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1 Groundwater Lecture Notes What is Groundwater? Groundwater is water that: lies beneath the earths surface occupies the space between grains in sediments and sedimentary rocks fills fractures and voids in igneous, sedimentary, and metamorphic rocks Porosity = a measurement of a rocks or sediments ability to store water Permeability = a measure of a rocks or sediments ability to transmit water The Water Table There are 3 major zones that describe the distribution of water in the earths subsurface (see Fig. 11.1) Vadose Zone: unsaturated, relatively dry material Capillary Fringe: moist (but not saturated) material in between the vadose zone and the saturated zone Saturated Zone: saturated material in which all pores/ fractures are filled with water The top of the saturated zone is called the Water Table. A Perched Water Table occurs where saturated materials are separated from the main water table by an unsaturated zone (Fig. 11.2) The Movement of Groundwater Most groundwate moves relatively slowly through earth materials Clay rich soils cm-m/yr Sandy soils 10s-100s m/yr Rock Fractures up to km/day In porous media (e.g. soils), groundwater moves down the slope of the water table Hydraulic Head Hydraulic head = elevation of water + pressure on water Hydraulic Gradient Hydraulic Gradient = change in head from a to b / distance from a to b. HG = head / distance = h/L 2 Rules of Groundwater Flow Groundwater flows from regions of high head to regions of low head Groundwater flows from regions of high fluid potential to regions of low fluid potential Water table Water table A B L h 3 Groundwater Flow Velocity Flow velocity depends on: Hydraulic gradient ( h / L) Permeability (K) Porosity (n) Velocity = (K / n)( h / L) This equation essentially shows that groundwater will flow faster where the ... View Full Document

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