Post on 29-Jan-2016
description
transcript
GROUNDWATERGROUNDWATER
Global Distribution of WaterGlobal Distribution of Water
The Hydrologic CycleThe Hydrologic Cycle
Groundwater-Related Terms to RememberGroundwater-Related Terms to Remember
• AquiferAquifer:: a body of rock or soil that stores and easily a body of rock or soil that stores and easily transmits a significant quantity of groundwatertransmits a significant quantity of groundwater– A A confined aquiferconfined aquifer is overlain by an aquitard is overlain by an aquitard– An An unconfined aquiferunconfined aquifer is overlain by the water table is overlain by the water table
• AquitardAquitard:: an impermeable bed that hinders movement of an impermeable bed that hinders movement of
groundwatergroundwater
• Artesian wellArtesian well:: a well in which the groundwater rises to a a well in which the groundwater rises to a level higher than where it was first encountered level higher than where it was first encountered
• Cone of depressionCone of depression:: a cone-shaped depression in the a cone-shaped depression in the water table surrounding a well from which water is water table surrounding a well from which water is pumped faster than it can move through the aquiferpumped faster than it can move through the aquifer
Groundwater-Related Terms to RememberGroundwater-Related Terms to Remember• DrawdownDrawdown:: is the difference in elevation between the is the difference in elevation between the
undisturbed water table and the bottom of a cone of undisturbed water table and the bottom of a cone of depressiondepression
• GeyserGeyser:: a type of hydrothermal spring that intermittently a type of hydrothermal spring that intermittently erupts jets of hot water and steamerupts jets of hot water and steam
• GroundwaterGroundwater:: water in the zone of saturation water in the zone of saturation
• Hard waterHard water:: does not lather readily with soap, due to high does not lather readily with soap, due to high concentration(s) of Ca concentration(s) of Ca 2+2+, Mg , Mg 2+2+, Fe , Fe 2+2+, and/or Mn , and/or Mn 2+2+
• Karst topographyKarst topography:: formed in limestone bedrock in formed in limestone bedrock in response to dissolution of the limestone by acidic waterresponse to dissolution of the limestone by acidic water– Characterized by the presence of caves, sinkholes, Characterized by the presence of caves, sinkholes,
disappearing streams, solution valleys, etc. disappearing streams, solution valleys, etc.
Groundwater-Related Terms to RememberGroundwater-Related Terms to Remember• Perched water tablePerched water table:: unconfined groundwater separated unconfined groundwater separated
from the underlying main body of groundwater by an from the underlying main body of groundwater by an aquitard and a zone of aerationaquitard and a zone of aeration
• PercolationPercolation:: slow movement of water through small slow movement of water through small openings within a porous materialopenings within a porous material
• PermeabilityPermeability:: a measure of the ability of a material to a measure of the ability of a material to transmit groundwater. Dependent upontransmit groundwater. Dependent upon– How many conduits are presentHow many conduits are present– How big the conduits areHow big the conduits are– How straight the conduits areHow straight the conduits are
• Pore spacePore space:: any open space within a body of sediment or any open space within a body of sediment or rockrock
Groundwater-Related Terms to RememberGroundwater-Related Terms to Remember
• PorosityPorosity:: the percentage of a material occupied by pore the percentage of a material occupied by pore spacesspaces
• Primary porosityPrimary porosity:: the spaces between grains composing the spaces between grains composing the rockthe rock
• Secondary porositySecondary porosity:: cracks and caves produced by cracks and caves produced by jointing, faulting, and dissolution of the bedrockjointing, faulting, and dissolution of the bedrock
• SinkholeSinkhole:: a depression formed by collapse of the roof of a depression formed by collapse of the roof of a cavea cave
• SpringSpring:: a flow of groundwater naturally emerging at the a flow of groundwater naturally emerging at the Earth’s surfaceEarth’s surface
Groundwater-Related Terms to RememberGroundwater-Related Terms to Remember
• StalactiteStalactite:: an icicle-like structure attached to the ceiling an icicle-like structure attached to the ceiling of a caveof a cave
• StalagmiteStalagmite:: a conical-shaped structure attached to the a conical-shaped structure attached to the floor of a cavefloor of a cave
• Zone of aerationZone of aeration:: the unsaturated region above the water the unsaturated region above the water table, the region where the pore spaces are filled partially table, the region where the pore spaces are filled partially with air and partially with waterwith air and partially with water
• Water tableWater table:: the top of the zone of saturation the top of the zone of saturation
• Zone of saturationZone of saturation:: the region below the water table, the the region below the water table, the region where the pore spaces are completely filled with region where the pore spaces are completely filled with groundwatergroundwater
Features Associated with Subsurface WaterFeatures Associated with Subsurface Water
Zone of aeration: Zone of aeration: Pore spaces contain Pore spaces contain air and waterair and water
Zone of saturation:Zone of saturation:Pore spaces are Pore spaces are filled with waterfilled with water
Water tableWater table
Perched water tablePerched water table
Formation of a Water Table
Perched Water TablesPerched Water Tables (Plummer, McGeary, and Carlson, 2003, Physical Geology, 9(Plummer, McGeary, and Carlson, 2003, Physical Geology, 9thth ed.) ed.)
Sandstone
SandstoneSandstone
Mudstone
Surface Exposure of the Water TableSurface Exposure of the Water TableThe surface of any sea, lake, pond, stream, or spring is the water tableThe surface of any sea, lake, pond, stream, or spring is the water table
Water table
A Gaining StreamA Gaining Stream
Water table
Note that groundwater flow (blue lines) is always Note that groundwater flow (blue lines) is always perpendicular to the equipotential lines (black lines)perpendicular to the equipotential lines (black lines)
Movement of Movement of GroundwaterGroundwater
During wet weather During wet weather the water table rises, the water table rises,
is rechargedis recharged
During drought During drought the water table fallsthe water table falls
Movement of GroundwaterMovement of Groundwater
Note that the topography of the water table Note that the topography of the water table usually mimics the topography of the landusually mimics the topography of the land
Gaining and Losing StreamsGaining and Losing Streams
A losing streamA losing stream::During droughts During droughts
streams lose waterstreams lose water to to the saturated zonethe saturated zone
In arid regionsIn arid regions:: The topography of the The topography of the
water table does not mimic water table does not mimic the topography of the landthe topography of the land
A gaining stream:During rainy seasons
streams gain water from the saturated zone
Cone of Depression Produced by a Pumping WellCone of Depression Produced by a Pumping Well
Drawdown:Drawdown: is the difference in elevation is the difference in elevation
between the undusturbed water between the undusturbed water table and the bottom of the table and the bottom of the
cone of depressioncone of depression
A A cone of depression: cone of depression: forms in vicinity of a pumped well forms in vicinity of a pumped well
because the groundwater is because the groundwater is pumped out faster than it pumped out faster than it
can move through the groundcan move through the ground
Formation of a Cone of Depression
Primary PorosityPrimary Porosity
PorosityPorosity:: the percent of a material occupied by pore spaces the percent of a material occupied by pore spaces
Primary porosityPrimary porosity: the spaces between : the spaces between the grains composing the rockthe grains composing the rock
Secondary PorositySecondary Porosity
PorosityPorosity:: the percent of a material occupied by pore spaces the percent of a material occupied by pore spaces
Secondary porositySecondary porosity: the cracks and caves produced: the cracks and caves producedby jointing, faulting, and dissolution of the bedrockby jointing, faulting, and dissolution of the bedrock
Effect of Porosity and Permeability on Wells:Effect of Porosity and Permeability on Wells:Mudstone versus SandstoneMudstone versus Sandstone
High porosity,High porosity,low permeabilitylow permeability
High porosity,High porosity,high permeabilityhigh permeability
Effect of Porosity and Permeability on Wells: Effect of Porosity and Permeability on Wells: Fractured versus Un-fractured BedrockFractured versus Un-fractured Bedrock
Unconfined and Confined AquifersUnconfined and Confined Aquifers
ConfinedConfinedaquiferaquifer
ConfinedConfinedaquiferaquifer
UnconfinedUnconfinedaquiferaquifer
ConfinedConfinedaquiferaquifer
Artesian SystemsArtesian Systems
Artesian systems are systems in which groundwater rises Artesian systems are systems in which groundwater rises higher than the elevation at which it was first encounteredhigher than the elevation at which it was first encountered
Flowing Artesian WellFlowing Artesian Well
Salt Water IntrusionSalt Water Intrusion ContaminationContamination
Problems Affecting the Water Table and GroundwaterProblems Affecting the Water Table and Groundwater