UNDERGROUND WATER

UNDERGROUND WATER

UNDERGROUND WATER

This is the water found below the earth surface in pores of permeable rocks and above an impermeable rock layer.

Also called groundwater

INFILTRATION

The movement of water vertically into the soil/rocks through pores, cracks or joints

PERCOLATION

The movement of water downwards and horizontally in the rocks/soil

EFFLUENT STREAMS

Underground streams supplied with water from the water table above them

INFLUENT STREAMS

They are underground streams supplied with water from the water table below their level

SOURCES OF UNDERGROUND WATER

There are four sources of underground water:

•   Rainwater;
•  Melt water
• Lakes, seas, oceans, rivers and swamps
• Magmatic water/ plutonic water; this is the water that gets trapped in the rocks beneath the surface during volcanism

Factors Influencing Existence of Underground Water

Precipitation/ rainfall:

Little rainfall has little or no infiltration as most of the water evaporates

Little rainfall over a long duration, gives time for infiltration, increasing underground water

Heavy rainfall in a short period has more surface run-off, and has little time for infiltration

Heavy rainfall over a long has more infiltration as it saturates the ground, increasing the underground water.

Slope gradient

Flat gentle slopes gives water more time to infiltrate into the ground, as it remains in the same place for long duration

Steep slopes have more run-off, and therefore water has little time to infiltrate into the ground.

Vegetation cover

Vegetation hold water on the ground by reducing surface run-off, giving water more time to sink.

Bare ground has more surface run-off and has little surface run-off

Plants also break the speed of rain drops, giving the water time to infiltrate into the ground

Level of saturation

Dry ground/soil has more open spaces which allows for more infiltration of water

Saturated and wet soils have minimal spaces to hold water reducing infiltration

Evapotranspiration

High rate of evaporation caused by low moisture content in the atmosphere reduce the amount of water that infiltrates into the ground

Evapotranspiration reduces the amount of water in the soil/ground. This makes the soil dry, increases the spaces in the soil, and in turn increases infiltration.

Nature of the rocks

Permeable rocks allow water to penetrate through.

Highly permeable rocks allow for a lot of infiltration.

Impermeable rocks do not allow water to penetrate through, reducing the level of infiltration

Some rocks such as clay allow water to enter them but does not allow it to pass through. This is because when clay particles absorb water, they expand reducing the air spaces, preventing percolation of water

Note

An aquifuge; is an rock that does not allow water to pass through/ infiltrate e.g. gabbro, shale and slate

A porous rock; is permeable rock that has air spaces/pores between the rock grains

A Pervious rock; is a rock that has cracks, fractures and joints through which water enters