Groundwater The mass of water stored beneath the Earth s surface How does groundwater form The Hydrologic Cycle Raindrops infiltrate soil and other unconsolidated surface materials sinking into cracks and crevices of bedrock T he main cycle o f wate r that trave ls fro m the o ce an to the atmo sphe re to the surface and back to the o ce ans Mainly the rain that falls fro m the sky e ithe r will so ak into the g ro und by infiltratio n o r it will flo w o ve r the surface as runo ff Ho we ve r the rain may also g e t so ake d up in plants and re turne d to the atmo sphe re via transpiratio n T he rainwate r may also e vapo rate dire ctly back into the atmo sphe re Wate r at o r be ne ath the Earth s surface mo ve s o r cycle s amo ng the main re se rvo irs the o ce ans the atmo sphe re and the land How do humans interfere with the natural operations of the hydrologic cycle Evapo ratio n is inc re as e d b y the us e o f irrig atio n wate rs in dry are as Runo ff patte rns are alte re d whe n wate r is dive rte d fro m o ne re g io n to ano the r Paving that c o ve rs Earth s s urfac e with hig hways parking lo ts and b uilding s de c re as e s infiltratio n Hum an c o ntrib utio ns to g lo b al and lo c al warm ing c an le ad to m e lting o f g lac ial ic e and c hang e s in the b alanc e o f wate r in o the r re s e rvo irs Re m o val o f natural ve g e tatio n and fo re s t de c re as e s infiltratio n and c hang e s in ve g e tatio n c an affe c t trans piratio n Porosity The amount of pore space in rock soil or sediment It depends on the size and shape of the grains and how they are packed together The smaller the particles and the more they vary in shape the more tightly they will fit together Permeability The ability of a solid to allow fluids through It depends on the sizes of the pores how well they are connected and how tortuous the path water must travel to pass through the material Recharge Recharge is the infiltration of water into a surface Discharge Aquifers Aquiclude The opposite of recharge The exit of groundwater from a surface Beds that store and transmit goundwater in sufficient quantity to supply wells Impermeable beds of geologic material that hinder or prevent groundwater movement Unconfined Aquifer Aquifers that have a direct connection to the surface Confined Aquifer A groundwater storage area trapped between two impermeable layers of rock Artesian Flow Artesian Well Unsaturated Zone The water in a confined aquifer It is under pressure equivalent to the weight of all of the water in the aquifer above that point A well that is drilled into a confined aquifer at a point where the elevation of the ground is lower than that of the water table at the recharge area is an artesian well It is free flowing requiring no pumping to get the water to the surface The level at shallower depths where the rock and soil is unsaturated that is the pores contain some air and are not completely filled with water Saturated Zone Cone of Depression Water Table The level below the unsaturated zone in which the pores of the soil or rock are completely filled with water Occurs in an aquifer when groundwater is pumped from a well In an unconfined aquifer this is an actual depression of the water levels In confined aquifers the cone of depression is a reduction in the pressure head surrounding the pumped well The line between the water saturated soil and the soil that is not saturated with water beneath the Earth s surface Perched Water Table A small local water table above the main water table Karst Topography A landscape formed from th e dissolution of soluble rocks including limestone dolomite and g ypsum Ch aracterized by sinkh oles caverns and a lack of surface streams Underg round drainag e ch annels replace th e normal surface drainag e system of small and larg e rivers In what regions is Karst most strongly advanced High rainfall climates with abundant vegetation providing carbon dioxide rich waters Places with extensively jointed limestone formations Places with appreciable hydraulic gradients Sinkholes A small steep depression in the land surface above the cavernous limestone formation How are sinkholes produced In some places dissolution may thin the roof of a limestone cave so much that it collapses suddenly Caverns A natural underground space large enough for a human to enter Saltwater Intrusion Movement of salt water into freshwater aquifers in coastal and inland areas as groundwater is withdrawn faster than it is recharged by precipitation Influent Streams Type of stream that flows above groundwater table and flows in direct response to precipitation Effluent Streams Hydraulic Gradient It is ephemeral Type of stream where flow is maintained during the dry season through seepage It intersects the water table and is perennial The ratio between the slope difference and the flow distance Just as a ball runs faster down a steeper slope than a gentler one groundwater flows more quickly down a steeper hydraulic gradient Hydraulic Head The elevation to which groundwater rises in a pipe drilled into the ground Hydrothermal Waters Hot waters deep in the crust that migrate rapidly upward without losing much heat and emerge at the surface sometimes at boiling temperatures Reservoir Each of the environments in which water is stored The oceans glaciers polar ice undergound waters lakes rivers the atmosphere and even the biosphere are considered natural reservoirs of water on the earth How much of the earth s fresh water does the enormous reservoir of groundwater account for 22 of all the fresh water stored in lakes and rivers glaciers and polar ice and the atmosphere What is residence time in a reservoir The average time a given quantity of water remains in a reservoir Depletion The loss of water from surface water reservoirs or groundwater aquifers at a rate greater than that of recharge How are reservoirs depleted Extensive pumping which withdraws water from aquifers faster than the slow recharge from far away can fill them Drawdown A lowering of the groundwater level caused by pumping Subsidence A depression of the land surface as a result of groundwater being pumped Cracks and fissures can appear in the land Subsidence is virtually an irreversible process Stalactites Formations in caverns and hang down from the ceiling of the cave Stalagmites Steep mounds or spikes of calcium carbonate that …
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