CHARACTERIZING A GROUND-WATER BASIN IN A NEW-ENGLAND MOUNTAIN AND VALLEY TERRAIN

A ground water basin is defined as the volume of subsurface through wh ich ground water flows from the water table to a specified discharge l ocation. Delineating the topographically defined surface water basin a nd extending it vertically downward does not always define the ground water basin. Instead, a ground water basin is more appropriately delin eated by tracking ground water flowpaths with a calibrated, three-dime nsional ground water flow model. To determine hydrologic and chemical budgets of the basin, it is also necessary to quantify flow through ea ch hydrogeologic unit in the basin, In particular, partitioning ground water now through unconsolidated deposits versus bedrock is of signif icant interest to hillslope hydrologic studies. To address these issue s, a model is developed and calibrated to simulate ground water flow t hrough glacial deposits and fractured crystalline bedrock in the vicin ity of Mirror Lake, New Hampshire, Tracking of ground water flowpaths suggests that Mirror Lake and its inlet streams drain a ground water r echarge area that is about 1.5 times the area of the surface water bas in. Calculation of the ground water budget suggests that, of the recha rge that enters the Mirror Lake ground water basin, about 40% travels through the basin along flowpaths that stay exclusively in the glacial deposits, and about 60% travels along flowpaths that involve movement in bedrock.