2. Aquifer
• An aquifer is a groundwater reservoir.
• It is composed of geologic units that are saturated with
water and sufficiently permeable to yield water in a
usable quantity to wells and springs.
• Water bearing materials that form aquifers are,
• Sand and gravel deposits
• Sandstone
• Limestone
• Fractured volcanic and crystalline rocks
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3. • Aquifers provide two important functions,
• They transmit ground water from areas of recharge to
areas of discharge
• They provide a storage medium for useable quantities
of ground water.
• The amount of water a material can hold depends upon
its porosity.
• The size and degree of interconnection of those openings
determine the materials’ ability to transmit fluid.
Aquifer,cont….
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4. Aquitard
• It is a geological unit that is permeable enough to
transmit water in significant quantities for large area and
long period.
• It can transmit water at a relatively lower rate compared
to aquifer.
• Its permeability is not sufficient to justify the
construction of production wells to be placed in it.
• It’s formations are predominantly,
• Clays
• Loams
• Shales 4
5. Aquiclude
• It is an impermeable geological unit.
• It does not transmit water at all.
• This geological formation can store water, but cannot
transmit it easily.
• Aquiclude is a saturated geological unit that is incapable
of transmitting significant quantities of water under
ordinary hydraulic head.
• Example: Metamorphic rocks.
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6. Aquifuge
• It is a geological formation that can neither absorbs nor
transmits water.
• It doesn’t have interconnected pores.
• Examples of aquifuge are rocks like basalt, granite, etc.
without fissures.
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7. Types of Aquifer
• There are three types of aquifer,
• Confined
• Unconfined
• Leaky
1. Confined aquifer
• It is also known as artesian or pressure aquifers.
• It is an aquifer which is bounded by an aquiclude both at
the lower and upper part.
• This aquifer is confined between two impervious layers.
• The confined aquifer is known as pressure aquifer.
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8. • In a confined aquifer, the pressure of water is higher than
atmospheric pressure.
• The water in a well which is constructed in confined
aquifer rises usually above the aquifer and even above
the ground surface due to high pressure.
• Rises and falls of water in wells penetrating confined
aquifers result primarily from changes in pressure rather
than changes in storage volumes.
• Confined aquifer cannot be recharged directly by
infiltration.
TypesofAquifer,cont…
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9. • A region supplying water to a confined area is known as a
recharge area.
• Water may also enter by leakage through a confining
bed.
2. Unconfined aquifer
• It is an aquifer which is bounded by,
• aquiclude at its lower side and
• water table at its upper side
• So that, the flow of water in the upper part of the aquifer
is not restricted by any confining layer.
• It makes the upper part a bounded free surface.
TypesofAquifer,cont…
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10. • Consequently, the free surface of unconfined aquifer is
under atmospheric pressure.
• Its upper boundary is water table which is free to rise
and fall.
• Unconfined aquifer is directly recharged by infiltration.
3. Leaky aquifer
• It is also known as semi-confined aquifer.
• Because either both the upper and the lower boundaries
are aquitards or one of them is aquiclude and the
remaining is aquitard.
• The water is free to move through aquitards either
upward or downward.
TypesofAquifer,cont…
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11. • These are a common feature in alluvial valleys, plains, or
former lake basins.
• Pumping from a well in a leaky aquifer removes water in
two ways,
• by horizontal flow within the aquifer and
• by vertical flow through the aquitard into the aquifer
TypesofAquifer,cont…
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13. TypesofAquifer,cont…
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Cone of depression
Dynamic water level
Piezometric level
s: Drawdown
h: Water level after pumping (dynamic water head)
H: Water level before pumping(static water head)
m: Saturated aquifer
R: Influence of radios
r: Radial distance
15. TypesofAquifer,cont…
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Cone of depression
Dynamic water level
Piezometric level
s: Drawdown
h: Water level after pumping (dynamic water head)
H: Water level before pumping(static water head)
R: Influence of radios
r: Radial distance
Rainfall
16. TypesofAquifer,cont…
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Cone of depression
Dynamic water level
Piezometric level
s: Drawdown
h: Water level after pumping (dynamic water head)
H: Water level before pumping(static water head)
R: Influence of radios
r: Radial distance
18. Isotropy and Anisotropy
• Groundwater hydraulic equations are based on some
assumptions.
• If the hydraulic conductivity (K) is independent of direction at
any point in a geologic formation, the formation is called
isotropic at that point.
• If the K is dependent on direction at a point in a geologic
formation, the formation is anisotropic.
• For example: Kx, Ky and Kz represent hydraulic conductivity
values in the x, y and z directions, respectively.
• If 𝐾𝑥=𝐾𝑦=𝐾𝑧 at any point, the formation is isotropic.
• If 𝐾𝑥≠𝐾𝑦≠𝐾𝑧 at any point, the formation is isotropic.
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19. • In addition, if the K is independent of spatial variation
within a geologic formation, the formation is termed as
homogeneous.
• And if the K is dependent on spatial variation within a
geologic formation, the formation is heterogeneous.
• In homogeneous geologic formation, K(x,y,z)=C=constant.
• In heterogeneous geologic formation, K(x,y,z)≠C.
Homogeneity and heterogeneity
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20. Steady state and unsteady state flow
• There are two types of well-hydraulic equations.
• Steady state flow equations
• Unsteady state flow equations
• Steady state is independent of time.
• In this flow state, the velocity may differ from point to
point.
• But it will not change with time at any given point in the
flow field.
• As a result, the steady state condition, water level does
not change with time.
• For example, the water level in the pumping well and
surrounding piezometers does not vary with time.
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21. • The steady state flow takes place if pumping aquifer is
recharged by,
• Outside water resource
• Rainfall
• Leakage through the aquitard (Leaky aquifer) from
upward or downward
• Directly from open water sources
• Steady state flow is attained if the changes in the water
level in wells and piezometers are very small with time
that they can be ignored.
Steadystateandunsteadystateflow,cont…
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22. • Unsteady state occurs from the time of the start of
pumping until steady state flow is reached.
• The flow can be assumed as unsteady state as long as
water level changes in the well and piezometers are
measurable and cannot ignored.
Steadystateandunsteadystateflow,cont…
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24. Water table
• It refers to the boundary between saturated zone and
unsaturated zone.
• It is the upper surface of saturated zone.
• On this surface, the fluid pressure in pores of porous
media is atmospheric (p=0).
• This implies that
ψ=0
• Hence ℎ=𝜓+𝑧, hydraulic head at any point on the water
table must be equal to elevation of the water table.
• Therefore,
ℎ=𝑧
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25. Negative pressure
• Ψ=0 at any point on the water table (boundary)
• Ψ>0 at any point under water table (saturated zone)
• Ψ<0 at any point above water table (unsaturated zone)
• Since water in the unsaturated zone is kept in the soil
under surface-tension forces, the pressure head, ψ is
taken as tension head or suction head when ψ<0.
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26. • As mentioned before, hydraulic head is algebraic sum of
elevation, z and pressure head ψ.
• Above the water table, where ψ is taken as tension head
or suction head, it is not appropriate to measure
hydraulic head with piezometers.
• But it can be measured with tensiometer.
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Negativepressure,cont…
27. Saturated zone
• The saturated zone occurs under water tables (ψ>0)
• The soil pores are filled fully with water.
• The moisture content (θ) is equal to porosity, n (θ=n)
• The fluid pressure is greater than atmospheric pressure
and the pressure head (ψ) is greater than zero (ψ>0).
• The hydraulic head must be measured with a piezometer.
• The hydraulic conductivity is a constant.
• It is not a function of pressure head (ψ).
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28. Unsaturated zone
• It occurs above the water table and above the capillary
fringe.
• The soil pores are only partially filled with water.
• The moisture content is less than the porosity (n).
• The fluid pressure is less than atmospheric pressure.
• This implies that the pressure head is less than zero.
• The hydraulic head (h) must be measured with a
tensiometer.
• The hydraulic conductivity (K) and moisture content (θ)
are both functions of the pressure head (ψ).
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29. Springs
• A spring is a concentrated discharge of groundwater appearing
at the ground surface as a current of flowing water.
• To be distinguished from springs are seepage areas, which
indicate a slower movement pond and evaporate or flow.
• It depends on the magnitude of seepage, climate and
topography.
• Springs occur in many forms and have been classified as to
cause,
rock structure
discharge
temperature
variability
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30. • Springs can be divided into
(1) those resulting from gravitational forces
(2) those resulting from gravitational forces.
• Under the former category are included volcanic springs,
associated with volcanic rocks, and fissure springs, resulting
from fractures extending to great depths in the earth’s crust.
• Gravity springs result from water flowing under hydrostatic
pressure.
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Springs,cont…
31. • Depression Springs – formed where the ground surface
intersects the water table.
• Contact Springs – created by permeable water-bearing
formation overlying a less permeable formation that intersects
the ground surface.
• Artesian Springs – resulting from releases of water under
pressure from confined aquifers either at an outcrop of the
aquifer or through an opening in the confining bed.
• Impervious Rock Springs – occurring in tubular channels or
fractures of impervious rock.
• Tubular or fracture Springs – issuing from rounded channels,
such as lava tubes or solution channels, or fractures in
impermeable rock connecting with groundwater.
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Springs,cont…
