 |
| Water |
|
| About 70-73% of earth is covered by water. Water is available in the form of oceans, seas, rivers, lakes, ponds, pools, polar ice caps and water vapour and this forms the hydrosphere. The main component of hydrosphere is water. Water exists in all the three forms i.e., solid (snow), liquid (water) and gas (water vapour). |
| |
| We all know that life on earth began in the sea. Water in some form or the other is absolutely essential for the maintenance of all kinds of life. Water consists of two atoms of hydrogen and one atom of oxygen and it is the universal solvent since it dissolves most of the compounds. The most important character of water is that its density is similar to that of protoplasm. |
| |
| Water is a valuable natural asset as it is the fundamental natural resource. Human beings depend on water for many purposes such as drinking, cooking, agriculture, transportation, hydropower etc. Water available in nature is of two types: |
| |
 Salt water: Its presence is more in nature because it constitutes the oceans and the seas. |
| |
 Fresh water: It is an unlimited natural resource. Nowadays, its quality is often degraded but not quantity. |
| |
| Sources of fresh water are: |
| |
 Rainwater |
| |
 Surface water (surface flow) |
| |
 Ground water |
| |
|
| India receives about 3 million m3 of water from the rainfall (or precipitation), which amounts to 105-117 cm annually. This is a huge quantity and the largest in the world. |
| |
| Intensity of rainfall in India varies from region to region. It forms four zones. They are: |
| |
 Wet zone: Here annual rainfall is very high (i.e. over 200 cm). West coast of India and northeastern parts of India come under this category. |
| |
 Intermediate zone: Rainfall is quite heavy (i.e. 100 to 200 cm). Parts of UP, Karnataka, Maharastra, Bengal, Orissa, Punjab, Himachal Pradesh and Kerala fall in this zone. |
| |
 Semi arid zone: Annual rainfall is moderate (i.e. between 50-100 cm). Most parts of central India, Southern peninsula and parts of Rajasthan and Gujarat comes under this region. |
| |
 Arid zone: In this zone the annual rainfall is very low (i.e., it ranges from 20 to 50 cm). Rajastan and parts of Gujarat fall under this region. |
| |
|
| In India, there are 14 major river systems such as Ganga, Brahmaputra, Godaveri, Krishna and Cauvery. Apart from the rivers, the other forms are ponds, lakes and streams. |
| |
|
| Underground reservoirs of fresh water are called aquifers. They are continuously recharged through infiltration, sewage and evapo transpiration. The total volume of ground water found in the aquifer is estimated to be 42.3 x 1010m3. |
| |
|
 The space between soil particles on the surface of earth is called pore space. |
| |
 It is of two types - micro and macro pores. Most of the water is held in micro pores. |
| |
 Pores, which are available for plant roots. |
| |
| Surface soil pore spaces are generally filled with air and water. Water that percolates down through pore spaces of rocks is available as ground water. The porous rocks are saturated with water at a certain level below the surface which is called as zone of saturation and the upper level of zone of saturation is called the water-table. Thus the depth in the soil where all the pore spaces of soil particles are saturated with water is called water table. The water table will be high in rainy seasons and near rivers, lakes and swamps and it is deeper in areas of low rainfall, on hilltops and in dry areas. |
| |
 The ground water provides moisture for plant growth. It supplements water in streams and lakes. The following factors tend to lower the water at any given place. |
| |
| i. Scanty rainfall |
| |
| ii. Use of more ground water |
| |
| iii. Cultivating of trees |
| |
| Note: |
Hygroscopic and Capillary water: Water, which is retained around the soil
particles. |
| |
Gravitational water: Water, which is free to drain downwards through the
soil. |
| |
| |
| |
 |
| |
| Three main types of soil water |
| |
| Leaching of water is due to washing out of minerals, including nutrients. |
| |
