UNIT I PHYSICAL GEOLOGY AND GEOMORPHOLOGY 9

Significance of Geology in Civil Engineering; Internal structure of the Earth;

Weathering: types, engineering classification of weathered rocks and relevance to Civil
Engineering; Fluvial, Marine, Glacial and Aeolian landforms and their importance in
Civil Engineering; Plate tectonics and its relevance to earthquakes; Groundwater: types
of aquifers, origin, movement and role of groundwater in Civil Engineering
constructions.

Significance of Geology in Civil Engineering

Engineering geology importance: Engineering geology provides a systematic knowledge

of construction material, its occurrence, composition, durability, and other properties.
Examples of such construction materials are building-stones, road materials, clays,
limestone, and laterite.

Engineering geology provides a systematic knowledge of construction material, its

occurrence, composition, durability, and other properties. Examples of such construction
materials are building-stones, road materials, clays, limestone, and laterite. The
knowledge of the geological work of natural agencies such as water, wind, ice and
earthquake helps in planning and carrying out major civil engineering works. For
examples, the knowledge of erosion, transportation, and deposition helps greatly in
solving the expensive problems of river control, coastal and harbour work and soil
conservation. The knowledge about groundwater that occurs in the subsurface rocks and
about its quantity and depth of occurrence is required in connection with water supply
irrigation, excavation and may other civil engineering works. The foundation problems of
dams, bridges, and buildings are directly concerned with the geology of the area where
they are to be built. In these works, drilling is commonly undertaken to explore the
ground conditions. Geology helps greatly in interpreting the drilling data. In tunnelling,
constructing roads, canals, and docks and in determining the stability of cuts and slopes,
the knowledge about the nature and structure of rocks is very necessary.

IMPORTANCE OF PHYSICAL GEOLOGY

This is also variously described as dynamic geology, geomorphology, etc. As the name
suggests it deals with:

(i) Different physical features of the earth, such as mountains, plateaus, valleys, rivers,
lakes, glaciers, and volcanoes in terms of their origin and development,
 (ii) The different changes occurring on the earth's surface, like marine transgression,
marine regression, formation or disappearance of rivers, springs and lakes,

(iii) Geological work of wind, glaciers, rivers, oceans, ground water, and their role in
constantly molding the earth's surface features, and

(iv) Natural phenomena like landslides, earthquakes, and weathering. The main cause for
surface changes is weathering. This is a natural phenomenon resulting directly or
indirectly due to changes in the atmosphere. It disintegrates and decomposes rocks. This
aspect is of special importance from the civil engineering point of view, because color,
appearance, strength and durability of rocks are adversely affected by weathering. Thus
even granite which is considered ideal for most of the civil engineering works becomes
weak and friable on thorough weathering, rendering it useless. Civil engineers deal with
structures like dams which are artificial barriers to the natural flow of rivers. Proper
understanding of the geological work of a river and its features will lead to their better
utilization for engineering applications.

Internal structure of the Earth

Layers of the Earth

To understand the details of plate tectonics, one must first understand the layers of the
Earth. Unfortunately, humankind has insufficient first-hand information regarding what is
below; most of what we know is pieced together from models, seismic waves, and
assumptions based on meteorite material. The Earth can be divided into layers based on
chemical composition and physical characteristics.

Chemical Layers

The Earth has three main divisions based on its chemical composition and makeup.
Indeed, there are countless variations in composition throughout the Earth, but only two
significant changes occur, leading to three distinct chemical layers.

Crust

The crust is the outermost chemical layer and the layer humans currently reside on. The
crust has two types: continental crust, which is relatively low density and has a
composition similar to granite, and oceanic crust, which is relatively high density
(especially when it is cold and old) and identical to basalt. In the lower part of the crust,
rocks start to be more ductile and less brittle because of added heat. Earthquakes,
therefore, generally occur in the upper crust.

At the base of the crust is a substantial change in seismic velocity called the Mohorovičić
Discontinuity, or Moho for short, discovered by Andrija Mohorovičić (pronounced mo-
ho-ro-vee-cheech) in 1909 by studying earthquake wave paths in his native Croatia. It is
caused by the dramatic change in composition between the mantle and the crust.
Underneath the oceans, the Moho is about 5 km down. Under continents, the average is
about 30-40 km, except near a sizeable mountain-building event, known as an orogeny,
where that thickness is roughly doubled.

Mantle

The mantle is the layer below the crust and above the core. It is the most substantial layer
by volume, extending from the base of the crust to a depth of about 2900 km. Most of
what we know about the mantle comes from seismic waves, though some direct
information can be gathered from parts of the ocean floor brought to the surface, known
as ophiolites. Also carried within magma are xenoliths, small chunks of lower rock
carried to the surface by eruptions. These xenoliths are made of the rock peridotite, which
is ultramafic on the scale of igneous rocks. We assume the majority of the mantle is made
of peridotite.

Core

The core of the Earth, which has both liquid and solid components, is made mainly of
iron, nickel, and oxygen. It was first discovered in 1906 by looking into seismic data. It
took the union of modeling, astronomical insight, and seismic data to realize that the core
is primarily metallic iron. Meteorites contain much more iron than typical surface rocks.
If meteoric material made the Earth, the core would have formed as dense material
(including iron and nickel) sank to the center of the Earth via its weight as the planet
formed, heating the Earth intensely.
Weathering: types, engineering classification of weathered rocks and relevance to Civil
Engineering

Weathering is the combination of processes that breaking down of rocks, soil

and minerals, eventually transforming into sediment. On the other hand, disintegration
or alteration of the rock surface in its natural or original position through physical,
chemical and biological processes induced or modified by wind, water and climate.

Weathering involves physical, chemical, and biological processes that act separately or
more often together to cause fragmentation and decay of rock material. Physical
decomposition causes mechanical disintegration of the rock and therefore depends on the
application of force. Weathering involves breaking up the rock into the forming minerals
or particles without disturbing the forming minerals. The main sources of physical
Weathering are the expansion and contraction of heat, the erosion of overlapping
materials, the release of pressure on the rock, alternatively the freezing and thawing of
water, the dissolution of water between the cracks and cracks in the rock, the growth of
plants and organisms in the rock. Organisms in the rock. Rock exchange usually involves
chemical deterioration in which the mineral composition in the rock is altered, rearranged
or redistributed. Rock minerals are subjected to solution, carbonation, hydration and
oxidation with circulating water. These effects on the Weathering of minerals are added
to the effects of living organisms and plants as nutrient extraction to rocks.

After the rock breaks, the remaining materials cause soil with organic materials. The
mineral content of the soil is determined by the parent material; therefore, a soil derived
from a single rock type may often be lacking in one or more minerals required for good
fertility, whereas a ventilated soil from a mixture of rock types (such as glacial, aeolian or
alluvial deposits) generally makes more fertile soils. In addition, most of the
Earth’s landforms and landscapes are the result of decomposition processes associated
with erosion and re-accumulation.
Explain the disintegration or dissolution of rocks and minerals on the Earth’s surface.
Water, ice, acids, salts, plants, animals and changes in temperature are all weather
conditions.

After a rock is shredded, a process called erosion removes rock and mineral fragments.
No rock on earth can resist erosion.

Physical weathering or Mechanical weathering

Physical weathering, also called mechanical weathering or disaggregation, is a class of

processes that cause rocks to break up without chemical change. The primary process in
physical weathering is abrasion (the process by which clips and other particles are
reduced in size). Temperature, pressure, freezing and so on. Physical weathering may
occur for reasons. For example, cracks resulting from physical weathering will increase
the surface area exposed to the chemical effect, thereby increasing the rate of
disintegration.

Frost wedging: Freezing water blows pipes and breaks bottles; because water expands
when the walls of the container freeze and push. The same phenomenon occurs on the
rock. When stuck water in a joint freezes, it forces the joint to open and may cause the
joint to grow. These freezing wedges allow the blocks to be freed from solid bedrock.

Salt wedging: In arid climates, dissolved salt in groundwater precipitates and grows as
crystals in open pore spaces in rocks. This process, called salt wedging, pushes apart the
surrounding grains and weakens the rock so that when exposed to wind and rain, the rock
disintegrates into separate grains. The same phenomenon happens along the coast, where
salt spray percolates into rock and then dries.

Root wedging: Have you ever noticed how the roots of an old tree can break up a
sidewalk? As roots grow, they apply pressure to their surroundings, and can push joints
open in a process known as root wedging

Thermal expansion: When the heat of an intense forest fire bakes a rock, the outer layer
of the rock expands. On cooling, the layer contracts. This change creates forces in the
rock sufficient to make the outer part of the rock break off in sheet-like pieces. Recent
research suggests that the intense heat of the Sun’s rays sweeping across dark rocks in a
desert may cause the rocks to fracture into thin slices.
Animal attack: Animal life also contributes to physical weathering: burrowing creatures,
from earthworms to gophers, push open cracks and move rock fragments. And in the past
century, humans have become perhaps the most energetic agent of physical weathering
on the planet. When we excavate quarries, foundations, mines, or roadbeds by digging
and blasting, we shatter and displace rock that might otherwise have remained intact for
millions of years more.

Chemical weathering

Chemical weathering changes the composition of rocks, often transforming them when
water interacts with minerals to create various chemical reactions. Chemical weathering
is a gradual and ongoing process as the mineralogy of the rock adjusts to the near surface
environment. New or secondary minerals develop from the original minerals of the rock.
In this the processes of oxidation and hydrolysis are most important. Chemical
weathering is enhanced by such geological agents as the presence of water and oxygen,
as well as by such biological agents as the acids produced by microbial and plant-root
metabolism.

The process of mountain block uplift is important in exposing new rock strata to the
atmosphere and moisture, enabling important chemical weathering to occur; significant
release occurs of Ca2+ and other ions into surface waters.

Dissolution: Chemical weathering during which minerals dissolve into water is called
dissolution. Dissolution primarily affects salts and carbonate minerals (Fig. B.6a, b), but
even quartz dissolves slightly.

Hydrolysis: During hydrolysis, water chemically reacts with minerals and breaks them
down (lysis means loosen in Greek) to form other minerals. For example, hydrolysis
reactions in feldspar produce clay.

Oxidation: Oxidation reactions in rocks transform ironbearing minerals (such

as biotite and pyrite) into a rustybrown mixture of various iron-oxide and iron-hydroxide
minerals. In effect, iron-bearing rocks can “rust.”

Hydration: the absorption of water into the crystal structure of minerals, causes some
minerals, such as certain types of clay, to expand. Such expansion weakens rock.

Organic or Biological Weathering

A number of plants and animals may create chemical weathering through release of
acidic compounds, i.e. the effect of moss growing on roofs is classed as weathering.
Mineral weathering can also be initiated or accelerated by soil microorganisms. Lichens
on rocks are thought to increase chemical weathering rates.

Fluvial, Marine, Glacial and Aeolian landforms and their importance in Civil Engineering

Landforms are distinct types of features on the Earth’s surface that are formed
naturally and usually take a certain shape. The shape of each feature differs depending on
the conditions of the region they are formed in. These shapes of landforms differentiate
all these natural formations from each other and thus have been named accordingly.

The main examples of the various types of landforms are mountains, plains, plateaux,
and valleys. The other types of landforms are coastal ones, such as peninsulas, and
underwater structures, such as ocean ridges and basins.

Types of Landforms

Many types of landforms form depending on various conditions and the structure of the
Earth’s surface in a particular area. As Earth also is not the same everywhere and is
characterized by different types of surfaces, there are a variety of landforms that are
created. At some points, the surface of the Earth is even, and at other places, the surface
might be rough and bumpy.

 Glacial Landforms
 Coastal Landforms
 Volcanic Landforms
 Fluvial Landforms
 Karst Landforms

Check here the various types of landforms that exist on the Earth’s surface in various
geographical locations of the world.

Glacial Landforms

Glacial landforms are a major type of landforms that are created as a result of the
activity of glaciers. They are also an important topic for the UPSC exam. A glacial
landform is a feature formed naturally due to ice flowing and water melting. These types
of landforms are created in areas like Antarctica, Greenland, and other regions that
consist of mountain ranges at much higher altitudes. These areas are called glaciated
areas. Examples of these glacial landforms include the following –

 Corries/ Cirque
 Bergschrund
 Hanging Valleys
 Rock basins
 Moraines
 U-shaped glacial troughs

Coastal Landforms

These are the type of landforms that exist alongside coastal areas. The coastal
landforms are formed as a consequence of various natural phenomena occurring on the
coast. These landforms that exist in the coastal areas can be categorized into two
types- Depositional and Erosional. A few examples of these landforms are-

 Beaches with gentle slopes

 Bays
 Capes
 Marine dunes
 High cliffs
 Sea cliffs

Volcanic Landforms

The landforms that are formed as a result of volcanic activity are called volcanic
landforms. Constant activity is happening on the Earth’s surface, and volcanic eruptions
constantly keep changing the Earth’s geographical conditions. They also result in the
creation of new formations sometimes.

The volcanic landforms are formed depending on the place or area where exactly the
molten magma coming out of the volcano cools down. Based on that, Volcanic landforms
are also divided into two categories-

 Intrusive Volcanic Landforms: These are the type of landforms that are formed
when the molten hot magma gets cooled down inside the crust of the Earth.
Examples are – Batholiths, Lacoliths, Lopoliths, Phacoliths, Sills and Sheets, and
Dikes.
 Extrusive Volcanic Landforms: These types of landforms are created when the
molten lava solidifies on the outer area. This happens when all of the resultant
products of the volcanic eruptions are oozed out of the surface. Examples of these
 types of volcanic landforms are- Cinder Cones, Conical Vent, Fissure Vent,
Caldera, Composite-type Volcanic Landforms, Craters, Domes, and Flood Basalt.

Fluvial Landforms

These types of landforms are formed as a by-product of any erosional or depositional

activity occurring in the rivers or streams. The landforms forming as a consequence of
erosion happening in the rivers are called fluvial erosional landforms.

Popular examples of fluvial landforms are Oxbow lakes (U-shaped), Peneplain, Gully,
Drainage basins, Island, Esker, Floodplain, Channel, Canyons, river delta, waterfalls,
Yazoo stream, etc.

Karst Landforms

These types of landforms are formed due to the breaking up of solvable rocks like
dolomite, limestone, and gypsum. The term karst is an English word with a Germanic
origin and refers to various geographical features discovered in the Dinaric Alps.

The drainage systems found underground, along with the caves and sinkholes, are perfect
examples of the Karst landforms or Karst topography. The kind of rocks that remain
unaffected by the process of weathering, such as Quartzite, also come under the category
of Karst landforms.

 Land Reforms in India

 Land Revenue System
 Wetlands in India

Major Landforms of the Earth

The major landforms of the Earth that contribute greatly to the surroundings as well
are Mountains, Plateaus, and Plains. There are a number of landforms that are classified
on the basis of various parameters. Therefore the major landforms on the basis of slope
and elevation are mountains, plains, and plateaus.

 Mountains: These are elevated structures that rise above the surface of the Earth
and reach as high as 2000 ft. in altitude. Due to the higher altitudes, the climatic
conditions in such mountainous regions are very different and tough to tackle.
This is why vegetation and habitation rarely become easy here.
 Plains: These are areas of flat land extending up to long distances. These are
formed by rivers along with their tributaries. The fertility of these lands is high and
 therefore makes it easy to survive in. Plains are the most inhabited lands and
climatic conditions also favor the survival of living beings.
 Plateaus: These can be considered as a slight mix of both mountains and
plains. Plateaus are both elevated and flat. They are the pieces of land that elevate
themselves to a certain height. They are formed as a result of volcanic activity and
are supposed to be rich in minerals. A big example of a plateau in India is the
Deccan Plateau.

Landforms are, therefore, shapes that are formed out of the surface of the Earth due to
various natural activities happening in the environment.

Plate tectonics and its relevance to earthquakes

The distribution of earthquakes across the globe is shown in Figure 11.7. It is relatively
easy to see the relationships between earthquakes and the plate boundaries. Along
divergent boundaries like the mid-Atlantic ridge and the East Pacific Rise, earthquakes
are common, but restricted to a narrow zone close to the ridge, and consistently at less
than 30 km depth. Shallow earthquakes are also common along transform faults, such as
the San Andreas Fault. Along subduction zones, as we saw in Chapter 10, earthquakes
are very abundant, and they are increasingly deep on the landward side of the subduction
zone.

Earthquakes are also relatively common at a few intraplate locations. Some are related to
the buildup of stress due to continental rifting or the transfer of stress from other regions,
and some are not well understood. Examples of intraplate earthquake regions include the
Great Rift Valley area of Africa, the Tibet region of China, and the Lake Baikal area of
Russia. provides a closer look at magnitude (M) 4 and larger earthquakes in an area of
divergent boundaries in the mid-Atlantic region near the equator. Here, as we saw in
Chapter 10, the segments of the mid-Atlantic ridge are offset by some long transform
faults. Most of the earthquakes are located along the transform faults, rather than along
the spreading segments, although there are clusters of earthquakes at some of the ridge-
transform boundaries. Some earthquakes do occur on spreading ridges, but they tend to
be small and infrequent because of the relatively high rock temperatures in the areas
where spreading is taking place.

Earthquakes at Convergent Boundaries

The distribution and depths of earthquakes in the Caribbean and Central America area are
shown in Figure 11.9. In this region, the Cocos Plate is subducting beneath the North
America and Caribbean Plates (ocean-continent convergence), and the South and North
America Plates are subducting beneath the Caribbean Plate (ocean-ocean convergence).
In both cases, the earthquakes get deeper with distance from the trench. In Figure 11.9,
the South America Plate is shown as being subducted beneath the Caribbean Plate in the
area north of Colombia, but since there is almost no earthquake activity along this zone, it
is questionable whether subduction is actually taking place.

The background seismicity at this convergent boundary, and on other similar ones, is
predominantly near the upper side of the subducting plate. The frequency of earthquakes
is greatest near the surface and especially around the area where large subduction quakes
happen, but it extends to at least 400 km depth. There is also significant seismic activity
in the overriding North America Plate, again most commonly near the region of large
quakes, but also extending for a few hundred kilometres away from the plate boundary.

The distribution of earthquakes in the area of the India-Eurasia plate boundary is shown
in Figure 11.11. This is a continent-continent convergent boundary, and it is generally
assumed that although the India Plate continues to move north toward the Asia Plate,
there is no actual subduction taking place. There are transform faults on either side of the
India Plate in this area.

Figure 11.11
Distribution of earthquakes in the area where the India Plate is converging with the Asia
Plate (data from 1990 to 1996, red: 0-33 km, orange: 33-70 km, green: 70-300 km).
(Spreading ridges are heavy lines, subduction zones are toothed lines, and transform
faults are light lines. The double line along the northern edge of the India Plate indicates
convergence, but not subduction. Plate motions are shown in mm/y.) [SE after Dale
Sawyer, Rice University, http://plateboundary.rice.edu]
The entire northern India and southern Asia region is very seismically active.
Earthquakes are common in northern India, Nepal, Bhutan, Bangladesh and adjacent
parts of China, and throughout Pakistan and Afghanistan. Many of the earthquakes are
related to the transform faults on either side of the India Plate, and most of the others are
related to the significant tectonic squeezing caused by the continued convergence of the
India and Asia Plates. That squeezing has caused the Asia Plate to be thrust over top of
the India Plate, building the Himalayas and the Tibet Plateau to enormous heights. Most
of the earthquakes of Figure 11.11 are related to the thrust faults shown in Figure 11.12
(and to hundreds of other similar ones that cannot be shown at this scale). The
southernmost thrust fault in Figure 11.12 is equivalent to the Main Boundary Fault in
Figure 11.11.

Figure 1 1.12 Schematic diagram of the

India-Asia convergent boundary, showing examples of the types of faults along which
earthquakes are focussed. The devastating Nepal earthquake of May 2015 took place
along one of these thrust faults. [SE after D. Vouichard, from a United Nations
University document at:
http://archive.unu.edu/unupress/unupbooks/80a02e/80A02E05.htm]

There is a very significant concentration of both shallow and deep (greater than 70 km)
earthquakes in the northwestern part of Figure 11.11. This is northern Afghanistan, and at
depths of more than 70 km, many of these earthquakes are within the mantle as opposed
to the crust. It is interpreted that these deep earthquakes are caused by northwestward
subduction of part of the India Plate beneath the Asia Plate in this area.

Groundwater: types of aquifers, origin, movement and role of groundwater in Civil

Engineering constructions

Groundwater engineering, another name for hydrogeology, is a branch of engineering

which is concerned with groundwater movement and design of wells, pumps, and drains.
The main concerns in groundwater engineering include groundwater contamination,
conservation of supplies, and water quality Hydrogeology (hydro- meaning water, and -
geology meaning the study of the Earth) is the area of geology that deals with the
distribution and movement of groundwater in the soil and rocks of the Earth's crust
(commonly in aquifers). The terms groundwater hydrology, geohydrology, and
hydrogeology are often used interchangeably. Water is an essential requirements for all
forms of the life and is considered as integral part of the living organisms life. GOD has
gifted our universe with bulk amount of this valuable substance in different forms such as

1. Rivers

2. Lakes

3. Natural springs

4. Rain

5. Snow

6. Glaciers

7. Aquifers etc

During the early era apart from drinking purpose water was usually used for general
usage such as agriculture, washing clothes, pots etc but With the passage of time the use
of water get increased and human being started using it in different fields such as:

1. Industries

2. Preparation of food stuff

3. Medicines

4. Steam engines

5. Vehicles

6. Paper industries

and so on About 70% portion of our planet earth is consists of water while the rest 30% is
consists of dry land. Apart from such a big amount of water there is also massive amount
of underground water reservoirs but the main difficulty in using of this water is the
difficulty to access it. Due to vast advancement of science and technology the demand for
water is also increased to very high level then before it was and causing the demand for
underground water usage. The ground water reservoirs are much more pure and safe the
usual water resources available at the earth's surface. Ground water constitute an integral
part of the human's life and now time demands to bring it to use so that we can fulfill our
fast growing demand of water. Following are the different types of ground water
reservoirs and the their details.

Hydrogeological Formations and Groundwater The behavior of ground water in the

Indian sub-continent is highly complicated due to the occurrence of diversified geological
formations with considerable lithological and chronological variations, complex tectonic
framework, climatological dissimilarities and various hydrochemical conditions. Studies
carried out over the years have revealed that aquifer groups in alluvial / soft rocks even
transcend the surface basin boundaries. Broadly two groups of rock formations have been
identified depending on characteristically different hydraulics of ground water, viz.
Porous formations and Fissured formations. 6 Porous Formations : Porous formations
have been further subdivided into Unconsolidated and Semi – consolidated formations.
Unconsolidated Formations The areas covered by alluvial sediments of river basins,
coastal and deltaic tracts constitute the unconsolidated formations. The hydrogeological
environment and ground water regime conditions in the Indo-Ganga-Brahmaputra basin
indicate the existence of potential aquifers having enormous fresh ground water
resources. Semi-Consolidated Formations The semi-consolidated formations normally
occur in narrow valleys or structurally faulted basins. The Gondwanas, Lathis, Tipams,
Cuddalore sandstones and their equivalents are the most extensive productive aquifers.
Under favourable situations, these formations give rise to free flowing wells. In select
tracts of northeastern India, these water-bearing formations are quite productive. The
Upper Gondwanas, which are generally arenaceous, constitute prolific aquifers. Fissured
Formations (Consolidated Formations) The consolidated formations occupy almost two-
third of the country. The consolidated formations, except vesicular volcanic rocks, have
negligible primary porosity. From the hydrogeological point of view, fissured rocks are
broadly classified into four types viz. Igneous and metamorphic rocks excluding volcanic
and carbonate rocks, Volcanic rocks, Consolidated sedimentary rocks and Carbonate
rocks. Igneous and Metamorphic Rocks Excluding Volcanic and Carbonate Rocks The
most common rock types are granites, gneisses, charnockites, khondalites, quartzites,
schists and associated phyllites, slates, etc. These rocks possess negligible primary
porosity but develops secondary porosity and permeability due to fracturing and
weathering. Ground water yield also depends on rock type and possibly on the grade of
metamorphism. Volcanic Rocks The predominant types of the volcanic rocks are the
basaltic lava flows of Deccan Plateau. The contrasting water bearing properties of
different flow units controls ground water occurrence in Deccan Traps. The Deccan
Traps have usually poor to moderate permeabilities depending on the presence of primary
and secondary porespaces. Consolidated Sedimentary Rocks excluding Carbonate rocks
Consolidated sedimentary rocks occur in Cuddapahs, Vindhyans and their equivalents.
The formations consist of conglomerates, sandstones, shales, slates and quartzites. The
presence of 7 bedding planes, joints, contact zones and fractures control the ground water
occurrence, movement and yield potential. Carbonate Rocks Limestones in the
Cuddapah, Vindhyan and Bijawar group of rocks are the important carbonate rocks other
than the marbles and dolomites. In carbonate rocks, the circulation of water creates
solution cavities, thereby increasing the permeability of the aquifers. The solution activity
leads to widely contrasting permeabilities within short distances[3]. Groundwater
Potential – A Glance Several attempts have been made to assess the ground water
resources in the country. The National Commission on Agriculture (1976), assessed the
total ground water of the country as 67 m. ha m, excluding soil mixture. The usable
ground water resource was assessed as 35 m. ha m of which 26 m. ha m was considered
as available for irrigation.The first attempt to estimate the ground water resources on
scientific basis was made in 1979 when a High Level Committee, known as Ground
Water over Exploitation Committee was constituted by Agriculture Refinance and
Development Corporation (ARDC). Based on the norms for ground water resources
computations recommended by this committee, the State Governments and the Central
Ground Water Board computed the gross ground water recharge as 46.79 m. ha m and the
net recharge (70% of the gross) as 32.49 m. ha m. Norms recommended by the Ground
Water Estimation Committee (1984) are currently utilized by the Central Ground Water
Board and the State Ground Water Departments to compute the ground water
Resources.Based on the recommendations of this committee, the annual replenishable
ground water resources in the country work out to be 45.33 m. ha m. Keeping a provision
of 15% (6.99 m. ha m) for drinking, industrial and other uses, the utilisable ground water
resource for irrigation was computed 38.34 m. ha m per year. The ground water resources
of the country have been estimated for freshwater based on the guidelines and
recommendations of the GEC-97. The total annual replenishable ground water resources
of the country have been estimated as 431 billion cubic meter (BCM). Keeping 35 BCM
for natural discharge, the net annual ground water availability for the entire country is 8
Fig 3.1 hydrogeological Map of India(Source: www.cgwb.in) 396 BCM. The annual
ground water draft is 243 BCM out of which 221 BCM is for irrigation use and 22 BCM
is for domestic & industrial use. Haryana, Punjab and Rajasthan receive less than 40 cm
annual rainfall and are deficient in surface water resources. As such, these states exploit
more than 85 per cent of the available ground water for irrigation. Large scale
exploitation of ground water is done with the help of tube wells. Gujarat, adjoining
Rajasthan, also receives less rainfall and has to depend upon ground water resources.
This state has developed over 55 per cent of her ground water resources. Uttar Pradesh
and Bihar in the Ganga valley are rich fertile tracts where intensive irrigation is 9
required to sustain agriculture. In the south, Tamil Nadu also has high level of 64.43 per
cent of ground water development. Here, ground water is primarily used to irrigate the
rice crop. Most of the north-eastern hill states like Assam, Arunachal Pradesh, Manipur,
Meghalaya, Mizoram, Nagaland and Sikkim have very low level of ground water
development. Goa also receives sufficient rainfall and surface water resources are enough
to meet the requirement. Therefore, the ground water resources are not much exploited.
Hilly and mountainous terrain in Jammu and Kashmir and Himachal Pradesh is not much
favorable for developing ground water resources.

Groundwater Quality

Quality of groundwater is greatly influenced with hydro geochemical processes of

groundwater with surrounding hydro geological formations. These hydrogeochemical
processes are responsible for the seasonal, temporal and spatial variations of groundwater
chemistry and consequently the quality .The relationship between the hydro geological
formations and groundwater status in terms of its quality and quantity has been expressed
by several researcherslisted in Table 2. It shows the significant impacts of urbanization
and anthropogenic reasons in the degradation of groundwater quality. Subsurface Water
Occurrence Underground rivers occur only rarely in cavernous limestone. Most
groundwater occurs in small pore spaces within rock and alluvium(unconsolidated
sediment)

1. Groundwater accumulates over impervious material

2. Water flow through porous medium is slow (range from few centimeters to meters per
day)

Porosity of Geological Material

1. Porosity is a parameter which describes the amount of open space in geologic material
12

2. Porosity can be stated as a fractional value (0.30) or percentage (30%) of open space
(i.e. 30% of volume in the material is open space)

3. Open pore spaces occur between sediment grains

4. Open pore spaces occur in cracks or fractures in rocks

5. Open pore spaces occur in cavernous openings formed by dissolution of rock

(limestone)
6. Porosity values range from 0 to 50% typically

7. Open pores can be filled with water or air or a mixture of both Permeability of
Geological Material

1. Rocks may have a high porosity but if the pore spaces are not connected, water cannot
flow through rock

2. Permeability is a parameter which describes the ability of geologic material to transmit

water

3. Geologic material which can transmit large quantities of water are highly permeable
and called aquifers Examples of geologic material which are typically aquifers are

1. Sand and gravel alluvium

2. Sandstone

3. Cavernous and/or fractured limestone Geologic material which cannot transmit

significant quantities of water are impermeable and called aquitards. Examples of
geologic material which are typically aquitards are: Clay and silt alluvium

 Shale and siltstone

 Water in the Ground Unsaturated Zone region of subsurface from ground surface to the
water table

 Pores are partially filled with water

 Unfilled pore space contains air

 Saturated Zone Region of subsurface in which pore spaces are saturated (completely
filled) with water

 Water Table Interface between unsaturated and saturated zone in unconfined aquifers
Capillary Fringe Zone above the water table where capillary forces pull water upward
into pore spaces

 Same effect seen with water in straws

 UNCONFINED AQUIFERS Water accumulates over an impermeable or impervious

surface

 Water table can freely rise to land surface

 CONFINED AQUIFERS

1. Aquifer is sandwiched between 2 layers of impermeable or impervious material 13

2. Water flows into aquifer from an area at surface where upper impermeable layer
(confining layer) is absent

3. Groundwater in confined aquifers is under pressure

4. Wells can be drilled through the upper confining layer

5. Pressurized water will rise within the well

6. Water levels are called piezometric water level

7. Wells are called artesian wells

8. Where water levels rise above the ground surface, water freely flows out of the well
(flowing artesian well)