The Minnewawa Dam :a case study

Flanagan, Timothy J.
Martin Johnson
Department of Environmental Studies
The Minnewawa Dam is a problematic structure in the town of Marlborough, New Hampshire. Evaluation of the social significance of the dam reveals paradoxical circumstances. It exists both as a flood protection structure and as a portent of the flood hazard; it has potential as an economic resource and simultaneously threatens to endanger significant social costs. The goal of this thesis is to examine the dilemma of managing the Minnewawa dam site. The methods were chosen for common availability to the resource manager, utility in the absence of adequate field data, and for low cost in investigative procedure. The results of this study provide a basis for the more detailed and specialized analyses which should be performed in deciding the fate of the Minnewawa Dam. The Minnewawa Brook courses through a narrowly incised valley in southwestern New Hampshire. The brook is a tributary to the Ashuelot river system, which flows into the Connecticut River, ultimately nourishing Long Island Sound. Minnewawa Brook is mapped on the U.S. Geological Survey Monadnock Quadrangle. The northwestern summit of Mt. Monadnock forms the headwater area of the 23 mi. ² Minnewawa watershed. The watershed is a true basin upheld by bedrock of the Littleton Formation (primarily mica-schists) with extensive intrusions of the New Hampshire Plutonic Series. The rocks were formed in the Devonian Period approximately 330 million years ago (Billings, 1949). The regionally metamorphosed bedrock is completely folded and jointed, and is relatively impervious to water. Consequently basin drainage is confined to surficial deposits and stream channels (Stuart, 1968). Eight miles downstream from the summit of Mt. Monadnock the Minnewawa Brook is impounded by a monolithic concrete arch. The coordinates of the structure are latitude N 42º55’ and longitude W 72º10’. The structure is referred to by various names in different social circles. To some area residents it is known as the “old power dam”, to others it is simply “big dam”. The New Hampshire Water Resources Board catalogs the dam as number 151.06. It is identified as dam number 00104 by the U.S. Army Corps of Engineers. It is also commonly known as the Minnewawa Dam, a name which reflects a status as the most prominent dam in the watershed.

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