Groundwater Occurrence and Types of Ground Water

Water is an essential requirements for all forms of the life and is considered as integral part of the living organisms life. GOD has gifted our universe with bulk amount of this valuable substance in different forms such as

1. Rivers
2. Lakes
3. Natural springs
4. Rain
5. Snow
6. Glaciers
7. Aquifers etc

During the early era apart from drinking purpose water was usually used for general usage such as agriculture, washing clothes, pots etc but With the passage of time the use of water get increased and human being started using it in different fields such as:

1. Industries
2. Preparation of food stuff
3. Medicines
4. Steam engines
5. Vehicles
6. Paper industries and so on

About 70% portion of our planet earth is consists of water while the rest 30% is consists of dry land. Apart from such a big amount of water there is also massive amount of underground water reservoirs but the main difficulty in using of this water is the difficulty to access it. Due to vast advancement of science and technology the demand for water is also increased to very high level then before it was and causing the demand for underground water usage.

The ground water reservoirs are much more pure and safe the usual water resources available at the earth's surface. Ground water constitute an integral part of the human's life and now time demands to bring it to use so that we can fulfill our fast growing demand of water. Following are the different types of ground water reservoirs and the their details.

Subsurface Water Occurrence

Underground rivers occur only rarely in cavernous limestone. Most groundwater occurs in small pore spaces within rock and alluvium(unconsolidated sediment)

1. Groundwater accumulates over impervious material
2. Water flow through porous medium is slow (range from few centimeters to meters per day)

Porosity of Geological Material

1. Porosity is a parameter which describes the amount of open space in geologic material
2. Porosity can be stated as a fractional value (0.30) or percentage (30%) of open space (i.e. 30% of volume in the material is open space)
3. Open pore spaces occur between sediment grains
4. Open pore spaces occur in cracks or fractures in rocks
5. Open pore spaces occur in cavernous openings formed by dissolution of rock (limestone)
6. Porosity values range from 0 to 50% typically
7. Open pores can be filled with water or air or a mixture of both

Permeability of Geological Material

1. Rocks may have a high porosity but if the pore spaces are not connected, water cannot flow through rock
2. Permeability is a parameter which describes the ability of geologic material to transmit water
3. Geologic material which can transmit large quantities of water are highly permeable and called aquifers

Examples of geologic material which are typically aquifers are

1. Sand and gravel alluvium
2. Sandstone
3. Cavernous and/or fractured limestone

Geologic material which cannot transmit significant quantities of water are impermeable and called aquitards.

Examples of geologic material which are typically aquitards are:

• Clay and silt alluvium
• Shale and siltstone

Water in the Ground

Unsaturated Zone

• region of subsurface from ground surface to the water table
• Pores are partially filled with water
• Unfilled pore space contains air

Saturated Zone

• Region of subsurface in which pore spaces are saturated (completely filled) with water

Water Table

• Interface between unsaturated and saturated zone in unconfined aquifers

Capillary Fringe

• Zone above the water table where capillary forces pull water upward into pore spaces
• Same effect seen with water in straws

UNCONFINED AQUIFERS

• Water accumulates over an impermeable or impervious surface
• Water table can freely rise to land surface

CONFINED AQUIFERS

1. Aquifer is sandwiched between 2 layers of impermeable or impervious material
2. Water flows into aquifer from an area at surface where upper impermeable layer (confining layer) is absent
3. Groundwater in confined aquifers is under pressure
4. Wells can be drilled through the upper confining layer
5. Pressurized water will rise within the well
6. Water levels are called piezometric water level
7. Wells are called artesian wells
8. Where water levels rise above the ground surface, water freely flows out of the well (flowing artesian well)

References

1. http:// www.geology.sdsu
2. Earth Geology and its exploration.
3. Design of Small hydropower projects.