Groundwater aquifer / aquitard water table groundwater flow groundwater contamination.
How does groundwater flow ?
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Transcript of How does groundwater flow ?
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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