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examBoard: Cambridge
examType: IGCSE
lessonTitle: Aquifers and Wells
Beneath our feet lies a hidden water world that supplies drinking water to nearly half the world's population. These underground water sources, called aquifers, are vital but often overlooked parts of the water cycle. In many regions, they're the main source of freshwater for drinking, farming and industry.
Key Definitions:
Did you know that about 30% of Earth's freshwater is groundwater? That's 100 times more than all the rivers and lakes combined! This hidden resource is stored in aquifers - underground layers of rock, sand, or gravel that are saturated with water. Think of aquifers like natural underground sponges that hold water in tiny spaces between particles.
Aquifers form when water from rainfall, snowmelt, or surface water bodies seeps down through soil and rock layers in a process called infiltration. This water continues moving downward until it reaches an impermeable layer that it cannot pass through. The water then collects above this layer, filling all the available pore spaces in the permeable material.
There are two main types of aquifers, each with distinct characteristics that affect how water moves through them and how we can access this water.
These are also called "water table aquifers" because their upper boundary is the water table itself. Key features include:
These are sandwiched between impermeable layers (called aquitards) that restrict water movement. Key features include:
Wells are structures that allow us to access the water stored in aquifers. They've been used for thousands of years, from simple hand-dug wells to today's sophisticated drilling operations.
The oldest type of well, created by digging a hole by hand until reaching the water table. Usually shallow (less than 15m deep) and lined with brick, stone, or concrete to prevent collapse. These are still common in many developing countries.
Created by driving a small-diameter pipe into soft earth. These are relatively shallow (up to 30m) and work best in areas with loose soil and a high water table. They're quicker and cheaper to install than dug wells.
Modern wells created using drilling machines that can reach hundreds of metres deep. These can access deeper aquifers and are lined with casing to prevent collapse and contamination. They typically use electric pumps to bring water to the surface.
A well creates an artificial opening that allows groundwater to flow from the aquifer into the well. When water is pumped out, it creates a pressure difference that causes more water to flow toward the well. This creates a cone-shaped depression in the water table around the well, known as a "cone of depression."
In some special cases, wells can produce water without pumping. These "artesian wells" occur when a well taps into a confined aquifer where the water is under pressure. If the pressure is high enough, water will naturally flow to the surface without pumping - sometimes creating natural fountains! The term comes from Artois, France, where such wells were first described in the Middle Ages.
Aquifers face significant challenges today, including overextraction, pollution and climate change impacts. Sustainable management is essential to ensure these vital resources remain available for future generations.
The Ogallala Aquifer is one of the world's largest aquifers, stretching beneath eight US states. It supplies about 30% of all groundwater used for irrigation in the United States and supports $20 billion in agriculture annually. However, it's being depleted at an alarming rate - in some areas, water levels have dropped by more than 30 metres since pumping began in the 1950s.
The problem? The aquifer recharges extremely slowly (less than 25mm per year in most areas), while extraction happens much faster. Some estimates suggest parts of the aquifer could be depleted within 25 years. Farmers are now adopting water-saving irrigation techniques and some areas have implemented pumping restrictions to extend the aquifer's life.
While wells provide essential water supplies, excessive extraction can cause serious environmental problems:
When water is removed from aquifers, the ground can actually sink! This happens because water helps support the weight of overlying rocks and soil. When it's removed, the ground compacts. In extreme cases, this can damage buildings, roads and other infrastructure. Mexico City has sunk more than 9 metres in some areas due to groundwater extraction.
In coastal areas, overpumping freshwater aquifers can allow saltwater from the ocean to move inland and contaminate the aquifer. Once saltwater intrusion occurs, it's very difficult and expensive to reverse. This is happening in coastal regions worldwide, from California to Bangladesh.
Once an aquifer becomes contaminated, it can remain polluted for decades or even centuries. Common sources of groundwater pollution include:
Protection measures include:
Australia, one of the driest inhabited continents, has pioneered techniques to artificially recharge aquifers. In Adelaide, during wet winter months, excess treated stormwater and reclaimed wastewater is pumped into aquifers for storage. This water is then recovered during dry summer months when demand is high. This approach helps prevent saltwater intrusion, provides water storage without evaporation losses and helps maintain groundwater levels. The system now provides about 20% of Adelaide's water supply and has become a model for similar projects worldwide.
As climate change alters rainfall patterns and population growth increases water demand, sustainable management of aquifers becomes even more critical. New technologies like remote sensing, improved drilling techniques and better understanding of groundwater systems are helping us manage these resources more effectively. However, the most important factor remains human decisions about how we use and protect these vital underground reservoirs.
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