how does groundwater flow ?
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How does groundwater flow ?. February 26, 2002. TOC. Definitions Groundwater flow overview Equipotentials and flowlines Wells Laplace Boundary conditions. Definitions. Unconfined Aquifer Confined Aquifer Water Table Piezometric surface Ground water well Piezometer Pumping well. - PowerPoint PPT PresentationTRANSCRIPT
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How does groundwater flow ?February 26, 2002
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TOC Definitions Groundwater flow overview
Equipotentials and flowlines Wells Laplace Boundary conditions
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Definitions Unconfined Aquifer Confined Aquifer Water Table Piezometric surface Ground water well Piezometer Pumping well
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Unconfined aquifer No confining layer at the top of the groundwater.
Groundwater levels are free to rise or fall
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Confined aquifer A layer of water bearing material that is
sandwiched between two layers of much less conductivity (aquicludes or aquitards)
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Semi-confined aquifer Confined aquifer that is “leaky”. Aquitards are
not impermeable.
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Water Table Top of an unconfined aquifer where pressure is
equal to the atmospheric pressure (p = 0)
Also known as phreatic surface or free surface
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Piezometric Surface The surface obtained by connecting equilibrium
water levels in piezometers penetrating the confined aquifer
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Groundwater well Measures the level of the water table
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Piezometer Measures the level of the piezometric surface
(or, in other words, measures the pressure at a point in a confined or semi confined aquifer)
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Pumping Well Well used to pump water from a confined or
unconfined aquifer to the surface. Can be screened over multiple depths, and pump from multiple aquifers
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Definitions Transmissivity Storativity Specific Yield Safe Yield
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Transmissivity Hydraulic Conductivity * Thickness of Aquifer
K * B = T
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Specific Storage Volume of water that a unit volume [of a porous
medium] releases from (or takes into) storage when the pressure head in the unit volume [of a porous medium] changes a unit amount
Also known as the storage coefficient in a confined aquifer
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Specific Yield Also known as ‘storativity’ or ‘storage coefficient’
in unconfined aquifer
Ratio of the volume of water that drains by gravity to the total volume of the porous media
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Safe Yield Economic term: Sustainable levels of water
extraction…
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How does groundwater flow? Darcy: Hydraulic Gradient
Velocity vs Flux
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Wells and well screening
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Continuum … Remember this ?
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Combine with Darcy
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Boundary Conditions No flow boundary Dirichlet boundary
Head is known for surfaces bounding the flow region Neumann boundary
Flow is known across surface bounding the region Combined head/flow knowledge