THE WATER TABLE
Water table
is the upper level of water saturated zone in the permeable rock layer, making
up the ground water.
Water
infiltrates into the ground, then percolates under gravity to reach an
impermeable rock.
The
permeable rock above the impermeable rock is filled with water; and is said to
be saturated.
The
upper limit of the saturated permeable rock is the water table.
The
water table fluctuates according to seasons leading to three main zones of saturation
Zones of Saturation
There are three zones of saturation:
- Zone of permanent saturation
- Zone of intermittent saturation
- Zone of non-saturation
Zone of Permanent Saturation:
is the zone where all the pores and air spaces in the rock are permanently
filled with water.
Also
called the phreatic zone
Zone of Intermittent Saturation:
is the zone which is only filled with water during rainy season and is
unsaturated during the dry season.
Water
content fluctuates according to the season.
Zone of Non-Saturation:
is a zone of rock layers found immediately below the surface, allows water to
pass through but does not stay long to make it saturated
The
top of this zone has the soil water
belt.
The
zone of intermittent and non-saturation are referred to as the vadose zone/zone of aeration
Diagram: zones of saturation
Note:
-An Aquifer
is a permanently saturated permeable rock layer above an impermeable rock
Existence
of underground water leads to the occurrence of:
- Springs
- Wells
- Artesian basins and artesian wells
SPRINGS
A spring is
a point where underground water flows out naturally as the water table is
exposed to the surface along a slope
Conditions/ ways in which a spring
is formed:
i.
When
a permeable rock overlies an impermeable rock layer
Rain
water percolates and saturates the permeable rock
A
spring forms where the permeable rock and the impermeable rock meet on the
surface
i.
When
water enters and saturates a well-jointed rock on a hill
Rain
water percolates through the joints ant saturates the rock
Water
comes out where the joints open up to the surface forming a spring
May
form a line of springs called vauclusian
springs
i.
Where
a dyke cuts across an aquifer/ a layer of permeable rock
The
water table is raised to the surface
Where
the water table meets the surface, water flows out forming a spring
Where a limestone/chalk escarpment lies on top of an impermeable rock
Water
percolates and saturates the limestone rock
Water
flows out to form a line of spring ate the foot of the escarpment where the
water table meets the surface.
.
