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Exploratory drilling in the state was commenced in the year 1954 with view to identify,
study and characterize the aquifers and to demarcate aquifer system. Central Ground water
Board, Northern Region has taken Ground Water exploration upto a depth of 750 metres below
ground level. The selection of sites based on hydrogeological and geophysical
investigations and approachability of the rigs is followed by drilling through suitable
rigs and pumping tests. The Northern Region has 11 rigs (2 -DTH, 7-Rotary and 2
-Percussion) of 300 to 750 m drilling capacity, through which drilling is performed in
different geological formations, for example, hard rock, bouldary formations, sedimentary
and unconsolidated sediments. Drill cuttings are collected to prepare lithological logs
and are standardized based on geophysical logs to demarcate aquifer zones. The ground
water exploration has enabled delineation of aquifers, both laterally and vertically,
evaluate various aquifer parameters, assess their yield potentials and identify areas
suitable for ground water development. It has drilled more than 894 wells in the state in
all the geological formations. The table given below shows the district wise breakup of
exploratory tubewells as on 31-03-2003. |
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The proper design of ground water structure has very important role in economical
production of water. In U.P. State the main ground water structures, dug well, mark-II
hand pumps and deep/shallow tubewells are being utilized for extracting ground water for
various uses. The shallow/deep tubewells are the main structure to obtain large quantity
of ground water supply, hence designing aspects of tubewells in different hydrogeological
set up have been dealt here. Design of a well involves selecting appropriate dimensions of
the various components and choosing proper materials to be used in its construction. A
good design of tubewell aims at efficient utilization of aquifer, long useful life of
tubewell, low initial cost and low maintenance and operation costs. In view of designs,
the hydrogeological units in the state can be, broadly, divided into two groups, soft rock
formations and hard rock formation. Soft rock formation includes semi consolidated and
unconsolidated formation while hard rock formation includes sedimentary rocks of Vindhyans
and Crystalline rocks of Bundelkhand area. For irrigation purpose mostly gravel packed
tubewells are used in the state. The shallow tubewells in Terai and Ganga plain area upto
50 m depth can be constructed through straight assembly of 250 mm diameter with 20 m
slotted pipe having 1.50 mm slot size. The annular space between borehole and well
assembly should be shrouded by 3 to 5 mm pea gravels of preferably 100-120 mm thick zone.
Such shallow tubewells in Terai area can yield 60-90 m3/hr at drawdown upto 5 m and such
tubewell in Ganga plain area can yield 30-60 m3/hr at draw down upto 7m. The shallow
tubewell can be fitted with maximum 190 mm, out side diameter of pumps to lift the water.
The shallow tubewells in Terai area where draw down is less than 5 m can be fitted with
centrifugal pump to lift the water from the well. Deep tubewells of large to moderate
yield are feasible in the state down to 200 m with 300/200 mm diameter well assembly with
40 to 50 m housing length in Terai area and 45 to 50 m housing length in Ganga Plain area.
In Bhaber area deep tubewells upto 200 m depth are feasible with 300 m straight assembly.
The construction of such deep tubewells would be possible through Direct Rotary rig in
Terai and Ganga plain and through combined Rig in Bhaber area to penetrate boulder bed.
About 40 to 50 m saturated granular zones in Bhaber area plain area would be required by
using 3.0 mm slot size in Bhaber area and 1.56 mm slot size in Terai and Ganga plain area.
In Bhaber area naturally packed tubewell can be developed but in Terai and Central Ganga
plain only gravel packed tubewells are feasible. The gravel size of 3 to 5 mm is desirable
to envelope 1.56 mm slot size. The expected yield of such deep tubewells would be around
120-150 m3/hr at heavy drawdown of 20 m in Bhaber area and 180-270 m3/hr at draw down upto
5 m in Terai area, and in the Ganga plain area the yield would be around especial
attention of designing deep tubewell is required due to saline zone occurring between
150-250 m below ground level. In these circumstances well should be constructed upto
100-150 m depth otherwise deep well tapping zones below 250 m should be tapped and cement
sealing should be done above 250m.against clay zone, such tubewell upto 150 m can yield
120-180 m3/hr at heavy drawdown of 20 m. Keeping in view heavy drawdown, cement sealed
wells the housing should have more than 50 m length. In the hard rock area of the state,
tubewells upto 100 m depth are feasible to yield 30 to 120 m3/hr at heavy draw down of 20
m. The telescopic well drilling 200/175/150 mm is suitable to construct tubewells by
casing weathered zone and keeping naked well below weathered zone. The selection of
material for the constructed of well assembly is very important aspect of the design of a
tubewell and has an important bearing on its useful life and cost. The maximum treat to
the life of the well assembly is from corrosion. Highly corrosive waters can destroy
screen by enlarging openings and allowing sand or even gravel pack to enter the inside of
the intake portion of the tubewell, which may lead to premature failure of the well. In
the parts of district Mathura, Agra, Etawah, Azamgarh, Jaunpur, Ghazipur, Kanpur, Unnao,
Sultanpur, Raebareli, Pratapgarh and Hamirpur etc are highly corrosive in nature. A study
of failed tubewells carried out at the U.P. Irrigation Research Institute, Roorkee has
revealed that about half of the well failures in the state are due to corrosion and
incrustation alone. The slot screens made up of stainless steel may be used as an
anticorrosion measure. These screens, though very costly, last much longer and thus pay
for the extra cost involved beside anticorrosive nature these screen also have
considerable more open area and as such they produce wells which have high specific
capacity for long period of time. The P.V.C. pipe is also resistant to corrosion but has
limited installation depth to about 100 m due to potential vertical stress failures. Such
pipe can successfully be utilized for shallow tubewells having corrosive water. However,
extra care has to be taken in handling and storage of P.V.C. pipe to prevent damage.
Recently fiberglass enforced plastic pipe have been developed to sue in tubewells. An
important aspect of the design of well is determination of the diameter of well Housing
and well screen, its length, percentage of open area, size and shape of each slot and
thickness of gravel pack of screen. The diameter of the housing should be large enough to
accommodate the pump with adequate clearance of installation and efficient operation. The
housing pipe should have diameter at least 5.00 cm greater than the nominal diameter of
the pump. Depending on the discharge to be lifted the optimum diameter of housing in the
state is 250 mm for straight assembly for Bhaber area and shallow tubewells in the rest of
the area of the state. For deep tubewell in the state except Bhaber area the diameter 300
mm would be suitable and economical. The diameter of well discharge and the characterizes
of the aquifer so that overall cost of the well is a minimum. An open area of well screen
should be kept 15 percent beyond which the head loss are no longer function of open area
and shape of the openings. The optimum thickness of the gravel pack designed has been
studied at U.P. Irrigation Research Institute Roorkee and results indicated that for sand
free discharge the thickness of gravel should be at least 12.50 cm. In view of this a
thickness of 15.0 cm to 20.0 cm thick gravel pack is recommended for the state. |
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