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Groundwater

Groundwater. Diana L. Duckworth Rustburg High School Campbell County Schools. Key Concepts. Porosity: percentage of the rock that is empty space Depends on grain size, shape, & sorting Permeability: ability of a rock to yield water

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Groundwater

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  1. Groundwater Diana L. Duckworth Rustburg High School Campbell County Schools

  2. Key Concepts • Porosity: percentage of the rock that is empty space • Depends on grain size, shape, & sorting • Permeability: ability of a rock to yield water • Depends on grain size (larger grains have larger pores), grain shape, & sorting • Large pores, less impact of friction • Rounded grains, larger pores • Poor sorting, small grains fill in pores & reduce permeability

  3. Distribution of Water Underground Zone of Aeration Pores filled with air Water Table Surface of Zone of Saturation Pore space filled With water Water infiltrates ground when it rains. Percolates down under the force of gravity.

  4. Water table reaches surface at springs, rivers, & lakes • Water table follows the shape of the land. • Water flows downhill underground. Lakes River Side View Water flows from high ground into streams, lakes & marshes.

  5. Man’s Usage of Groundwater • Two kinds of wells: • Ordinary well that requires pumping • Artesian well where water rises to surface without pumping Recharge Area Aquaclude Artesian Aquifer

  6. Ordinary Wells • Two water levels • Static water level • Pumping water level Static Pumping Drawdown Cone of depression Side View

  7. Problems with Overexploitation • Withdrawals in excess of recharge rates: • Artesian wells lose pressure, must be pumped • Ordinary wells can produce overlapping cones of depression • Lead to dewatering of aquifer • Lower stream levels in drought • Salt water intrusion in coastal areas island ocean lagoon Salt water table Fresh water floats on salt water

  8. Hillside Springs Perched water table Spring Aquaclude Roaring Springs, North Rim Grand Canyon

  9. Groundwater Budget • Income = precipitation • Outgo = runoff + evapotranspiration • Surplus: precipitation is greater than evapo-transpiration & runoff • Water table rises • Deficit: precipitation is less than evapo- transpiration & runoff • Water table falls • Steady state: precipitation = evapotranspiration & runoff • Water table stays steady • Water Balance Equation P = E + R + G • Where G = change in water table

  10. Caves • CO2 dissolves in groundwater • Becomes acidic • Dissolves limestone • Joints enlarged into caves • Dry caves • Dripping water evaporates • Creates stalactites & stalagmites

  11. Sinkholes • Roof of cave collapses • Leaves circular depression • May fill with water Map view sinkhole cave SIDE VIEW

  12. Groundwater Topography • Karst topography • Sinkholes • Caverns • Disappearing streams • Ponds with no surface outlet • Limestone terrain http://mapserver.maptech.com/bp/mapserver/index.cfm

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