This document discusses key properties and concepts related to aquifers and groundwater flow. It defines terms like porosity, permeability, hydraulic conductivity, specific yield, and water table. It describes different types of aquifers such as unconfined, confined, and perched aquifers. Pumping from confined aquifers can create a cone of depression. Storativity describes how much water an aquifer can gain or lose from storage. Aquifer units can be homogeneous, heterogeneous, isotropic, or anisotropic depending on their properties.

1. Al-Azhar University-Gaza
Master Program of Water and Environmental
Science
November 2013

2. Properties of aquifer

3. Porosity
 Porosity: the percentage of rock or sediment that
consists of voids or openings.
 porous: a rock that holds much water

4. Porosity

5. Effective Porosity
 •ne
 Effective porosity is the fraction of the porosity that is
available for transporting water (excludes fraction of pores
too small to hold water, or those that are not interconnected
 - can be measured in the lab directly by saturating a dried
sample of known volume and measuring water uptake in a
sealed chamber over time
 - for unconsolidated coarse-grained sediments there is no
significant difference

6. Porosity of Sedimentary
Rocks
 •Primary porosity
 –Pores between grains
 •Secondary porosity
 –Fractures

7. Permeability
 permeability: the capacity of a rock to transmit a fluid
such as water or petroleum through pores and
fractures
 permeable: a rock that allows water to flow easily
through it
 impermeable: a rock that does not allow water to flow
through it easily

8. Specific Yield (Sy)
 •Specific Yield Sy the ratio of the volume of water that
drains from a saturated geomaterialowing to the
attraction of gravity to the total volume of the
geomaterial

10. Specific yield & material

11. Specific Retention (Sr)
 •Specific retention Sr the ratio of the volume of water a
geomaterial can retain against gravity drainage to the
total volume of the geomaterial.
 n = Sy+ Sr

12. Hydraulic Conductivity

13. Darcy’s Experiments

14. Darcy’s Experiments
 Flow through sand filters
 Discharge (Q) proportional to
 Area, A
 Head drop, h1-h2
 Inverse of length, L

15. Hydraulic Conductivity
 K hydraulic conductivity (L/T)
 A function of properties of both porous media and the
fluid passing through it
 A function of porous media only
intrinsic permeability
density
=
dynamic viscosity
gravitational constant
=Ki
ρ
=
µ
=
g

16. Factors Affecting
Measurement of K
 Effective stress
 Hydraulic gradient
 Volume of Flow

17. Ground water
 the water that lies beneath the ground surface, filling
the pore space between grains in bodies of sediment
and clastic sedimentary rock, and filling cracks and
crevices in all types of rock

19. The Water table
 water table: the upper surface of the zone of saturation
and pore water pressure is equal to atmospheric
pressure.
 saturated zone: the subsurface zone in which all rock
openings are filled with water

20.  vadose zone: a subsurface zone in which rock openings
are generally unsaturated and filled partly with air and
partly with water; above the saturated zone.
 capillary fringe: a transition zone with higher moisture
content at the base of the vadose zone just above the
water table

23. The Water table
 The following generalizations are valid:
 1. In the absence of flow the water table will be flat
 2. A sloping water table indicates flow
 3. Ground-water discharge occurs in low zones
 4. The water table has the same general shape as the
surface topography (but less relief change)
 5. Ground water generally flows from topographic
highs to lows

24. Aquifers
 Aquifer: A formation, that contains sufficient
saturated, permeable material to yield significant
quantities of water to wells and springs.

25. Types of Aquifers
 •Unconfined aquifer(Water-table aquifer)
 •Confined aquifer(Artesian aquifer)
 Semi confined aquifer.

26. 1. Unconfined Aquifer
 •An aquifer that is close to the ground surface, with
continuous layers of materials of high intrinsic
permeability extending from the land surface to the
base of the aquifer.
 •Recharge from downward seepage through the
unsaturated zone, lateral ground water flow, or
upward seepage from underlying strata.

27. 2.Confined Aquifer
 •An aquifer that are overlain by a confining layer.
 •Recharge occurs in recharge area, where the aquifer
crops out, or by slow downward leakage through a
leaky confining layer.
 •Potentiometric surfaceis the surface representative of
the level to which water will rise in a well cased to the
aquifer

28. 3.Semi confined aquifer
 Are overlain by a semi confining layer.

29. Unconfined & confined Aquifer

30. Artesian Wells
A well whose source of water is a confined aquifer•
The water level in artesian wells is at some height above the water •
table due to the pressure of the aquifer
Water Table Well
Artesian Well
Pot. Surface
Flowing Well
Confined Aquifer
and
Confining Unit
Above
Bedrock Zone

31. artesian well: a well in which water rises above the
aquifer

32. Perched Aquifer
 Perched Aquifer - aquifer in the vadose zone because
of a lens of impermeable material
 - common in glacial outwash (clay from ponds),
volcanic deposits .
 the top of a body of ground water separated from the
main water table beneath it by a zone that is not
saturated

33. Perched Aquifer

34. Confining layer
 - layer having low or no peremeability
 - whether a layer is considered “confining” or not will
depend on main aquifer material
 - usually confining layers have some permeability, just
very low
 permeability –less than about 10-2darcy.

35. Types of confining layers:
 Aquiclude - layer of low permeability that can store
and transmit groundwater slowly between aquifers
(now more commonly referred to as “leaky confining
layer”)
 Aquifuge - absolutely impermeable and contains no
water

38. Pumping in confined aquifer
 Pumping lowering the aquifer surface in a cone of
depression.
 cone of depression: a depression of the water table
formed around a well when water is pumped out; it is
shaped like an inverted cone

39. Pumping in confined aquifer

41. Storativity
 Storativity (S) or Storage coefficient
 •The volume of water that a permeable unit will absorb
or expel from storage per unit surface area per unit
change in head.

42. Specific Storage
 pw density of water
 g the acceleration of gravity
 α compressibility of aquifer skeleton (1/(M/LT2))
 βcompressibility of water (1/(M/LT2))
 n porosity (L3/L3)

43. Storativity
 Confined aquifer
S = B Ss
 Unconfined aquifer
S = Sy+ h Ss

45. Homogenous unit
 Is one that has the same properties at all location.
 For a sank stone this would indicate that the graine
size ,porosity, thickness are variable in a small unit , so
the value of transmissivity and storativity of the unit
would be the same wherever present.

47. Heterogeneous unit
 Formations , hydraulic properties change.

49. Isotropic & anisotropic
 If a porous medium has equal intrinsic permeability in
all directions it is said to be isotropic
 If the pattern of voids allows for a path of least
resistance (i.e. direction in which Ki is higher) the unit
is said to be anisotropic
 - fractured rocks, basalts often highly anisotropic
 - sedimentary rocks may have many homogenous
units

50. Grain shape and orientation can affect the
isotropy or anisotropy of a sediment

51. Anisotropy of fractured rock units due to
directional nature of fracturing