Aquifers and Geologic Media

 Origin of groundwater

Total water existing on earth is 13, 84,12,0000 cubic kms, out of which 8,00,0042 cubic kms is groundwater. Apart from this, 61,234 cubic kms is in form of soil moisture. Groundwater and soil moisture together constitute the sub-surface quantity of water.
Groundwater mainly comes from three sources. They are, Meteoric Water’, which is the main source of groundwater and is received in the form of rain and snow; Connate Water also known as "sediment water," is water contained in pores and cavities of sedimentary rocks under seas and lakes. It is the second important source of groundwater.  Connate water is highly mineralized. Connate water is usually found deep down in the lower layers of the zone of saturation; Magmatic Water which converts into water after condensation of vapour as a result of volcanic action at the time of entering hot rocks. Apart from it, other sources are those in which groundwater becomes again available on the surface of the earth. They are mainly springs, wells, and geysers. 

Groundwater lie underneath most of the land surface of the Earth, in geologic media capable of storage and transmission. It's existences as had been explained in the previous post is linked to the water cycle which  is the most fundamental principle that explains the existence and occurrence of groundwater.

 Water-bearing geological units

These materials can either consist of unconsolidated deposits or consolidated rock. The void spaces within these rocks/materials makes it possible for water to be stored in them.

Unconsolidated deposits comprise materials derived from the breakdown of consolidated rocks whereas consolidated materials consist of those whose mineral grains have been joined closely by chemical reactions, heat and pressure. Voids between mineral or sediment grains and fractures are important as far as groundwater occurrence is concerned.

Geologic formations

Aquifer

This is a geologic media that can store and permit a substantial amount of water to flow through it under ordinary field conditions.

Aquiclude

This is a geological formation which permits the storage of water but is not permeable enough to allow its transmission.

Aquifuge 

This is formation neither holds nor transmits water because of its impermeable nature. Examples include Basalt, and Granite. 


Other Posts

Groundwater System

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Image Credit: Courtesy   As crucial as groundwater is, the resource is vulnerable and hence needs to be protected and managed. Groundwater is poorly understood and managed in many parts of the world despite its pivotal role in the sustenance of ecosystems and the provision of water supply. Understanding groundwater and its linkage with surface water and other members of the ecosystem is paramount to proper management of these resources. Studies have shown that some groundwater resources might have been accumulated eons ago and whereas there is increasing demand as a result of increasing population, chances are that these resources are no longer replenished. A system can be defined as a group of interrelated entities that form a unified whole. Groundwater systems can be defined as a system comprising the sub-surface water, geologic media containing the water, flow boundaries, sources, and sinks. These systems necessitate the storage and flow of groundwater within them. Groundwater syste
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Geologic Boundaries & Structures

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Geologic Structures  The structures found on the Earth make it possible to understand the dynamic nature of the Earth. It helps us know the forces that caused the upwelling and down-warping of the Earth. In a hydrogeological context, geologic boundaries and structures impact how water gets stored or flows within the Earth's surface. The development of these structures is influenced by the variation in the properties of the Earth's crust. Groundwater is usually stored in openings beneath the Earth. The openings can be in igneous, metamorphic or sedimentary environments. In hard rock domains such as igneous and metamorphic environments, geologic boundaries and structures are crucial when one is searching for groundwater resources. The proper siting of a water well in such an area will largely be determined by the correct mapping and location of these structures. Hard Rock Domains A hard rock domain is a geologic environment dominated by consolidated rocks. Such an area has metamo
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Types of Aquifers

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  Depending on the presence or absence of water table, an aquifer can either be classified as confined or unconfined. A special kind of aquifer known as leaky aquifer represents a combination of the two. A perched aquifer occurs where a groundwater body is separated from the main groundwater body by an impermeable layer of a limited extent. Unconfined aquifers These are aquifers whose upper surface of saturation zone is under the influence of the atmospheric pressure. The lower boundary is usually defined by a less permeable or impermeable layer. They are also known as  water table aquifers, free aquifers or phreatic aquifers .  Confined aquifers They are characterized by complete saturation, with the upper and lower layers being impermeable. They are not under direct influence of the atmospheric pressure since they are separated from the atmosphere by an impermeable stratum. Water in this aquifer imparts an upward hydrostatic pressure on the upper confining layer. Borewells tapping th
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