Groundwater is not in underground lakes, nor is it water flowing in underground rivers. It is simply water that fills pores or cracks in subsurface rocks. When rain falls or snow melts on the surface of the ground, some water may run off into lower land areas or lakes and streams. What is left may be absorbed by the soil, seep into deeper layers of soil and rock, or evaporate into the atmosphere.
Below the topsoil—the rich upper layer of soil in which plants have most of their roots—is an area called the unsaturated zone. In times of adequate rainfall the small spaces between rocks and grains of soil in the unsaturated zone contain at least some water, whereas the larger spaces contain mostly air.
After a major rain, however, all the open spaces may fill with water temporarily. During a drought, the area may become drained and almost completely dry, although a certain amount of water is held in the soil and rocks by molecular attraction.
Groundwater is the largest source of usable, fresh water in the world. In many parts of the world, especially where surface water supplies are not available, domestic, agricultural, and industrial water needs can only be met by using the water beneath the ground.
The World Economic Forum ranks water crises as the world’s third greatest risk by impact and extreme weather the top risk by likelihood. Aquifer depletion in agricultural regions could threaten nearly half the world’s food sources and deny 1.8 billion people reliable access to water by 2050.
Causes for depletion of groundwater
The bursting population is a reason for insufficient water per head. While it has been estimated that the amount of usable water should be between 700-1200 billion cubic meters, India has only 1000 cubic meters of water per head.
Water in most rivers is polluted, making it unfit for drinking or any other use. The poor quality rises from insufficient and delayed investment in urban water-treatment facilities. Industrial effluent rules are not implemented due to inadequate technical and human resource availability with the state pollution control boards.
Excess extraction by farmers has led to the dwindling groundwater supplies. This is so because access to groundwater is free and anyone has a right to pump water from their own land.
Poor monsoon due to climate change has further aggravated the groundwater situation since the latter heavily depends on rains. Poor rainfall compels the farmers to dig further down for groundwater to irrigate the field. This results in pushing the tables deeper down.
Unrestrained urbanization has contributed in a big way and despite India being one of the richest nations in water supply, the government and citizens have exploited the water reserves.
Quality of groundwater is another issue, especially where it is used for human consumption. A number of factors contaminate the groundwater like sewage, run off from landfills, use of pesticides and fertilizers etc.
Depleting groundwater has posed such a threat that cities are now compelled to look for alternate supplies either because of polluted groundwater or that it will cease to exist very soon.
Effects of groundwater depletion
Groundwater depletion will force us to pump water from deeper within the Earth. The more we extract groundwater right below the Earth’s surface, the further down we have to go in order to get more. As we have to extract water from deeper within the Earth, we find that there is less water available.
A groundwater shortage keeps additional water from flowing into lakes, rivers and seas. This means that over time, less water will enter as the existing surface water continues to evaporate. As the water becomes less deep, it will affect everything in that particular region, including fish and wildlife.
Groundwater that is deep within the ground often intermingles with saltwater that we shouldn’t drink. When freshwater mixes with saltwater, it is called saltwater contamination. This sort of contamination would raise the prices of drinking water for everyone because it will cost much more to pump and filter.
Aquifers collect groundwater and are extremely important. Wildlife, marine animals, and agriculture continue to suffer as the water table lowers and creates sinkholes that destroy buildings and homes.
Solutions to prevent groundwater depletion
As aquifers and other groundwater sources are depleted at a rate greater than the recharge rate, artificial recharge is needed to maintain a lasting water supply to prevent complete withdrawal of groundwater in the near future. To combat overpumping of groundwater and achieve stability in the water table, artificial recharge is another water source that will help alleviate the stress on groundwater supply. For arid climates with little precipitation, recharging groundwater can be achieved through using treated wastewater, natural runoff, and runoff from irrigation. Soil-aquifer treatment (SAT).
The primary challenge of desalination is its high cost and energy consumption. Electricity makes up 63 per cent of the operational costs of seawater desalination plants. The plants contribute to water security but add stresses to the energy security.
Some of the other methods and techniques for groundwater recharge:
Roof Top Rain Water, runoff harvesting through Recharge Pit, Recharge Trench, Tubewell, Recharge Well. Rain Water Harvesting through Gully Plug, Contour Bund, Gabion Structure, Percolation tank, Check Dam, Cement Plug, Nala Bund, Recharge shaft, Dugwell Recharge Ground Water Dams, Subsurface Dyke.
Benefits of artificial recharge schemes
To maximise storage (long-term & seasonal), Water quality improvement through dilution.
Preventing saline-water intrusion & land subsidence. Maintaining declining groundwater levels
– NAVEED AHAMAD