Question 1 Describe how increase in population is responsible for the depletion of water table?
Question 2 What is meant by water table?Name the factor which raises water table?
Question 3 Name the various factors which are responsible for the depletion of water table?
Question 4 What is an aquifer?
Question 5 What is groundwater? Name the various sources of ground water?
Question 6 Describe how increasing industrial and agricultural activities are causing depletion of water table?
Question 7 Explain how deforestation is causing depletion of water table?
A large number of people draw water from wells, tube-wells (bore-wells) and hand pumps. So, wells, tube-wells and hand pumps are the sources of water. They get it from water present below the surface of earth. This is called groundwater.
If we dig a hole (or well) in the ground, we will find that after a certain depth, the soil which comes out of the hole is appreciably moist(or wet). This moisture in the dug up soil indicates the presence of water under the ground. If we dig deeper and deeper, we would reach a depth in the ground where all the spaces between the particles of soil, gaps between rocks and pores in permeable rocks are filled with water.
The upper level of water under the ground which occupies all the spaces in the soil and rocks, is called water table.
Water table represents a depth in the ground below which soil and rocks are completely filled with water. The water table varies from place to place, and it may even change at a given place.
If the water table at a place is low, we will have to dig very deep into the ground to obtain groundwater. The water table rises and falls depending upon the amount of rainwater which seeps into the ground, and on how much groundwater is drawn out (for irrigation and industry etc.).
If there is more rainfall and more rainwater seeps into ground, the water table rises. And if excessive amount of groundwater is withdrawn for irrigation and industries, then the water table falls. The water found below the water table is called groundwater. This water is held in soil and pores of permeable rocks under the ground. Thus, groundwater is not above the ground, it is deep under the ground.
The main source of groundwater is the rain. The rainwater and water from other sources such as rivers, lakes and ponds, seeps through the ground and fills the empty spaces between the soil and the rocks below the earth. The water keeps on seeping deeper and deeper into the ground through the soil and permeable rocks until it reaches an impermeable rock (hard rock).
The impermeable rock does not allow water to pass through it. So, water starts collecting above the impermeable rock and fills the soil and permeable rocks completely with water up to the level known as water table.
The underground layer of soil and permeable rocks in which water collects under the ground is called an aquifer. In aquifer, water is held between particles of soil, and in the cracks and pores of permeable rocks. An aquifer is the water-bearing layer of the earth. The top of aquifer is referred to as water table. Aquifer stores and provides groundwater. Water from the aquifer can be pumped out with the help of tube-wells and hand pumps, or drawn out through the wells. The rainwater which seeps into the ground ultimately reaches the aquifer and gets stored there.
We draw groundwater for our use with the help of wells, tube wells and hand pumps.This decreases the amount of groundwater. But when it rains, the rainwater seeps into the ground and the groundwater is recharged. If we keep on drawing more and more groundwater for various purposes than can be recharged (or refilled) by rains, then the water table will go on falling. The water table will get deeper and deeper under the ground. If this happens, then many of the wells, tube wells and hand pumps will dry up.
Depletion means reduction or lowering the amount of something. For example: depletion of water table means reduction in water table or lowering of water table.
Replenish means to replace something which has been used.
Depletion of Water Table
The water table at a place does not get affected (or does not get depleted) as long as we draw as much groundwater as is replenished by natural processes like seepage of rainwater. The water table at a place may get depleted and go down if the water drawn from the ground by us is not sufficiently replenished naturally.
Some of the factors which affect the water table (or deplete the water table) at a place and make it go down are :
(1) Increase in population
(2) Industrial and agricultural activities
(3) Scanty rainfall
(4) Deforestation, and
(5) Decrease in the effective area for seepage of rainwater.
(1) The increasing population needs more and more water for its day to day activities. As the population is increasing, more houses, shops, offices, schools, industries, roads and pavements, etc, need to be constructed.
(2) A huge amount of water is required for the construction work. Usually groundwater is used for construction work. This leads to the consumption of a lot of groundwater.
(3) When more and more houses, shops, offices, schools, industries, roads and pavements, etc, are constructed, then the open spaces like parks and playgrounds having unpaved ground for the seepage of rainwater into ground are reduced. This decreases the seepage of rainwater into the ground.
(4) Due to increasing population we are consuming more groundwater and on the other hand we are allowing less rainwater to seep into the ground.
(1) Everything that is made in industries needs water at some stage during its production process. Due to this, water is used by all the industries.
(2) As the population is increasing, the demand for various industrial goods is increasing, and hence the number of industries is also increasing continuously.
(3) Water used by most of the industries is drawn (or pumped out) from the ground. As the number of industries is increasing, the water drawn from the ground for their use is also increasing. This results in the depletion of water table
(1) The growing of various crops in agriculture requires a lot of water for irrigation.
(2) Irrigation systems such as reservoirs, dams and canals exist in some places but these irrigation systems usually get their water supply from rains.
(3) In the times of erratic rainfall (irregular rainfall) or scanty rainfall (inadequate), the farmers have to use groundwater for the irrigation of their crops. As more and more food has to be grown for the increasing population, the use of groundwater for agriculture is increasing day by day. This leads to the depletion of water table.
Sometimes there is scanty rainfall during the rainy season. Since there is less rainfall, less rainwater seeps into the ground. In such a situation, much more groundwater is drawn out by the people for various purposes than gets replenished by rainfall. This results in depletion of water table.
The cutting down of trees and plants from the forest for various purposes is called deforestation.
(1) Forests help in bringing rain. So lesser number of trees and plants in the forest will bring less rainfall.
(2) The trees and plants of forests also help in the seepage of rainwater into the ground. If there are lesser number of trees and plants in the forest, less rainwater will seep into the ground. This depletes the water table.
Decrease in Effective Area for Seepage of Rainwater
(1) Due to increasing urbanisation and industrialisation, more and more space is being covered by houses, other buildings, roads and pavements, etc. and the open spaces having unpaved ground are getting reduced day by day.
(2) It is the unpaved ground which lets the rainwater seep into the ground and recharge water table. Since the effective area for seepage of rainwater in urban areas is decreasing day by day, less and less rainwater seeps into the ground. This leads to the depletion of water table.