Groundwater is an essential aspect of the water cycle, and is vitally important to pretty much all life on Earth.
It is defined as the water present below the surface of the Earth, in soil and rock pore spaces, and the space in fractured rock formations.
Groundwater is replenished in two ways, via direct or in-lieu recharge.
In this article, we’ll be discussing how groundwater is replenished in greater detail, along with how this process fits into the wider hydrologic cycle.
How Is Groundwater Replenished?
The water that is present beneath the surface of the Earth is held there by geological formations known as aquifers.
This water moves very slowly through the aquifers to an area known as the saturated zone.
If you imagine taking a side on view of a piece of land, the areas you would see are defined as:
- Land Surface
- Unsaturated Zone
- Water Table
- Saturated Zone
As mentioned above, there are two ways in which groundwater is replenished.
Within the hydrological cycle (we discuss this in further detail further down) replenishment of groundwater happens naturally when rain, storm water, and flow from rivers/streams seeps into the ground and is caught by aquifers.
Agricultural processes, like irrigating fields and orchards also allow water to seem into the ground.
In the context of groundwater management (our interaction with groundwater), replenishment happens at faster rates than natural conditions allow.
This is a good thing as it means that groundwater levels are maintained or even improved faster.
In groundwater management, there are two recharging methods used: aquifer injection and direct spreading.
Aquifer injection is the use of ponds/infiltration basins or injection wells.
These aquifer injections are typically sourced from either flood water or treated wastewater.
In-lieu recharge works slightly differently.
In this recharging method, an alternative source of water is used. By leaving the groundwater alone you will be able to use it at a later date, and even give it the potential to recover.
Do We Depend On Groundwater?
The short answer is, yes, we depend on groundwater to a great extent.
The condition and replenishment of groundwater both have far-reaching consequences if disrupted.
51% of the total population of the US rely on groundwater for their drinking water. This is a huge amount of people. On top of that 99% of the rural population of the US relies on groundwater.
In terms of agriculture, groundwater is absolutely essential for growing crops and feeding live stock.
64% of all groundwater is used as part of the irrigation system used to grow crops.
It’s also an essential part of numerous industrial processes.
Groundwater also feeds into lakes, rivers, and wetlands.
The Hydrological Cycle
The Hydrologic cycle refers to the fact that water is in constant motion. Water circulates through this cycle all the time, and has been doing so since the earth was formed.
The Groundwater state in this cycle is an important part of the process.
We’ve outlined the cycle in very simple terms below:
Water on the surface evaporates – this water vapor condenses to form clouds – the water then falls back to the surface as rain, sleet, snow, or hail (depending on temperature) – at this point the water either stays on the surface or flows to a body of water, or seeps into the ground and becomes groundwater.
Are There Potential Threats To Groundwater?
Yes, there are potential threats to both groundwater quality and elevation levels.
Some of these threats are naturally occurring, but the vast majority of them are a direct result of human activity.
As we rely heavily on groundwater, it’s vital that we prevent as much damage to it as possible.
Below is an outline of some main threats to groundwater.
Nitrates are, in basic terms, naturally occurring chemical compounds present in drinking water supplies.
They are harmless in small quantities, but high levels of these compounds can be harmful to humans and wildlife.
These compounds get into the water supply via several sources. The most common way is from fertilizer run off. They can also infiltrate the water through leaking septic tanks, improperly disposed sewage, and industrial waste to name a few.
Personal Care Products/Pharmaceuticals
Whilst the potential long term effects of PPCP (Pharmaceuticals and Personal Care Products) levels in our water supply is still being investigated, there are some signs that they could damage groundwater supplies.
PPCPs are defined as a variety of chemicals. They are grouped as follows:
- Dietary Supplements
- Human and Veterinary Drugs
- Cleaning/Laundry Products
- Cosmetics and Sunscreen
A 2002 study from the U.S. Geological Survey found that, in 139 streams in 30 states, there were minute traces of PPCPs in 80% of these streams.
In areas of the world where surface water supplies are limited, water needs can only be met by pumping it up from beneath the surface.
Overuse of groundwater supplies is down to a mishandling of the resource and can lead to groundwater depletion.
Groundwater depletion can have extreme long term effects, some of these effects include:
- Lowering The Water Table
- Drop In Water Quality
- Increased Cost Of Water Supply
Generally speaking, groundwater is replenished in two main ways: naturally or through human intervention.
Under natural conditions, groundwater is recharged via water seeping through the surface of the earth, from the unsaturated zone to the saturated zone. The saturated zone contains the water table and aquifers holding the groundwater.
Humans are able to manage and restore groundwater levels in a number of ways.
The two main ways are known as aquifer injection and direct spreading. Using either of these methods usually means that groundwater levels can replenish faster than they would under natural conditions.
Not only is groundwater conservation essential to the water cycle , it is a vital part of all human life.