AQUIFERS
AQUIFER
 A body of saturated rock which water can easily move. It
must be both permeable and porous and include such
rock types as sandstone.
 It is an underground layer of water-bearing permeable
rock or unconsolidated materials (gravel, sand or silt)
from which groundwater can be extracted using a water
well.
AQUIFER
 Water-bearing rocks are permeable, meaning that they
have openings that liquids and gases can pass through.
Sedimentary rocks such as sandstone, as well as sand and
gravel, are examples of water-bearing rock.
 An aquifer easily supplies water to well, installed in the
formation. The formation composed of sand and fine
gravels are the good aquifers.
TYPES OF AQUIFER
UNCONFINED AQUIFERS
 Where groundwater is in direct contact with the
atmosphere through the open pore spaces of the
overlying soil or rock, then the aquifer is said to be
unconfined. The upper groundwater surface in an
unconfined aquifer called the water table.
 These are aquifers which water seeps from the
ground surface directly above the aquifer.
UNCONFINED AQUIFERS
 These aquifers are not covered from the upper side
with impervious formation, while essentially covered
by an impervious layer from its bottom side. Water
table is the upper surface of this aquifer sometimes, it
also referred as water table aquifer.
CONFINED AQUIFERS
 Confined aquifers are permeable rock units that are
usually deeper under the ground than unconfined
aquifers. They are overlain by relatively impermeable
rock or clay that limits groundwater movement into,
or out of, the confined aquifer.
CONFINED AQUIFERS
 It is one which is covered by impervious layer from its
top and bottom, both the sides. In other words “it lies
between two impermeable layers.”
 One in which groundwater is confined under pressure
greater than atmospheric by overlying impermeable
strata. It is also known as artesian or pressure aquifer.
Natural Recharge of the Aquifers
 For 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.
 Unconfined aquifers receive recharge directly
rainfall and surface water infiltrating downward.
Natural Recharge of the Aquifers
 For Confined Aquifers:
 A regional confined aquifer is directly recharged
by precipitation in the area where the aquifer
crops out, having the same characteristics as an
unconfined aquifer.
 Confined aquifers are connect to unconfined
areas where water can flow in.
Transmissivity
 It is a measure of the ease of water
movement in the soil.
 It is the hydraulic conductivity, (K)
multiplied by aquifer thickness
𝑚2
𝑚
 T ( )= K ( )
𝑑𝑎𝑦
𝑑𝑎𝑦
x b (m)
Hydraulic Conductivity
 The ability of a porous material to
transmit a fluid.
 In Darcy’s Law, the hydraulic conductivity
is a proportionality factor which
essentially expresses an interaction
between the porous media (soil) and
flowing fluid (water).
Permeability
 It is the property of rocks that is an
indication of the ability of fluids (gas or
liquid) to flow through rocks.
 It is essentially related to the quantity of
pores and other entities in a rock.
Is an Aquifer an Underground River?
 No. Almost all aquifers are not rivers. Since water
moves slowly through pore spaces in an aquifer's
rock or sediment, the only life-forms that could enjoy
floating such a 'river' would be bacteria or viruses
which are small enough to fit through the pore
spaces. True underground rivers are found only in
cavernous rock formations where the rock
surrounding cracks or fractures has been dissolved
away to leave open channels through which water
can move very rapidly, like a river.
Why is Groundwater so clean?
 An aquifer is filled with moving water and the amount
of water in storage in the aquifer can vary from season
to season and year to year. Ground water may flow
through an aquifer at a rate of 50 feet per year or 50
inches per century, depending on the permeability.
But no matter how fast or slow, water will eventually
discharge or leave an aquifer and must be replaced by
new water to replenish or recharge the aquifer. Thus,
every aquifer has a recharge zone or zones and a
discharge zone or zones.
END