Chennai receives approximately 1,200 mm of annual rainfall, equivalent to four feet of water. The city's groundwater level rose 2.84m after the northeast monsoon last year due to rainwater harvesting structures. However, the groundwater level has risen but is still not enough to meet the city's growing water needs. While rainwater harvesting helps recharge groundwater by tapping and storing or recharging rainwater, only 10% of rainfall typically recharges underground aquifers as most runs off. Proper maintenance of rainwater harvesting structures needs to be done every five years by cleaning and refilling to keep them functioning effectively.

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Satish says that Chennai gets
an annual rainfall of approxi-
mately 1,200 mm, which is
equivalent to four feet of water.
"The groundwater level in the
city rose by 2.84m after the
northeast monsoon last year. In
a recent policy note, the state
government announced that the
RWH structures have 'reaped
rich dividends' with a rise in
groundwater level by 8tmcft
since their inception in 2001,"
says Satish. Adding to this, Ku-
mar says that ground water table
level has significantly risen up
than the past; however it is not
up to the mark to feed the city's
burgeoning water needs.
The rainwater harvesting in-
volves tapping rainwater where
it falls. "The rainwater collected
can be stored for direct use or
can be recharged into the
ground water. A major portion of
the rainwater that falls on the
earth's surface is wasted, as it
runs off in streams to rivers and
finally to the sea or gets lost in
evaporation. On an average, only
less than 10 percent of the total
rainfall recharges the ground
water aquifer," says Siddharth
Thyagarajan, an architect based
out of Chennai.
While norms are in place and
the idea is great, inefficient im-
plementation is a huge hurdle.
"The concept has helped save
water but 50 per cent of these
structures still do not follow the
best methods of rain water har-
vesting. Some erstwhile struc-
tures have been under repair
and need to be rectified before
they can function effectively,"
says Satish.
Adding to this, Siddharth says,
" The RWH structures that were
built 10-12 years back were bare-
ly maintained properly. Besides
06 MIXEDBAG
T I M E S P R O P E R T Y
THE RWH STRUCTURES THAT WERE BUILT 10-12
YEARS BACK WERE BARELY MAINTAINED PROPERLY
A TIMES OF INDIA PRESENTATION
A MAJOR PORTION OF THE RAINWATER
THAT FALLS ON THE SURFACE IS WASTED
SATURDAY, JANUARY 9, 2016
TAPTHERAIN
PROPER MAINTENANCE
OF RWH SHOULD BE
DONE BY CLEANING THE
DUST THAT SETTLES IN
THE PIT, REFILLING IT
WITH A NEW LAYER IF
NEEDED AND THIS HAS
TO BE DONE AT LEAST
ONCE IN FIVE YEARS
FASTFACT
many buildings constructed
before that period and a large
number of buildings that do
not come under the radar of
the CMDA do not have effec-
tive RWH structures."
The problem could also be
due to lack of awareness
among the people in the city.
R Sundar, secretary of an
apartment association, feels
that most people install an
RWH structure due to com-
pulsion. "In our apartment
there is a provision for rain
water harvesting. Every
apartment owner is aware of
it but they don't come for-
ward for maintenance or pe-
riodic upkeep of the structure
as it involves additional costs.
"Proper maintenance of RWH
should be done by cleaning
the dust that settles in the pit,
refilling it with a new layer if
needed and this has to be
done at least once in five
years."
This can also help in divert-
ing rainwater to more useful
channels. "Effective RWH
might definitely help in pre-
vent flooding. Water from the
rooftops have to be chan-
nelled into a percolation pit,
where it is filtered and made
potable. If a site where con-
struction takes place happens
to be a dried lake, rainwater
should get diverted to
recharge open wells and
borewells. This will prevent
flash floods. The colony also
needs to be built on high con-
crete stilts," says Satish.
While the recent rains have
helped recharge the ground
significantly, Siddharth feels
that the excess rains might
also have caused some silting
within the RWH sump. These
have to be restored for better
use in the time to come.
Effective RWH will signifi-
cantly reduce the dependence
on water supply from the lo-
cal municipal body. It can
happen only when it is imple-
mented on a large scale by
every building in the city with
the best RWH structures in
place. The government has to
establish strong enforcement
mechanisms in this regard so
as to realise the full potential
of the RWH system.
- Saivinai Cheithanya R