With the steady increase in global population and continued mismanagement of water usage, many of the world's water reserves have reached critical condition.
The Middle East, the American Southwest, and Southern Asia have all seen gross overuse of its water resources which has led to a dramatic decrease in groundwater supply.
Read our relate article: Water Conflicts: Looking at our World from Past to Future
Unlike surface water, groundwater volume is quite difficult to estimate. And since groundwater supply isn't naturally recharged as quickly as surface water, it is unfortunately common for aquifers to be depleted in areas of excessive pumping.
Many water initiatives understand the sensitivity of the groundwater situation and are advocating for better management of the world's aquifers. Supplementing water supply using artificial and natural methods provides a cost-effective means of boosting ground water availability.
In this article, we will give an overview of how groundwater works in relation to nature's hydrologic cycle, we'll discuss the causes and effects of groundwater depletion, and finally, we'll discuss the importance of implementing artificial groundwater recharge projects.
In this article, we'll cover:
- How the groundwater gets naturally recharged through the hydrologic cycle
- The major causes of groundwater depletion
- How artificial groundwater recharge can help counter groundwater depletion
Groundwater Recharge and the Hydrologic Cycle
A greater amount of water still lies beneath the earth's surface in aquifers –layers of porous rock which groundwater freely flows through.
These aquifers exist at different depths throughout the earths crust, but most of them are far to deep to be accessed safely and effectively.
The level at which the water in these aquifers rests is known as the water table. The higher the water table, the easier it is to access. The lower the water table, the more difficult and more indicative of depletion.
There are many topographical, meteorological, geological, and human factors which affect the availability of water in these aquifers. Rocks have different permeability and porosity and therefore hold water at different capacities. The process of refilling the aquifers is known as recharging and can happen both naturally and artificially.
How Does the Natural Groundwater Recharging Process Work?
Groundwater is recharged naturally by precipitation, ice, and snow melt. Through the hydrologic cycle, nature goes through a unique process to resupply the earth's groundwater.
When the earth's surface water is vaporized into the atmosphere through evaporation, it condenses in the atmosphere and falls back to the earth as rain and snow. It then sips through the soil and get enclosed in aquifers as groundwater. A minimal amount of surface water from lakes and rivers can also contribute to the groundwater recharging process (USGS).
Groundwater recharge is impeded by human activity such as industrial development and paving. These activities result in the loss of top soil permeability, and instead, increase the likelihood that the water remains on the surface. Using groundwater for agricultural activities such as irrigation lowers the water table as well.
Protecting the natural groundwater recharging process is a good initiative to ensure groundwater sustainability since the volume of water pumped from aquifers should always be lower or equal to the volume recharged.
What is Groundwater Depletion?
Groundwater depletion is simply the act of gathering or "depleting" the groundwater supply by pumping it to the surface. It becomes a serious concern when the rate at which groundwater is being depleted surpasses the rate at which it can be replenished. Because groundwater supply is difficult to measure, the amount of available water for any given region can be easily miscalculated. Overuse is unfortunately all too common.
Even though the 70% of the earth's surface is covered in water, almost all of it is undrinkable saltwater. Most of the freshwater that is consumable by humans exists as groundwater in aquifers beneath the surface. Because groundwater remains one of the primary sources of potable water on earth, protecting its supply is of vital importance.
Major Causes of Groundwater Depletion
There is a finite amount of water that circulates through the earth's hydrologic cycle – continuously being evaporated, precipitated, soaked through the earth into groundwater, over and over again. In theory, because of this continuous cycle, the earth needn't worry about the amount of available water since it will always be returned at some point. Issues arise when this hydrologic cycle is disrupted as we'll see with the following reasons given.
The primary cause of groundwater depletion is excessive and continuous pumping of underground water reserves. Groundwater is naturally recharged by the hydrologic cycle as rain seeps through the soil, "recharging" the groundwater. But when the water is depleted at a rate that is faster than it can be recharged naturally it is considered, "water-stressed." The world pumps about 30 billion gallons of water per day (Barlow and Clarke, 2005).
It is much less labor-intensive and more cost-efficient to harvest water from surface-water sources such as lakes, rivers, and springs as opposed to pumping from underground. However, when surface water becomes polluted with chemical waste and other contaminants, other means of retrieving potable water must be sought – usually groundwater. Surface water pollution is one of the major reasons for excessive groundwater depletion. Furthermore, when water is polluted with chemicals, it can essentially become unfit to contribute to the hydrologic cycle – unable to be absorbed back into the earth and therefore taking away from the groundwater recharge quota.
Due to overgrazing, changes in climate, and in some cases, paving and industrial contact, soil erosion has become an ongoing problem. The earth's surface is hardened to the point where rainwater can no longer replenish the groundwater beneath it.
Excessive Dam Building
While dams certainly are helpful in providing water and energy to a specific region, having too many dams can disrupt the hydrologic cycle by preventing water from flowing to areas where it would otherwise naturally reach. This leads to the withholding of water and nutrients to certain areas, creating deserts, eroded soil, and unreplenished groundwater.
Read our relate article: How Much Water on Earth is Drinkable and Why Do We Care?
Effects of Groundwater Depletion
Drought and Famine
When water supplies are threatened, communities face the risk of drought and famine. Large aquifers are often used as irrigation and agricultural resources which directly affect the food supply. An example of this is the Ogallala River Basin beneath the Great Plains of the United States, which has seen mass depletion as a result of over use. If the aquifer isn't replenished more quickly than it is being depleted, it will cause major problems for the inhabitants of the region in future (Conserve Energy Future).
Groundwater depletion will cause surface water to become shallow. Because groundwater flows into freshwater bodies and underlays seas and oceans, a shortage of groundwater will also reduce surface water drastically and in turn affect aquatic life and the ecosystem at large.
Though we categorize our water sources by name – groundwater, seawater, surface water – there technically are no barriers which separate these bodies; they flow freely into each other. Groundwater flows into rivers and rivers flow into the ocean. If groundwater is depleted excessively, there is potential for the less occupied aquifers to get contaminated with seawater. This can eventually lead to higher prices of drinking water due to higher purification costs.
According to the USGS, groundwater pumping has a direct connection to the appearance of sinkholes on the surface of the earth. As groundwater is pumped, the negative pressure and excess movement of water causes unnatural disruption in the porous rock, allowing for instability in the rock formation and ultimately collapse.
Even Greater Depths
Groundwater depletion will require us to go deeper into the earth in order to find water, which will require more resources and sophisticated equipment.
The Gravity of the Situation
Groundwater depletion has become a regular discussion among geographers, hydrologists and earth scientists. If we don’t understand the consequences surrounding this, we could easily use up more water than required and the effects can be more catastrophic than merely drought alone.
Artificial Groundwater Recharge
Natural recharge is very slow and cannot satisfy the water needs of the teeming population. Humans can help by purposefully injecting water into aquifers.
What is Artificial Groundwater Recharge and How Does it Work?
Artificial recharge is the process of helping the natural recharge process by guiding water back into aquifers under controlled conditions using special recharging wells. Canals and irrigation furrows can be used to assist the water's natural flow back into the ground. Water can also be pumped from a dewatering system into a recharge location and then injected back into the ground. The water is purified before injection to prevent clogging of aquifers.
Direct Surface Recharge Technique
This is a process by which excess water is collated and passed into a lake or shallow water body while it naturally sips into the earth. The effectiveness of this method is dependent on the porosity and permeability of the underlying rocks which the water is passed unto (University of Pisa).
Direct Subsurface Recharge Technique
Like the name implies, this is a process where water is injected beneath the earth crust. This is also referred to as direct injection because water is passed into very deep aquifers. Water treatment is advised as there is less natural purification with this method. The draw back to this method is the cost of drilling and piping systems for such great depths. Filtration costs should also to be considered (Hydrology and Earth Systems Sciences, 2013).
Advantages of Artificial Groundwater Recharge
- The technology is well understood by experts and the general populace.
- Construction of wells is often done in rocky areas. It will require less strengthening materials like rods, stones, etc.
- Artificial groundwater recharge ensures there is water all-year-round for agricultural purposes.
- Aquifer water can be improved by injecting high quality water.
- Recharge systems are relatively easy to operate.
- Controlling surface water runoff for water recharge reduces sedimentation in most water basins.
Aquifer Storage and Recovery (ASR)
Aquifer Storage and Recovery (ASR) is a process that replenishes ground water in specific aquifers with the purpose of accessing it at a later time. They are usually done on a smaller scale than most Artificial Groundwater Recharge operations, and focus on smaller, enclosed aquifers.
Objectives of ASR projects
- To store excess water when it is available.
- To recover stored water and make it available for use during dry periods
Criticisms of Artificial Groundwater Recharge
- Lack of financial backing and appropriate laws to put land owners in check on the management of drainage wells will lead to break down of the wells. This will further lead to contamination of ground water and clogging of aquifers.
- Aquifers can degrade if injected water is not controlled.
- Ground water recharge technology might not be as beneficial when small volumes of water are involved. Efficiency is key.
- Even though it’s an easy process to understand, adequate knowledge on hydrology is required for a large-scale process.
- Construction of dams, water pathways and facilities may cause damage to the environment.
Ground water depletion and recharging are very vital issues to our ecosystem. Adequate funding should be granted to support research and implementation of related projects. Looking forward, questions on flood water, ground water contamination, and chemical reactions between aquifer water and recharge water are issues that should be studied critically.
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Barlow, M., & Clarke, T. (2005). Blue gold: The fight to stop the corporate theft of the world's water. New York, NY: New Press.
Conserve Energy Future. (2016, December 25). Causes, Effects and Solutions of Groundwater Depletion. Retrieved from https://www.conserve-energy-future.com/causes-effects-solutions-of-groundwater-depletion.php
FEMA. (n.d.). Aquifer storage and recovery. Retrieved from https://www.fema.gov/media-library-data/1487160966426-3e774ec4315295499f45a25bc8915c90/ASR_Fact_Sheet_Feb2017_COMPLIANT.pdf
Hydrology and Earth System Sciences. (2013). Natural vs. artificial groundwater recharge, quantification through inverse modeling. Retrieved from https://www.hydrol-earth-syst-sci.net/17/637/2013/hess-17-637-2013.pdf
United Nations Environment Programme. (n.d.). Artificial recharge of groundwater. Retrieved from http://www.unep.or.jp/ietc/publications/techpublications/techpub-8e/artificial.asp
University of Pisa. (n.d.). Artificial groundwater recharge. Retrieved from http://www.eolss.net/sample-chapters/c07/e2-09-06-06.pdf
USGS - U.S. Geological Survey Office of Groundwater. (2017, December 18). USGS Groundwater Information: Artificial Recharge. Retrieved from https://water.usgs.gov/ogw/artificial_recharge.html
USGS. (2016, December 15). Groundwater Storage. Retrieved from https://water.usgs.gov/edu/watercyclegwstorage.html
Water for All. (n.d.). Depletion and Artificial Recharge. Retrieved from http://12.000.scripts.mit.edu/mission2017/depletion-and-artificial-recharge/
Water in the West. (2014, July 31). Understanding California's Groundwater. Retrieved from http://waterinthewest.stanford.edu/groundwater/recharge/