of this, development in the potential reservoir area is limited, and many structures have been removed. Most of the time, and normally, the Contoocook River flows through the bottom of dam, but is otherwise unobstructed. If activated, the dam would block the river, first filling a diversion canal at the base of the dam, moving water eastward. At its maximum, the lake would hold 50 billion gallons of water. This “potential” reservoir, with its two dams and half a dozen passive flood control walls, was completed in 1962, and is one of several in New Hampshire that were built by the Army Corps of Engineers starting in the late 1930s to control flooding, following a disastrous flood in the spring of 1936, which especially effected areas along the Merrimack, from Concord, to the coast, including cities in Massachusetts. Though these dams look small and park-like, causing them to go unnoticed in the rolling landscape of the state, they significantly control drainage, and operate as a system over a wide area. The system is operated out the Reservoir Control Center, in Waltham, Massachusetts.