What is Freshwater ?
Fresh water is naturally occurring water on Earth’s surface in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams.
- Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids.
- The term specifically excludes seawater and brackish water although it does include mineral-rich waters such as chalybeate springs. The term “sweet water” (from Spanish “aguadulce”) has been used to describe fresh water in contrast to salt water.
- The term fresh water does not have the same meaning as potable water. Much surface fresh water and some ground water are unsuitable for drinking without some form of purification because of the presence of chemical or biological contaminants.
Sources of Freshwater In general :
The source of almost all fresh water is precipitation from the atmosphere, in the form of mist, rain and snow.
- Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled.
- In industrialized areas rain is typically acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories, trains and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of lakes and rivers.
- In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds. This can give rise to elevated concentrations of sodium, chloride, magnesium and sulfate as well as many other compounds in smaller concentrations.
- In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but also by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa.
Freshwater around the world :
- Canada has approximately 7% of the world’s renewable fresh water. Canadians access their water from ground water, lakes and streams; it is then cleaned and purified in water treatment plants.
- United Statesuses much more water per capita than developing countries. For example, the average American’s daily shower uses more water than a person in a developing country would use for an entire day. Las Vegas, a city that uses an extreme amount of water to support spectacular lush greenery and golf courses, as well as huge fountains and swimming pools gets 90% of its water from Lake Mead,which is now at a record all-time low
Sources of Freshwater in India and where it comes from ?
India has about 4% of world’s freshwater resources ranking it among the top ten water rich countries.
- Rainfall :Rainfall in India is dependent largely on the southwest and northeast monsoons, on shallow cyclonic depressions and disturbances, and on violent local storms. Most of the rainfall takes place under the influence of southwest monsoon between June to September except in Tamil Nadu and some other Southern States where it occurs under the influence of northeast monsoon during October and November.
- The rainfall shows great variations, unequal seasonal distribution, still more unequal geographical distribution and frequent departures from the normal. As much as 21 percent of the area of the countries receives less than 750 millimetre (mm) of rain annually while 15 percent receives rainfall in excess of 1500 mm. It generally exceeds 1000 mm in areas towards the east of Longitude 780 E. It extends to 2500 mm along almost the entire west coast and over most of Assam and sub-Himalayan West Bengal.
- The large areas of peninsular India have rainfall less than 600 mm. Annual rainfall of less than 500 mm is experienced in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Rainfall is equally low in the interior of the Deccan plateau east of the Sahyadris.
- A third area of low precipitation is around Leh in Kashmir. Rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region.
The River Systems :
The main Himalayan river systems are the Indus and the Ganga-Brahmaputra-Meghna (Barak) system. The Ganga rising from the snow capped Himalayan mountains, flows through the great indo-gangetic plains.
- The Brahmaputra rises in Tibet where it is known as the Tsangpo and runs a long distance until it crosses over into India in Arunachal Pradesh under the name of Siang or Dihang. The Ganges and the Brahmaputra join inside Bangladesh and continue to flow under the name Padma forming the Sunderban delta.
- The Indus, which is one of the great rivers of the world, rises near Mansarovar in Tibet, flows through India and thereafter through Pakistan and finally falls in the Arabian Sea near Karachi. Its major tributaries the Jhelum, Chenab, Ravi, Beas and Sutlej originate in India and after flowing through the Punjab plains join the Indus.
- The important river systems in the Deccan are the Narmada and the Tapi, which flow westwards into Arabian Sea. The east-flowing rivers of the Deccan, the Brahmani, the Mahanadi, the Godavari, the Krishna, the Pennar and the Cauvery fall into Bay of Bengal.
- There are numerous coastal rivers, which are comparatively small. While only handful of such rivers drain into the sea from the east coast, there are as many as 600 such rivers on the west coast.
Ground Water :Based on large volume of hydro-geological and related data generated by Central Ground Water Board and State Ground Water Organizations and the existing knowledge of ground water regime, replenishable ground water resources in the country have been estimated as 43.2 million hectare metres.
- In the alluvium plains of the Indo-Gangetic valley, ground water depths measure upto 450 metre. The coastal aquifers also have similar depth range of ground water availability. Inland river basins in the country have recorded shallower depth within the range of 100 -150 m.
- Static Ground Water resource also sometimes known as “fossil” water, considered as ground water available in the aquifer zones below the zone of water level fluctuation, available in the country has been assessed as 1081.2 million hectare metres, on the basis of the depth of availability of ground water and the productivity of deeper aquifers.
- However, as per the National Water Policy, development of ground water resources is to be limited to utilisation of replenishable component of naturally occurring ground water available in sub-surface domain.
Ground water is widely dispersed. It is an important source of water for drinking and irrigation. Ground water contributes 51 percent of the irrigation potential created in the country through more than 4 million dug wells, 5 million shallow tube wells and some ninety thousand public tube wells.
Assessing Freshwater Resources :
- Water resources assessment is the determination of the sources, extent, dependability and quality and the above parameters are based on our evaluation of its utilization.
- Planners and decision makers require such information on ways of meeting the expected demands. The existing and future uses of water must be determined giving due consideration to quality and ecosystems needs of the aquatic environment as a legitimate user of the resources.
- The river basin is recognized as the appropriate unit for planning and development of our water resources. Measurement of its quantity and quality, and of other characteristics of the environment affecting water, are essential requisite basis for adopting effective water management strategies.
- Measuring on a regular basis the hydrological elements, which control water resources, is necessary to determine how much water is available for use. These elements include precipitation, evaporation and river flow, as well as the water stored in soil, aquifers, reservoirs and glaciers. The water’s quantity, quality and biological characteristics are to be measured regularly.
Assessment of Ground Water
- Ground water is an important source of irrigation and caters to more than 45% of the total irrigation in the country. The contribution of ground water irrigation to achieve self-sufficiency in food grains production in the past three decades is phenomenal.
- In the coming years the ground water utilization is likely to increase manifold for expansion of irrigated agriculture and to achieve National targets of food production. Although the ground water is annually replenishable resource, its availability is non-uniform in space and time. Hence, precise estimation of ground water resource and irrigation potential is a prerequisite for planning its development.
- A complexity of factors – hydrogeological, hydrological and climatological, control the ground water occurrence and movement. The precise assessment of recharge and discharge is rather difficult, as no techniques are currently available for their direct measurements.
- Hence, the methods employed for ground water resource estimation are all indirect. Ground water being a dynamic and replenishableresource, is generally estimated based on the component of annual recharge, which could be subjected to development by means of suitable ground water structures.
For quantification of ground water resources proper understanding of the behaviour and characteristics of the water bearing rock formation known as
- Despite this, according to the Working Group II report of the Fourth Assessment of the Intergovernmental Panel on Climate Change, India is designated a ‘water stressed region’ with current utilizable freshwater standing at 1122 cubic meter (cu m) per year and per capita compared to international limiting standards of 1700 cu m.
- In future, at the current rate it is expected that India with high demands will be termed a ‘water scarce region’ as utilizable freshwater falls below the international standard of 1000 cu m per year and per capital.
- Water demand is on a high due to rapid urbanization and industrialization along with the traditional demand for agriculture. Overall, every year, precipitation in the form of rain and snowfall provide over 4000 cu km of freshwater to India, of which 2047 cu km return to oceans or is precipitated. A small percentage is stored in inland water bodies and groundwater aquifers. Topographic constraints, distribution pattern, technical limitation, and poor management do not allow India to harness its water resources efficiently.
- In India, rivers have been the lifelines of growth and culture. India is drained by twelve major river systems with a number of smaller rivers and streams. Major river systems in the north are the perennial Himalayan rivers – Ganga, Yamuna, Indus and Brahmaputra. The south has the non-perennial but rain fed Krishna, Godavari, and Cauvery while central India has the Narmada, Mahanadi and Tapti.
- The Ganges-Brahmaputra and the Indus systems are the largest as they drain almost half of the country carrying more than 40% of the utilizable surface water from the Himalayan watershed to the ocean. Over 70% of India’s rivers drain into the Bay of Bengal, mostly as part of the Ganges-Brahmaputra system. The Arabian Sea receives 20% of the total drainage from the Indus and other rivers. The remaining 10% drains into interior basins and natural lakes.
- Flow in India’s rivers is strongly influenced by monsoon resulting in an annual peak in most rivers. The northern rivers with sources in the Himalayas see an additional peak during the spring snowmelt. Because of this, water levels increase and flooding is a common phenomenon that also leads to yearly calamity in states like Bihar and Assam. During the dry season, the flow diminishes in most large rivers and even disappears entirely in smaller tributaries and streams. Due to low rains, and dry rivers, drought is another common calamity across vast areas, especially the Deccan trap. Hence, some parts of India suffer from flood and some parts from drought.
- Apart from the floods and droughts, most Indian rivers are cesspools of waste dumped from various urban and industrial centres. In 1995, the Central Pollution Control Board identified severely polluted stretches on 18 major rivers in India. The pattern of destruction is similar for any river – industrial and domestic pollution, jagged urbanization and encroachment, agricultural fertilizer and pesticide runoffs, erosion and silting, over withdrawal of water, and inconsiderate religious practices. All 44 rivers in Kerala face extinction through deforestation, sand mining, riverbank brick making and pollution.
- The rivers are the sources of drinking water for urban and rural areas, raw water for industries, and irrigation. The demand for water is ever increasing leading to over-extraction. This abstraction of water in excess from the river lessens the flow in it.
- It is very important to maintain the flow as it helps in diluting and carrying the sewage and pollutants away. Irrigation canals and industrial units extract huge volumes of water, and in return, discharge agricultural runoff waste and poisonous effluents.
- Many rivers suffer from silt deposition in its bed — reducing flow, and disturbing the ecosystem. Deforestation near the source of the rivers, is leading to soil erosion, landslide, floods, silt formation and sedimentation in rivers. In Indian rivers, siltation rate is among the highest in the world. It has been estimated that about 135 thousand million metric tonnes of sediment load and 32 thousand million tonnes of soluble matter enter into ocean through various rivers.
- Water flowing through Indian rivers is 5 % of the water flowing through all the river of the world but carry 35 % of sediments. To regulate the flow in these rivers and store water and divert water for irrigation, and generate power, a number of large dams and barrages have been built on many rivers. However, these measures have been detrimental to the flow of water resulting in silt deposition. With the storage of water, the natural flow in rivers is obstructed affecting the ecosystems.