UNDERGROUND WATER- CONTINUED

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.

 

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