Water Resources Engineering

1. Unit-3
Ground Water
Mr. Dipesh Rajput
Lecturer in Civil Engineering
Dr. S. & S. S. Ghandhy College of Engg. & Tech., Surat
Email: dipesh_rajput2000@yahoo.com
Water Resources
Management (3340604)
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2. 2

3. CO-3: Develop Strategies for
watershed management and
rain water harvesting.
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4.  Out lines
1. Introduction
2. Ground water
3. Occurance of Ground Water
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5. Lecture-1
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6.  Introduction
 Ground water may be defined as the underground
water that occurs in the saturated zone of
variable thickness and depth, below the surface.
 Cracks and pores in the existing rocks and
unconsolidated layers, make up a large under
ground reservoir.
 Where part of precipitation is stored.
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7.  Ground water hydrology is the science of occurrence, distribution and
movement of water below the surface of earth.
 The largest available source of fresh water lies underground.
 The total ground water potential is estimated to be 1/3 of the capacity of
oceans.
 The study of subsurface flow is important since about 30% of the world's
fresh water resources exist in the form of ground water.
 Further, the subsurface water forms a critical input for the sustenance of
life and vegetation in arid zones.
 Ground water has been a popular resource water in many tropical
countries.
 Ground water is largely tapped for irrigation in India.
 So much so that about 46% of our total irrigated area, gets its irrigation
water from this source.
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 Introduction Conti…..

8.  Besides its irrigation, ground water is also used as a source of water supply for
municipal purposes.
 The ground water is utilised through wells and tube wells.
 The use of open wells is a traditional method of tapping ground water in areas
where ground water table is high.
 The use of tube wells, however, is a subsequent development in the technique of
tapping ground water.
 Ground water is easy to extract and it remains well protected from the hazards of
pollution that the surface water has to put up with.
 However, situations wherein we have encountered overexploitation of ground
water resources are not uncommon.
 Lack of detailed knowledge about the basics of ground water is the primary
reason why we have not been able to use groundwater resources to their full
extent.
 Thus, there is a growing emphasis on groundwater management.
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 Introduction Conti…..

9.  Importance of Ground Water
Ground water is widely distributed under the ground
and is a replenishable resource unlike other resources of
the earth.
 The quantity of ground water is huge, but it is
gradually decreasing.
 The distribution of ground water and its availability is
not uniform.
 The rate at which ground water is being recharged, is
less than the extraction rate.
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10.  Importance of Ground Water Conti….
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 Ground water is relatively free from pollution and therefore,
very important for domestic, and industrial use.
 Ground water is an important phase of hydrologic cycle.
 The most of the sources of perennial rivers are from ground
water or subsurface water.
 The ground water is superior to surface water in terms of
biological characteristics, but inferior in terms of chemical
characteristics.
 Ground water reservoirs are economical as compared to
surface reservoirs, because there is no need of construction of
reservoir and no siltation problem.
 Evaporation loss from ground water is less.
 If properly planned, the life of ground water is indefinite.

11.  Importance of Ground Water Conti….
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 In India, 60 % of agricultural water demand is fulfilled by
ground water, 40 % of land is irrigated by ground water.
 10 litre of water is used to produce 1 litre petrol.
 100 litre of water is required to produce 1 kg paper.
 22,000 litre of water is required to produce 1 tonne
cement.
 2500 litre of water is required to produce 1 kg wheat.
 4500 litre of water is required to produce 1 kg rice.
 For growing crops, 5000 m3 of water is required in 1 hectare
land.

12.  Occurrence of Ground Water
 The some part of precipitation that fall on the
surface of the earth gets evaporated.
 Some portion of water flows on the surface of the
earth and certain portion infiltrated in to the
ground and stored as subsurface water or ground
water.
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13.  Occurrence of Ground Water Conti….
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14.  Occurrence of Ground Water Conti….
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 The rainfall that percolates below the ground surface, passes through
the rocks, and joins the water table.
 These voids are generally interconnected, permitting the movement of
the ground water.
 But, in some rocks, they may be isolated, and thus, preventing the
movement of water between the interstices.
 The mode of occurance of ground water, therefore, depends mainly
upon the type of formation, and hence depends upon the geology of the
area.
 The possibility of occurance of ground water mainly depends upon two
geological features :
 (i) the porosity of the rocks
 (ii) the permeability of the rocks

15. 1. Porosity
 The porosity of a rock which is the major geological criteria for
occurrence of ground water.
 It is a quantitative measure of the interstices (voids) present in the
rock.
 The porosity is defined as the percentage of the voids present in a
given volume of soil or rock.
 Occurrence of Ground Water Conti….
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16.  Occurrence of Ground Water Conti….
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17.  Occurrence of Ground Water Conti….
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 Porosity of soil/rock depends upon the shape, packing and degree of
sorting of the component grains in a given material.
 Uniform and well sorted grains (Fig.) give rise to high porosity;
 whereas, heterogeneous grains with irregular arrangement (Fig.)
decrease the porosity.
 The porosity of rocks and unconsolidated materials may vary
considerably.
 It may be less than 1% or more than 50%. But generally, it does not
exceed 40% except in very poorly compacted soil.
 Porosity is classified as :
 20% or more = large
 5 to 20% = medium
 less than 5% = small

18.  Occurrence of Ground Water Conti….
Table:3.1 Porosity values of a few rock formations
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19.  Occurrence of Ground Water Conti….
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 Permeability is defined as the property of a rock or unconsolidated sediment, to permit
flow of water through it.
 Ground water can get stored in the underground rocks, only if, they are sufficiently porous.
 The porosity, however, in itself, does not ensure the storage of underground water.
 Infact the water can enter into a rock, if the rock permits the flow of water through it,
 i.e. it depends on whether the rock is permeable or not.
 It may be clarified, here that a rock which is porous, may or may not be permeable.
 For example, shale is a porous rock, but its pore spaces are so minute that the rock remains
impermeable.
 The size of pores, is thus, quite and important factor, and it should be sufficiently large to
make the rock permeable.
 Gravels are highly permeable.
 Clays are less permeable.
 Granite rocks are impermeable.

20.  Occurrence of Ground Water Conti….
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 Transmissibility represents the same physical meaning as
that of permeability, but only differing mathematically.
 The capacity of the entire soil of full width (b) and depth
(d)
 i.e. area bd is represented by permeability, while that of
the soil of unit width and full depth (i.e. b = 1 and d = d,
 i.e. A = is known as transmissibility. = d)