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56 Cards in this Set
- Front
- Back
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two types of aquifers
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confined aquifer and unconfined aquifer
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confined aquifer
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high-permeability, water-bearing formation (sand and gravel) confined below by less permeability (clay)
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unconfined aquifer
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water-bearing formation with water table, subjected to atmospheric pressure above and saturated soil below
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two types of groundwater movement
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gravity and pumps
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what does permeable mean
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having pores that permit liquids or gases to pass through
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what does piezometric mean
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one for measuring the change of pressure of a material subjected to hydrostatic pressure
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what is definition of porosity
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the ratio of void space to the total volume of the sample
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describe groundwater velocity
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it is proportional to the hydraulic gradient in direction of flow
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apparent velocity is governed by
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Darcy's Law
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apparent velocity equation
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V = K(dh/dL), where (dh/dL) = hydraulic gradient, K= coefficient of permeability (aka hydraulic conductivity)
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what is a stratum
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it is a sheet like mass of sedimentary rock
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how to calculated the coefficient of permeability
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K=(Cd^2γ)/μ, where Cd^2 is the property of aquifer material, gamma is the specific gravity, and mu is the viscosity of the fluid
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what forms during a drawdown
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the cone of depression
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how far does the cone extend during drawdown
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the the limits of the well
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what does steady state mean
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it means that equal volume leaving must result in equal volume entering
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what is transimissivity (T)
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it is a confined aquifer characteristic
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T is defined as
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T=Kb
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when is the principle of superposition used
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used of multiple wells in one location
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what does unsteady mean
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flow conditions change with time
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what is the definition of a storage coefficient (S)
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-relationship between changes in volume in storage to changes in piezometric (pressure) head
-dimensionless |
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u is a dimensionless parameter defined as (equation)
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[(r^2)s]/(4Tt)
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how does water leave an unconfined aquifer
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by gravity
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how is an unconfined aquifer treated when a pump is first turned on
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it is treated like a confined aquifer using Eq. 7-20 (p. 243) and Eq. 7.21 (p. 243)
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as a pump continues to pump an unconfined aquifer, what takes over and what parameter changes
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gravity takes over and S (storage coefficient) will change
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calculating drawdowns
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Eq. 7.30 (p. 245) through Eq. 7.33 (p. 246)
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well functions
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Figure 7.8 (p. 246)
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what type of condition do pumping tests take place (confined aquifers)
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under steady conditions
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what do pumping tests provide
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they determine transmissitiy (T) of confined aquifers
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how do you test equilibrium in an unconfined aquifer
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requires two observations wells
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what does equilibrium testing in unconfined aquifers solve for
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K (permeability coefficient) measured for well-pumping tests
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what is a nonequilibrium test
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it is used to only determine the storage coefficient (S) if unsteady-state drawdown data is available
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s vs. t graph results in what slope
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slope of 1 or 45º
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s vs. (r^2)/t graphs has a slope of
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-1 (negative one)
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a solution of aquifer boundary problems
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method of images
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what are hydraulic image wells
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imaginary sources or sinks with same strength (ex. flow rate) as original well
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lakes, rivers, and other large bodies of water (increases/decreases) flow of well
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increases
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what is divination and name two methods
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locating subsurface groundwater using information obtained on the earth's surface
-two methods: Electrical Resistivity Method and Seismic Wave Progagation Methods |
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which divination method is this:
-varies from one rock formation to another -depends on size, shape, distribution of pores, water content -two rods are placed into ground |
The Electrical Resistivity Method
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which divination method is this:
-using explosives or heavy weight and determining the time to get through such mediums |
Seismic Wave Progagation Methods
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what is seawater intrusion
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when freshwater aquifers get saltwater
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fresh groundwater is discharged into
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the sea under the water table
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explain the reverse of what usually happens in aquifers by saltwater intrusion
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with large demand in fresh water, seawater enters freshwater aquifers by forcing its way it
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with is the line between saltwater and freshwater called
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the interface
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how deep does the interface occur below sea level
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40 times
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which method is used to precent seawater intrusion when saltwater is removed with some freshwater as well
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pumping trough
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which method recharges a well by pumping freshwater into the ground
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pressure ridge
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what are subsurface barriers
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built along coastline to reduce the coastal aquifer permeability, usually used in narrow canyons; expensive but no maintenance
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what is seepage
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movement of water through soil
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water movement caused by seepage is governed by
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Darcy's law (like in groundwater flow)
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what is a flow net
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graphical representation of flow patterns expressed by a family of streamlines and corresponding equipotential lines
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what is a cutoff wall
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thin layer of impermeable material or sheet piling partially penetrating the aquifer under the dam
-alters the seepage pattern therefore causing resistance to flow |
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what is sloughing
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aka slipping, excessive seepage through an earth dam of the downstream embankment
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what is piping
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removal of soil by exiting seepage water
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what causes complete failure to dams
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sloughing and piping
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seepage through an earth dam can be treated as flow through what
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through unconfined porous media
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what is the surface of saturation
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aka phreatic surface: the upper surface of flow
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