Detailed case study of groundwater recharge through 73 recharge wells and usage of shallow aquifer through 7 open wells at Cubbon Park.

1. Groundwater recharge at Cubbon Park
1.0 Introduction
Cubbon Park is a much sought-after green space in the heart of Bengaluru City. It was
created in 1870 and initially covered an area of 100 acres. Subsequently, it was expanded,
and as of today, it spans an area of around 200 acres. It was initially called Meade’s Park
after John Meade, Commissioner of Mysore State, since the park was created during his
tenure. It was later renamed Cubbon Park in 1873 after Sir Mark Cubbon. In 1948 the name
was changed to Sri Chamarajendra Park in honour of Maharaja Sri Chamarajarendra
Wadeyar. The park plays multiple roles; as a garden, it hosts various botanical species, both
native and exotic. It has 196 species, with a total of 8866 trees. It is a preferred destination
for early-morning walkers and joggers and hosts important government buildings like the
Karnataka High Court, State Archeological Museum, etc. Hence, this place is rich in history
and diverse in terms of its utility to Bengaluru. *
(*https://cubbonpark.in/history/, https://cubbonpark.in/tree-info/tree_mapping_report.html)
2.0 Water situation prior to 2017
Given that the park hosts nearly 6000 trees and plants, and considering the vast area it
spans, it can be imagined that water is an indispensable resource for the upkeep of this park.
The park has seven old open wells that are around 20-40 feet deep. Over a period of time,
these wells had fallen into disuse. The well water had become dirty, mixed with the garbage
thrown inside. The park also has three ponds, which had silt and required maintenance.
Most of the water needs were met by sourcing Cauvery water from BWSSB.
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2. 3.0 Rejuvenation of open wells, ponds and digging of recharge wells
A project to rejuvenate the old wells and ponds in Cubbon Park and also to recharge
groundwater was taken up by Biome Environmental Trust, India Cares Foundation (ICF) and
Friends of Lakes (FoL), together called the Waterlife Consortium. The project was funded by
First American India (FAI). The concept of this project came from the thought that the park
could be self-sustainable for its water requirements and should not have to depend on
external water sources. Given the presence of a robust shallow aquifer and open wells, it
was planned to see if the park could demonstrate best practices for water management by
highlighting the use of the shallow aquifer. The recharge wells and the ponds recharge
groundwater, and the open wells are sources from which groundwater can be drawn. The
wells can also be monitoring points, which can instruct future groundwater management
actions in the park. This project was completed in two phases: Phase I and II.
3.1 Phase I
Phase I was carried out in May 2017. The objective of this phase was to revive the 7 open
wells and to interconnect them. A team of well-diggers led by Peddanna cleaned the wells
and de-silted them. Pumps were installed in each of the wells. Water from 6 wells is pumped
into the 7th well located near the library building. All the collected water is pumped from the
7th well to a storage tank and then to the overhead tank (OHT). The water drawn from the
wells is used to water trees, the lawn and the rose garden. Within a year, by Sept 2018, the
open wells together started yielding 80,000 litres per day.
3.2 Phase II
Phase II was started around Oct 2018. The objective of this phase included the digging of
recharge wells and rejuvenation of three ponds. In order to make the withdrawal of water
from the open wells sustainable, it is important to put water back into the underlying
shallow aquifer. For this, around 73 recharge wells were planned. There are three ponds in
the park, which help recharge groundwater, control flooding, and host local biodiversity,
apart from being landscape features. Two of the ponds were taken up for rejuvenation. This
included cleaning the ponds, desilting them and strengthening the bunds.
Recharge wells
As part of this project, a total of 73 recharge wells were dug. The dimensions of these wells
were 3 ft wide and an average depth of 15 ft (actual depth varies between 14 ft to 16 ft,
depending on the soil condition of a particular well). The wells have three-foot diameter
concrete rings stacked on top of one another, with four one-inch holes on the side of each
ring. Surrounding these rings is coarse aggregate - large, rough gravel which creates many
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3. holes for the water to flow through. Each well is covered by a concrete slab, either three or
four feet in diameter, with two small holes in it. This slab is quite heavy, requiring two men
to lift it, and acts as protection so that no debris or person falls in. In addition, there is a wire
mesh grill below the top concrete ring to prevent anything large from falling into the well.
The aggregate is filled right up to the slab, and around it, long grasses have been planted.
This makes the wells recognisable around the park.
A silt trap cum filter has been created around each well by placing aggregates to a depth of 1
ft and a width of 1 ft around it. This ensures that large amounts of silt do not enter the well
directly from the top. There is also planting that has been taken up around the well. This is
not only for beautification but also ensures that silt does not enter the well.
Map of 73 recharge wells in Cubbon Park
Mural at Cubbon Park Metro station
The mud from the digging of the recharge wells was put to use in a unique way - mud of
different colours was used to create a large mural on one of the walls of the Cubbon Park
Metro station, telling the water story of Bengaluru, and depicting the lives of the traditional
well-diggers. During a two-week period in the latter half of 2019, passing commuters could
participate in the painting of the mural under the guidance of the Srishti School of Art and
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4. Design, which executed the project in collaboration with Biome Environmental Trust. The
funding for this project was provided by the Bangalore Sustainability Forum.
When the mural was unveiled to the public, some events were organised involving the
well-diggers who dug the wells, including a Kaavya Sanje and a virtual tour of the mural (due
to the pandemic), called Namma Ooru Namma Neeru.
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5. Recharge capacity of 73 wells
Each well has a static volume of around 3 kilolitres (KL), and each well can potentially
recharge around 4.5 KL each time it rains (assuming each well can recharge one and a half
times its static volume of 3 KL). This means the recharge potential of all the wells is
73 x 4.5 KL = 328.5 KL
We have around 60 rainy days a year in Bengaluru. Assuming that the wells recharge to their
full capacity on at least 30 of those days,
328.5 x 30 = 9855 KL = 9.8 million litres (ML)
of rainwater will get recharged annually through the recharge wells (the actual recharge
volume is likely to be higher, as rainfall intensity will vary through the 60 rainy days, with at
least a few really heavy showers).
Natural groundwater recharge
To estimate the annual natural recharge that occurs, we need to consider the overall park
area, which is around 200 acres. This means annually, the park receives
809371 sqm (200 acres) x 970 mm (average annual rainfall) = 785090 KL = 785 ML
of rainfall annually. If we assume a natural recharge rate of 5% (natural recharge rates vary
between 5% and 10% in the peninsular hard rock regions of India), a volume of at least
5% x 785 = 39.25 ML
of rainwater is available for recharge. The actual volume of natural recharge may be more.
The park has mostly loamy and silty soil, which is good for water percolation; however, the
tree roots can trap most of the moisture in the top surface of the soil and consequently
affect how much water reaches the shallow aquifer. A recharge well can bypass this root
layer and provide an easier pathway from the surface for water to reach the groundwater
table.
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6. Clockwise from top left: Concrete rings with gravel aggregate around them, wire mesh grill in
the well, completed recharge well, concrete slab well cover
Pond rejuvenation
Of the three ponds, two were taken up for rejuvenation. These are
● Karagada Kunte (0.005 hectares, or 50 square metres) and
● The pond behind the Wodeyar statue (0.023 hectares, or 230 square metres)
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7. 3 feet of dirt and silt were removed from these ponds, and the bunds were strengthened.
Channels which lead rainwater into the ponds were also opened up. Desilting the ponds
helped improve their groundwater recharge rates. One of the ponds (behind the Wodeyar
statue) has a recharge well in it, which means the percolation rate is higher. The other pond
(Karaguda Kunte) does not have any recharge well in it; it tends to hold water for a longer
duration due to a lower percolation rate. This is intentionally designed so that there is a
presence of a water body in the park, which attracts local fauna and is also a landscape
feature.
The third pond (Lotus pond) was not taken up due to its bigger size and because bamboo
grows in it.
Recharge potential of the revived ponds
The recharge potential of these ponds was calculated as follows. Assuming a recharge rate
of 5 mm / day for the ponds, and assuming that the ponds hold water for at least 240 days (8
months) of the year, the annual recharge volume (in litres) of each pond would be
Recharge rate x no. of days x area of pond in sqm
For Karagunde Kunte (KK), this works out to
5 x 240 x 50 = 60000 litres = 60 KL
For the pond behind Wodeyar Statue (PWS), this works out to
5 x 240 x 230 = 276000 litres = 276 KL
However, PWS also has a recharge well inside it, which would be able to recharge 4.5 KL for
at least 240 days of the year = 1080 KL. So the total annual recharge potential of PWS is 276 +
1080 = 1356 KL
The total annual recharge potential of both ponds is 60 + 1356 = 1416 KL = 1.41 ML
So annually, the total volume of rainwater recharged at Cubbon Park (not considering the
Lotus pond) is at least
9.8 (from recharge wells) + 39.25 (natural recharge) + 1.41 (from two ponds) = 50.46 ML,
which is several times more than the volume of groundwater drawn (0.55 ML).
We have had to make assumptions about several of the parameters used because of the lack of
data.
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8. Ponds being desilted and cleaned
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9. Cleaned pond filled with rainwater
4.0 Conclusion and next steps
Cubbon Park is a confluence of the old and the new. It is a historical place, seamlessly
blending with the modern world. The revival of old wells and ponds, and the digging of the
recharge wells have made shallow groundwater available for park needs. It has also brought
back the tradition of the Tigala community that uses the well water and soil for their annual
Karaga festival. The murals in the nearby Metro station tell the story of these wells and the
relevance of the well-digger Mannu Vaddar community.
Situated in the heart of the city, Cubbon Park is one of the areas that has a robust shallow
aquifer. The huge volume of rainwater that it recharges helps replenish the groundwater
table of not only the park but the surrounding areas as well. Regular monitoring of the well
water levels and documentation of the usage of well water for the park’s needs would help
greatly in understanding this shallow aquifer’s behaviour. A hydrogeological study of the
park and surrounding areas would help delineate this aquifer’s extent and, thereby, its
volume. This would provide valuable information on the capacity of this aquifer and its
potential to meet the park’s water needs. A study of the borewells and open wells (if any) in
the surrounding areas would help in understanding the park’s role in keeping the water
table replenished.
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