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Vaseys Paradise
Groundwater discharges from the wall of Marble Canyon to form a series of natural springs.
(Grand Canyon)
Major Groundwater Regions of the USA
Porosity= The percent void space in a rock or sediment.
It is a measure of the potential volumeof water that can be stored in a rock.
Permeability= The ability of a material to transmit a fluid.
It is a measure of how fast the fluid can travel through the rock or sediment.
Aquifer= A geologic unit capable of storing and transmitting water in sufficient quantities to supply wells.
Porosity varies with % Cement
Size-Sorting
Fracturing
Uncemented SandCemented Sand
Types of AquifersUnconfined Aquifer - The permeable layer extends to the surface. It consists of an unsaturated zone separated from the saturated zone by the groundwater table.
Confined Aquifer - The permeable layer is sandwiched between less-permeable layers (aquitards or aquicludes).
Unsaturated Zone:Pores include both air and waterSaturated Zone:Pores filled with waterGroundwater TableUnconfined Aquifer
Water Table The top of saturated zone of groundwater
The level to which water will rise in a hole The level to which water will rise in an unconfined aquifer
Dynamics of an Unconfined Aquiferin a Temperate Climate
During the Wet Season
During the Dry Season
Darcys LawAn equation by which the discharge (rate of flow) of groundwater can be calculated.
Darcys LawQ = A ( K x S )
Darcys Law Q = A x ( K x S ) = A x ( K x H / L )Q = Discharge
A = Cross-sectional area of flowK = Permeability (hydraulic conductivity)S = Slope of water table = ( H L ) H = vertical drop L = flow distance
V = ( K x ( h1 - h2 ) / ( d x n )Permeability = 60 m/dayPorosity = 30% (=0.3)Hydraulic gradient = 1 m / 1000 mV = (60 m/day x 1 m) / (1000 m x 0.3)1 m
Darcys Law
The recharge area of a confined aquifer is the area where rainfall enters (recharges) the aquifer.
The pressure surface is the level to which water will rise in wells in confined aquifers.
Note the Difference Between:Groundwater Table: The level to which water will rise in an unconfined aquifer
Pressure Surface: The level to which water will rise in a confined aquifer *
* If the pressure surface is above the ground surface, the water will flow freely out of the ground. Such wells are called flowing artesian wells.
Confined Aquifer
Pressure Surface Ground Surface Flowing artesian well
Artesian Well in Glacial Sands & Gravels (MA)
Perched Water Table
Formation of a Cone of Depression
The OgallalaAquifer:
Mining Groundwater
U.S. Groundwater Withdrawals: 1950-1995
Fissures and depressionscaused by ground subsidence due to overpumpingof groundwater
(Antelope Valley, CA. January 1991. 625 meters long!)
The Winter Park Sinkhole, Florida(Photo by Leif Skoogfors)
Dynamics of the Saltwater - Freshwater Interface
The thickness of the fresh groundwater floating on top of the salty groundwater is affected by the balance between groundwater recharge and discharge
If the rate of discharge increases too much (by overpumping), the saltwater will rise, causing saltwater intrusion in the well. InvertedCone of depression
Some Major Features of a Karst Landscape
Subsurface Features of a Karst Landscape
Some Human Activities that Can Contaminate Groundwater
Cape Cod Sewage Plume (MA)
Detergent in groundwater (Cape Cod, MA).From abandoned military base (wastewater & sewage disposal).
(Maryland)
Hand-dug well in Sinai.Ancient river sediment.
Lancaster County, PA