GROUND WATER

Ground water
Refers to the water that exists below the surface of the earth (is the part of the subsurface water that fully saturates the pore spaces in bedrock, regolith, or soil).

They are found within pore spaces of the soil (soil air spaces) and in the rocks beneath the surface which are above an impermeable layer.
NOTE: water which is contained in underground (subterranean) rivers is not included in category of ground water.

Sources of ground water.

• Rain water: rain water is among the sources of ground water. When it pours onto the surface infiltrate and percolate further into the ground to make ground water. Where the rain is heavy surface run off is dominated while where rain is light water infiltrate and percolates to form ground water.
• Melt water: in springs and summer seasons regions which experiences snows and ice during  winter season, the snow starts to melt slowly in summer. Because the rate of melting is slow melted water seep, infiltrate and percolates further and forms ground water.
• Lake and sea water: also water existing on the surface of the earth in variety of forms like sea, ocean, lake, ponds, swamps and rivers partly seeps and percolates through the rocks to become ground water.
• Magmatic water/plutonic water: refers to the water which has been trapped to the rock below the surface during volcanic eruption

Types of ground water.
The types of ground water are categorized basing on the origin for their existence within the ground.

1. Connate water.
2. Juvenile water.
3. Oceanic water
4. Meteoric water

Factors influencing the existence of ground water.
Amount of ground water is the outcome of rate of infiltration and percolation. This rate is determined by number of factors including the following:

1. Precipitation: amount of rainfall received in the area determine amount of water to infiltrate and percolate into the ground. Where there is heavy rainfall with short duration most of water will be flowing as surface run-off while moderate rainfall falling over long period results into high rate of infiltration and percolation of water to the ground to form ground water.
2. Slope: infiltration and percolation of water is greater on flat areas because water collects for a long period of time enough to allow process of infiltration and percolation. On steep slope, nature of the surface favors surface run off hence little infiltration.
3. Nature of the rock: in well jointed rock or rock with pore spaces (porous and pervious rock irrespectively) water passes through pores and joints to accumulates into the ground. Thus amount of ground water is determined by permeability or impermeability of the rocks (surface rocks).
4. Vegetation cover: vegetation also plays crucial role in influencing presence of ground water. First vegetation through roots opens the soil by creating joints through which water seep into the ground. Also vegetation especially thick vegetation slow down the speed of surface run- off to allow water to infiltrate the ground.
5. Level of saturation of the ground: where the soil is dry pore spaces becomes wide enough to allow water to infiltrate and percolate into the ground to form ground water. In saturated soil pore spaces (air spaces) are filled with water thus water seepage is limited and thus surface run –off is dominating.
6. Evapo-transpiration: where there is high rate of evapo-transpiration soil becomes dry and airspaces become wide open enough to allow easy infiltration and percolation of water into the ground. On the other hand excessive evapo-transpiration reduces amount of ground water and lower the water table.

WATER TABLE.
Refers to the level of ground water bellow which all available space is filled with water. Water infiltrate the ground then percolate further down ward until it reaches a layer of impermeable rock where it saturates all available pore spaces to form saturated zone.
The upper limit of the saturated zone is called water table.
The level of saturation fluctuates depending on seasons of the year.


Underground saturation zones:
There are three main underground saturation zones which are:

• Zone of permanent saturation/phreatic zone: it is the zone where by all pore spaces are filled with water permanently.
• Zone of intermittent saturation: it is a zone where during wet season (rain season) the zone becomes saturated while during dry seasons the zone becomes dry. i.e it is a zone where water fluctuates seasonally.
• Zone of non-saturation: it is a permeable rock layer found immediately below the surface where water passes to the other zones without remaining to saturate the pores.

Both the zones of intermittent and zone of non saturation are called vadose zone or zone of aeration.
Permeable rock layer underlain by an impermeable rock layer and which is permanently saturated with water is called an Aquifer.
Presence of ground water results into the formation of springs, wells and artesian basins.
SPRINGS
A spring is a point or place where underground water flows out naturally onto the land surface. They occur where water table has been exposed onto the surface.
Some springs are temporary while others are permanent and are the source of some rivers.
Ways in which springs occurs:

1. A spring can occur where permeable rock overlies impermeable rock and where water table is exposed onto the surface at the hillside.
2. Spring can occur at the foot of the scarp slope or dip slope of cuesta. if spring occurs at the scarp slope it is called scarp slope spring while if it occurs at dip slope it is called dip slope spring.
3. A spring can also occur along a fault where permeable rock layer has been brought against an impermeable rock layer. Such spring is called fault spring.
4. A spring can occur in a well jointed rock where water infiltrate and percolate through rock joints and later came to be exposed and flow onto the surface through other rock joints. Such  springs are called rock jointed springs
5. A spring may occur in area where an aquifer lies on the upper part of outcropped dyke. Water flow out onto the surface to form a spring called dyke spring.
6. A spring may occur where limestone escarpment is underlain by an impermeable layer; a spring may form at the foot as water table meets the surface causing water to oozes out as spring.

Wells and boreholes:
They are deep holes dug in the ground often with the purpose of getting water. A well can be permanent if it has been sunk deep bellow to a zone of permanent water saturation. And it can be temporary if it as been sunk to a zone of intermittent saturation.
ARTESIAN BASIN
Artesian basin is a saucer-shaped like depression which consists of a layer of permeable rock that is sandwiched between two layers of impermeable rock. It forms broad syncline with either ends or one end of the permeable rock exposed onto the surface.
Rain water enters artesian basin through exposed ends of permeable rock layer and saturate to for aquifer.
Artesian well: it is a well which has been sunk into an aquifer of artesian basin where water comes onto the surface due to hydraulic pressure.
Necessary conditions for the formation of artesian wells.

• The permeable rock layer(aquifer) must be enclosed between two layer of impermeable rock.
• Either one or both sides of the aquifer must be outcropped in region which is a source of water.
• The mouth of artesian well must be lower than the intake area. This allows the water to be forced to the surface by pressure.
• The aquifer must dip from the region of water intake and the rock layers must form a broad syncline or basin.

Significance of groundwater:

1. Source of rivers: some rivers originates from natural springs which are consequence of ground water.
2. Source of water: ground water provide water for industrial activities.
3. Agriculture
4. Settlement
5. Provision of hot water
6. Tourist attraction
7. Source of minerals.