Lecture 18 - GEOS 1004 Spotila/10/09 EARTH SURFACE II...

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GEOS 1004 Spotila Lecture 18, 11/10/09 EARTH SURFACE II: GROUNDWATER AND WATER RESOURCES groundwater = water stored underground in pore spaces and cracks in rock. 1.05% of total water (100x more than lakes and rivers). Why is groundwater important? =water resources; lot of people get water from the ground, particularly in arid regions. Where does groundwater come from? What is juvenile water? Nearly all ground water is meteoric = from the surface (percolation through ground) -rarely is the water juvenile (from the deep earth) What does this mean for groundwater resources? Because groundwater is meteoric, groundwater is a renewable resource -water resources is a question of finding water that already exists I. FINDING GROUNDWATER Drilling for groundwater: you must pay careful attention to the geology; rock type, rock structure, topography, and climate. A. Two important aspects of groundwater: 1) storage – how much water is there 2) flow- does it move through the rock (can you get it out) porosity = volume of open space in a volume of rock (measured as %) =storage Porosity varies by rock type: sand = 35% mud = 40% shale = 10% igneous rock = 1% permeability = ability to transmit fluid through a material =flow Permeability depends on total porosity (need open space to flow), size of pores (surface tension slows flow), and connectivity of pores. What is an example of a permeable layer? How about an impermeable layer? What rock types are good for water, which are bad? What about igneous and metamorphic rock? Shale has small pores that are not connected = impermeable: bad Sandstone= porous, relatively permeable = good Because of variable porosity and permeability, rock type is fundamental for finding groundwater (other factors = time, climate)
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Because of variable porosity and permeability of rocks, rock type is fundamentally important for finding groundwater. (other factors = time, climate. ..) Other rock types: Limestone – high permeability and porosity, but not necessarily good for groundwater (too fast!). Karst
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Lecture 18 - GEOS 1004 Spotila/10/09 EARTH SURFACE II...

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