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Term Paper on Groundwater
Term Paper # 1. Introduction to Groundwater:
Liquid water occurs on our planet in three forms – as very large, medium and small bodies of standing water such as oceans, seas and numerous lakes; as bodies of flowing water, in the form of major rivers, streams, rivulets and springs; and as subsurface water, in the form of films around grains, droplets in pore spaces and cavities in rocks filling them partly or completely over variable areas and creating underground reservoirs.
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The subsurface water is further distinguished into two main types:
(i) Vadose Water:
It occurs from surface downwards upto a variable depth and is in a state of downward movement under the influence of gravity. Its movement is commonly described as INFILTRATION. The thickness of soil and rock through which the vadose water infiltrates is called zone of aeration. Obviously, in the zone of aeration, the soil and rocks remain unsaturated with water.
(ii) Groundwater:
This includes all the subsurface water reaching a depth below which all the pore spaces, openings and other cavities of the soil and rock are completely filled with water. The thickness, length and width of the saturated strata, the aquifer, constitute the groundwater reservoir in a given area. In this zone (of saturation), movement of water is principally under the influence of a hydrostatic head. It is commonly described by the term percolation, and is generally lateral in character.
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Water Table is the name given to the upper surface of the zone of saturation and is of fundamental importance in the study of groundwater reservoirs.
Term Paper # 2. Groundwater and Man:
Groundwater is considered a very important natural resource. In arid, semi-arid and dry regions, this may be the only source of water supply. Even in humid areas, groundwater is considered a better resource for many economic and hygienic reasons.
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The role of groundwater in sustaining the race of man on this planet can hardly be overemphasized. Presently, all the big and small countries are giving top priorities to short and long- term schemes envisaging exploration and exploitation of ground water reserves in their respective regions.
Already, millions of gallons of groundwater are being pumped out everyday in the world to meet industrial, agricultural and domestic needs of the man. With population and industrialization increasing at a tremendous pace and the agricultural and drinking-water requirements multiplying everyday, it is easy to guess the enormously greater quantities of water that would be required by the man in future.
It is true that seas, oceans – the surface bodies of virtually inexhaustible water sources – are available for exploitation. But it is also true that water from none of these surface sources can be naturally suitable and as economically exploitable as the groundwater.
Thus, compared to the above-mentioned sources, groundwater:
(i) Has a suitable composition in most cases and is free from turbidity, objectionable colours and pathogenic organisms requiring not much treatment;
(ii) Is relatively much safe from hazards of chemical, radiogenic and biological pollution to which surface water bodies are badly exposed;
(iii) Supplies are not quickly affected by drought and other climatic changes and hence are more dependable;
(iv) Being available locally in many cases may be tapped and distributed at much lesser costs using very little network of pipes. In fact, in many areas it is directly pumped up by the users.
Term Paper # 3. Sources of Groundwater:
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Most of the groundwater occurring below the surface is derived from the following three sources:
(a) Meteoric Water:
It is the water derived from precipitation (rain and snow). Although bulk of rainwater or meltwater from snow and ice reaches the sea through surface flows or run off, a considerable part of precipitation gradually infiltrates into the ground. This infiltrated water continues its downward journey till it reaches the zone of saturation to become a part of the groundwater in the aquifer.
Almost entire water obtained from groundwater supplies belongs to this category. The process of infiltration of rainwater may start almost immediately after a rainfall. It may take, however, varying periods before the infiltrated water reaches the aquifer below. This depends on the original condition of the ground at the time of rain, duration of rainfall, grain size and porosity of the soil and rocks that make the ground and so on.
Water may also be contributed to the ground by surface water bodies (which are themselves supplied by precipitation) such as rivers, lakes and seas. In the case of streams, it happens when the water table is lower than the water level in the stream. Such streams are often referred as Influent Streams. A reverse condition is also common when groundwater nourishes a stream; in this case water table is higher than the level of water in the stream and the stream is called effluent stream.
(b) Connate Water:
This is the water present in the rocks right from the time of their deposition in an aqueous environment. During the process of formation of sedimentary rocks in a lake or sea or river, deposition is followed by compaction, which leads to the squeezing out of most of the water present between the sediments.
Sometimes, however, incomplete compaction may cause retention of some water by these rocks. This is the connate water and may be encountered in sedimentary rocks like limestones, sandstones and gravels. It is commonly saline in nature, and is of no importance as a source for exploitable groundwater.
(c) Juvenile Water:
It is also called magmatic water and is of only theoretical importance as far as water-supply schemes are concerned. It is the water formed in the cracks or crevices or pores of rocks due to condensation of steam emanating from hot molten masses or magmas existing below the surface of the earth. Some hot springs and geysers are clearly derived from juvenile water.
Term Paper # 4. Hydrological Cycle and Groundwater:
For a proper understanding of groundwater in all its aspects, the concept of hydrological cycle must be understood clearly. The so-called hydrological cycle is merely a chain of events involving water as it exists in all its forms on or within the Earth. It is almost a continuous process – a cycle – having neither a beginning nor an end in a broad sense.
Water exists on the Earth in three forms – gaseous, liquid and solid. The gaseous water is a part of the atmosphere that surrounds the earth and is present in it upto a height of 10-15 km. The liquid water is spread over 70 percent surface of the globe forming huge oceans, seas, rivers, lakes, streams and springs. Included in this category is also the water occurring as an easily-transferable part in plants and other types of vegetation.
Similarly, liquid water present in the pores, crevices and variety of openings of soil and rocks below the surface also makes an important part of this group. Solid water occurs in the form of extensive ice-bodies, the glaciers and the snowfields covering millions of square kilometers in polar and mountainous regions (Fig. 18.2).
As a part of the hydrological cycle, the liquid (and solid) water evaporates from the surface waterbodies and is lost from the vegetation by transpiration and thereby becomes a part of the atmosphere. Under suitable conditions, these water vapours condense into clouds and subsequently get precipitated in the form of rain, snow, sleet and hail etc.
The groundwater also moves in many cases to sea through subterranean movement and eventually becomes a part of the water cycle. Thus, essential feature of water cycle are – evaporation (from land and oceans), condensation and precipitation, return to land and oceans (through interception, run off, infiltration, percolation etc.).
Just as a large quantity of water returns from the atmosphere directly to the oceans through precipitation over their vast surface, some water may join atmosphere directly from the land due to evaporation and transpiration. These direct conversions are novelties of the hydrological cycle rather than exceptions to the rule (Fig. 18.2).
Term Paper # 5. Zonal Distribution of Subsurface Water:
The water that goes below the surface of the land may be found to exist in two main zones or environments classified as:
A. Vadose water and
B. Phreatic water or groundwater.
A. Vadose Water:
In the vadose water zone itself, three different types of environments are distinguished:
1. Soil water,
2. Intermediate vadose water and
3. Capillary water.
1. Soil Water:
The soil water forms a thin layer confined to the near surface depth of the land. It may occur at depths between 1.0 to 9 meters, and is held up by root zone of vegetable cover and soil chemicals. This water is very important for the life and growth of the vegetable cover of the globe. It is lost to the atmosphere by transpiration and evaporation.
2. Intermediate Vadose Water:
The intermediate vadose zone occurs immediately below the zone of soil water. It is, in fact a zone of non-saturation – water in this zone is moving downwards under the influence of gravity. It is generally of small thickness and may be even absent in many cases. The above two zones are sometimes collectively referred as zone of aeration.
3. Capillary Water:
The zone of capillary water, called capillary fringe is present only in soils and rocks of fine particle size underlying the vadose zone. It is absent in the coarse sediments. In the fine particle size zone, groundwater is drawn upwards by capillary action, sometimes to heights of 2-3 meters above the saturated zone lying underneath.
Growth of vegetation observed in some deserts is very often dependent on the presence of the capillary fringe. The cause of rise of water (rather than its downward movement) in the capillaries of fine sediments is the well-known force of surface tension.
B. Phreatic Water:
The Phreatic Water Zone, also called the zone of saturation lies below the capillary fringe, and it is the water held in this zone that is called groundwater in the real sense. The upper surface of water in the zone marks the water table in the area. In this zone, the layers or bodies of rocks which are porous and permeable, have all their open spaces such as pores, cavities, cracks etc. completely filled with groundwater. All these openings are thoroughly interconnected so that a well dug into this zone receives water from the entire saturated rock mass, called the aquifer.
Since in this zone all the openings are completely filled with water, there is no or very little downward movement of groundwater. The predominant movement is a type of lateral flow, controlled by the head of the water (or level at different places) flowing from a higher head to lower head in order to achieve a level surface everywhere. In all groundwater exploration programmes, the main objective is to locate this zone and determine its extent, geometry and character.
In many cases a significant rise and fall in the level of zone of saturation is observed as a characteristic feature during different parts of the year depending upon rainfall and recharge. A third zone, zone of intermittent saturation is then easily recognized which marks the depths between the zone of vadose water (aeration) and the zone of permanent saturation. This zone (of intermittent saturation) will yield water only during and immediately after rainy seasons becoming a non- yielding zone for rest of the year.
Term Paper # 6. Wells and Its Types:
Wells are defined as openings or holes dug or drilled into an aquifer (water-bearing formation) with a view of withdrawing water for drinking, agricultural or other uses. Mostly these are vertical holes drilled or dug into the ground upto the aquifer. Water may flow through these wells either due to natural hydrostatic pressure or may have to be pumped out. These may be quite shallow or deep depending on the depth at which the water-bearing strata are encountered.
Types:
i. Gravity Well:
It is also called a water table well and is a vertical or nearly vertical hole penetrating the zone of saturation below the ground. The essential character of such a well is that surface level of water in the well which is at atmospheric pressure, and represents, when at rest, the water-table of the area around the well.
Water will not normally flow out of such a well on its own; it has to be pumped out or taken out. Most wells driven in the aquifers for withdrawal of water are actually gravity wells. When water has to be pumped out of these wells, these form the locations of the Tube Wells.
ii. Galleries:
These are horizontal tunnels or open ditches that are dug out through a water-bearing formation to intercept water. These are dug generally perpendicular to the direction of flow of water in the aquifer.
iii. Artesian Wells:
These are the holes drilled through the confined or artesian aquifers. In such wells water generally flows out at the ground surface, and even may gush out to some height.
Basic Concepts:
Well hydraulics is an exhaustive subject requiring a thorough study of aquifer characteristics and hydrology.
The definitions of some basic terms are:
(1) Static Water Level:
When a well is dug into an unconfined aquifer, water enters into it and after some time acquires a stable level. This level, when expressed as distance from the surface is termed static water level. It is disturbed when water is drawn out or pumped and re-established in most cases when pumping is stopped (Fig. 18.12).
(2) Pumping Water Level:
When water is withdrawn from a well through pumping or other means for some time, the level of water in the well is lowered down. The level of water in the well as determined during pumping is called pumping water level at that point of time. It will-go down with further pumping and recover when pumping is stopped.
(3) Discharge or Yield:
Each well will yield only a specific quantity of water per unit time depending upon the characteristics of the aquifer on the one hand and design elements of the well on the other hand. The volume of water discharged through the well per unit time is called its Yield and is expressed in terms of gallons per minute or cubic meters per day.
(4) Drawdown:
This term gives the difference between the static water level and the pumping water level. In actual practice, when water is drawn from a well, originally at a static water level, there is a general lowering of water table in and around the well. The maximum lowering (of level) is within the well itself, the effect decreasing away from the well.
As such, any time after the beginning of pumping, the level of water at different points from the well may be actually at different heights (with respect to the level in the well). It is then best represented by a curve. This is a drawdown curve. Drawdown then simply represents the head available to water in the aquifer to flow through the surrounding rocks towards the well (Fig. 18.12).
(5) Cone of Depression:
During withdrawal of water from a well, water from all the sides moves into the well. This effects the level of water all around, which is lowered down because of removal of water from the formation. The lowering down of water level is, however, not uniform around the well. Maximum effect is felt within and in the immediately vicinity of the well and it gradually decreases with increase in distance from the well in all directions.
When plotted all around the well, the upper surface of water in the formation will form a cone, with apex in the well. This is often called Cone of Depression or cone of exhaustion. When pumping is stopped for some time, the water-level within and around the well becomes normal again.
(6) Radius of Influence:
It is the horizontal distance from the centre of a well to the extreme of the cone of depression and is an indicator of the nature of an aquifer, especially its transmissibility. Thus, a very large radius of influence and a related shallower cone indicate a highly permeable formation.
Conversely, a smaller radius of influence with a deeper cone of depression is found in less transmissive aquifers (Fig. 18.12). In coarse gravel formations the influence line may extend for as much as 400-800 meters around the well whereas for similar pumping conditions for silty sands, the radius of influence may lie within 100 meters or so.
The stability of cone of depression (and hence radius of influence) is dependent on a number of factors such as volume of water being pumped out, transmissivity of the aquifer and conditions of recharge existing around the well.
(7) Recharge:
This simply signifies water added back into the aquifer naturally or by artificial methods. Recharge from natural sources may be on continuous basis or on an intermittent seasonal pattern. Thus, when an aquifer is geologically linked with a surface water body such as a lake or a river, a condition of recharge is established when the cone of depression intersects the water body.
In fact, in such a situation a condition may arise when the rate of recharge may be so pronounced as to be equal to rate of discharge from the well (due to pumping) and the cone of depression becomes stabilized.
Similarly, periodic recharge of an aquifer may occur during rainfall when water infiltrates through the vadose zone. This water reaches the zone of saturation below from a wide area and may replenish the inventory of water in the aquifer.
Recharge of a tapped aquifer may also take place by leakage from a saturated strata overlying at a distance from the well and spread over a greater extent. The collective amount of water supplied by such an overlying formation having low transmissivity compared to the formation in which the well is located may be quite large to balance the discharge.
Artificial methods of recharge as adopted in some advanced countries include disposing waste waters or used waters over the known aquifers. Special spreading basins are created to which the waste waters from various directions can be directed. Water from such a basin percolates downward and gets filtered naturally before becoming a part of groundwater inventory of the aquifer.
Term Paper # 7. Springs and Its Classes:
A spring is a natural outflow of groundwater. Principally, there are two classes of springs- descending and ascending.
Descending types of springs, also called non-pressure type, include all those types of springs in which groundwater pours out from a water-bearing formation due to one or other of following geological conditions:
(i) A part of water-bearing formation is exposed on the surface due to erosion of the covering rock;
(ii) A groundwater reservoir starts overflowing;
(iii) An aquifer forms a natural wedge due to faulting etc.;
(iv) A fissure or system of fissures connects the surface with the saturated formation.
Ascending type of springs come into being from artesian water sources in which the water is always under some hydrostatic head. Where such a layer is intercepted by a natural fissure or geological discontinuity, water gushes out with a force. In another group of ascending springs, called geysers, water may be moved up from below due to pressure from hot gases and vapours, generally emanating from magmatic bodies.
Springs of either class are found occurring on the land surface and also along the coastal, submarine areas. On the basis of occurrence, springs are sometimes distinguished as surface and submarine springs.
In quality, the spring waters may vary from crystal clear purest and cold sweet water to turbid, highly mineralized and/or hot waters. Hot waters are commonly derived from deeper sources and in most cases these are meteoric waters that travel back to surface after coming in contact with hot rocks at depth. In their upward journey at elevated temperatures they dissolve a number of minerals, many of which are re-deposited as the spring water reaches surface.
Sometimes the hot water may be derived as is the case with many geysers, directly from the magmatic emanations, and carries original dissolved components of magmas. Exceptionally cold water springs are often glacial meltwaters emerging out of crevice after having seeped into the rock beds in the higher reaches under glaciers.
The rate of flow of a spring depends on the situation of the spring with reference to the saturated bed on the one hand and recharges conditions on the other hand. Most springs show fluctuations in water yield during different parts of the year; some may even dry up during unfavourable periods. The rate of precipitation has been found to directly influence the rate of flow of many springs. The artesian springs are rather more constant in their yield and rate of flow throughout the year.
Term Paper # 8. Engineering Considerations for Groundwater:
Civil Engineers have to deal with groundwater in one way or another throughout their professional career. In case they are dealing with water resources management, groundwater becomes their direct concern. This is because in almost all countries groundwater forms a very important source of water supply.
Where they are involved in planning and execution of major civil engineering projects such as dams, reservoirs, tunnels, multistoreyed buildings, nuclear reactors and towers, they cannot afford to overlook critical importance of groundwater in relation to these projects.
The stability, safety and economy of these costly structures are all influenced considerably with the presence of groundwater in and around the sites.
A detailed study of all the aspects of groundwater forms, therefore, an important field of specialization:
(a) As Source of Water Supply:
The importance of groundwater in water supply system can hardly be over emphasized. It is in no way subordinate to that of surface waters.
The Water Resource Engineer will look for the following details in this regard:
(i) Nature, Location and Geometry of an Aquifer:
The presence of a free groundwater aquifer of reasonable thickness and area at a shallower depth (5-10 meters) requires little or no exploitation systems. Such is the situation in many flood plains. The consumers can use this water directly by installing pumping sets or even hand pumps. However, where such an aquifer occurs at great depth or at considerable distance from the populated area, detailed investigations will have to be made for developing a system for exploitation and distribution of groundwater.
These investigations will include mapping of the aquifer, its relationship with other topographical and geological features and conditions of recharge. When the aquifers happen to be of an artesian type, conditions of its inclination, exposure of the rim in an area of recharge and absence of leakage points become some additional characters to be investigated.
(ii) Functions of an Aquifer:
An aquifer, though a natural geological rock formation, performs a number of functions simultaneously similar to an artificial storage reservoir, conduit and filter plant. These aspects of an aquifer must be thoroughly investigated while planning a water supply project based on its development.
As a storage reservoir, the aquifer behaviour is controlled by:
(i) The nature of rock and its porosity;
(ii) Structural disposition, with regard to the recharge points or places; and
(iii) Climate conditions (annual precipitation etc.).
It must be remembered that an aquifer can hold water only temporarily, as the water is always in a state of flow in it. However, the rate of flow of water through an aquifer is very slow compared to surface waters. Hence, when a proper balance is established between the recharge and withdrawal for consumption, crisis-free water supply from groundwater source can be assured. In fact by adopting better management techniques, these sources can be depended upon even during dry (drought) spells.
An aquifer serving in an area of demand may be replenished through artificial recharge at a higher point and thus virtually serve as a system of conduits. Similarly, an aquifer may be made to serve as a filter plant when artificial recharge is made to pass through an intervening layer of rock, which acts as a natural filter.
To illustrate this, when an aquifer located near a river is pumped heavily, water-table in it will fall quickly thereby causing the river water to flow to the aquifer. But this flow has to be through a thickness of the aquifer which removes most of the suspended sediments and bacteria and even chemical pollutants before the river (recharge) water actually becomes a part of the groundwater inventory.
(iii) Operational Yield:
An aquifer is a natural reservoir, conduit and filter-plant all at the same time, yet its capacity to yield water is quite limited in the strict sense. It has to be on a regular, recurring basis. In this respect, it differs from a gold mine from where even the last ounce of metal is desired to be extracted. The mine is then abandoned.
The yield from an aquifer depends as much on the management aspects as on the natural features of the aquifer.
It depends on:
(i) The capacity of the aquifer to hold water;
(ii) Rate of annual recharge from natural and artificial sources; and
(iii) Rate of annual withdrawal.
The quantity of water that can be withdrawn annually and also the rate at which this withdrawal could be made without adversely affecting the inventory of the aquifer, therefore, determine what may be called operational yield, from an aquifer. Arriving at a figure for operational yield requires a thorough knowledge of hydrogeological characteristics of aquifer and essential principles of water resource management.
In summary, following six point programme is deemed as minimum for planning a reliable water supply project based on free groundwater:
i. A broad assessment of geological structure, petrological character and hydrogeological features of the entire region under consideration must be available.
ii. Distribution (areal), geometrical characters (thickness, width, length and slope) and hydrological properties (porosity, permeability, specific yield etc.) of the aquifer or set of aquifers should be established.
iii. Determination of thickness, chemical and granulometric composition of the soil as also the type of vegetative cover that made up the zone of aeration and moisture dynamics of this zone should also be made.
iv. Conditions of recharge in various zones related to the area due to infiltration from precipitation, from filtration through surface waters (lakes and rivers) and from other water-bearing strata not directly included in the area of productive aquifer should be established.
v. Conditions of drainage by springs, rivers, lakes, drainage installations and through leakage to any adjacent dry but porous strata must be determined.
vi. Records of basic natural factors including meteorological, hydrogeological and hydrological records of the area on daily, seasonal, annual and perennial basis and those of changes in the quality of water in terms of chemical composition and bacterial content must be obtained and studied.
(b) Groundwater in Engineering Projects:
The economy, safety, design and construction of all major engineering projects like dams and reservoirs, tunnels and highways etc. are intimately related to the groundwater regime of the area in which projects are located. It is, therefore, a matter of importance that the project engineer obtains fullest possible information through direct and indirect explorations and investigations about the position of water-table, type and condition of aquifers and hydraulic characteristics of rocks. Not only that, he must be capable to correlate this information with the safety, stability and design considerations of the project.
At this place only a passing reference in this regard may be sufficient:
i. Dams and Reservoirs:
A dam is built across a river primarily to store water in the form of a reservoir. The whole idea of a dam would become irrelevant if the foundations on which it is built are made of porous rocks or if a stretch of a reservoir rock is permeable. When the water table is quite low as compared to the level of water in reservoir quite an appreciable amount of water may leak into the rocks below thus effecting the inventory of the reservoir adversely. Also, the leaking water may initiate failure at the abutments or even under the dam in a number of ways.
As such, the position of water table and hydrogeological qualities of rocks forming foundations and abutments of dams and reservoirs must be known.
ii. Tunnels:
All tunnels are underground passages either for traffic of one type or another or for the conduct of water.
Any tunnel may pass through one or more of the following three situations viz-a-viz groundwater:
(a) The entire length of the tunnel is located above the water table.
(b) The entire length is below the water table, i.e. it passes through the zone of saturation.
(c) The alignment is partly above and partly below the water-table.
Obviously, the design, construction and maintenance of a dry tunnel (condition ‘a’), will demand an entirely different type of consideration than for a wet section (condition ‘b’) or for combined sections. These considerations, would in turn, depend on a full knowledge of the groundwater parameters of the rocks in and around the proposed alignment of the tunnel.
iii. Highways and Cuts:
Groundwater may present very complex problems in laying out highways and air fields. In either case, the site is considered unsafe and unstable if the water table is very high, that is, is just near the surface. Some sort of reliable drainage system must be provided if the site has to be selected at any cost.
Similarly, groundwater is a major source of trouble for the stability of slopes. Many slope failures, especially in hilly regions are due to direct or indirect involvement of groundwater. Soil creep and solifluction are caused mainly due to groundwater. The lubricating action of water besides its negative effect on the strength parameters of rocks is the major cause in initiating massive landslides. The study of groundwater regime, therefore, rightly forms a primary step in the studies dealing with stability of slopes.
iv. Irrigation Projects:
A rise in the water-table to the root zone of plants causes waterlogging. This phenomenon which may take place during or after excessive rains or flooding or influent canals and rivers is greatly harmful for crops. The root system of crops in water-logged areas gets decomposed. Large areas of land in Indian subcontinent are affected by water-logging.
An associated trouble with rising water-table is the development of salinity of the soils. The rising groundwater may be rich in some undesirable salts that are left at or near the surface during its loss to atmosphere due to evaporation. This increased salt content (generally alkaline salts are precipitated) of the soil makes it most useless for cultivation. A thorough study of groundwater regime in irrigated and water-logged areas forms an important step in their reclaiming for cultivation.
Term Paper # 9. Groundwater Potential of India:
According to estimates arrived at by Ministry of Water Resources, Government of India, the total replenishable groundwater resources of the country are around 434 billion cubic meters (BCM) per year (2006). Of these resources, 361 BCM/year are available for irrigation although actually net draft for irrigation during last couple of years has been around 150 BCM/Year which formed more than 50 percent of total irrigation needs of the country.
The distribution pattern of ground water reserves in India, geographically speaking, presents an interesting scenario that is easily explained by the geological set up of the country.
As is well known, India, considered as a whole, is made up of three prominent geomorphological features:
The northern mountainous belt covered by the Himalayan System mountains starting from Ladakh and Kashmir in the North West and extending up to Assam and beyond in the North East covering Himachal, Punjab, Uttaranchal and Nepal in between. In these regions, runoff is the most characteristic feature, infiltration being least on hill slopes. Hence, potential of ground water in these areas is limited to the intermountain valleys and plains.
The ground water situation is drastically different in the Indo-Gangetic—Barhamputra plains extending from Punjab in the west to Bihar and beyond in the East. The large alluvial tract constitutes ONE OF THE LARGEST AND MOST POTENTIAL GROUNDWATER RESERVOIRS OF THE WORLD.
This tract has been extensively studied and exploited and is known to be made of large number of aquifers. Most of these aquifer systems are extensive, thick and hydraulically interconnected. No wonder then that they are by and large of high and moderate yielding class.
The Peninsular India including Maharashtra and the entire group of Southern states present varying situations with respect to groundwater potential depending primarily on the geological make up. As we know, the entire Peninsular country is made up of hard, massive, quite deep and thick rock but variously fissured formations.
These include crystalline rocks, trappean basalts and the inter- trappean sedimentary formations. These formations are generally covered by a mantle of weathered rocks which at most places is a good receptacle for rain water and conducts the infiltration to the underlying fractured rocks. Hence there are areas of good potential with respect to groundwater development down to a depth of 100 m or so.
As regards the coastal and deltaic belt developed in the Peninsula, presence of sufficiently thick alluvial sedimentation’, groundwater reserves are sufficiently large and suitable for consumption and irrigation. However, a common hazard encountered in the wells located in the narrow marginal belt is the ingress of sea water especially during the periods when over draft lowers down the water table in these aquifers.
The Arid Tracts of Rajasthan and adjoining areas offer problems in groundwater resources due to scanty precipitation, unfavourable geological set up and to some extent degree of mineralization, which is often higher.
Quality:
It may be said as a generalization that the groundwater quality as available in greater part of India is quite suitable for all types of uses – drinking, irrigation and industrial.
Term Paper # 10. Fresh Water Crisis in India:
It has been widely accepted now that despite vast groundwater reserves, India is fast heading towards a fresh water crisis. Millions of Indians are already facing great shortage of drinking water and the number may increase in coming years, especially during dry spells of the year.
The shortage of freshwater supplies has been attributed mainly to two causes both of which are man-made viz.:
i. Firstly:
Improper management of available water resources, and
ii. Secondly:
Increasing environmental degradation leading to pollution of water reserves, both on surface and underground.
During the last thirty years or so the total water requirements for all type of uses has increased tremendously due to:
(a) Increase in population;
(b) Fast growing urbanization;
(c) Fast growing industrialization;
(d) Expansion in irrigated areas.
The supplies of fresh water for these needs from the surface sources have been gradually dwindling because of increasing pollution of these bodies from discharge of huge volumes of untreated waste water into them. The pressure has been increasing on the extraction of greater and greater volumes of groundwater, almost in an absolutely uncontrolled manner.
The fierce but generally unobserved competition that went on for years between the user sectors – domestic, agriculture and industrial resulted in so obvious a situation – the groundwater level has recorded a steep fall in several parts of the country year after year.
The situation has worsened additionally because of unscientific disposal of domestic and industrial wastes which leak into the potential aquifers affecting the quality of ground water supplies. Increasing deforestation and resulting soil degradation also contributes in decreasing the replenishment.
In fact, when seen in totality, environment pollution in general (of air, water and land) has been a major source of pollution of groundwater also in particular. Clouds coming down through industrially polluted air cannot be expected to bring down fresh water rains.
Such polluted rains cannot become source of pure groundwater supplies. The whole system is interlinked. The water crisis problem, therefore, needs an integrated multidirectional approach involving environmental systems at local, state and national level.
Our national government has already come up with the needed legislatory acts in the form of the Water (Prevention and Control) Act, 1974, the Environmental Protection Act, 1986, which stand applicable in the entire country.
But more than legislation, the water crisis needs an integrated effort involving:
(a) Creating full awareness among all the sections of society about the magnitude of the problem;
(b) Integrating water use as effectively as possible with water regeneration, that is, extraction and replenishment of water resources must be managed meticulously.
This is the sum and substance of the National Water Policy of Government of India. There are, however, some areas where groundwater reserve becomes inferior due to salinity and occurrence of harmful minerals in larger than permissible values.
Salinity is a common hazard expected and encountered in aquifers located in peripheral zones of coastal regions, for example, in Gujarat, Maharashtra, Tamil Nadu, Orissa and West Bengal.
There is another type of salinity—the inland salinity, which is quite common in arid regions like Rajasthan, Haryana and Punjab. Here the salt content of groundwater is related to the geological set up prevailing in and around the aquifer. Sodium salt contamination is quite common.
At places in Bihar, Assam and U.P, arsenic contamination has also made groundwater reserves useless. Iron contamination has also been observed in many tracts of the country. Fluoride contamination (exceeding 1.5 mg/1) has been found in almost all the states but generally in isolated tracts.
Term Paper # 11. Groundwater Estimates of India:
The estimates published by Central Groundwater Board give us sufficient hope that if the Policy and Programmes as envisaged are implemented rigorously, the crisis can be met successfully. India is a vast country and blessed with ample reserves of water resources both on ground and underground.
The crisis is because of mismanagement of the resources. 