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 a porous medium is slow (ranging from few centimeters to meters per day)

Porosity of Geological Material

1. Porosity is a parameter that 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 the rock
2. Permeability is a parameter that describes the ability of geologic material to transmit water
3. Geologic materials which can transmit large quantities of water are highly permeable and called aquifers

Examples of geologic materials which are typically aquifers are

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

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

Examples of geologic materials which are typically aquitards are:

• Clay and silt alluvium
• Shale and siltstone

Water in the Ground

Water in the ground refers to the presence of water within the Earth's subsurface, below the land surface. It exists in various forms and zones, including the unsaturated zone, saturated zone, water table, capillary fringe, and different types of aquifers.

Unsaturated Zone

The unsaturated zone, also known as the vadose zone or zone of aeration, is the region above the water table where the soil and rock contain both air and water but are not fully saturated. The pore spaces in the unsaturated zone are filled with a combination of air and water, with the water content decreasing as you move upward from the water table.

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

Saturated Zone

The saturated zone is the region below the water table where the soil or rock is fully saturated with water. In this zone, the pore spaces are completely filled with water, and the water pressure is greater than the atmospheric pressure. Groundwater flows within the saturated zone, and wells are typically drilled into this zone to extract water.

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

Water Table

The water table is the boundary between the unsaturated zone and the saturated zone. It represents the upper level of the groundwater in the subsurface. The position of the water table can vary depending on factors such as precipitation, evaporation, groundwater pumping, and geological characteristics of the area.

• The interface between unsaturated and saturated zone in unconfined aquifers

Capillary Fringe

The capillary fringe, also known as the zone of capillary rise, is the region above the water table where groundwater is drawn upward by capillary action. In this zone, the water is held against the pull of gravity due to the capillary forces within the small spaces between soil particles or rock fractures. The capillary fringe typically extends a short distance above the water table.

• The zone above the water table where capillary forces pull water upward into pore spaces
• The same effect is seen with water in straws

UNCONFINED AQUIFERS

Unconfined aquifers are groundwater reservoirs where the water is not confined by impermeable layers above or below. Water can freely flow into or out of unconfined aquifers through the upper surface, and the water table can rise to the land surface. The recharge to unconfined aquifers primarily occurs through direct infiltration of precipitation or surface water.

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

CONFINED AQUIFERS

Confined aquifers, also known as artesian aquifers, are groundwater reservoirs that are confined between two impermeable layers, such as clay or rock formations. These impermeable layers restrict the movement of water in or out of the aquifer. When a well is drilled into a confined aquifer, the water may rise above the top of the aquifer under its own pressure due to the confined conditions.

1. The aquifer is sandwiched between 2 layers of impermeable or impervious material
2. Water flows into the aquifer from an area at the surface where the 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.