Subsurface water :

-downward movement under the influence of gravity.

-commonly described as INFILTERATION

Ground water:
-all the cavities are completely filled with water.
-the thickness, length and width of the saturated
strata, the aquifer, constitute the ground water
reserves in an given area .
Where does the ground water comes from?
 Essential
components of
groundwater
The rate of infiltration is a
function of soil type, rock
type, antecedent water, and
time.

The vadose zone includes all the material between the Earth’s surface and the zone
of saturation. The upper boundary of the zone of saturation is called the water table.
The capillary fringe is a layer of variable thickness that directly overlies the water
table. Water is drawn up into this layer by capillary action.
AN AQUIFER
IT IS DEFINED AS A ROCK MASS THAT IS
CAPABLE OF HOLDING GROUND WATER
SUPPLIES BY VIRTUE OF ITS PROPERTIES .
IT YIELDS THE WATER WHEN TAPPED , AT A
REASONABLY GOOD VELOCITY AND IN GOOD
VOLUME . GRAVELS , LIMESTONES AND
SANDSTONES ARE GOOD AQUIFERS.
what is an aquifer?
A water bearing geologic formation or stratum capable of
transmitting water through its pores at a rate sufficient for
economical extraction by wells is called aquifer .

formations that serve good aquifers are:

 Gravels, sands, alluvium
 Lake sediments, glacial deposits
 Sand stones
 Lime stones with cavities
 Granites and marbles
 Quartzites
 Vesicular basalts
 TYPES OF AQUIFERS

CONFINED UNCONFINED
Aquifuge is an absolutely impermeable unit that
will not transmit any water

•Aquiclude a rock body which may be porous

enough to hold some quantity of water , but , which
by virtue of its very low hydraulic conductivity, does
not allow an easy and quick and good flow of
water through it , is called an aquiclude . it is a
practically impermeable rock mass

•Aquitard is a layer of low permeability that can

store ground water and also transmit it slowly
from one aquifer to another; also know as leaky
confining layer.
 Aquifers
• An aquifer is a formation that allows water to be accessible at a
usable rate. Aquifers are permeable layers such as sand, gravel,
and fractured rock.
• Confined aquifers have non-permeable layers, above and
below the aquifer zone, referred to as aquitards or aquicludes.
These layers restrict water movement. Clay soils, shales, and
non-fractured, weakly porous igneous and metamorphic rocks are
examples of aquitards.
• Sometimes a lens of non-permeable material will be found
within more permeable material. Water percolating through the
unsaturated zone will be intercepted by this layer and will
accumulate on top of the lens. This water is a perched aquifer.
• An unconfined aquifer has no confining layers that retard
vertical water movement.
• Artesian aquifers are confined under hydraulic pressure,
resulting in free-flowing water, either from a spring or from a well.
UNCONFINED AQUIFER
 If there is a homogeneous porous formation extending from
ground surface up to an impervious bed underneath, rainwater
percolating down in soil saturates the formation and build up
GWT.
This is unconfined aquifer and the well drilled is water table well.
CONFINED AQUIFERS
 It is a rock formation saturated
with water and capable of yielding
water tapped but unlike
unconfined aquifer, has an
overlying confining layer (an
impermeable rock mass) that
separates it from the influence of
atmospheric pressure.
 Water is not held under
atmospheric pressure but under
pressure of confining bed.
Difference between confined and unconfined aquifer
Artesian aquifers
 It is an confined aquifer in suitable geological situations so
that piezometric surface is always above ground level.
 It may be flowing artesian well.
 ARTOSIS in central europe
 Monoclinical strata and broadly synclinal are considered
ideal
 If there are leakage points they will reduce hydraulic head
 They are used for water supply and irrigation and chemical
industries also
 Integral part of water resource management
Summary of Groundwater Systems
NOTE: Study each term, and the associated concepts and
geologic processes.

(from Keller, 2000, Figure 10.9)

Porosity of Earth Materials

n= Vv /v

•n porosity
•Vv volume of void space in a unit volume
of earth material
•V unit volume of earth material, including
both voids and solids
POROSITY VALUES OF FEW ROCK
FORMATIONS
TYPE OF ROCK FORMATION POROSITY

GRANITE , QUARTZITE 1.5 %

SLATE , SHALE 4%
LIMESTONE 5 TO 10 %
SANDSTONE 10 TO 15 %
SAND AND GRAVEL 20 TO 30 %
ONLY GRAVEL 25 %
ONLY SAND 35 %
CLAY AND SOIL 45 %
The igneous and metamorphic rocks are permeable only
where they are fractured, and they generally yield only
small amounts of water to wells. However, because
these rocks extend over large areas, large volumes of
groundwater are withdrawn from them, and, in many
places, they are the only reliable source of water
supply.
 PERMEABILITY
THE PERMEABILITY IS DEFINED AS THE ABILITY
OF A ROCK OR UNCONSOLIDATED SEDIMENT, TO
TRANSMIT OR PASS WATER THROUGH ITSELF .

THE PERMEABILITY IS MEASURED IN TERMS OF

COEFFICIENT OF PERMEABILITY .
IT DEPENDS UPON
 SIZE AND SHAPE OF THE CONSTITUENT
GRAINS
 SORTING OF THE GRAINS
 CONTINUITY AND NATURE OF THE
INTERSTICES
Other Similar terms
Conductivity
Transmissivity
PERMEABILITY VALUES OF FEW
ROCK FORMATIONS
TYPE OF ROCK FORMATION AVG VALUES OF PERMEABILITY
COEFFICIENT IN CM/SEC

GRANITE , QUARTZITE 0.6 × 10 5

SLATE , SHALE 4× 10 5
LIMESTONE 4× 10 5
SANDSTONE 0.004× 105
SAND AND GRAVEL 0.4
ONLY GRAVEL 4.0
5
ONLY SAND 0.04 10
CLAY AND SOIL 0.04×
 Groundwater Movement
SPECIFIC YIELD (Sy) is the ratio of the volume of water
drained from a rock (due to gravity) to the total rock
volume. Grain size has a definite effect on specific yield.
Smaller grains have larger surface area/volume ratio,
which means more surface tension. Fine-grained
sediment will have a lower Sy than coarse-grained
sediment.
SPECIFIC RETENTION (Sr) is the ratio of the volume of
water a rock can retain (in spite of gravity) to the total
volume of rock.
Specific yield plus specific retention equals porosity
Specific Yield

•Specific Yield (Sy) is the ratio of the

volume of water that can be drained from
an aquifer to the total volume of the
aquifer.

Depends on Permeability of rocks

Specific Yield
Material Maximum Minimum Average
Clay 5 0 2
Sandy clay 12 3 7
Silt 19 3 18
Fine sand 28 10 21
Medium sand 32 15 26
Coarse sand 35 20 27
Gravelly sand 35 20 25
Fine gravel 35 21 25
Medium gravel 26 13 23
Coarse gravel 26 12 22
Storativity

•Storativity(S) or Storage coefficient

•The volume of water that a permeable unit can

store

Depends on Porosity of the rocks

 Groundwater -- Recharge and Discharge
• Water is continually recycled through aquifer systems.
• Groundwater recharge is any water added to the aquifer zone.
• Processes that contribute to groundwater recharge include
precipitation, streamflow, leakage (reservoirs, lakes,
aqueducts), and artificial means (injection wells).
• Groundwater discharge is any process that removes water
from an aquifer system. Natural springs and artificial wells are
examples of discharge processes.
• Groundwater supplies 30% of the water present in our
streams. Effluent streams act as discharge zones for
groundwater during dry seasons. This phenomenon is known as
base flow. Groundwater overdraft reduces the base flow, which
results in the reduction of water supplied to our streams.
S. Hughes, 2003
Groundwater Movement -- General Concepts
The water table is
actually a sloping (from Keller, 2000, Figure 10.6)
surface.
Slope (gradient) is
determined by the
difference in water
table elevation (h)
over a specified
distance (L).
Direction of flow is
downslope.
Flow rate depends on
the gradient and the
properties of the
aquifer.
 Groundwater Movement -- Darcy’s Law
Q = KIA -- Henry Darcy, 1856, studied water flowing through porous material.
His equation describes groundwater flow.

Darcy’s experiment:
• Water is applied under
pressure through end A, flows
through the pipe, and
discharges at end B.
• Water pressure is measured
using piezometer tubes

Hydraulic head = dh (change in height between A and B)

Flow length = dL (distance between the two tubes)
Hydraulic gradient (I) = dh / dL
 Groundwater Movement
General Concepts

• Hydraulic gradient for an

unconfined aquifer =
approximately the slope of
the water table.
• Porosity = fraction (or %) of void space in rock or soil.
• Permeability = Similar to hydraulic conductivity; a measure of
an earth material to transmit fluid, but only in terms of material
properties, not fluid properties.
• Hydraulic conductivity = ability of material to allow water to
move through it, expressed in terms of m/day (distance/time). It
is a function of the size and shape of particles, and the size,
shape, and connectivity of pore spaces.
Groundwater Movement
Determine flow direction from well data:

Well #1 4252’ elev

depth to WT = 120’ Well #2 4315’ elev
4220
(WT elev = 4132’) 4180 4200 4240 depth to WT = 78’
(WT elev = 4237’)

1. Calculate WT
4260 elevations.
4140 2. Interpolate
4160 contour
4180 intervals.
4200 4280

3. Connect
4220 N
contours of 4240
equal elevation. 4260 4300
4280
4. Draw flow lines
perpendicular to
contours. Well #3 4397’ elev
depth to WT = 95’
(WT elev = 4302’)
S. Hughes, 2003
Groundwater
Movement
Use of contours
 Perennial
Stream
(effluent)
(from Keller, 2000,
Figure 10.5a)

• Humid climate
• Flows all year -- fed by groundwater base flow (1)
• Discharges groundwater
 Ephemeral
Stream
(influent)
(from Keller, 2000,
Figure 10.5b)

• Semiarid or arid climate

• Flows only during wet periods (flashy runoff)
• Recharges groundwater
 Discharge of unconfined aquifers
The unconfined aquifers supply with water to the
permanent river network through the basic flow thus, the
rivers represent the main discharge zones of the
unconfined aquifers
Natural Recharge of unconfined aquifers

Natural recharge of the unconfined aquifers is mainly due

to the downward seepage (or percolation) through the
unsaturated zone of the excess water over passing the field
capacity of the soil. Recharge can also occur through
upward seepage (leakage) from underlying aquifers
 Recharge of confined aquifers

 A regional confined aquifer is directly recharged by

infiltration through precipitation during rains or snowmelt
in the area where the aquifer crops out.
 Discharge of confined aquifers

 The confined aquifers are less influenced by the topography than the
unconfined aquifers.
 The discharge of the confined aquifers occurs usually by leakage, either in an
unconfined aquifer, or in a confined aquifer, having a smaller hydraulic head.
 In some cases, the discharge of a confined aquifer is made through an outcrop
area, situated in a plain region at the opposite side to the recharge zone
 If the water table intersects the ground surface a
spring can occur. if an impervious layer does not allow
the normal percolation and a perched aquifer is
formed, a spring can flow at a higher elevation
DIFFERENT ROCKS AS AQUIFERS
 Hydrogeological diversity

Unconsolidated rocks: Consolidated rocks: Consolidated rocks:

• Pore spaces • Fractures • Karsts (enlarged fractures)
• Large storage • Small storage • Large storage
SEDIMENTARY ROCKS
HYDRAULIC POROSITY SPECIFIC YIELD
CONDUCTIVITY
(m/day)
GRAVELS 100-1000 25-40 15-30
SANDS 10-100 25-40 15-25
SANDSTONES 1-100 5-30 5-15
LIMESTONES 100 1-20 1-20
Gravels K=100-1000 m/day
n=15-31%
s.y=15-30%
-best to yield ground water
-show great variation in water bearing properties
-degree of assortment
-packing of grains
-cementing of grains

Sands K=10-100m/day
n=25-40%
s.y=15-25%
-next to water in yielding capacity
-compacted and cemented sandstones are best example
Sandstones
-vary according to the texture and nature
-coarse grained sandstones are excellent aquifers
-fine grained sandstones are useless
-sandstones formations are most important ground
water reservoirs the world over
Limestones- extremely permeable
-best known productive aquifers of the world but
unproductive in some regions
-availibility of water is controlled by-
Secondary fracturing, cavities and crevices
IGNEOUS ROCKS
INTRUSIVE EXTRUSIVE

ACID BASIC
VOLCANIC VOLCANIC
INTRUSIVE IGNEOUS ROCKS
 Dense in structure
 No openings and pores
 Non porous and impermeable
 The ground water will behave as vein water instead of
ground water
 If subjected to folding and faulting then it carries
some water
Extrusive-acid volcanic rocks
 Acidic lavas are viscous and fragmentary
 The interstices are filled with ash
 May or may not be holding water
 Eg. Rhyolites
Extrusive basic volcanic rocks
 Greater gas content and mobility at the time of
eruption
 Rich in cavities(escape of gases on cooling) and cracks
and joints(contraction on cooling)
 High porosity and permeability
 Good source of ground water
 They are weathered and disintegrated and hence water
bearing
 eg.basalt
Metamorphic rocks
--Crystalline and compact metamorphic rocks(quartzites,
marbles and gneisses) are
-non-porous
-impermeable
-holding no ground water reserves
--metamorphic rocks which are fractured and foliated
(schites, slates,phyllites)are
-exceptionally good aquifers
-confining layers have better chances of
aquifers than depth since fracture surfaces
disappear with depth.
 Assessment of groundwater
resources
 Different ways to assess groundwater:
 Observation of groundwater levels
 Pumping tests, to test the response of groundwater
abstraction
 Hydrogeological investigations to built a first
concept on groundwater resource;
 Geophysical surveys to find the groundwater
resource, to sit borehole
 GW budgeting, modelling for better resource
development planning
 Groundwater Quality need to be assessed to protect
GW resources:
 Salinity monitoring, Other field measurements of water
quality parameters
 Analysis of groundwater samples (in field or in laboratory)
Critical issues of GW Management
 Recharge rate quantification
 Recharge area vs land-use
(GW protection)
 Interactions (quantity/
 quality) with surface water
bodies
 Impacts of GW pumping
 Inter-basin / inter-boundary
aquifer
 To ascertain trends and Safe Yields (maintenance of a
long-term balance between the amount of annual
withdrawal and the amount of annual recharge)
 to predict implication of impacts through Modelling
Methods of Artificial Recharge
a. Direct surface techniques
. Flooding
. Basins or percolation tanks
. Stream augmentation
. Ditch and furrow system
. Over irrigation
b.Direct subsurface techniques
. Injection wells or Recharge wells
. Recharge pits and shafts
. Dug well recharge
. Bore hole flooding
. Natural openings,cavity filling
c.Combination of Surface-Subsurface techniques
. Basin or percolation tanks with pit shaft or wells
d. Indirect Techniques
. Induced recharge from surface water source
.Aquifer modification
MANAGED AQUIFER RECHARGE (MAR)

All efforts wherein availability of

groundwater may be enhanced through
several methods so that the water may be
extracted later for use.

Quality of groundwater is generally good

so quality concerns must be top priority
during recharge.
Rain water Harvesting
a. Storage of rain water on surface for future use
b. Recharge to ground water
- Pits
- Trenches
- Dug wells
- Hand pumps
- Recharge wells
- Recharge shafts
- Lateral shafts with bore wells
- Spreading techniques
•Surface Spreading Techniques

These are aimed at increasing the contact

area and residence time of surface water over
the soil to enhance the infiltration and to
augment the ground water storage in phreatic
aquifers.
The downward movement of water is
governed by a host of factors including
vertical permeability of the soil, presence of
grass or entrapped air in the soil zone
a. Flooding
This technique is ideal for lands adjoining rivers or
irrigation canals in which water levels remain deep even
after monsoons and where sufficient non-committed
surface water supplies are available.
b. Ditch and Furrows method
This method involves construction of shallow, flat-bottomed and
closely spaced ditches or furrows to provide maximum water contact
area for recharge from source stream or canal.

The ditches should have adequate slope to maintain flow velocity

and minimum deposition of sediments.

The widths of the ditches are typically in the range of 0.30 to 1.80 m.
A collecting channel to convey the excess water back to the source
stream or canal should also be provided.

Three common patterns viz. lateral ditch pattern, dendritic pattern

and contour pattern

Though this technique involves less soil preparation when compared

to recharge basins and is less sensitive to silting, the water contact
area seldom exceeds 10 percent of the total recharge area.