ROOF TOP RAIN WATER HARVESTING FOR ARTIFICIAL
RECHARGE TO THE DEEPER AQUIFER IN BISHNABGHATA-PATULI
AREA (KOLKATA)
Kolkata
is one of the most densely populated
cities of the world. With the
increase in population and industrial
activity, demand of water is increasing
every day in Kolkata and it has
caused increase in use of surface
water from Hugli river and also
that of ground water from the
aquifer, which is under confined
condition. Though the city’s
average annual rainfall is 1600mm
but tremendous ground water development
has caused decline in ground water
level.
To augment the water resources
of the deeper aquifer, Central
Ground Water Board, ER, Kolkata
has taken a pilot project for
artificial recharge to the ground
water of the deeper aquifer through
roof top rainwater harvesting.
The site is located at Baishnabghata-Patuli
township, which is in the southern
corner of Kolkata city (Fig- 1).
In Kolkata it is the first scheme
of roof top rainwater harvesting
for artificial recharge to ground
water of the confined aquifer.
HYDROGEOLOGY
OF KOLKATA AREA :
Kolkata is underlain by Quaternary sediments
consisting of a sequence of alternation
of clay, silty clay, sand and sand mixed
with occasional clay. Clay horizon ranging
in thickness from 30-50m occurs at he
top of the sedimentary sequence. This
clay is underlain by a granular zone
made up of sand of different sizes with
occasional gravel and this forms the
aquifer. The principal productive aquifer
generally occurs within the depth range
of40-100m in the north, 50-160m in the
central and southern part and 180-300m
in the southwestern part of the city.
A minor aquifer consisting of fine to
medium has also been found to exist
in some parts within the depth range
of 20-40m. The value of transmissivity
varies from 1700-5200m2/day.
Depth to ground water level ranges from
3.34m to 16.32m bgl in pre monsoon period
and from 1.57m to 15.71m bgl in post
monsoon period. Study reveals that water
level in the confined aquifer in the
city area has declined around 3-4m in
the last 14 years (Fig-2&3).The
chloride concentration in ground water
is above 500ppm in the northern and
western part of the city, 250-500ppm
in the area between Belgachia and Park
street and within 250ppm in Garia -
Jadavpur area.
HYDROGEOLOGY OF
THE PROJECT AREA (BAISHNABGHATA-PATULI
(AREA) :
The Project area is underlain by a thick
layer of impervious clay upto 27m bgl.
from the surface and it is underlain
by thin layer of sand of 3m thickness.
This sand layer is followed by thick
layer of clay down to a depth of 49m
bgl. The productive aquifer consisting
of fine to medium grained sand occurs
below this clay layer down to the explored
depth of 152.45 m bgl. Depth to water
level varies from 14.68m bgl to 16.32m
bgl in pre monsoon period and from 13.41m
bgl to 15.71m bgl in post monsoon period.
The study reveals that the presence
of thick clay layer near the surface
in Kolkata city area act as a barrier
to the natural ground water recharge
to the underlying aquifers.
Design of the
artificial recharge structure in Baishnabghat-Patuli
area.
Baishnabghat-Patuli
area
Head
Description
Location:
In the campus of ALL INDIA
SOIL AND LAND USE SURVEY,
GOVT. OF INDIA, KOLKATA.
Roof
area:
724 sq.m.
Average
annual rainfall:
1600mm.
Quantity
of rain water available:
1158.4
m3
Quantity
of rain water available
for recharge:
926.72
m3 (80%)
Aquifer
material:
Fine
to medium sand.
No.
of recharge well: 2
Depth
of recharge well:
119.38mbgl.
Diameter
of recharge well:
150mm.
Zone tapped:
102.61-114.77mbgl.
Slot
size:
1.0mm.
Clay
sealing:
GL
to 85.0mbgl.
Gravel
shrouding:
85mbgl
to 119.50mbgl.
Static
water level:
13.0mbgl.
Discharge:
284
lpm.
Drawdown:
i1.1m
(After 220 minutes of
pumping).
Nos.
of recharge trench: 1
Length:
11.57m
Width:
1.65m.
Depth
:
3m.
Filter
media:
sand, gravel and boulder.
Control
unit:
2 Nos. control units are
situated near the recharge
trench.
Developed and Hosted by NIC. Ccntents
provided by the respective Department.
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ROOF TOP RAIN WATER HARVESTING FOR ARTIFICIAL
RECHARGE TO THE DEEPER AQUIFER IN BISHNABGHATA-PATULI
AREA (KOLKATA)
