What is Aquifer? – Meaning, Types and Importance
Written by Stanley Udegbunam || Nov 29, 2020
AFRILCATE
WHAT IS AN AQUIFER?
An aquifer is a body of porous rock or sediments saturated with groundwater.
Aquifers are both permeable and porous and made of unconsolidated materials like sand, gravel, and rocks that store and transmit water.
Fractured limestone and volcanic rocks such as columnar basalts also make good aquifers.
Rocks such as granite and schist are generally poor aquifers because they have very low porosity.
However, if these rocks are highly fractured, they will make good aquifers.
The study of water movement on and beneath the earth’s surface is called hydrology and one who studies hydrology is called a hydrologist.
But there’s another field of study that focuses on aquifers. It’s called hydrogeology.
Hydrogeology is the study of water flow in aquifers and the characterization of aquifers.
A practitioner of hydrogeology is called hydrogeologist.
One major difference between a hydrologist and hydrogeologist is that:
While hydrologist studies the occurrence and movement of both surface water and groundwater, hydrogeologist is focused only on water flow and distribution of groundwater which is the water stored and transported in aquifers.
HOW IS AN AQUIFER RECHARGED?
Surface water enters the aquifer as precipitates fall on the earth’s surface and seep through the soil.
This is possible due to the porosity of the soil, causing infiltration of the water content into the soil.
The water is further pulled down between the aggregate soil particles and this gives rise to water percolation.
A permeable soil will allow for faster water percolation since the pore spaces are connected together.
The combined process of infiltration and percolation is called recharge
Some types of soils allow more water to infiltrate than others depending on the soil’s characteristics.
During recharge, water is pulled down into the earth by gravity through two zones.
The upper zone, called the zone of aeration, is where a mixture of water and air fills the pore spaces.
Below the zone of aeration is the zone of saturation, where the pore spaces are completely filled by water.
The upper boundary of the zone of saturation is known as the water table.
Aquifers are found in the area saturated with water.
As the groundwater transcends to this region, the aquifers get recharged.
Unlike surface water, groundwater can move as slow as a meter per year. This means it can take several thousands of years for underground aquifers to become replenished.
Wells are drilled into the aquifer to pump out water to the earth’s surface.
When water is pumped from a well, the water table is generally lowered into a cone of depression at the well.
Groundwater normally flows down the slope of the water table to fill the void space in the well.
Nevertheless, if water is pumped from a well faster than it is replenished, the aquifer may go dry and the water table is lowered.
In such cases, the aquifer can be recharged through a man-made process known as artificial recharge
TYPES OF AQUIFERS
There are generally two types of aquifers:
- Unconfined Aquifer
- Confined Aquifer
1. What is an Unconfined Aquifer?
An unconfined aquifer has a layer of permeable material above it.
This allows water directly above its surface to seep into the aquifer.
The shallowest aquifer at a given location is mostly unconfined.
Unconfined layer simply means that the layer is not restrictive, a surface layer that allows easy passage of water and particles.
A good example is the Biscayne Aquifer.
In some cases, an unconfined aquifer is guarded by an aquitard.
Aquitards are porous layers that retards water flow into or out of the aquifer but still don’t prevent it.
This means that water will still get into an unconfined aquifer whether it’s guarded by an aquitard or not.
The only difference is that it will take a much longer time for the aquifer to be recharged if it has a layer of aquitard above it.
Unconfined aquifers are usually recharged by rain or stream water infiltrating directly through the overlying soil.
2. What is a confined Aquifer?
A confined aquifer is overlain by impermeable rock or clay which hinders the passage of water.
Confined aquifers could also be referred to as “Artesian aquifers”.
The confining layer offer some protection from surface contamination unlike the unconfined aquifer.
AQUIFER AND THE WATER CYCLE
In this section, we’ll look out how water stored in the aquifer finds it’s way back into the atmosphere to join the water cycle.
The water cycle describes the continuous movement or circulation of water in the earth-atmosphere system.
The outflow of water from aquifers occurs naturally to springs and river beds especially in cases where the groundwater pressure is higher than the atmospheric pressure in the vicinity of the ground surface.
The water content in springs and river beds then finds its way back to the atmosphere through evaporation from the water surface.
Groundwater is one of the most important sources of fresh water on earth.
Therefore, wells are drilled into aquifers and water is extracted to the earth’s surface where it’s used for various purposes like irrigation, industrial applications and consumption.
Water is lost from the plant to the atmosphere through transpiration or from the combined surrounding through evapotranspiration as well as other phase changes.
At this point, we all can agree that the aquifers are indispensable contributors to the water cycle.
FREQUENTLY ASKED QUESTIONS ON AQUIFERS
I have compiled various frequently asked questions across the web to give you a clearer understanding of aquifers.
Without further ado, let’s get started✨
1. Is an aquifer an underground River or lake?
No. It’s just a common misconception. Groundwater seeps slowly into and out of aquifers, the process can never be fast to be compared to the flows of a river or lake.
2. What makes groundwater clean?
Aquifers acts as a natural filter for groundwater by forcing it to pass through small pores and between tight layers.
Dirt and particles are trapped as water seeps through the aquifer serving as a means of natural purification for groundwater.
3. How is an aquifer contaminated?
Aquifers are contaminated through wrongly managed man-made activities like septic tank leaks, excessive spray of pesticides and herbicides, improper lined landfills and deliberate disposal of toxic materials on the soil.
4. What aquifer type do you think is in more danger of contamination?
Unconfined aquifer is easily contaminated because it has is no restricting or confining layer.
Water seeps into unconfined aquifer easily and directly from the earth surface placing it at a higher risk for contamination.
5. Which aquifer would you want to drill into for a drinking water well?
The confined aquifer is better for drilling a drinking water well. Since confined aquifers are overlain by impermeable materials, it serves as a protective coating making it difficult to get contaminated by bacteria and dirt particles.
Unconfined layer allows easy passage of particles and water making it less suitable for drilling a drinking water well.
DO YOU KNOW?
Soil Porosity and Permeability are two different soil characteristics that affect recharge rate.
Porosity refers to the amount of empty pore spaces within a given material.
While permeability is a measure of the ease with which a fluid can move through porous rock.
DO YOU KNOW?
Soil Porosity and Permeability are two different soil characteristics that affect recharge rate.
Porosity refers to the amount of empty pore spaces within a given material.
While permeability is a measure of the ease with which a fluid can move through porous rock.
