Here is an essay on ’Ground Water’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Ground Water’ especially written for school and college students.
Essay on Ground Water
- Essay on Ground Water Resources
- Essay on Ground Water Recharge
- Essay on Ground Water Development in India
- Essay on the Chemical Composition of Ground Water
- Essay on Ground Water Potential in India
- Essay on the Methods of Exploitation of Ground Water
- Essay on Ground Water Development
- Essay on the Fluctuations in Ground Water Levels
- Essay on Ground Water Investigation
- Essay on the Conjunctive Use of Ground Water
- Essay on Maximising Irrigation Efficiency and Water Management
- Essay on Ground Water Legislation and Pollution
Essay # 1. Ground Water Resources:
Ground water is a precious and the most widely distributed resource of the earth and unlike any other mineral resource, it gets its annual replenishment from the meteoric precipitation. The world’s total water resources are estimated at 1.37 × 108 million ha-m. Of these global water resources about 97.2% is salt water mainly in oceans, and only 2.8% is available as fresh water at any time on the planet earth. Out of this 2.8%, about 2.2% is available as surface water and 0.6% as ground water.
Even out of this 2.2% of surface water, 2.15% is fresh water in glaciers and icecaps and only of the order of 0.01% (1.36 × 104 M ha-m) is available in lakes and reservoirs, and 0.0001% in streams; the remaining being in other forms -0.001% as water vapour in atmosphere, and 0.002% as soil moisture in the top 0.6 m. Out of 0.6% of stored ground water, only about 0.3% (41.1 × 104 M ha-m) can be economically extracted with the present drilling technology, the remaining being unavailable as it is situated below a depth of 800 m.
Thus, ground water is the largest source of fresh water on the planet excluding the polar icecaps and glaciers. The amount of ground water within 800 m from the ground surface is over 30 times the amount in all fresh water lakes and reservoirs, and about 3000 times the amount in stream channels, at any one time.
At present nearly one fifth of all the water used in the world is obtained from ground water resources. Agriculture is the greatest user of water accounting for 80% of all consumption. It takes, roughly speaking, 1000 tons of water to grow one ton of grain and 2000 tons to grow one ton of rice. Animal husbandry and fisheries all require abundant water. Some 15% of world’s crop land is irrigated. The present irrigated area in India is 60 million hectares (M ha) of which about 40% is from ground water.
The average annual rainfall (a.a.r.) of India is around 114 cm. Based on this a.a.r., Dr. K. L. Rao has estimated that the total annual rainfall over the entire country is of the order of 370 M ha-m and one third of this is lost in evaporation. Of the remaining 247 M ha-m of water, 167 M ha-m goes as runoff and the rest of the 80 M ha-m goes as subsoil water. Out of this 80 M ha- m of subsoil water that seeps down annually into the soil, about 43 M ha-m gets absorbed in the top layer, thereby contributing to the soil moisture; the balance of 37 M ha-m is the contribution to ground water from rainfall.
The average annual ground water recharge from rainfall and seepage from canals and irrigation systems is of the order of 67 M ha-m of which 40% i.e., 27 M ha-m, is extractable economically. The present utilisation of ground water is roughly half of this (13 M ha-m), and about 14 M ha-m is available for further exploitation and utilisation.
The excavations at Mohenjo-Daro have revealed brick-lined dug wells existing as early as 3000 B.C. during the Indus Valley Civilisation. The writings of Vishnu Kautilya (in the reign of Chandragupta Maurya—300 B.C.) indicate that ground water was being used for irrigation purposes at that time.
Sinking of wells and a variety of water devices were well known from Vedic times.
The first irrigation Commission in 1903 affirmed the importance of irrigation wells. The Well Sinking Department of the Government of Nizam at Hyderabad made interesting studies on ground water in the Deccan Basaltic Terrains.
In 1934, a project for construction of 1500 community tubewells in the Ganga basin was initiated in U.P. The success of this project led to the constitution of a Sub-Soil Water Section in the Government of India in 1944, which was converted later into the Central Ground Water Organisation which functioned till 1949. During this period a Central Drilling School at Roorkee was established which trained more than 100 officers of the Central and State Government.
The Exploratory Tube-wells Organisation (ETO) was set up during 1954 under Indo-US Technical Cooperation Operational Agreement No. 12, under the Ministry of Agriculture and concomitantly, the Ground Water Exploration Section was set up in the Geological Survey of India.
In October 1970, the Ministry of Agriculture upgraded the Exploratory Tube-wells Organisation into the Central Ground Water Board (CGWB) merging it with the Ground Water Regional Directorates and District Offices of the Geological Survey of India to effectively shoulder the ground water investigation programmes; it started functioning from August 1972. As an apex body at the national level, the Board is concerned with all matters relating to exploration, assessment, development, management and regulation of the country’s ground water resources.
Large scale ground water investigation programmes have been taken up since 1967 in Rajasthan, Gujarat, and Tamil Nadu with the assistance of the UNDP, the Canadian assisted project in AP, the Upper Betwa River Basin Project in MP and UP with UK assistance, Narmada Valley Project in MP, Vedavathi and Tungabhadra River Basin in Karnataka under UK assistance and many such projects.
During the middle and late sixties, the Government of India urged all State Governments to set up a State Level Ground Water Organisation to deal with problems of ground water surveys and development and utilisation for minor irrigation and eventually they have been set up as State Directorates of Ground Water or as a Ground Water Cell (in Karnataka). The Central Ground Water Board is contemplating special measures for ensuring coordination of work among the various States and between the Centre and States so that overlapping or duplication is avoided.
Since 1970, major programmes with the assistance of UNICEF for provision of drilled wells for rural water supply have been launched in the hard rock areas of AP, Karnataka, MP, Maharashtra, Tamil Nadu and Rajasthan. These utilises the air hammer drilling rigs.
The updated hydrogeological map of India of scale 1:5,000,000 (released by GSI in 1969 to scale 1:2,000,000 and updated by CGWB in 1976) gives many hydrological details.
In recent years there has been an increasing tendency towards drilling deep wells as well as towards revitalisation of existing open (dug, shallow) wells. Advances in the field of ground water development have made it possible to lift ground water from depths of 60 to 100 metres. With the extension of electricity in the rural areas, there has been a great spurt in the lift irrigation from tube wells and open wells.
The Government, voluntary agencies, Agricultural Refinance Corporation, Land Development Banks, State Agro Industries Corporation etc. are all coming forward to help the poor and marginal farmers by giving short and long term loans, grants technical advice, and making technical feasibility and economic viability studies, thus accelerating the pace of ground water development and bringing more land under intensive irrigation.
Essay # 4. Chemical Composition of Ground Water:
The chemical composition of ground water is related to the soluble products of rock weathering and decomposition and changes with respect to time and space. Geochemical studies provide a complete knowledge of the water resources of a hydrological regimen. Sampling and testing in an area with some good quality and some poor quality water should serve to differentiate areas and aquifers of varying quality and on the results of these study recommendations can be made regarding different uses to which water in various areas and aquifers can be put.
Geochemical studies are also of value with respect to water use. They provide a better understanding of possible changes in quality as development progresses, which can in turn provide information about the limits of total development, or can permit planning for appropriate treatment that may be required as the result of future changes in the quality of water supply.
For analysis of chemical quality of water, tracing the movement of ground water is important. Induced tracers, including salt solutions, dyes such as fluorescein, and radioactive materials have been used as well as other techniques through the knowledge of hydrogeology.
Analysis of water samples for geochemical studies requires a high degree of accuracy. The intensity of sampling should be gauged by the needs of the investigation and the severity of any water quality problems. The chemical characteristics of water are very important with respect to requirements for various uses.
To determine sea water intrusion, lines of piezometers are inserted at various depths at different distances from the sea coast. A 300 m cable may be used in a portable conductivity bridge or meter. A sudden increase in the EC (of the order of 50,000 µ mhos/cm) or chloride concentration (of the order of 19,000 ppm) at a particular depth, has sometimes indicated sea water intrusion. Fogged or connate water may also contribute to chloride concentration.
Temperature measurements are usually made in ground water studies. These are particularly important in places where wide variations in the temperature are recorded. The depth of the source of ground water could be gauged from the temperature of the water (geothermal gradient ≈ 30 to 50 m/°C). Temperature results may lead to the discovery of an unsuspected source of pollution.
Essay # 5. Ground Water Potential in India:
About two-third of the total land area in the country comprises consolidated formations, 75% of this being made up of crystalline rocks and consolidated sediments, the remaining 25% being trap. The remaining one-third of the total land area comprises semi-consolidated and unconsolidated formations like alluvial tracts. There is ample scope for development of ground water in these areas.
1. Springs in the Himalayan Highlands:
All types of rocks are present; the chief types include granites, basalts, sandstones, limestones, shales, conglomerates, slates, quartzites, gneisses, schists and marbles; favourable conditions exist with springs forming a major part of water supply; in valleys alluvial deposits of thickness is = 30 m; soft water with TDS (total dissolved salts) < 500 ppm.
2. Fresh Water Sediments of Kashmir Valley:
The Kashmir valley which was a vast lake during the Pleistocene times shows a large scale development of fresh water sediments of lacustrine, fluvial and glacial origin = 600 m thick.
3. Indo-Gangetic Alluvium (Vast Reservoir of Fresh Sweet Water):
Coarse sands, gravel and boulders of variable thickness—3 to 60 m. TDS < 400 ppm, water commonly hard; shallow and deep aquifers interconnected (leaky); aquifer soil -D10(effective size) = 0.075-0.38 mm, D50 = 0.17-0.30 mm, Cu(uniformity coefficient) = 1.1-3.3, T = 1.7 × 105-5.0 ×.106 lpd/m (litres per day per metre), S = 2 × 10-2 to 4 × 10-6, leakance K’/b’ =0.3 lpd/ m3, accretion to g.w.t. (ground water table) = 21% of a.a.r., tubewell yield
= 50-100 m3/hr. (Here T is the transmissibility coefficient; K’, the permeability and b’, the thickness of the semi-pervious layer, and S, the storage coefficient.) The exploitation of ground water is usually done by using spiral augers, hand boring (H.B.) sets, cable tool and rotary rigs.
The alluvial material of Punjab constitutes an extensive heterogeneous and anisotropic unconfined aquifer with lateral permeability ranging from 26 to 156 m3/day/m2. There are about 120,000 tubewells in this area and the extraction of ground water should be limited to the annual recharge to avoid undue depletion of the aquifer.
4. Coastal Alluvium: Malabar and Coromandel Coastal Areas:
Depth 15-150 m, yield = 12-50 m3/hr; low TDS; water in tertiary aquifer associated with lignite or carbonaceous clays is sulphuretted (H2S) and contains iron > 1 ppm. Extensive saline patches occur in Ramnad, Tirunelveli, Ongole, Nellore and Krishna districts.
In Ramanathapuram and Tirunelveli, the ground water in the unconfined aquifers is generally of poor quality with CI > 1000 ppm and at some places even > 3000 ppm.
In the west coast areas of Kerala and Karnataka, the substratum is mostly lateritic and a good yield of ground water may be expected.
Saline water influx in response to tides is noticed at places in Goa, up to distances of 25-40 km inland. In the upper reaches, the tidal streams show cyclic fluctuation in salinity, the salinity flows corresponding to low tides when waters are utilisable.
5. Cretaceous Sandstones of Kathiawar and Kutch Areas:
Moderately potential aquifers; depth 100-300 m, yield = 10-120 m3/hr; water commonly brackish with TDS 2000-5000 ppm.
In Gujarat, sandstone aquifers are of depth 60-200 m; yield = 10-50 m3/hr, TDS 1000- 2500 ppm.
6. Mesozoic Sandstones of the Lathi Region in Rajasthan (Jaisalmer, Barmer, Bikaner):
Moderately potential aquifers, depths 100-150 m, yield = 45-150 m3/hr; water is generally brackish to saline, TDS 1000-5000 ppm, CI 1000-5000 ppm, EC (electrical conductivity) > 3000 µmhos/cm, Na% > 80, SAR 25-55, waters C4-S4 or C4-S3 types (for explanation of these notations see Fig. 9.7).
7. Cavernous Limestones of Vindhyan System in Borunda and Ransingaon areas in Jodhpur District:
Potential aquifers, yield 40-70 m3/hr. Potable water, TDS < 2000 ppm; fractured up to 150 m.
In arid zones of Rajasthan and Gujarat excess concentration of fluoride (5 to 20 ppm) has been observed, resulting in mottling of teeth.
Recharge of some arid zones in Haryana and Rajasthan can be done by diverting the flood waters of Yamuna River through Saraswathi and Ghaggar rivers by making suitable connections.
8. Boon Valley Gravels:
Boulders, pebbles, gravel, sand and clay are possibly of fanglomeratic and collovial origin. Major portion of the valley is hilly, sloping ground; only the central part (= 388 km2 which is approximately one-fifth of the total area of 2090 km2) can be developed.
As a rough estimate of the potential of Doon gravels:
Which can support more than 200 tubewells yielding = 150 m3/hr each; a.a.r. = 216 cm; therefore accretion to g.w.t. = 44%. Thickness of fill 150-200 m; TDS 100 to 500 ppm, CI > 30 ppm, pH 7.8; water—bicarbonate to sulphate type. Lower areas yield = 30-50 m3/hr.
In the Terai zone, ground water is available under artesian conditions and at shallow depths of 3-50 m. Sands and gravels confined in the silts and clays make good aquifers under confined conditions. Wells are usually bored with augers and/or hand boring sets.
9. Quaternary Alluvium of Narmada, Puma, Tapti, Chambal and Mahanadi Rivers:
Thickness 75-150 m (lenses of sand and gravel); tubewell yield 20-150 m3/hr; good quality water with TDS 100-500 ppm.
10. Vesicular Basalts in the Deccan Trap Formations of Maharashtra and Madhya Pradesh:
Form good aquifers; ground water occurs under both confined and unconfined conditions in the Satpura range and Malwa plateau; tubewell yields in Indore, Bhopal, Raisen, Vidisha and Sagar districts ≈ 10-40 m3/hr.
In central Maharashtra the tubewells drilled in weathered basalts yield = 2-10 m3/hr while in exceptional cases the yields are = 25 m3/hr, mostly within depths of 50-100 m. Borewells, due to their low yield, are mainly a source of drinking water supply and only in exceptional cases can they be used for irrigation; TDS < 1000 ppm.
11. Carbonate Rocks with Solution Cavities in Madhya Pradesh:
In the Vindhyan, Cuddapah and Bijawar region, the carbonate rocks with interconnected solution cavities and caverns form good aquifers. The limestones of Raipur, Charmuria, Kajrahat (Sidhi district), Karstic areas of Chhatisgarh basin and Baghelkhand region of MP yield ≈ 10-60 m3/hr.
12. Dharwarian and Bundelkhand Granite Region of Madhya Pradesh:
Igneous and metamorphic rocks; the movement of water is mainly through joints and openings. Tubewells in Tikamgarh, Chattarpur, Balaghat and Gwalior area yield ≈ 10-30 m3/hr, mostly under water table conditions.
The water quality in all regions of MP is generally good, except in the water logged areas of the Chambal valley (due to seepage from canals).
13. Tertiary Sandstones and Quaternary Sand to Pebble Beds in the Godavari-Krishna Inter-stream Area:
Form potential aquifers with artesian conditions. Near Muppavaram the piezometric surface is 19 m above the land surface and falls towards the coast at a gradient of 4-25 m/km. Aquifer thickness 3-184 m, T = 80-6485 m3/day/m, K = 1-80 m3/day/m2. Tubewell yield ≈ 20-120 m3/hr. for a drawdown of 6 m. For a similar drawdown, Rajahmundry sandstones yield ≈ 42 m3/hr. for a screened thickness of 20-140 m. Similar yields are in the Tirupathi, Gollapalli and Chitalpudi sandstones.
As a rough estimate of the ground water flow (Q), with a hydraulic gradient (i) of 1/304 near Tadikalapudi, the length of the aquifer (w) of 90 km between Viravalli and Guddigudem and an average transmissibility (T) of 945 m3/day/m, it follows from Darcy’s law that-
Q = Tiw = 945 × 1/304 × (90 × 103) = 280 × 103 m3/day
With two-thirds of this yield (allowing for short duration data) about 375 to 400 tubewells can be constructed with an average yield per tubewell of 500 m3/day.
The quality of ground water in the sandstones is fresh while that in alluvium is highly saline in the vicinity of Kolleru Lake, along the coast and at depths; TDS 1800-15,000 ppm, CI 600-8000 ppm, making the ground water unsuitable for any purpose.
14. Alluvium in Palar and Kortallaiyar-Araniyar Rivers in Tamil Nadu:
Form potential aquifers- water of good quality within 50 m; CI < 250 ppm, EC 750-2,000 µmhos/cm.
15. Tertiary Sediments of Cauvery Delta:
The tertiary sediments in Tanjore and South Arcot districts form extensive aquifers up to 200 m depth. Water is of good quality; CI < 150 ppm, EC < 1,500 µmhos/cm. Many of the tubewells have free flow, some exceeding 2 m3/hr.
In the Cauvery delta rocks ranging in age from Precambrian Crystalline to Quaternary Sediments are encountered. Multiple aquifer systems are quite prevalent in a sufficiently thick sedimentary basin. The deep-seated aquifers are generally under confined conditions and there is hydraulic interconnection (vertical leakage) between aquifers. Recharge facilities are more for the top aquifers than the bottom aquifers. A fair yield of 76,500 m3/day may be expected in the Cauvery delta of Tanjore as per UNDP investigations.
T = 1.2 × 105 – 8.2 × 105 lpd/m
S = 3.3 x 10-4 – 6.8 × 10-5
EC = 800 – 1100 μmhos/cm
Q = 30 – 60 m3/hr
UNDP, in 1972, estimated the presence of 5000 Mm3 of groundwater in the delta and north of the Coleroon River.
Although artesian wells are quite prevalent, large scale development will lower the piezometric head and free flow condition would cease. For example, a decade ago there were many flowing wells in and around Neyveli. But now the piezometric head has been lowered and many flowing wells have become sub-artesian wells.
In Coimbatore and the central districts of Tamil Nadu, the substratum consists of rock at a moderate depth and the yield is very poor.
Near Pondicherry, deep wells even very close to the coast yield potable water.
Ground Water Potential in Chennai Environs (UNDP):
Minjur – 33750(G.W. potential, m3/day)
Duranallur—Panjetti – 40500(G.W. potential, m3/day)
Tamarapakkam—Villanur – 49500(G.W. potential, m3/day)
These well fields presently supply 45000 m3 /day to industrial units at Manali (Chennai).
16. Granitic Gneisses and Schists of Karnataka:
The principle rock types of Karnataka are igneous and metamorphic granites, gneisses and schists of Precambrian age and basalt of the Deccan trap of Eocene-Upper Cretaceous age in the extreme northern part of the state. The yield is very low and the borewells drilled up to depths of 30-75 m yield 5.40 m3/hr.
The yield of wells in the crystalline rocks depends on the presence of weathered pockets, joints and fractures, of which there may be no indication at the surface. The yield of a well may be strikingly different from that of another well a few metres away. Surface geophysical resistivity survey may however indicate depth and extent of concealed weathered pockets, which may ensure against risk of failure.
17. Upper Gondwana Sandstones and the Alluvial Tract of Orissa:
Form potential aquifers. The a.a.r. = 142 cm and about 20% of this, i.e., ≈ 28 cm may be assumed as the recharge; also ≈50% of the recharge potential can be utilised by the installation of filter point tubewells with a spacing of = 330-580 m and the remaining 50% utilised by dug wells and deep tubewells.
The yield of filter point tubewell of size 7.5-10 cm penetrating aquifers of 7-12 m thick (located within 50 m b.g.l.) is in the range of 20-50 m3/hr, which provide irrigation for 4-6 ha of land. The draw-down usually does not exceed 7 m and a low head centrifugal pump (2-4 kW) coupled directly to the filter point tubewell.
The capital cost of installation of a filter point tubewell varies from Rs. 8000-12,000 depending on the depth and size of the filter point and requires a simple hand boring set with a tripod for drilling the bore. At present there are about 800-1,000 filter point tubewells in Orissa state, most of them being located in the Balasore district and under the World Bank loan assistance programme there is a proposal to take up installation of 15,000 filter point tubewells.
In the alluvial tract where the granular aquifer material occurs within 8-10 m below ground level and also in the semi-consolidated sedimentary sandstones, weathered within 5 m b.g.l. open wells fitted with 2-4 kW centrifugal pump can be installed for irrigation purpose, with a minimum spacing of 150-200 m in alluvial tracts. Such wells can irrigate 2-2.5 ha of land in Kharif and 1-1.25 ha in Rabi season.
The capital cost of such wells varies from Rs. 10,000-15,000 with benefit cost ratio ranging from 1.5 to 3.1. Small wells of 1.5-2 m diameter fitted with indigenous type of water-lifting devices can irrigate about 0.4 ha of land in Kharif and 0.2 ha in the Rabi season. The capital cost of such small wells varies from Rs. 3,500-5,000 and the benefit cost ratio is very low due to the involvement of high cost of man power; yet it is a prized possession for a small farmer and has a significant influence on his economic condition.
It is estimated that 65% of the ground water potential of the state can be developed by installation of open wells. At present there are about 2 lakh open wells meant for irrigation in Orissa, and there is World Bank loan assistance for the installation of 2 lakh open wells for the irrigation during the next five years.
18. The Quaternary Sediments in the Deltaic Tract around Digha, District Midnapur, West Bengal:
These are of depth 140 m and yield fresh water.
19. The Multilayered Lacustrine Aquifer in Nepal in the Centre of the Kathmandu Valley Basin:
Extends to 350 km2 out of the total area of a roughly circular basin of 607 km2. It has a depth of sediment of > 450 m, deposits becoming coarser towards the north where most of the catchment is mountainous. The sediment consists of silt, coarse sand and cobbles with electrical resistivity ranging from 40-120 ohm-m. The a.a.r. = 174 cm, mostly during summer monsoons.
Wells with rather low yields could be constructed in the northern potential areas, the recharge being only 3,600 m3/day. Mud-flush rotary drilling rigs are found suitable. T = 92-301 m2/day, K = 2-12 m/day, 48 hour specific capacity = 113-137 m3/day/m, S = 2.3 × 10-4– 3.7 × 10-3; these rather high values indicate a high degree of elasticity of the confined aquifer. For unconfined aquifer Sy ≈ 0.1.
20. Karstic Limestones in the North Coastal Belt of Sri Lanka:
Nine-tenths of the areas of the island are underlain by the crystalline rocks such as gneisses, schists, quartzites and crystalline limestones of the Precambrian basement complex; low yields are obtained from the locally developed fissures and fractures. The soil overburden is 2-15 m and large diameter dug wells are generally suitable.
The remaining one-tenth of the island, in the north and north-western coastal belt, consists of deep sedimentary formations, where the Miocene limestone formations provide the major Karst aquifers under artesian and phreatic conditions; depth 90 m (average); piezometric level 15-33 m b.g.l. (free flowing wells at low ground levels). Tubewell yield 50-150 m3/hr, specific capacity 36-72 m3/hr/m, CI 100-770 ppm, T = 7900 m3/day/m.
The a.a.r. of the island is 220 cm and the ground water potential ≈ 24.6 Mm3.
21. Thermal and Mineral Springs:
They are found in many parts of India—Bombay, Punjab, Bihar, Assam, in the foothills of Himalayas and Kashmir.
Any programme of ground water exploitation should have the following equipment for well sinking (boring or drilling) or revitalization:
(i) Tractor/compressor for blasting or extension drilling.
(ii) Compressors (VT-4, VT-5 etc.) for drilling rigs and development of wells.
(iii) Bencher units for extension drilling.
(iv) Cobra units for drilling blast holes.
(v) Auger rigs and hand boring sets for boring shallow wells, say, in terai region, in coastal aquifers of Cauvery data, in the alluvial tract of Orissa, or boring cavity wells as in Delhi IARI Pusa area.
(vi) Cable tool or percussion rigs as may be suitable in the areas of Indo-Gangetic alluvium, sediments of Jammu and Kashmir valley, unconsolidated formations in Bengal, Gujarat and Madhya Pradesh, and soft and boulder formations.
(vii) Rotary rigs (straight rotary) in semi-consolidated formations and reverse rotary (reverse circulation) for large diameter and deep holes in soft consolidated formations.
(viii) Air rotary is especially suitable for limestones and air foam is used to remove cuttings.
(ix) Rotary-cum percussion rigs in the consolidated formations of Madhya Pradesh, Bihar, Orissa, Gujarat etc.
(x) Jetting drill is suitable for unconsolidated formations for holes up to 15 cm diameter and plenty of water is required for the water jet.
(xi) Down-the hole hammer (DTH) rigs like Ingersoll Rand, Halco-625, Sanderson Cyclone, RMT, etc., for fast drilling of deep borewells in the hard rock areas of peninsular India, i.e., in crystalline areas.
(xii) Down-the hole hammer rigs like Halco Tiger, Halco Minor, Atlas Copco etc., for fast drilling of borewells in the Deccan traps of Maharashtra or the hard rock areas of Coimbatore and North Karnataka where the yield of borewells is very low.
(xiii) Calyx drills can drill bore wells in hard rock areas (the rock cores are cut by feeding chilled steel shots) but they are very slow. Calyx drills can be used for drilling bores at the bottom of open wells either for well revitalisation or dug-cum-bore wells, centrifugal pump can be installed at the bottom of the dug well with the suction pipe in the bore).
As on March 1979, there are about 4500 hand boring sets, 230 percussion rigs, 330 rotary rigs, 80 reverse circulation rigs, 20 rotary-cum-percussion rigs, 225 down-the-hole hammer rigs, 150 Calyx rigs and 500 pneumatic rigs in the 17 States of the country.
Ground water can be developed at a small capital cost and the time taken for development is very small. The chemical quality of ground water is found to be generally good and can be used for drinking, agriculture and industrial purposes. The hard rock drilling programme by UNICEF has significantly lowered the unit cost ‘per capita’ of making available a safe water supply; water is usually struck at a depth of 30-60 m in hard rock formations and requires no treatment.
The tapping of ground water—location, spacing and yield, in a well field should be so phased that the annual recharge and discharge of the aquifer are almost balanced without causing an overdraft in the area. As the ground water development increases, problems of well field management will become dangerously critical in many places and the studies on optimum well spacing will be required in order to minimise mutual interference between pumped wells.
The recharge depends upon the rock or soil formation and the a.a.r. of the region and is given below:
Recharge Rates for Different Formations:
Hard rock formations and Deccan traps – 10
Consolidated formations (sandstones) – 5 – 10
River alluvium – 15 – 20
Indo-Gangetic alluvium – 20
Coastal alluvium – 10 – 15
In several areas, the recharge estimates made on the above assumed rates have agreed well with the estimates of recharge based on actual water level rise in the region and the specific yield of the formations.
Essay # 8. Fluctuations in Ground Water Levels:
Fluctuations in ground water levels are caused by a pumping well in the vicinity, earthquake, loading and wind. Fluctuations in water levels sometimes occur when railroad trains or trucks pass aquifer test sites. Drawdown data must be adjusted for these changes in loading before they are used to determine the hydraulic properties of aquifers and confining beds.
The ground water level rises when there is a decrease in the atmospheric pressure and the water level falls when the atmospheric pressure increases. Drawdown data are adjusted for atmospheric pressure changes occurring during an aquifer test by obtaining a record of atmospheric pressure fluctuations and using the equation-
BE = ∆W/∆B × 100 …(5.35)
Where BE = barometric efficiency (%); ∆W = change in ground water level corresponding to a change in atmospheric pressure (m) and ∆B = change in atmospheric pressure (m of water).
Water levels in wells near surface water bodies are often affected by surface water stage fluctuations either because of a loading effect or a hydraulic connection between the surface water body and the aquifer. As the surface water stage rises, the water level in the well rises and as the surface water stage falls, the water level in the well falls. The ratio of the change in water level in a well to the change due to a loading effect is known as the tidal efficiency and the ratio of the change in the water level in a well to the change in the surface water stage because of a hydraulic connection is known as the river efficiency-
TE = ∆W/∆R × 100 …(5.36)
RE = ∆W/∆R × 100 …(5.37)
Where TE = tidal efficiency (%), RE = river efficiency (%), ∆W = change in water level in the well corresponding to a change in the surface water stage (m), and ∆R = change in surface water stage (m).
Jacob (1950) derived expressions relating to barometric and tidal efficiencies and the elasticity of artesian aquifers, and obtained the relations-
S = γw bβ = 1/BE …(5.38)
BE + TE = 1 …(5.39)
Drawdown data are adjusted for surface water stage change during an aquifer test by obtaining a record of surface water stage fluctuations and using Eqs. (5.36) and (5.37).
Essay # 9. Ground Water Investigation:
The problems facing any ground water investigation programme are the zones of occurrence and recharge.
The various phases of a ground water investigation programme are given below:
(a) Hydrometeorological study.
(b) Hydrogeological Study:
(i) Geological mapping
(ii) Test drilling, sampling and logging
(iii) Pumping tests (aquifer tests)
(c) Geophysical Survey:
(d) Aerial Photographic Survey:
(i) Black and white
(iv) Radar imagery
(e) Tracer techniques
(f) Geochemical and geothermal surveys
(g) Systems analysis, mathematical modelling and computer applications for ground water basin management
(h) Water Balance Studies:
(i) Intensive irrigation and water management.
The objectives of any hydrogeological investigations are:
(i) Define recharge and discharge areas,
(ii) Define major water bearing units,
(iii) Define location, extent and inter-relationship of aquifers,
(iv) Establish physical parameters of aquifers like transmissibility, storage coefficient and specific yield,
(v) Estimate total subsurface storage capacity, and
(vi) Establish geologic factors which affect quality of ground water.
(vii) Arrive at the location, probable depth of drilling and yield from the bore well (tubewell)
Aerial and infra-red photography, electrical resistivity surveys and logging techniques can provide valuable information in regard to the zones of occurrence and recharge. The U.S. Geological surveys (USGS) by the use of an infra-red scanner, has published an atlas of Hawaii’s coastal areas, pinpointing the location of underground fresh water flows.
With the advancement of space technology, it has been possible now to resort to the remote sensing technique for the estimation of surface and subsurface waters over large areas. This technique employs the surveying of ultra-violet visible microwave radiations emitted and reflected from the surface of the earth. This method would be extremely useful for rapid hydrogeological mapping of large and inaccessible areas. Areas of dry and wet rocks, aquifers, open water surfaces, springs etc., can be delineated by skillful interpretation.
With the hydrometeorological data combined with geophysical and hydrogeological investigations and pumping tests, it is possible to develop and manage the ground water resources of a basin.
Surface water and ground water may be viewed as two different forms of occurrence of the same total water resources. Tubewell schemes may be integrated with the canal irrigation schemes (composite irrigation) by suitably spacing them along a line in between the distributary and the drainage line and so designing that the subsoil water level is kept steady at a desired level.
The tubewells intercept the canal seepage and serve as an anti-water logging measure and enable the benefit of irrigation facilities to be spread to wider areas. Supplemental ground water irrigation is proposed to be introduced in the command areas of a number of major irrigation systems like the Yamuna canal, the Cauvery and the Krishna deltas to enable intensive agricultural development.
As old varieties of cereals, pulses and millets are being replaced by new high yielding varieties which respond to chemical fertilisers, fresh studies on soil-water-plant relationship are being carried out to determine the irrigation requirements of different crops at different stages of growth. This has to be carried down to the level of the farmer through extension services for introducing improved and intensive agricultural practices.
By charging for the water supplied (by measuring the tubewell discharge over the V- notch or by noting the power units consumed) and lining the water courses by any cheap material locally available like clay tiles, laterite sheets, cuddapah slabs with joints finished with 1:4 cement mortar or soil cement, brick in cement mortar, etc., the economic use of water is achieved.
Hence, it is necessary to have an All India Water Resources Council to coordinate, compile and computerise data and apply modern methods of ‘systems approach’ to irrigation.
There is need for legislation for ground water exploitation and regulation to check indiscriminate draining of ground water resources. Precautions should be taken against pollution of surface and subsoil waters by enacting legislation.
Water is a national asset available in a finite quantity. One cannot afford to forget that if one cannot afford to pollute air which is available in unlimited quantities, much less can one afford to take liberties with the use of the limited asset of water.