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4 Groundwater and Surface Water Hydrology Otto S. Zapecza, Donald E. Rice, and Vincent T. dePaul Introduction Highlands water has long been recognized as a critical resource necessary to meet long-term public water-supply needs. As early as the nineteenth century , prior to the construction of major reservoirs, water-supply reports began documenting the region’s potential as an important source of water for the developing urban centers in northeastern New Jersey and New York City (Vermeule 1894; La Forge 1905). These studies urged conservation, noting the natural advantages of the region as a collecting ground owing to its many natural storage basins, abundant rainfall, and elevation, which allowed for economical delivery of water by gravity flow to the growing population centers immediately to the east. The Highlands Coalition has estimated that the Highlands region of Pennsylvania, New Jersey, New York, and Connecticut provides and protects water for more than 15 million people. Large population centers in New York City and New Jersey alone are dependent on much of the water supply provided by Highlands sources. As discussed in greater detail in chapter 5, major reservoir systems within the New Jersey, New York, and Connecticut Highlands supply more than 640 million gallons of water per day (mgd). Almost 90 percent of this surface water is exported from the Highlands to supply the adjacent major metropolitan areas. Groundwater is the primary source of water supply for businesses and residents within the Highlands region. Highlands aquifers supply more than 280 mgd of groundwater for public, domestic, irrigation, commercial, and industrial uses. The Highlands natural landscapes and undisturbed forests protect water quality in aquifers and streams; however, Highlands watersheds and the water they protect are considered to be at risk based on indicators such as increasing impervious surface, urban runoff, population growth, land-use change, and hydrologic modification of streams. An understanding of the region’s groundwater and surface hydrology, the science behind the resource, provides a basis for making informed water-supply planning and management 60 Zapecza, Rice, and dePaul decisions, which can ensure a sustainable supply of clean water for human needs while maintaining the region’s stream habitat and ecological health. The Groundwater System Groundwater is the primary source of water used within the Highlands region. The characteristics of Highlands aquifers and the function of the groundwater flow system are directly related to the underlying geology and soils that control the infiltration, storage, movement, availability, and chemistry of water. The geologic nature and prevalent soil types of the Highlands region are presented in chapters 1 through 3. Highlands Aquifers Highlands aquifers are classified in two categories: bedrock and glacial valley fill. Bedrock aquifers include those composed of crystalline metamorphic rock and those composed of sedimentary limestone, sandstone, and shale. Groundwater flow in bedrock aquifers is through a complex series of interconnected fractures, joints, solution openings, and bedding planes. Low storage capacity and well yields typify these aquifers owing to the smaller volume of interconnected openings in consolidated bedrock when compared to the porous sand and gravel of valley-fill aquifers. Carbonate aquifers composed of limestone or dolomite with larger solution openings can provide substantially higher well yields than other bedrock aquifers, particularly where overlain by the more permeable sand and gravel of glacial valley-fill deposits. Glacial valley-fill aquifers are composed mainly of permeable sand and gravel deposits, and like carbonate aquifers they are typified by higher well yields. The distribution of bedrock and glacial valley-fill aquifers in the Highlands region is shown in plate 4. Crystalline rock aquifers are composed of crystalline metamorphosed sedimentary and igneous rocks of Precambrian age and are exposed over more than 50 percent of the region. Rock types consist primarily of coarsegrained gneiss, schist, and granite of various mineral composition. Finegrained metamorphic slates such as phyllite are common in New York State. Crystalline rocks are typically more resistant to erosion than other rock types and form the upland regions. Crystalline rocks generally provide the high elevations and relief typical of Highlands topography. Production wells in crystalline rock aquifers commonly yield ten to one hundred gallons of water per minute. Carbonate rock aquifers are composed predominantly of Paleozoic-age limestones and dolomites and are exposed over 18 percent of the region. These rock types are less resistant to erosion and are subject to dissolution and therefore found on the valley floors interspersed between more resistant crystalline and clastic (sedimentary) rocks that form the valley walls. Produc- [3.142.98.108] Project MUSE...

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