Presentation on theme: "Groundwater Diana L. Duckworth Rustburg High School Campbell County Schools."— Presentation transcript:
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 –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
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.
Water table reaches surface at springs, rivers, & lakes Water table follows the shape of the land. Water flows downhill underground. River Lakes Side View Water flows from high ground into streams, lakes & marshes.
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
Ordinary Wells Two water levels –Static water level –Pumping water level StaticPumping Drawdown Cone of depression Side View
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 ocean lagoon island Salt water table Fresh water floats on salt water
Hillside Springs Aquaclude Spring Perched water table Roaring Springs, North Rim Grand Canyon
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 EquationP = E + R + G – Where G = change in water table
Caves CO 2 dissolves in groundwater –Becomes acidic –Dissolves limestone –Joints enlarged into caves Dry caves –Dripping water evaporates –Creates stalactites & stalagmites
Sinkholes Roof of cave collapses –Leaves circular depression –May fill with water cave sinkhole Map view SIDE VIEW
Groundwater Topography Karst topography –Sinkholes –Caverns –Disappearing streams –Ponds with no surface outlet –Limestone terrain http://mapserver.maptech.com/bp/mapserver/index.cfm