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HYDROGEOLOGY: Groundwater, Types, Factors Affecting Groundwater Distribution

Groundwater Measurement Hydrogeology
Groundwater Measurement Hydrogeology [CREDIT: Pixabay]

Last Updated on February 13, 2023 by Okoro Daniel O.

What Is Hydrogeology

Hydrogeology (or Hydrology) is the aspect of Geology that studies about water. It studies water in the air, ground, chemical composition, and how it evolves. Hydrology can also be defined as the study of the distribution and movement of water both on and below the Earth’s surface, as well as the impact of human activity on water availability and conditions. 5 – 8. Biology, Ecology, Chemistry, Conservation, Earth Science, Oceanography.
There are two types of water (H2O); Groundwater, and Surface water.


Groundwater is the water that occurs in the SATURATED ZONE. It is found in the voids, pore fractures, and crevices of rocks. The distribution of groundwater is with respect to the percentage of the void to a given rock material.
Naturally, groundwater is held under the hydrostatic pressure and can be distributed to streams, wells, and rivers.


The vertical distribution of groundwater is a vertical profile which sows the categories of groundwater from the surface of the earth into the earth interior. Basically, the vertical profile can be classified into two (2).

  1. Saturated Zone. And;
  2. Unsaturated Zone.
Vertical Distribution of Groundwater
Vertical Distribution of Groundwater [CREDIT:]


Saturated zone is the zone in which the pores and the void are completely filled with water. It extends from the water table down beneath the earth up to the aquifer region. The saturated zone is the source of supply to groundwater aquifers.


The unsaturated zone is also referred to as ZONE OF AERATION. This is the zone where the void or the pore spaces are partially filled with air water. They are sometimes called VARDOSE.
The unsaturated zone is divided into three (3), they are:

  1. Intermediate vardose zone.
  2. Capillary zone.
  3. Surface water zone.

SURFACE WATER ZONE: (also known as Soil Water Zone) is the part of unsaturated zone that begins from the surface of the earth. In the soil (surface) water zone, the water is held under capillary pressure and they drain under gravity.

INTERMEDIATE VARDOSE ZONE: It occurs from the top of the capillary zone and extends to the bottom of the soil water zone. In this zone, greater part of the void is filled with air.

CAPILLARY ZONE: Is the zone where the water is held under hydrostatic pressure. They occur from the top of the water table and extend to intermediate vardose.

Earth Water
Earth Water [CREDIT:]


There are lot of factors that affect groundwater distribution, however, two basic factors are important;

  • Porosity
  • Permeability
Vertical Distribution of Groundwater
Vertical Distribution of Groundwater [CREDIT:]


Porosity is the amount of pores or pore space in a given geologic rock material. The pores are inherent during the period or stage of formation of the rock.
Porosity can also be defined as the measure of the ability of rock to hold or retain water.

Mathematically, it can be expressed as a percentage (%);
P = W/V × 100%

P is Bulk Porosity
W is Volume of void
V is Total volume of rock.

Porosity can be described/categorized into three (3), they are;

  1. Primary Porosity.
  2. Secondary Porosity. And;
  3. Effective Porosity. (Divided into; Inter-granular, and intra-granular).

PRIMARY POROSITY: Is the inherent porosity that is acquired at the time of formation of the rock.

SECONDARY POROSITY: Is the type that is acquired by the rock when it has undergone process of tectonics.

EFFECTIVE POROSITY: Is the net porosity in a rock. This has to do with inter-connectivity of the pores.

INTRA-GRANULAR POROSITY: Is the porosity that is inherent in a particular grain.

INTER-GRANULAR POROSITY: is the porosity that occur between grains as inherent in a rock material.


This is the ability or potential or capacity of a rock material to transmit water from one point to another. Permeability measures the relative ease of fluid flow. Permeable rocks allow water to flow through them. Most sedimentary rocks such as sandstone, and limestone are highly permeable, while, shale (also “sedimentary”) is impermeable. Other hand rocks like granite, schist are said to be impermeable. It is also worthy of note that FRACTURED ROCKS are mostly PERMEABLE.

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