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Location
Physiography
Drainage
Climate
Archean
and Proterozoic Rocks
Mesozoic
Formations
Deccan
Trap
Tertiary
Formations
Quaternary
Formations
Ground
Water Level Behaviour |
The State of Gujarat covers a total geographical
area of 1,95,984 sq.km in Western part of India.
Gujarat State is situated between 20°06’
to 24° 42’ North latitude and 68 °
10’ to 74° 28’ East longitude.
The state has the longest coastline in the country
measuring about 1,600 kms along western parts
of India, extending from Lakhpat in north to Valsad
in South. Gujarat State has common borders with
the State of Rajasthan, Madhya Pradesh and Maharashtra
along North, East and South and with Pakistan
in the North-West. |
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The State of Gujarat can be divided into five
major Physiographical zones :
- Alluvial Plains extending from Banaskantha
in north Gujarat to Valsad in the south. The
alluvial plains also extend westwards to the
little Rann and Banni area of Kachchh.
- The Eastern hilly tract lying between altitude
of 300 and 1400 m above msl forms a major
divide. Majority of rivers in Gujarat originate
from the hills in the east and flow towards
south and south-west except Narmada and Tapi
(inter state rivers), which cut across the
hilly tract along the faulted zones.
- Uplands of Kachchh-Saurashtra comprising
sedimentaries and volcanic rocks with elevations
of about 150 to 500m. The Mount Girnar is
an isolated mountain (1117m above msl) in
Saurashtra region.
- The low-lying coastal tract ranging in elevation
from 3 to 25m above msl makes the coastal
areas of Saurashtra and Kachchh. These low
lying areas extend from Rann of Kachchh through
the Little Rann of Kachchh and low lying delta
region of Bhadar, Bhogavo, Sabarmati, Mahi
Dhadar, Narmada and Tapi rivers.
- Marshy to saline desert of Rann of Kachchh
and Little Rann of Kachchh extend into the
saline tracts around the Gulf of Kachchh.
This vast expanse of salts mixed with clay
is devoid of any vegetation or habitation.
The general elevation of this tract varies
between 1and 4 m above msl.
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Drainage of all five physiographical regions of
Gujarat State is distinct with the prevailing
topographical and physical characteristics of
the rock formations. The flow direction of some
of the major rivers is controlled by major tectonic
activity.
All rivers of the state except Tapi, Narmada and
Mahi originate in the eastern hilly tract. The
rivers flow with highly meandering courses in
westerly direction and cut across the alluvial
plains. The rivers Narmada and Tapi flow along
structural troughs in a westerly direction. The
rivers in Saurashtra originate from the central
uplands and represent a radial drainage pattern.
The Gujarat State has varied climate ranging from
humid, sub-humid , semi arid to arid type . Maximum
rainfall of about 2000 mm is recorded in the southern
part, which gradually decreases to about 300 mm
in western part in Kachchh. The rainfall pattern
has conspicuous impact on its economy. The droughts
are frequent in north Gujarat, Kachchh and Saurashtra
regions due to poor and erratic rainfall.
The Summer temperature in many parts of the State
rises to as high as 46°C , while the minimum
winter temperature of 4°C is also recorded
at few locations in the State. |
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Groundwater Conditions
These rocks mainly occupy the northeast and
eastern parts of the state in the districts
of Banaskantha, Baroda, Kheda, Panchmahals,
Sabarkantha and Mahesana. This group of rocks
is mainly represented by gneisses, phyllites,
and quartzites and metamorphosed intrusives.
Due to very poor primary porosity and permeability,
these rocks do not form good aquifers. It is
only under favourable conditions that the locations
where either due to more thickness of weathered
rock or due to highly fractured and jointed
nature of the rock, dug wells, dug- cum-borewells
and even deep borewells are found to be feasible.
The groundwater structures are generally within
30 to 40m depth except borewells of deeper depths.
Jurassic and cretaceous formations are mainly
sedimentary formations occurring in Baroda,
Kachchh, Surendranagar and Sabarkantha districts.
Of the sedimentary rocks in Kachchh district.,
Bhuj series mainly consist of friable, medium
to coarse grained sandstone and variegated shales.
In this sedimentary formation tubewells of about
200m.depth have been constructed, which yield
about 70 m3/hr at drawdown of 15 to 20m. In
Bhuj series the salinity in groundwater is generally
low, but gradually increases towards the discharge
areas and towards contact areas with younger
formation.
The sedimentary formation in Surendranagar district
namely Dhangadhra series are mainly fine to
coarse grained sandstone inter bedded with shales.
In this formation tubewells of about 150m. depth
have been constructed which yield about 45 to
60m3/hr at 20 to 25m drawdown. At certain places
these formations are intruded by trap sills
of 30 to 50m thickness. The trap sills at places
form a marker horizon below which the quality
of groundwater is generally saline.
Recently the Dhrangdhra sandstones have been
tapped through a large number of borewells in
Rajkot and Jamnagar districts under a cover
of 200-250m of basalts under semi artesian conditions.
The sedimentary formations of Sabarkantha district,
namely Himmatnagar group are exposed in the
form of a strip. This group also consists of
coarse to medium grained sandstone inter bedded
with shales. The tubewells constructed in Himmatnagar
sandstone yield nearly 40 to 50m3/hr at a drawdown
of 20 to 25m.
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These are essentially consolidated basaltic lava
flows with almost horizontal disposition forming
the mainland of Saurashtra consisting of basalts
intruded by dykes The basaltic rocks vary from
massive to vesicular in nature. Inter-trappeans
ie. erosional products of traps and other rocks
occur between two successive lava flows at many
places. The weathered, jointed and fractured basalt
and the inter trappeans constitute reasonably
productive aquifer.
The discharge from dug wells constructed in trap
rocks varies from insignificant quantities to
30 m3/day except under very favourable conditions.
The successful exploratory tubewells have discharges
varying between 4 - 10 lps but at certain locations
reduction in tubewell yield is also reported due
to fall in water levels. The quality of groundwater
in basalt is generally good.
These sedimentary formations are exposed
between the Narmada and Tapi rivers in parts of
Bharuch and Surat districts. They also occur along
the coastal areas of Saurashtra and Kachchh.
Saurashtra
Gaj beds occur all along the Saurashtra coast
and consist of limestone, clay and gypsiferous
grit with thin sand layers. The thickness of Gaj
beds varies from a few meters to more than 300
meters. However, they do not form good aquifer.
The deeper sections in particular yield meagre
discharge with high salinity. The quality of groundwater
is inherently saline. However, at places the quality
of groundwater within shallow depths is comparatively
good.
Dwarka beds rocks comprise gypseous and calcareous
clay and sandy limestone. They are about 50m in
thickness in Okhamandal taluka of Jamnagar district.
The groundwater quality from has high chloride
contents and dug wells yields are low. A few tubewells
constructed in this formation yield about 30 to
40m3/day at some select locations.
Kachchh
In Kachchh district Tertiary formations do not
form promising aquifer mainly because of clayey
nature and poor groundwater quality.However, the
sandstones of Manchar series form relatively good
aquifer. The tubewells drilled down to 120-160m
depth, yield between 70-90m3/hr. with chloride
contents ranging between 100 and 600 ppm.
South Gujarat
The Tertiary formations consists of sandstones,
shales and limestones with gravel beds over 100m,
in thickness at certain locations. However these
formations yield moderate to good discharge. The
quality of groundwater from these formations is
mostly brackish to saline. |
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The quaternary sediments occupy an area of about
86,680 sq.km .This group includes miliolite limestone,
alluvium and aeolian deposits.
The miliolite limestone with limited thickness
mainly occur along coastal areas of Saurashtra
and form good aquifers. The quality of ground
water is usually good. The dug wells yield up
to 200 m3/day at favourable locations. However,
along the coast, the quality of groundwater has
gradually deteriorated due to overexploitation
resulting into salinity ingress.
The alluvial and aeolian deposits occur as one
continuous alluvial plain extending from north
to south in Gujarat mainland. They also occur
as valley fill deposits in hard rock areas. Their
thickness in the Cambay basin is over 600 m .Howeveer,
groundwater development is restricted down to
about 300 m general in north and central Gujarat
. In South Gujarat the alluvial deposits mostly
overly the trap rock and the Tertiary sediments.
The thickness of alluvial deposits in this part
is limited.
Groundwater in the alluvial areas occurs both
under unconfined, semi-confined, confined and
free flowing artesian conditions. The detailed
hydrogeological investigations have indicated
occurrence of multi-layered aquifer system in
alluvial plains of Gujarat within a depth of about
600m. The recharge zone of confined aquifers occurs
along the contact areas with hilly region of the
north east. Most of the aquifers coalesce into
the phreatic aquifer in the recharge area., but
these aquifers are identified as separate aquifers
occurring under semi-confined to confined conditions
in the central parts and western parts i.e. in
the discharge area.
Due to over exploitation of groundwater in alluvial
plains of North Gujarat both unconfined and confined
aquifers have shown decline in water levels at
alarming rates of 3 to 5 meters per year. The
tubewell yields have also considerably reduced
from 35 lps to 15 lps. The artesian conditions
which existed in the western parts in parts of
Ahmedabad, Banaskantha and Mahesana districts
till 1960's have shifted further west-wards.The
artesian pressure heads have also considerably
reduced. Now the artesian conditions are mainly
observed along the Rann of Kachchh where the quality
of groundwater from deep tubewells is highly saline.
Ground water level in the state varies considerably
depending on aquifer geology, geomorphology and
rainfall. South-West monsoon is the main source
of ground water recharge. Shallowest level is
observed in the month of August, while the deepest
is observed in the month of May. For 2002 during
pre-monsoon (May) water level ranges in general
from 2 to 20 m bgl, while during post-monsoon
(November) it varies in general from less than
1 to 10 m below ground level(bgl). |
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