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1. WATER RESOURCES AND UTILZATION
1 Water is an indispensable resource for the survival of life. Probably, you may survive without food for a few days, but not without water! Green plants, the primary producers of food, require large quantities of water continually for their growth and sustenance. Rainwater is the primary source of water for all organisms. Plants utilize rainwater once it becomes part of soil as soil water. Animals utilize it once it is stored in some storage structures such as ponds, wells, and streams. We often have to confront two situations regarding the availability of rainwater. The first is a situation of too little rainwater, especially in arid and semi arid regions. We may confront this situation during summer in humid and semi-humid regions as well. If the supply of water to the crops through rainfall is insufficient, it must be supplemented through irrigation. Irrigation is defined as the controlled application of water to soil for supplementing moisture essential for crop growth. The second is a situation of too much rainwater during the rainy season. This situation of too much water can occur in all the climatic regions. If there is too much rain, soil will be saturated with water, and a situation called waterlogging results. The removal of excess water either from the ground surface or from the root zone is called drainage. The requirement of drainage may be for a few days to ward off the problems from flash floods or throughout the year as in water logged areas. Control and management of water resources are important for their equitable and effective utilization. Water management envisages control of all human interventions on water resources. In a broader sense, every planning activity that has something to do with water can be looked upon as water management. It involves integrated management of surface water resources, ground water resources, and rainfall. Water management is the process of integration of all the activities aimed at exploiting water in a technically and economically optimal way, and at the same time, minimizing damages caused by it. “ Agricultural water management ’ is water management in agricultural lands. The process of agricultural water management includes the intake, conveyance, regulation, measurement, and application of water in appropriate quantities at the right time to crops to increase production and timely and effective drainage of excess water from the farms, which otherwise hamper production of crops. Remember that the removal of excess water is also a part of water management. Water available to plants can be distinguished by a colour convention as green water and blue water. Green water means the precipitation and water on and in the soil, directly relevant to local vegetation or crops. A part of this ‘green water’ is returned to the atmosphere through transpiration and a part through evaporation. At the same time, blue water is the fresh water in streams and lakes, in groundwater below the roots, and in aquifers, which can be utilized for irrigating the crops or for direct domestic and industrial uses. When we say ‘land’, it includes the green water, which comprises of local precipitation and water in the soil and any local runoff and run-on. Land, however, does not include blue water or irrigation supplies up to the field boundary. Globally, sustainable use of water resources is an important issue. The International Water Management Institute (IWMI) at Colombo, Sri Lanka under the aegis of CGIAR functions focusing on the sustainable use of water and land resources in developing countries. At the national level, Indian Institute of Water Management (IIWM), Bhubaneshwar functions under ICAR. Water Technology Centre of Indian Agricultural Research Institute, New Delhi is another important institute dealing with water resources and management in the country. (^1) Two lectures
1. WATER MANAGEMENT AND WATERSHED MANAGEMENT
Water management is concerned with the judicious management of water, which includes both irrigation and drainage. Water for irrigation is obtained from surface water resources such as rivers, streams, ponds, tanks, lakes, or artificial reservoirs like dams, barrage, and diversionary weirs, and ground water resources such as open dug wells and tube wells. From different river valley projects, irrigation is done through canals profitably as the water from the river is carried to the field by gravity flow. Removal of excess water from any system is drainage, an integral part of water management. We resort to artificial removal of water from farmlands to keep the moisture level within the tolerance limit of crops. Drainage is also needed for special requirements like leaching and reclamation of problem soils. An irrigation project such as an irrigation dam or weir has a watershed area or more specifically a catchment area and a command area. The land area that can be irrigated by an irrigation project is called its command area as opposed to catchment area or watershed area from which the dam collects water drained through surface runoff. Ayacut is the Indian name for command area of a river and Anicut the dam and the storage area. Command area can also be envisaged for a pond or well for the area irrigated through these sources. In irrigated areas, we pursue c ommand area development approach for its comprehensive development. In such areas, availability of water, the most critical factor in crop production, is assured, and therefore, intensive farming of a specialized nature is practiced. The emphasis is to maximize production from unit area. In many states, Command Area Development Authority (CADA) has been formed for the overall development of command areas of irrigation dams. It is mainly though participatory irrigation management with the active co-operation of all stakeholders. Unlike water management, watershed management is an entirely different concept. In watershed management, holistic management of the contributing area of runoff for a particular drainage structure such as a stream, river, or lake is considered. Remember that watershed is a land area bounded by a natural ridge line from which all the surface runoff drains to a common drainage point such as a stream, river, or lake. Watershed area development approach is followed for rainfed areas where availability of water is dependent on rainfall. An element of uncertainty and risk is prevalent in the production systems as the rainfall may be erratic in amount, intensity, and distribution. Therefore, diversified and mixed farming systems are commonly practiced along with appropriate land husbandry measures including soil and water conservation. However, command area development cannot be seen in isolation with watershed management. Command areas may face problems, if the catchment areas (that is, the watershed areas) of the dams are degraded resulting in silting and low storage. The same is true with the watershed areas of various streams or rivers, which contribute water to various water storage structures.
2. RAINFED AGRICULTURE AND IRRIGATED AGRICULTURE Land areas of the world are often classified into arid, semiarid, and humid regions mainly based on precipitation and evapotranspiration. Crops grown in different climatic regions differ greatly with respect to the requirement of irrigation. In regions with humid climates, usually receiving more than 120 cm of rainfall per year, the rainfall is often sufficient to cover the water needs of various crops. Tree crops are predominant in such regions. In the sub-humid and semi-arid climates, where the annual rainfall is in the range of 40 cm to 120 cm per year, the amount of rainfall is not sufficient to cover the water needs of the crops. In such regions, especially in the dry season, crop production is possible only with irrigation. However, in the rainy season, crop production may be possible without irrigation by utilizing rainfall. In arid and desert climates, where the rain
1000 kilograms of water for every unit of dry matter produced (Zonn, 1986). Water has several functions to perform in the plants:
- Water present in plants creates turgor pressure, which in turn, provides turgidity to plants.
- It acts as a solvent and carrier of many substances in plant cells and the medium in which biochemical reactions occur.
- Water is a reactant or substrate of many biochemical processes in photosynthesis and respiration.
- Water is necessary for the transpiration process in plants.
- It is the transport medium for organic materials through phloem and inorganic nutrients through xylem.
- Many organic constituents of plants such as carbohydrates, proteins, nucleic acids, and enzymes lose their physical and chemical properties in the absence of water.
- Water is important in stomatal opening. With water stress, stomata closes and photosynthesis is affected.
- Cell elongation or expansion is reduced or stopped with water stress. This indicates that water is essential for the growth of leaves, stems, roots, flowers, and fruits
- Water also acts as a temperature buffer and coolant.
4. THE HYDROLOGIC CYCLE The hydrologic cycle describes the continuous circulation of water between the land, the ocean, and the atmosphere. The cycle has no beginning or end, and its many processes occur continuously in a circular way. The phenomenon is quite complex, containing many sub-cycles. The major processes include precipitation, infiltration, evaporation, transpiration, groundwater flow, and surface runoff involving many phases. All these are interrelated as could be seen from the hydrologic cycle (Fig.1.1). In a watershed, evaporation, transpiration, and runoff—three major phases of the hydrologic cycle, can be altered, modified, controlled, or regulated by vegetation, better land husbandry, and structural management practices. There are several proven techniques, which control and regulate evapotranspiration and runoff. There is neither a beginning nor an end to the hydrologic cycle. However, for convenience, we assume that the cycle begins from the oceans. Remember that 97.13 percent of water on earth is in the oceans. Because of solar radiation, water in the oceans heats up, and the evaporated water escapes to the atmosphere. Evaporation also occurs from other fresh water and ground water bodies. The evaporated water vapour is transported through winds and lifted to the atmosphere forming clouds. Under favourable situations, the clouds condense and precipitate on the land and oceans as rain, hail, sleet, snow, or other forms of precipitation. Before the precipitation reaches the earth’s surface, there is some evaporation in the atmosphere. This increases atmospheric humidity, lowers the temperature, and reduces evapotranspiration from crop plants. Water vapour may also be blown away by winds to the surrounding area. Although this fraction is partially useful, it is not taken into consideration in ordinary calculations because of the difficulty in its estimation. When precipitation begins, a small part may be intercepted by the vegetation through the leaves and stems. Some of it may be absorbed and retained by leaves as interception
storage ; eventually being lost as evaporation. If rain continues, the storage on the leaves and stems become nearly constant, and all the water falling on them reach the ground by drippings from the leaves or flowing down the stem. During light showers, the entire rainfall may be intercepted by the vegetation. The interception storage by vegetation may vary from 0.25mm to 9.14mm rainfall. For most crop plants, the mean value could be taken as 2.5mm. Fig. 1.1 Hydrologic cycle The fate of rains falling on soil surface is also not uniform. Some water infiltrates in to the soil; some may stagnate on the surface; some portion evaporates back to the atmosphere; while some may flow over the surface as run-off as a thin sheet of water and become the overland flow over the surface. A natural soil is usually protected by litter and plant cover. When the vegetative cover over soil is destroyed or removed, several problems come up. The first effect is a reduction of infiltration capacity. When infiltration is impaired, overland flow occurs excessively, and this causes rapid run-off , often accompanied by erosive action. If there occurs a relatively impermeable stratum in the subsoil, the infiltrating water moves laterally and joins the stream flow as interflow or subsurface flow. The rainwater stagnated on the soil surface as depression storage is lost by evaporation or by infiltration in due course. It can be useful for meeting the water needs of crops, but may be harmful and can create drainage problems. Depression storage can be increased by various biological, bio-engineering and engineering conservation practices, and are helpful in reducing the threat of runoff. Under ideal conditions, as much as 6.25cm of water may be stored in contour furrows and about 5cm in level bench terraces. However, the water storage capacity of surface soils decreases as the degree of slope increases. Rainwater lost by run-off may be pumped back and re-used at the site where it was received, or may be used elsewhere downstream. After the entry of water into soil, some or all of it is held there by the molecular attraction of the soil particles. Any additional water above this limit moves under the force of gravity to some surface outlet or aquifer. Water retained in the capillary soil pores against the force of gravity is called capillary water and is said to be in retention storage. The amount so held depends on the depth and other physical properties of the soil mantle. Water held in retention storage is not available for stream flow. However, it is available for plants; in fact, it
atmosphere. The remaining 45,000 km^3 (38%) flow into lakes, reservoirs and streams or infiltrate into the ground to replenish the aquifers. Although this represents the renewable water resources”, not all of these 45,000 km^3 are accessible for use because of many reasons. A part of this flows into distant rivers, or lost during seasonal floods, or some percolate deeper into groundwater. An estimated 9,000 km^3 –14,000 km^3 can be considered economically available for human use. Annual withdrawals of water for human use come to about 3600 km^3 , the equivalent of 580 m^3 per capita per year. A part of surface water must be left to follow its natural course to ensure effluent dilution and to safeguard conservation of the aquatic ecosystem. The instream flow needs are estimated at 2350 km^3 per year. If we add this amount to the amount withdrawn for humans, the figure will be 5950 km^3. This is the easily accessible freshwater resources. Global water figures show a tightening situation, because human water use has increased more than 35 folds over the past three centuries. As both water and population are unevenly distributed and some countries are overpopulated or water scarce, the situation is already grim. Many regions of the world are suffering from freshwater shortages, and competition among the users for water is rising unabated. Agriculture is by far the biggest user of water, accounting about 69 percent of all withdrawals worldwide. Domestic and municipal use amounts to about 10 percent and industry uses some 21 percent. Water use varies considerably around the world. Most of the developed countries use less water for agriculture and more for industrial and domestic uses. In India, the figures are 92 for agriculture, 5.0 for industry and 3.0 for domestic uses. In Kerala, 71 percent is utilized for agriculture, 11 percent for industry and 18 percent for domestic uses.
6. WATER RESOURCES OF INDIA India, which has more than 17 percent of the world’s population, has only 2.45 percent of world’s land resources and 4.0 percent of the world’s fresh water resources. Monsoon rains are the main source of fresh water in India. Rainfall in India is dependent on the south-west monsoon, north-east monsoon, shallow cyclonic depressions and disturbances, and on local storms. Most of the rainfall occurs under the influence of south-west monsoon between June and September except in Tamil Nadu, where it is under the influence of north-east monsoon during October and November. Variations in climatic characteristics both in space and time are responsible for the uneven distribution of precipitation in India. Rainfall and melting snow contribute water to various surface water resources such as streams, rivers, lakes and ponds. Rainfall pattern The mean annual rainfall over India is 119cm. However, 76 per cent of the total rainfall is received during the southwest monsoon season (June-September), and 10 percent each is received during the post monsoon season (Oct-Nov.) and summer season (March- May). The remaining 4.0 per cent is received during winter (Dec. - Feb.). This is the trend in almost all the North Indian states. However, in the south and southeast regions, substantial rainfall occurs during October – December under the influences of Northeast Monsoon. For example, Tamil Nadu receives 49 per cent of their total rainfall from Oct.-Nov. from northeast monsoon. In the country, there are regions, which receives rainfall in the range of about 1100 cm (North East regions), whereas in Rajasthan, it is less than 10 cm. As most rainfall occurs only during 3 to 4 months of the year, assured water supply to agriculture, industries, and drinking purposes is a great challenge to the nation. Based on the mean annual rainfall of 119 cm over a geographical area of 328 million ha, total annual rainfall is estimated to be about 392 M ha-m. Considering the contribution from snow fall, this can be rounded off to 400 M ha-m. Of the annual precipitation of 400 M ha-m, about 215 M ha-m infiltrates into the soil (54%). A major part of it 165 M ha-m (77%), is retained as soil moisture, and about 50 M ha-m percolates to water table (23%). About 12.
per cent of the total precipitation percolates deeper into the ground water table. Along with this, there occurs some influent discharge from flood flows (4M ha-m), and from irrigation systems (11 M ha-m). Thus, 65 M ha-m of water may be present as ground water. Surface water resources Water for human use inclusive of irrigation and drinking water is obtained from various sources, broadly grouped under surface water resources and ground water resources. Surface water resources include the natural flowing water through the rivers and streams or the still water from ponds, tanks, lakes, or artificial reservoirs such as dams, barrage, and diversionary weirs. From different river valley projects, irrigation is done through canals profitably as the water from the river is carried to the field by gravity flow. India is blessed with many major rivers spread over the entire country. These rivers can be broadly classified into two groups, the perennial rivers of the Himalayan region: and the rainfed rivers of peninsular India. The perennial rivers of Himalayan region are fed by the melting snows and glaciers of Himalayan region are often uncertain and capricious in their behaviour. The lean period of these rivers is the winter, but at no time the flow is reduced as in the peninsular rivers. The main Himalayan river systems are those of the Indus, the Ganges and the Brahmputra. The Indus River rises north of Mansarover in Tibet and flows through Kashmir for a distance of 650 km and enters Pakistan. The tributaries in the plains are the Jhelum, the Chenab, the Ravi, the Beas and the Sutlej. The Chenab flows through Himachal Predesh. The Ravi and Beas flow through Punjab and Sutlej form the boundary between India and Pakistan. The Ganges rises in Gangotri and travels a distance of 2525 km before joining the Bay of Bengal. The most important river feeding the Ganga are the Yamuna, the Ghaghara, and the Kosi. The Ganges has the largest catchment area (86.1 M ha) in India. The Brahmputra rises in Kailash range in Tibet and enters Arunachal and Assam. For estimating the surface water resources of the country, Dr. A. N. Khosla divided the country into six water resources regions (Khosla, 1949). Khosla estimated the mean annual runoff of the six water resources regions of the country at 167.23 M ha-m (Table 1.1).
Table 1.1. Water resources regions in the country
Name of basin Catchment area (M ha) Mean annual runoff (M ha-m) Indus system* 35.40 7. Ganga system 97.60 48. Brahmaputra system* 50.62 38. West flowing river basins 49.16 41. East flowing river basins 121.03 31. Luni and Ghaggar basins (Rajputana )
Total 370.61 167. *The catchment areas of the Indus and Brahamputra basin extend beyond the boundary of India. The rainfed rivers of peninsular India includes the coastal rivers and inland rivers. The coastal rivers are comparatively small streams. About 14 percent of the water resources of the country are in these coastal rivers. The inland rivers are of great antiquity. Those flowing westwards are the Narmada and the Tapti. The east flowing rivers are the Mahanadi, The Brahmani, the Godavari, the Krishna and the Kavery. The National Commission for Integrated Water Resources Development estimated the basin-wise average annual flow in Indian river systems at 1953 km^3.
(total catchment 19489 km 2 ) are minor rivers. Periyar is the longest river in Kerala with a length of 244 km followed by Bharathapuzha with a length of 209km. Annual average rainfall over the state is 2963mm, 68 per cent of which is received during the southeast monsoon (June-Sept.), followed by 16 percent in northeast monsoon (Oct.-Nov.). Winter months (Dec.-Jan.) are almost rainless period (2.0%) and during summer months (March- May), the state may receive 14 per cent rainfall. The total runoff from all the rivers of the state amounts to 78,041 Mm^3 including regenerated flow from ground water, of which 70, 323 Mm^3 is the contribution from catchments in Kerala and the remaining from Karnataka and Tamil Nadu. Nearly 40 percent of available water resources are lost as run off. The quantity of water considered utilizable is computed as 42,772 Mm3. Groundwater potential in the state is estimated at 7900Mm^3. It is tapped mainly for drinking and irrigation purposes. The net groundwater availability is 6229 M m^3. The gross groundwater draft is 2693 Mm^3 and the net groundwater available for future use is 3536 Mm^3. There are 18 completed major and medium irrigation projects and 7 ongoing projects in various stages of completion. All the major and medium irrigation projects in Kerala except Kallada are meant for rice farming.
7. NATURE OF GROUNDWATER Pore spaces present in the soil and rocks are filled with air and water. Water can saturate the tiny spaces between the soil materials or the crevices or fractures in the rocks. Water that percolates into the ground passes through a zone of aeration, also called unsaturated or vadose zone, where the open spaces between soil particles are filled with both air and water. This is the zone just above the water table. Below the zone of aeration lies the zone of saturation where all of the spaces between soil particles are filled with water. The dividing line between the two zones, that is, the upper surface of this saturated zone, open to atmospheric pressure, is known as the water table or phreatic surface. This level may be just below the ground level or many metres deep below the ground level. Fig. 1.2. Nature of ground water Groundwater moves through the subsurface supplying water to streams and lakes. In the zone of aeration, capillary water that moves upward from the water table by capillary action occurs. When we say soil moisture , we mean water in the ground, but above the water table in the soil layers. This water can move slowly in any direction from a wet particle to a
dry one. While most plants rely on moisture from precipitation present in the unsaturated zone in the soil, their roots may also tap capillary contribution from the underlying saturated zone. This is a common feature where water table is high. The water occurring below the ground water table in saturated condition is commonly called ground water and is available for pumping and extraction by other means. It is stored in the interstices of the soil or rocks. It should be borne in mind that ground water reserves are not in the form of lakes or streams of water inside the ground. It is similar to water stored in a sponge, not visible but can be extracted. Most groundwater occurs as aquifers. Aquifers are underground layers of porous soil or rocks saturated with water from above or from structures sloping towards it, which yield significant amounts of water. The thickness of an aquifer can range from a few meters to hundreds of meters, and it can underlie a few hectares or thousands of hectares. Aquifer capacity is determined by the porosity of the subsurface material and its area. Confined and unconfined aquifers An aquifer, the underground formation of porous soil or rocks saturated with water, may be confined or unconfined (Fig.1.2). Confined aquifers occur where the groundwater system is between layers of clay, dense rock, or other materials with very low permeability. This impermeable layer shows very low intrinsic permeability and acts as a layer confining the underground aquifer. Any such impermeable water bearing soil or rock strata is called an aquiclude. The geologic strata such as silts and mudstones that are slowly permeable and retard groundwater are called aquitard s. Ground water in confined aquifers may be very old, collected millions of years ago. Water in the confined aquifer is not in direct contact with the atmosphere. Ground water within a confined aquifer occurs under pressure greater than atmospheric pressure. When such a confined aquifer is pierced through a well, water rises in the well due to release of pressure within the confined aquifer. The level upto which water rises in the wells is known as potentiometric level. This potentiometric level indicates the magnitude of pressure within the confined aquifer. If the potentiometric level is above the ground water surface, a flowing well known popularly as Artesian well results (A flowing well of this kind was first observed in Artois in France, hence the name Artesian well). Such confined aquifers are known as Artesin aquifers and the confined pressure is also known as Artesian pressure. Unconfined aquifers are more common, and do not have a low-permeability deposit above it. Water in unconfined aquifers may have arrived recently by percolation through the land surface. This is why water in unconfined aquifers is often considered very young in geologic time. In fact, the top layer of an unconfined aquifer is the ‘water table’. It is affected by atmospheric pressure and changing hydrologic conditions. Discharge and recharge rates depend on the hydrologic conditions above them. The water level in a large dug well can be taken as the water table. It is also called water table aquifer or phreatic aquifer. Perched aquifer Perched aquifer is a special case of unconfined aquifer. A perched aquifer is formed when the infiltrated rainwater is intercepted within the zone of aeration by an impermeable layer and a local zone of saturation is formed. The upper surface of such local zone of saturation is known as perched water table. Such aquifers usually occur at higher elevations. Although the perched aquifer exhibits all the characteristics of unconfined aquifer, its extent is limited to the dimensions of impermeable layer, and therefore, its storage is also limited.
The amount of water consumed in the production process of a product is called the virtual water. The term virtual water was coined at a seminar at the University of London in 1993 for what was earlier being described as ‘embedded water’ by J.A. Allan. The water is ‘virtual’ because it is not contained anymore in the product. Although self-sufficiency in food grains is a dream of many nations, the current trend is away from food self-sufficiency to partial reliance of food imports. A major reason for this change is water scarcity, caused by rapidly growing populations, resulting in reduced per capita water and land availability. Some countries have also found that there are higher returns on labour in industries other than agriculture. In short, it is easier and more profitable to earn foreign exchange to buy food imports than to grow water- hungry crops. However, some countries of the world should produce enough food for every one! Table 1.2. Water required for the production of some items (virtual water) Items Water in litres consumed per kg Wheat 1200 Rice 3350 Vegetables 5460 Mango 1600 Banana 272 Potato 262 Beef 13500 Chicken 4100 Pork 4600 Egg 2700 Milk 790 Steel 150 Paper 900 Synthetic rayon 2000 We can also estimate the virtual water content of our daily diet. We may be directly drinking only 2-3 litres of water daily. However, it is estimated that to produce enough food to satisfy a persons’ daily diet, 2000-3000 litres of water has to be spent!
9. INTEGRATED WATER RESOURCES MANAGEMENT Water, apart from its role in plants and animals, has a basic function in maintaining the integrity of the natural environment. Population growth, urbanisation, industrialisation, expansion of agriculture, tourism, and climate change—all put water under increasing stress. The pressure on water resources highlights the hydrological, social, economic, and ecological inter-dependencies in river, lake, and aquifer systems. To address the multi-faceted nature of water management, many countries are now introducing an integrated approach to water resources management at the national and watershed level, which includes improving institutional arrangements and working practices. The problem of diminishing water supplies and ever-increasing demands has to be tackled realistically. The traditional reductionist approach of water resources management is no longer viable and a more holistic approach is essential. This is the background of the Integrated Water Resources Management (IWRM) approach, which has now been accepted internationally as the way forward for efficient, equitable, and sustainable development and management of the world’s limited water resources and for coping with conflicting demands. According to the Global Water Partnership (GWP), which is a network of organizations working in the field of water resources management ( includes government institutions, UN agencies, professional associations, research institutions, NGOs, and private agencies), Integrated Water Resources Management (IWRM) is “a process that promotes
the coordinated development and management of water, land, and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems” (GWP, 2009). At the river, stream, and aquifer level, IWRM can be defined as “a process that enables the co-ordinated management of water, land, and related resources within the limits of a watershed so as to optimize and equitably share the resulting socioeconomic well-being without compromising the long-term health of vital ecosystems”. Multiple uses and needs of water Water is of fundamental importance for crop production, drinking, sanitation, and hygiene. Agriculture uses about 69 percent, domestic and municipal use amounts to about 10 percent, and industry uses some 21 percent. In addition, substantial amount of water must be there in the environment for healthy ecosystems. All these water uses must be in harmony with each other. A coordinated action is required for ensuring availability and sustainability of sources. An IWRM approach focuses on three basic pillars that together act as the overall framework for ensuring sustainability. Social equity : To ensure equal access to users especially marginalized and poorer user groups to an adequate quantity and quality of water necessary to sustain human well being. Economic efficiency : To bring the greatest benefit to the greatest number of users possible with the available financial and water resources. Ecological sustainability: Aquatic ecosystems are acknowledged as users and that adequate allocation is made to sustain their natural functioning. Water for social and economic development is clearly linked to the IWRM focus on social equity, economic efficiency, and ecological sustainability. Water for social development includes the provision of education and health care. Without clean water supplies and good sanitation facilities in schools and hospitals social development is blocked. Water is of fundamental importance for economic development through energy and industrial production. It is needed for many forms of energy—hydropower and the water for cooling of thermal and nuclear power stations. Energy is also needed for pumping, including extraction of water from underground aquifers. Industry also needs water in a big way. Water is needed for many industries. The industries, through pollution and abstraction, have an influence on water quality that affects both downstream users and natural ecosystems. All these have significant implications for water resources management. Interlinking of rivers The concept of linking of rivers or inter-basin transfer of water has been accepted as a partial solution to address water availability in water scarce regions. It is essentially based on the availability of surplus of water in a donor river especially at the point of diversion to a deficit river basin. The surplus or deficit in a basin is determined based on availability at 75 per cent dependability, import, export, and existing and future needs. A river basin is said to be reasonably in surplus of water, if the surplus water is available after meeting the irrigation needs of at least 60 per cent of the cultivable area in the basin. Only this water from such a basin can be diverted to deficit basins. In India, the National Watershed Development Authority (NWDA) indicated that Himalayan rivers, especially, the Brahmaputra and the Ganges have exceedingly surplus quantum of water, and therefore, proposed transfer of water from these surplus basins to deficit basins in the peninsular region. In 2012, India announced plans to connect 37 rivers
