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| Physiography And Drainage |
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Topographically, the entire State of
Maharashtra represents an easterly-sloping plateau. The Sahyadri and
the Satpura are the main mountain ranges. From the Sahyadri in the
west, which attains a variable height (600-1646 m. amsl) to the
Wardha-Wainganga plain in the east showing occasional low trends
(less than 100 m. amsl), the plateau represents a variety of
features. West of the Sahyadris is a longitudinal coastal strip
separated from the Western Ghats by an escarpment (600 m.) and
presents lowlands where the heights range from sea level to 350 m.
amsl. |
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Thus, the physical features of the state can be
grouped under three broad divisions i.e. (i) the Konkan Coastal
Plain, (ii) the Western Ghats and (iii) the Maharashtra Plateau. |
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The narrow coastal plain in the west stretches
N-S to a distance of about 500 km. The northern part of this is
relatively flat with occasional hillocks. Numerous streams
originating on the Sahyadrian scarp, meander their way to the sea.
Around Mumbai, the coast is dotted with a number of off-shore
islands. East of Mumbai, falling in the Ulhas Basin, is a flat
plain. This plain also has some outliers of the Western Ghats, the
most well-known being the Matheran hills (700 m. amsl). |
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Almost all the rivers originating from the
Western Ghats descend to the coast. These are controlled and guided
by fractures and lineaments and forming deep gorge upto 200 m. The
estuaries of these rivers are submerged and the tidal impact is felt
as far as 25 km. inland. |
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The coast is bordered by cliffs. At places,
these cliffs are as high as 60-70 m. plunging into the sea. At other
places, littoral terraces or line of dunes occur behind the beach.
In the South Konkan extending upto Sindhudurg district, there are no
coastal plains as found in the North Konkan. |
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The Sahyadris, commonly known as the Western
Ghats, represent the western edge of the Deccan Plateau. Here, the
basaltic plateau reaches a height varying from 800 to more than 1600
m. amsl. The western edge of the plateau ends abruptly with an
escarpment descending to a coastal lowland. The escarpment at places
is more than 600 m. and looks like a wall. The Western Ghat
escarpment, in all probability, is a fault escarpment. The general
height of the Ghats at the coast ranges between 800 and 1600 m.
amsl. However, wherever the crest line is breached by headward
erosion of the easterly-flowing streams, the continental divide
lowers itself to even less than 700 m. (Lonawala). The highest point
of the Sahyadris in Maharashtra is Kalsubai (1646 m. amsl.). |
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The Sahyadris are the main source of all the
major rivers, not only of Maharashtra but the whole of Deccan
Plateau. The most important of these, the Godavari and the Krishna,
have their sources in the. Western Ghats. The river Godavari
originates near Nasik while the Krishna near Mahabaleshwar. A number
of off-shoots project from the main axis of the Western Ghats
eastwards. The Sahyadris are reduced to a saddle wherever they have
been dissected by headward erosion of plateau streams and rise to
form mountainous high plateaus and peaks where the projecting spurs
join them. |
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The Sahyadri mountains are also the sites of
deep valleys and deep ravines due to which numerous irrigation and
hydro-electric projects have been commissioned. The rainfall is also
high due to which there is luxurious growth of plants and the entire
range is covered by forest, much of it in denuded state. |
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East of the Sahyadris extends the Maharashtra
PI'ateau for a distance of more than 700 km. It comprises numerous
small plateaus and valleys. The main plateau shows declining
heights, both towards the eastern and northern periphery of the
State. In the extreme eastern part, especially east and south of
Nagpur, the average height varies from 250 to 300 m. amsl, though
occasional residual hills are as high as 450 m. amsl. The Umrer
hills and the Chimur hills, forming the divide between the Wardha
and the
.Wainganga rivers, attain a height of 418 and 450 m.
amsl respectively.
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The Tapi-Purna valley, an east-west furrow in
the Deccan table land, extends over a distance of more , than 300
km. and shows a variation in height ranging between 200 and 300 m.
amsl. The entire valley is asymmetrical in cross-profile and is
covered with alluvium. It stands in sharp contrast to the barren
Deccan plateau in the south and the Satpura hills in the north. The
broad valleys of the Bhima, the Godavari and the Krishna are
separated by flat-topped divide which project eastward from the
Sahyadrian Range.
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The height of the plateau varies between 450
and 700 m. amsl. The valleys are broad, bordered by 100 -200 m. high
escarpment. Down these escarpments (Ghats) are the Piedmont, gently
sloping areas and merges with the terraces on either side of the
streams. Extensive flat-topped hills are seen everywhere and even
major water divides are flat-topped. |
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Topographically, there are two more areas in
Maharashtra which attain considerable heights i.e. "the
Satmala-Ajanta chain" that forms the southern rim of the Tapi trough
and the other is "the Melghat- Gawilgarh hills" which is sandwiched
in the Tapi-Purna fork. In the Satmala-Ajanta scarp face, the famous
Ajanta Caves are located. The Satmala-Ajanta chain branches off from
the Saptashringi peak, close to the Sahyadris, with progressively
decreasing heights. |
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The Melghat complex overlooks the Tapi valley
in the north and the Purna valley in the south. The highest point of
the plateau is Chikaldara (1016 m. amsl), which, incidentally, is a
hill-station. |
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The major part of the state is drained to the
Bay of Bengal by two major rivers, the Godavari and the Krishna and
the rest of the part is drained to the Arabian sea by the
west-flowing Tapi river and the Konkan rivers emerging from the
Western Ghats and joining directly to the sea. |
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The Godavari basin roughly covers half of the
area of the State. The river has 1465 km. length in the State. The
major tributaries of the Godavari are the Pravara, the Purna, the
Manjra, the Penganga, the Wainganga, the Wardha and the Pranhita. A
characteristic feature of the Godavari is its deep channel enclosed
between its bank, which are more like embankments and the narrow
alluvial flood plains. The annual discharge of the Godavari at
Dhavaleshwaram (in Andhra Pradesh) is around 1,00,000 mcm. |
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The river emerges from the Western Ghats near
Mahableshwar. It has a total length of about 1400 km. in the State.
The principal tributaries of the Krishna are the Bhima and the
Koyna. The major tributaries of the Bhima, are the Ghod, the
Indrayani, the Mula-Mutha and the Nira. An important feature of the
Krishna basin in the State is the enormous amount of sedimentation.
The annual discharge of the Krishna at Sangli is around 14,700 mcm.
The earliest irrigation project named Nira Canal in Maharashtra, was
constructed in 1846 in the Krishna basin on the river Yelwandi at
Bhatghar. |
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It is the only large river of Maharashtra
joining the Arabian sea. It rises from the Betul Plateau in Madhya
Pradesh. It has a total length of about 724 km. covering an area of
about 52,226 sq.km. which is about 16.96 per cent of the entire
state's area. The valley and large plain associated with it are
drained by a number of parallel tributaries which join the main
river at right angles, though in a few cases a downstream bend close
to the Tapi is observed. The tributaries of the Tapi as well as the
Purna form an important element in the Tapi-Purna river system. The
most important tributary of the Purna is the Chandrabhaga, which
descends from the Melghat Plateau. The other important left-bank
tributaries are the Murna, the Mun and the Nalganga. The most
important tributaries of the Tapi is the Girna which originates from
the Western Ghats. The other left-bank tributaries include the
Waghur, the Bari, the Panjhara and the Buray. The Waghur passes
through the Ajanta hills in which the world famous Ajanta Caves are
located. The valley-side slopes as well as slopes on the transverse
profile of the entire basin are very steep. |
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| Coastal Rivers or Konkan Streams |
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The coastal rivers flow east-west roughly
parallel to each other and their length is 100 km. Most of these
river courses are structurally controlled. The important rivers of
North Konkan are the Pinjal, the Vaitarna, the Bhatsal and the
Ulhas, while the Amba, the Kundalika, the Savitri, the Vaishishti,
the Shastri, the Kajvi, the Waghotan and the Ghod are the principal
South Konkan rivers. The coastal rivers, particularly the ones south
of 18°N latitude are deeply entrenched in the lateritic plateau
which has a general height of 200 m. The valley forms in Konkan are
greatly influenced by the laterites which behave like permeable
rocks. |
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Maharashtra frequently experiences drought
conditions like other parts of the country which affects
agricultural production and economy. Long-term rainfall data
(1901-1990) for 90 raingauge stations of the State were used to
compute normal rain- fall and the departure of the yearly rainfall
from the normal to study the recurrence of drought and to demarcate
drought-prone area of the State. |
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A period of drought is defined as a year in
which the total rainfall is less than 75 per cent of the normal and
accordingly classified as moderate, severe and acute drought where
the departure of annual rainfall range is -25 to -49 per cent, -50
to -74 per cent and more than -75 per cent respectively. If in an
area drought conditions are experienced for 20 per cent or more
years, then the area is classified as drought area and if the
frequency is 40 per cent or above, the area is termed as chronically
drought-prone. Climatologically, the State can be divided into four
regions i.e. Konkan, Marathwada, Madhya Maharashtra and Vidarbha.
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The probability of occurrence of drought of all
categories ranges from 8 per cent (Vengurla and Kudal, Sindhudurg
district) to 22 per cent of the years (Dahanu, Thane district). The
moderate drought conditions ranged from 7 per cent (Vengurla, Kudal)
to 20 per cent (Dahanu), while severe drought conditions ranged from
1 to 6 per cent of the years and acute drought conditions were not
experienced in this part of the State. Thus, the frequency of
occurrence of drought in Konkan region ranges from once in 12 years
at Vengurla and Kudal to once in four years at Dahanu. |
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The probability of occurrence of all categories
of drought ranges from 14 per cent (Osmanabad) to 26 per cent of the
years (Parbhani). Moderate drought conditions range from 13 per cent
(Ahmadnagar and Osmanabad) to 23 per cent of the years (Parbhani)
while severe drought conditions range from one (Osmanabad) to 6 per
cent (Beed). Only the area around Nanded experienced acute drought
conditions for one, per cent of the years,. Thus, the frequency of
occurrence of drought in Marathwada region ranges from once in four
years around Parbhanl to once in seven years in Osmanabad. |
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The probability of occurrence of all categories
of drought varies from 12 per cent (Kolhapur) to 32 per cent of the
years (Rahuri, Ahmadnagar district) in the plains, while in the
hilly region it varies from 7 per cent (Chandgad, Kolhapur district)
to 12 percent of the years (Gaganbavda, Kolhapur district), Moderate
drought conditions range from 11 per cent (Kopargaon and Shlrala) to
26 per cent of the years (Rahurl) while severe drought conditions
range from one (Bhusaval, Nasik etc,) to 10 per cent of the years
(Karjat, Karmala), Acute drought conditions in this region were
experienced only in areas around Pandharpur and Indapur for one per
cent of the years. Thus, in general, the frequency of occurrence of
drought, except around Jalgaon, Kolhapur and Shirala, ranges from
once in eight years around Kolhapur to once in three years around
Rahuri. |
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The probability of occurrence of all categories
of drought varies from 10 per cent (Hinganghat, Wardha district) to
25 per cent of the years (Digras, Yavatmal dis- trict), Moderate
drought conditions ranges from 8 (Digras) to 23 per cent of the
years (Arvi), while severe drought conditions were experienced in
most parts of Vidarbha region. However, around Shegaon it is 7 per
cent of the years. Only around Shegaon acute drought conditions
occurred for one per cent of the years. Thus, the frequency of
occurrence of drought in this region ranges from once in 10 years
(Hinganghat) to once in four years (Digras). |
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Based on the probability of occurrence of
rainfall, drought-prone areas located in Vidarbha, Madhya
Maharashtra, Marathwada and Konkan have been shown in the Plate
-IV. |
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| Ground Water Surveys and Exploration |
Top | |
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The entire State has been covered by systematic
hydrogeological survey by 1990-91. In the areas where stage of
ground water development is relatively high, reappraisal
hydrogeological surveys are being carried out since 1991-92. In the
State programme of ground water exploration was first started during
1956-58 in the Purna alluvial area of Amravati, Akola, Buldhana,
Jalgaon & Dhule districts. Intensive exploration was also
carried out in the Sina-Man basin as a part of special study. Since
then regular ground water exploration is being carried out in the
State under normal exploratory programme. Upto March, 1991 in the
State 388 exploratory wells, 180 observation wells, 27 piezometers
and one slim hole have been drilled in various districts and
different formations. |
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Alluvial Area |
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In 7,400 sq.km. alluvial area of the Purna,
exploratory drilling was carried out at 78 sites. Exploration has
revealed that Younger alluvium is about 70 m. thick while Older
alluvium extends from 70 to 450 m. depth. Further, an area of 2,300
sq.km. was delineated for further ground water development through
shallow tubewells upto 65 m. depth. In parts of the Purna alluvium,
quality of water is saline at all levels. The yield of tubewells
varies from 0.5 to 20.0 Ips, while transmissibility (T) varies from
0.72 to 1,576 m2/day. |
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It covers 5,200 sq.km. in Dhule and Jalgaon
districts. Thickness of alluvium varies from 50 to 300 m.
Exploratory drilling was carried out at 60 sites which reveals that
the first potential aquifer is within 100 m. bgl. while the second
is below 250 m. bgl. The intervening zone between 100 and 250 m. is
generally clayey. It is further suggested that the scope of
development is mostly in deeper aquifers. The yield of tubewells
varies from 0.5 to 31.5 Ips, while 'T' varies from 7.2 to 3,162
m2/day. |
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| Shallow Alluvial Area of Shivna
(Aurangabad district) |
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It covers an area of about 150 sq.km.
Exploratory drilling at 7 sites revealed that thickness of alluvium
is less than 30 m. and aquifer occurs between depth range of 15 and
26 m. bgl. The yield of tubewells varies from 0.1 to 4.5 Ips. |
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| Pravara -Godvari Alluvium (Ahmadnagar
district) |
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It covers an area of 400 sq.km. Exploratory
drilling at 7 sites reveals that thickness of alluvium is less than
30 m. and aquifer zones between 19 and 26 m. bgl are suitable for
ground water development. The yield of tubewells varies from traces
to 2.1 Ips. |
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| Shallow Alluvium OF Brahmapuri Area
(Chandrapur district) |
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Exploratory drilling carried out at 6 sites
shows that thickness of alluvium is less than 23 m. Permeable
granular zones (aquifers) with thickness of 2 to 5 m. occur at a
depth of 9 to 15 m. bgl. The yield of tubewells varies from 0.13 to
3.0 Ips. |
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| Gondwana Sediments (Semi-consolidated
formation) |
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These semi-consolidated formations occur in an
area of about 4800 sq.km. covering parts of Gadchiroli, Yavatmal,
Chandrapur and Nagpur districts. |
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(A) Gadchiroli District |
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It occupies an area of 960 sq.km in Sironcha
Tahsil. Exploratory drilling at 9 sites upto a maximum depth of 300
m have revealed that potential aquifers exist. between 30 and 100 m
& 160 and 230 m. which can be developed. The yield of tubewells
varies from 1.3 to 15 Ips, while 'T' varies from 15 to 87 m2/day.
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(B) Yavatmal District |
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In an area of about 800 sq.km. 9 exploratory
wells were drilled upto a depth range of 118 to 170 m. Permeable
granular zones are encountered in Kamthi and Barakar formations
beneath the thick sequence of clay in Motur formation. Chemical
quality of ground water in deeper aquifers is doubtful. |
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(C) Chandrapur District |
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Around 2,920 sq.km. area was explored by
drilling 58 boreholes to a depth varying from 35 to 300 m. The “T"
of the Kamthi sandstone ranges from 18 to 500 m2/day and storativity
(S) varies from 3.6 x 10-2 to 9.4 x 10-4. It is also observed that
hydraulic conductivity of Kamthi aquifer is generally higher as
compared with Barakar formations. The Kamthi aquifers yield upto 35
Ips. The 'T' ranges from 300 to 500 m2/day. |
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(D) Nagpur District (Alluvium-covered
Gondwana) |
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A well-field was constructed in Silewara coal
field of Nagpur district which suggests that 'T' varies from 85 to
250 m2/day and 'S' is 4.4 x 10-5. |
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In Nagpur district, 14 exploratory wells were
drilled in the orange belt to a depth range from 79 to 264 m. bgl
and encountered Gondwana formation at a depth ranging from 10 to 137
m. bgl. The yield of wells ranged from 0.78 to 16.4 Ips. which
suggests that Gondwanas below the Trap have a potential for ground
water development. |
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a) Sina-Man Basin:
In an
area of 5800 sq.km. (Ahmadnagar, Beed, Osmanabad, Solapur, Sangli
and Satara districts) exploratory drilling was carried out (1976-79)
and 47 exploratory borewells were drilled down to a depth ranging
from 80 to 170 m. Based upon exploration broadly three aquifers have
been identified: (i) shallow aquifers (10 to 20 m.) (ii)
semi-confined aquifers (20 to 40 m.) and (iii) confined aquifers
beyond 40 m. The average 'T' of shallow aquifers varies from 107 to
160 m2/day and of confined aquifers varies from 6 to 90 m2/day. The
yield of boreholes upto 8 Ips has been observed. It has suggested
that around 95,500 shallow wells and 760 deep borewells can be
constructed in this area. |
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b) Yesoda
river basin: Exploratory drilling at 20 sites in the Yesoda basin
reveals the three aquifers upto a depth of 86 m. bgl i.e. (i)
shallow aquifers (0-20 m., phreatic), (ii) semi-confined aquifers
(20-50 m.) and (iii) con- fined aquifers «50-70 m.). The 'T' of deep
confined aquifers is higher (10 to 60 m2/day) than the other two
aquifers. It was suggested that shallow aquifers may be developed
through dug wells. |
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c) Wardha district:
27 borewells down to a depth of 103 to 201 m. were drilled which
suggests that the yield ranges from traces to 14.9 Ips. Higher yield
was observed along or near lineaments. At places, negative zones
(dry vesicular zones) occur between depth range of 55 and 180 m. The
'T' varies from 10 to 90 m2/day. |
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d) Nagpur district:
Exploratory drilling at 12 sites was taken up to a
depth range of 85 to 201 m. bgl. The yield of wells varies from
traces to 38 Ips. It was observed that hydraulic parameters and
yield of wells is good in weathered and fractured basalts. The 'T'
upto 250 m2/day has been observed. |
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e)
Ahmadnagar district: In the district, explorat6ry drilling was carried
out at .29 sites to a depth ranging from 55 to 202 m. and
encountered red boles, inter-trappean clay beds which poses
difficulty during drilling. The yield of wells ranges from traces to
22 Ips. while 'T' varies from less than 10 to over 30 m2/day. The
yield of borewells is normally higher which have proximity to
lineaments and also in thick vesicular zones.
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f) Satara
district: Exploratory drilling was carried out at 18 sites to depth ranging
from 69 to 301 m. and encountered red bole, inter-trappean clay
posing difficulty in drilling. The yield ranges from 0.6 to 15 Ips
while 'T' varies from less than 10 to over 50 m2/day. Borewells
tapping vesicular zones and interflow zones are moderate yielding.
Higher yields were observed in wells located near lineaments in
which 20 to 70 m. thick fractured zones were saturated.
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| Ground Water Exploration in Purna Alluvial
Area |
Top | |
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| (Buldhana, Akola and Amravata
Districts) |
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The Purna alluvial tract is an oval-shaped area
tapering along the western margin covering about 7,400 sq.km.
comprising parts of Amravati (3,460 sq.km.), Akola (2,560 sq.km.)
and Buldhana (1,390 sq.km.) districts. In this alluvial tract,
ground water exploration was carried out in two phases between
1956-58 and 1972-85. Exploration down to maximum depth of 426 m. at
78 sites has brought to light that thickness of alluvium is more
than 426 m. in the northern part. The entire thickness of alluvium
can be broadly divided into two zones: Younger alluvium, upto a
depth of 70 m. and Older alluvium, beyond 70 m. The Younger alluvium
is more sandy and at places, sub- angular to sub-rounded, basaltic
gravel has been encountered. In contrast to this, Older alluvium is
more clayey and, in general, sandy aquifer with gravel is
encountered towards its base. |
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Exploration has revealed that in the northern
part of this alluvial tract ground water is generally fresh and
potable, while in the southern parts, covering an area of about
3,000 sq.km., ground water is saline. An area of about 2,300 sq.km.
as shown in the Plate -IX is delineated for future ground water
development through shallow tubewells of 65 m. depth. The yield of
tubewells in this zone is expected to be around 10 Ips for 30 m. of
drawdown. Aquifer geometry along with disposition of Older and
Younger alluvium is shown in Fence diagram. |
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| Ground Water Exploration in Tapi Alluvial
Area |
Top | |
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| (Jalgaon and Dhule Districts) |
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Longitudinal tract of the Tapi alluvium covers
an area of about 5,200 sq.km. comprising parts of Dhule (2,560
sq.km.) and Jalgaon (2,680 sq.km.) districts. Its length is around
250 km. and average width is around 25 km. Exploratory drilling was
carried out at 36 sites to a maximum depth of 300 m. which reveals
that thickness of alluvium ranges from 50 to over 300 m. The
alluvium comprises clay, silt, sand, gravel, pebbles and
occasionally boulders. The potential sandy aquifers is generally
restricted to 100 m. bgl, while between 100 and 250 m. bgl alluvium
is mainly clay. The second promising aquifer is encountered beyond
depth of 250 m. Ground water development through dug wells,
dug-cum-bore wells, tubewells has reached its optimum stage from the
first aquifer. The discharge of exploratory wells ranges from less
than one to 7.5 Ips. suggesting that alluvium of the Tapi is not
very potential as com- pared to the Purna. The quality of ground
water at all levels is generally good and potable. Aquifer geometry
and their disposition is shown in Fence diagram. |
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The lineament map of Maharashtra is prepared
based on the landsat imagery on 1:1 million scale. It is observed
that in the State lineaments have NW-SE trend which is major,
followed by NE-SW. A few lineaments have N-S and E-W trend. The
Azimuthal frequency diagram based on number and direction of
lineaments shows that in west coast (Mumbai-Ratnagiri) the major
trend is N-S followed by NE-SW. In Maharashtra plateau the general
trend is NE-SW followed by NW-SE. The general trend around Nagpur
area is NW-SE followed by NE-SW. The density of lineaments is higher
in Mumbai, Ratnagiri, Nasik and Dhule districts. |
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In general, the lineament pattern in the State
is guided by the trend of older formations. The Aravalis have a
NE-SW trend in Gujarat (just north of Dhule) and same is reflected
as N-S direction along the western coast and NW-SE and NNW -SSE in
southern Maharashtra. The older Dharwarian trend appears to change
N-S and further eastwards as seen along the Satpura belt. The
Satpura trend (ENE-WSW) is reflected by the Deccan Trap in northern
Maharashtra and a little beyond. A similar effect is also seen
between the northern Sahyadri ranges and the Satmala-Ajanta ranges.
The Satmala-Ajanta ranges are a likely continuation of the Satpura
(ENE-WSW) trend into Maharashtra. |
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The Tapi lineaments define the northern
boundary of the Purna alluvium and cuts across the Deccan Trap lava
flows in the west. This lineament marks a pronounced fault that
defines the southern margin of the Satpura Horst. The Purna
lineament displays a WNW-ESE trend along the course of the Purna
river. It joins the lineaments to the east of Jalgaon. |
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The Godavari lineament with NW-SE trend extends
over the Deccan Trap terrain. The Kadam lineament has given rise to
northerly dips in Deccan Traps in Yavatmal district. The Upper
Godavari lineament extends in WNW-ESE direction from west of Nasik
to near Parbhani in the east. This lineament cuts across the lava
flows and is characterised by the Quaternary tectonic movements. The
Ghod lineament is a set of fracture in lava flows. The Varna
lineament trends in a NW-SE direction and is considered as a fault
affecting the Deccan Traps. |
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The Sahyadri lineaments are restricted to
north-south coastal plains and the Sahyadri range. These lineaments
represent fractures in lava flow. The Chiplun linea- ment extends in
a NNW-SSE directions. |
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Further, the NW-SE and NE-SW weak zones are
well reflected in the overall drainage pattern and as well as ridge
line separating the basin. Thus the dominant NW- SE weak zones are
aligned by all major rivers. |
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Thermal springs are generally associated with
lineaments. The concentration of thermal springs are more along the
major lineaments in the Western Coast and the Satpura range
(northern Maharashtra). |
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The yield of dugwells and borewells is
generally high if these are located along the lineaments. It is
observed that around 80 per cent of high yielding borewells are
associated with lineaments. Still higher yield is observed at the
intersection of two linea- ments. Yield upto 50 Ips. is recorded in
the borewells tapping fractured zone associated with lineaments. |
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Hydrogeology of the State is exhibited through
hydrogeological formations, their lithology, aquifer types and their
yield characteristics. Apart from this, area with high salinity of
ground water is also shown. Lithology of various water-bearing
formations have been shown with symbols while aquifer types have
been divided into three i.e. granular, granular and fissured and
fissured. The yield characteristics of various aquifer types have
been shown with shades of different colours. |
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In a major part of the State, basalts with or
without intertrappean sediments form the water-bearing formation.
Quaternary sediments comprise sand, silt, clay, calcareous
concretions and are mainly confined to Tapi and Purna basins and
form extensive granular aquifers. The yield of wells in these
formations is generally above 50 m3/hr. Laterites of Quaternary Age
occur at places mainly in Sindhudurg district which are
discontinuous and yield of wells varies from 10 to 50 m3/hr.
Granular-and- fissured formations as an aquifer comprises basalts,
sandstones, (Mesozoic to Ceno- zoic) grit, shale, conglomerate,
limestone (Mesozoic/Upper Palaeozoic). In these water-bearing
formations, the aquifers are generally discontinuous. The yield of
wells in basalt varies from 2 to 20 m3/hr. while in the rest of the
formations under this group ranges from 10 to 50 m3/hr. Fissured
aquifer type consists of Pre-Cambrian (Vindhyan) sediments
comprising sandstones, quartzites, shale, limestone, partly
cavernous etc. Pre-Cambrian formation comprises gneisses, granites,
shales, phyllites etc. which also are grouped under this aquifer
type. The fissured type of aquifers are mainly discontinuous and
yield of wells ranges from 2 to 20 m3/hr. |
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In parts of the Purna alluvium, ground water is
highly saline. Water-logged area is mainly confined to the Nira
Canal Command. Along the Western Ghats, there are numerous hot
springs in which, temperature of water, is as high as 69°C. |
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The Deccan Trap, which forms a major
water-bearing formation in the State, has definite characteristics
which consists of a sequence of lava flows and each lava flow can be
divided into lower massive and upper vesicular units. In the massive
unit, ground water occurs in joints, fractures, faults and similar
other zones of weakness. In the vesicular unit, which has primary
porosity and permeability, ground water occurs in intra-granular
porous space. In other consolidated formations, comprising Vindhyan
sedimentaries and Pre-Cambrian meta-sediments, ground water mainly
occurs in the weathered mantle and also along joints, fractures and
foliation planes. The semi consolidated formations which forms
granular/and/fissured aquifers of Upper Palaeozoic to Cenozoic
sedimentaries, ground water occurs in inter-granular pore space and
also in secondary openings such as fractures, joints, etc. In
unconsolidated granular formations which mainly comprise alluvium,
ground water occurs in inter-granular pore spaces and by far the
best aquifers in the State. The thickness of alluvium in Tapi and
Purna basins varies from 100 to more than 450 m. |
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| Electrical Conductivity of Ground Water |
Top | |
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The quality of ground water is controlled by
mineralogical composition of the Formation, climate, depth to water
level, etc. Electrical Conductivity (EC) of water is indicative of
total salt content of water. It also decides suitability of its uses
for parts of irrigation, human and cattle consumption. Based on the
water samples collected form the hydrograph network stations during
the year 1990, a map showing EC of ground water has been prepared.
In general, quality of ground water in the State is within
permissible limit and water can be used for domestic and irrigation
purposes. Higher EC (more than 2,000 micro mhos/ part of the m. at
25°C) of ground water was observed in parts of Amravati, Akola,
Aurangabad, Jalna, Pune, Satara, Sangli and Nagpur districts. In
major part of the State EC of ground water is between 750 and 2,000
micro mhos/ cm. at 25°C. In the Konkan and parts of Nasik, Dhule,
Ahmadnagar, Aurangabad, Nanded, Parbhani, Jalgaon, Beed, Osmanabad,
Latur, Nagpur, Bhandara, and Gadchiroli districts the EC of ground
water was less than 750 micro mhos/cm. at 25°C. Eight isolated
pockets having EC of ground water more than 3,000 micro mhos/cm. are
observed in Chandrapur, Amravati, Akola, Buldhana, Aurangabad,
Ahmadnagar, Sangli and Solapur districts. Incidentally, most of
these areas also falls in surface water irrigation projects. In
major part of the Purna alluvium ground water is saline in shallow
and deeper aquifers.
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| Quality of Ground Water |
Top | |
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The quality of ground water is indicative of
the nature of water-bearing formation and at times it differentiates
between recharge and discharge areas. Since rainfall is the main
source of recharge to ground water, mostly water which is recharged
to ground water will be of bicarbonate type. However, during the
passage through aquifers, the water becomes mineralised as it
travels from recharge to discharge areas. In the State, principally,
five types of water are observed based upon the analysis of water
samples of hydrograph network stations and the same have been shown
in the Plate -XIX. These types are: |
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1. Calcium bicarbonate type
2. Magnesium
bicarbonate type
3. Sodium bicarbonate/Sodium chloride type
4. Magnesium chloride type
5. Calcium chloride type
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This type of water mainly occurs in the Coastal
Tract of Maharashtra and also on either side of the Western Ghats.
Apart from this, it occurs in other parts of the districts except in
central part which is under canal command and covers around 20 per
cent of the State. |
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| Magnesium bicarbonate type |
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This type of water occurs throughout the State
leaving parts of the Coastal Tract covering around 40 per cent of
the area of the State. Generally, EC is less and such water
generally occurs in the recharge areas. |
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| Sodium bicarbonate/Sodium chloride
type |
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This type of water occurs in around 27 per cent
of the State's area. In the entire alluvial patch of the Tapi and
the Purna alluvium, this type of water is very common. |
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This type covers an area of around 8 per cent
of the State. In the process of ground water movement, bicarbonate
type of water normally changes to chloride type depending upon the
composition of water-bearing formation. This type of water is found
in isolated patches throughout Maharashtra except in Coastal tract.
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These waters are generally characterised by
higher EC values and chloride con- tent of more than 50 per cent and
are generally found in lower reaches of the basin/ watershed. These
are found in three isolated pockets of the State. |
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In general, in the entire State, ground water
is mainly of bicarbonate type. This may be because of the fact that
more than 90 per cent of the State is underlain by hard rocks and
movement of ground water is relatively fast. |
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