Before we go for hydrological and GW-Factor analysis; lets us understand the structure of the Earth Crust and the real configuration of the existence of underground water between the aquifers.
An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using water well. The study of water flow in aquifers and the characterization of aquifers; is called hydrogeology. Aquifers are underground layers of porous rock or sand that allows the movement of water between layers of non-porous rock (sandstone, gravel, or fractured limestone or granite). Many people tend to think of aquifers as “underground lakes” which is not the case because water is held between rock particles. Water infiltrates into the soil through pores, cracks, and other spaces until it reaches the zone of saturation where all of the spaces are filled with water (rather than air). The zone of saturation occurs because water infiltrating the soil reaches an impermeable layer of rocks so that it is not able to penetrate any further into the earth (this impermeable layer is known as an “aquitard” or “aquiclude”). Water held in aquifers is known as groundwater.
The top of the zone of saturation is known as the water table. The water table typically follows the form of the above ground topography. The depth of the water table is typically greater in regions with low rainfall than in regions with high rainfall. The water table can rise in wet years and fall in dry years.
In the figure-1 given below unconfined aquifer and confined aquifers are shown. Between any two aquifers a confining bed is running which is marked as impermeable rock layer which prevents the flow of water from one aquifer to another. In this pattern there are many aquifers between the confining beds holding unlimited underground water source, which was exploited by human civilization only by digging the wells from the upper unconfined aquifers from the centuries. The impermeable rock layer consists of layer with different rock properties. Many impervious layers may also known as aquitards which do not completely act as impervious layer but may allow some quantity of the water through it with low hydraulic conductivity. The thickness of the impermeable layer is not justified as it may be from couple of meters to several hundreds of feet.
One more factor is considerable for the impervious layers that they are in the form of waves with up and down structure have very large storage of water between the two rises/heads of the impermeable layers. Every rises/head of the impermeable layers that may be several miles wider could sustain the water towards the high lands. These rises of the impermeable layers are responsible for the water table.
An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using water well. The study of water flow in aquifers and the characterization of aquifers; is called hydrogeology. Aquifers are underground layers of porous rock or sand that allows the movement of water between layers of non-porous rock (sandstone, gravel, or fractured limestone or granite). Many people tend to think of aquifers as “underground lakes” which is not the case because water is held between rock particles. Water infiltrates into the soil through pores, cracks, and other spaces until it reaches the zone of saturation where all of the spaces are filled with water (rather than air). The zone of saturation occurs because water infiltrating the soil reaches an impermeable layer of rocks so that it is not able to penetrate any further into the earth (this impermeable layer is known as an “aquitard” or “aquiclude”). Water held in aquifers is known as groundwater.
The top of the zone of saturation is known as the water table. The water table typically follows the form of the above ground topography. The depth of the water table is typically greater in regions with low rainfall than in regions with high rainfall. The water table can rise in wet years and fall in dry years.
In the figure-1 given below unconfined aquifer and confined aquifers are shown. Between any two aquifers a confining bed is running which is marked as impermeable rock layer which prevents the flow of water from one aquifer to another. In this pattern there are many aquifers between the confining beds holding unlimited underground water source, which was exploited by human civilization only by digging the wells from the upper unconfined aquifers from the centuries. The impermeable rock layer consists of layer with different rock properties. Many impervious layers may also known as aquitards which do not completely act as impervious layer but may allow some quantity of the water through it with low hydraulic conductivity. The thickness of the impermeable layer is not justified as it may be from couple of meters to several hundreds of feet.
One more factor is considerable for the impervious layers that they are in the form of waves with up and down structure have very large storage of water between the two rises/heads of the impermeable layers. Every rises/head of the impermeable layers that may be several miles wider could sustain the water towards the high lands. These rises of the impermeable layers are responsible for the water table.
Figure-1
A few decades back in India and other developing countries we had only the option of "digging wells" for water exploitation, that time we don’t have tube wells drilling machines. The human civilization was able to reach only the depth of 100-200 feet by 'digging wells' to exploit water for drinking and agriculture purposes from the upper unconfined aquifer of the surface of the earth, which was the largest source of potable water collected by percolation of the rain water.
In the upper unconfined aquifer the percolation is also continuous from the rivers basin flowing on the surface of the earth from centuries. We can say the recharge is still going on throughout the year from the rivers when there is no rainfall in the area. We are still exploiting a percent of water for drinking and irrigation purposes from the unlimited storage of groundwater. The Depletion of Groundwater due to ‘immense pumping’ may be incomplete prediction. Logically, it can be proved again that the downfall of groundwater level is still not due to immense pumping for irrigation ‘completely’ by considering the following illustrations: -
Our scientists already mentioned that the groundwater is always recharging by the percolation of rain water into the soil from the various recharge area as potable water in unconfined aquifer. The rain occurs for few weeks in a year only; only 10-15% of water absorbed by the soil rest of it flows towards the sea and gets evaporated, whereas the groundwater is pumping out of the tube wells for irrigating the crops for 365 days; and a sufficient water must also goes under percolation, which should be collecting in the unconfined aquifer, with already percolated river and rainwater. Logically when a few percentage of rain water could percolate into the soil could bring the impact of rise in groundwater level then why the 365 days tube well used for irrigation water does not bring the rise in groundwater? Where that amount of water goes, which can result the Depletion of the Ground Water? Evaporates away, absorbed by the crop; how much?
Let us see the possibility of quantitative evaporating of the groundwater used for irrigation pumped from the tube wells. The maximum groundwater is pumped out during the winter seasons for the irrigation of Rabi Crops. We have seen that the rate of evaporation depends on the rise in the temperature of the surface which is directly exposing to the solar radiation or sunlight. In the crop lands, the land area is covered with the various types of crops preventing the solar radiation or sunlight to touch the ground, decreases the rate of evaporation of water into the atmosphere under the roots of the plants. When we had upper water table due to safer impermeable layer a few decades back, we had lot of humidity in the atmosphere due to ‘controlled’ evaporation of water from the vegetation and forest land.
We also need to estimate for the quantity of rainwater absorbed by the plants and evaporates into the atmosphere in vast open land area in comparison to the percolating groundwater under the roots/cool shadow of the crops. The summers are exception due to dry atmosphere but, combat with the Global Warming we essentially need the water for evaporation to keep our earth cool. Today, due to Groundwater Depletion we do not have upper level of groundwater to create humidity due to evaporation.
The best examples to understand the concept is the temperature of water in a clay-pot and in a metallic-pot. The temperature of water in the clay-pot decreases when there is an expansion of the water molecules in the form of water vapor, when evaporation of water take place, whereas maximum heat enters into a metallic pot in the absence of water evaporation.
In the same way due to Depletion of Groundwater the upper surface loses the upper water table which was responsible for the humidity with the development of new vegetation and forest land which brings a controlled and balanced evaporation of water between the solar radiation and the earth surface. Currently we do not have evaporation in most of the areas where the groundwater level had reached several feet below the earth surface. In the absence of evaporation our Earth act as metallic-pot; the heat enters its surface up to maximum depth. Where there is humidity in the soil and vegetation/forestry due to higher water level, the Earth act as a clay-pot. We can imagine a situation of the environment and the temperature of our Earth after “few years” when we do not have groundwater at higher levels, because the same principal is applicable for the earth as well for the water in a clay pot and a metallic pot.
In the past we had forest vegetation in abundance holding immense water in it and moisture in the soil that we are losing today because of drastic fall in the groundwater level, which is due to millions of deeper holes in impermeable layer. We also have to analyze that how much evaporation of water is there from the area of 5 sq. km. of the sea surface and the land surface under the same weather conditions. Hopefully, we will find too much evaporation of water from the land area in comparison of the sea surface that is very essential for cloud formation.
Hence, due to Depletion of Groundwater we do not have water to evaporate. A percentage of immense water being pumping from the tube well goes under percolation after we irrigate for crops. The amount of water used for irrigation currently, is much less than the presence of water in the form of humidity in the upper earth surface, vegetation in abundance holding water and surrounding moisture and higher water table in unconfined aquifers before more than a Century; and we had lot of water evaporation also that brings cooling for the Earth Surface. We can still try to find the possibility to improve the Groundwater Depletion and could balance the water evaporation from the surface of the earth to control the Global Warming.
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