We will continue on discussion on sustainable water management in urban areas, I would like
to take the example of Adyar River in Chennai which is close to my home.
In the next slide I’ll show you the catchment of Adyar River and the surrounding areas.
Adyar River starts somewhere here in this map and then it’s going like this, this
is the way it’s flowing here and then this is the catchment area I have and then this
entire thing is the catchment area this is main where it’s starting and this is an
Adyar Estuary an important point, and it also receives water, the excess water from this
Chembarambakkam lake whatever we can store this water in Chembarambakkam lake they store
it for drinking water purpose, this water from this lake is treated and supplied to
the entire Chennai city, if there is more water in this lake during the rainy season
then the surplus water also comes to Adyar River.
Here you can see the Adyar River catchment, this area, this entire area is highly urbanized
in fact this area is also urbanized whereas the upstream portions this is what we call
the Peri-Urban area, it’s getting urbanized now and then probably in few years time these
place also will be having lot of habitation, okay.
And this Adyar River actually origin is in Kancheepuram district, Pillaipakkam and Kavanur
tank groups, the total catchment area of the river is 860 kilometer square, and total length
is 42.5 kilometers and the length within the city is 15 kilometers.
Now length in Chennai metropolitan area is 24 kilometers, width of the river ranges from
10 meters and certain locations to 200 meters at other locations, the average discharge
per year is 89.4 million cubic meters, and this is the tidal river so you have a backwater
effect from the Bay of Bengal due to tidal fluctuations, during high tight the backwater
effect is felt up to 4 kilometers in land.
Now what are the problems with Adyar River?
First pollution, you can see how much of solid waste is there and how polluted the river
is at certain and many of the locations the scenery is like this, if you look at the pollution
where it is coming from, the 97 infalls into the river,
basically 58 sewage discharge points, effluent from CETP of about 150 tanneries this is CETP
means common effluent treatment plant of about 150 tanneries discharges at Anakaputhur.
Effluent from Nesapakkam sewage treatment plant this is a domestic waste water treatment
plant Nesapakkam sewage treatment plant this is also discharged into the Adyar River.
The industrial effluents amount to 1 million liter per day, whereas domestic sewage that
is discharged into the river is about 8 million liters per day.
DO that is dissolved oxygen which is a good indicator of a general indicator of the health
of the river because if dissolved oxygen content is more than it supports fish life and other
water life and then the plants, if DO is very low that means the river health is very bad,
in general DO is alright at Nandambakkam which is on the upstream side whereas dissolved
oxygen content at Saidapet which is within the city, which is 8 kilometers downstream
from Nandambakkam is closed to 0, if you look at BOD biochemical oxygen demand that gives
an indicator of how polluted the river is, it’s as high as 375 milligrams per liter.
Now there heavy metals like chromium are also found and the concentration is around 1.25
milligrams per liter, nitrates the concentration is 16 to 125 tons per day, phosphates that
are coming in 1 to 18 tons per day, and lead is coming 1 KG per day.
Now ground water in areas close to river are polluted, in fact many wells which are in
nearby to this river when they have taken the samples and they tested them, they were
all found to be polluted, there is absence of minimum ecological flows, high deposits
of solid waste and there is presence of bacteria and virus in this waters is very high, it’s
estimated that thousands of crores at least more than thousand crores of rupees is required
for restoring all of Chennai waterways, there are other water ways other than Adyar, to
all of waterways in Chennai more than thousand crores is required to restore.
The other problems, other than the pollution is encroachment, the lot of encroachment on
the banks of this river and the slums and if you want to clean this river and then keep
it clean after, I mean keep it clean forever after you clean first time then you need to
see how much of pollution is coming from this encroachments whether we would like to have
the encroachments there, whether we can led them continue to live there, if we don’t
want to have this encroachments in fact the government has taken a decision that we would
like to you know resettle this people who are living on the banks of the Adyar, who
have encroached the space into the Adyar, now where do we move them?
What are the issues while moving them?
Because many of the people who are living in this slums or in this encroached areas
are actually contributing to the economy of the surrounding area many of them work in
the industrial units which are located nearby, so if you remove all of this people from here
and then move them somewhere else how did they commute, what is the effect of this resettlement
on the economy of this place, these are some of the questions which are important, which
we need to answer before we move them.
Of course we also need to find a space where we can resettle them.
Now as far as the ecology is concerned, we have looked at the pollution, we have looked
at the encroachment problem, now if we look at the ecology, now Adyar estuary is an important
part of Chennai eco system, it has been a haven for migratory and resident birds, however
the population of migratory and resident birds has declined in recent years because of pollution,
it has been estimated I mean emission fluxes for the whole Adyar system is around 2.5 into
10 to the power of 8 grams of methane per year and 2.4 into 10 to the power of 6 grams
of N2O, nitrous oxide per year, this is equivalent to total Chennai motor vehicle CO2 emissions
in one month, thus because this river this is lord of untreated and partially treated
waste water, and because of that you have these emissions of methane and N2O because
you may have the conditions for emission of this greenhouse gases.
The next and most talked about problem of the Adyar is the floods, as we have seen earlier
surplus water from Chembarambakkam lake and not only Chembarambakkam lake about 40 tanks
in lakes is discharged into Adyar River, we had major floods in the year 1943, 1978, 1985,
2002, 2005 and of course 2015 very recently we had major floods, until about 2015 when
they did analysis they found that estimated maximum discharge was 1950 meter cube per
second, but the estimated discharge in 2015 was a huge 3700 meter cube per second the
reason for this floods is heavy rain plus cyclonic activity, and a lot of waterway is
silted up, there are obstructions due to encroachments, there is a conversion of tanks in the catchment
area into residential areas and of course geology is not that conducive for infiltration
of rain water.
Showing some pictures of Adyar River in floods in 2008, 28th November 2008, what are the
effects that this floods have?
It’s obvious there is loss of property, there is disruption of lives of slum dwellers
about displacement of 50,000 persons so, and we have to spend lot of money for relief operations,
and there is of course of loss of manpower, and there is also health problems which are
malarial mosquitos have return in full measures after the floods, a crores of rupees is required
to be spent every year if you go for temporary measures like desilting, you desilt the river
and then probably it gets silted up again in another 4 or 5 years, so how many times
you can go ahead and do this desilting or can we find some kind of a permanent solution
to this?
These are the questions one should wonder.
If you look at the floods, normally hydrologist would like to work in terms of what we call
rainfall intensity duration frequency curves, here is I know at your level you may not be
aware of what this rainfall intensity duration frequency curve is, so I’ll explain a little
bit, what it shows here is what kind of rainfall intensity normally have in a particular area
depending upon what is the frequency of occurrence of that particular storm, so here if you say
there is a 100 year rainfall that means the probability of occurrence of that kind of
rainfall is one in 100 years, and then if you have look at the duration that is how
long the rainfall is going to last that kind of a rainfall is going to last, and then you
have what we call the intensity on the other side, this access, one of my colleagues has
done this hydrologic analysis for 2015 floods, in fact here done this rainfall analysis and
from the measured rainfall you find that the rainfall in Numgambakkam this curve shows
for Numgambakkam that is within the city whereas this
curve here it shows the curve for Chembarambakkam, what it is saying here this picture is there
is lot more rainfall in Chembarambakkam area in the upstream areas than within the city,
okay, that means most of the water that has come into the river during the December 2015
floods is because of very high intensity rainfall in the catchment areas rather than within
the city, now that is very crucial for our discussion.
Here I show a picture of the Landuse, the red areas show the areas which are highly
urbanized which you can see which are in the downstream portions of the river where it
is completely urbanized whereas from here this area is not yet urbanized as much as,
as compared to the areas here.
The Landuse pattern the change in the Landuse pattern has a significant effect on the floods,
it works this way, there are lot of this little blue, blue bodies those are the tanks, so
when the rain comes down many of this tanks have to be filled first and then they have
to overflow before the water goes into the river and then gets carried to the downstream
side, so they are acting like springs to take the load of the rain, if there is urbanization
then all these water bodies would, I mean if there is bad urbanization or if we don’t
control how the urbanization is taking place all this tanks would disappear, and if the
tanks disappear then the spring effect on the floods will also disappear and then definitely
for the same amount of rainfall that you may get one in 30 years you may have a worse floods
in future because lot more water will come into the river, not only that when the urbanization
takes place lot of area gets paved that means whatever the rainfall is falling on this area
because it’s paved and then it’s impervious that rainfall will not go into the ground
through infiltration process, so you have more generation of overland flow or the run
off into the river and that certainly will increase the frequency of flooding in the
river, so it’s very crucial this area how we allow the development, if we allow uncontrolled
development in this area and we allow the disappearance of this water bodies then certainly
the people here will find that there is an increase in flood frequency, the damage due
to the floods will increase here, so whatever we do here we have to keep in mind what is
its effect on the downstream side.
Now if you look at 2015 floods, one has to think about whether it is flood or whether
it is water logging, that is flooding versus water logging, we can ask one question, could
the flooding in December 2015 have been prevented, definitely we say that Chembarambakkam release,
what I mean here there has been a debate where they say a lot of water which has been released
from the Chembarambakkam reservoir because that was getting full and one could not have
kept the water in Chembarambakkam without breaching, so a lot of water got released
from the Chembarambakkam, so there is a feeling that the releases from Chembarambakkam could
have cost this floods in 2015 December, as per our analysis we feel that Chembarambakkam
release is only a small piece in the entire scheme that lead to Chennai flooding in 2015.
An efficient, well designed, well maintained storm drainage system could have minimized
the level of water logging and damage, a lot of flood, a lot of water that we have seen
during that period may not have come from the Adyar River or overflowing of the Adyar
River it is more so because the rain water which has fallen in those areas could not
be drained easily and so there was a water logging.
And we have here a picture of storm water drainage system that I am showing, we have
an insufficient coverage with storm water drains
in the city, there is lack of proper connectivity, there is linkage to major canals and waterways
from many areas is not existent, and many of this drainage channels, okay which are
designed and construct to drain the rainwater, there is storm water drainage system, there
original design intensity I mean there they have to be designed for certain rainfall intensity,
there original design intensity was only 31.39 millimeters per hour, and they have designed
for 1 hour storm duration and 2 year return period, this seems to be very less based on
the analysis of intensity duration frequency curves, they should have been of course this
have been designed quite a while ago, they should have been designed for more than 50mm
per hour, in fact in 2014 there has been a revision by the government, the government
has revised the design intensity to 68 millimeters per hour but this is only meant for all the
new drains, and the question arises what do we do with the old ones?
How do we retrofit them?
Another thing road network length is about 6000 kilometers, but we have only 1660 kilometers
of storm drains, there is 205 kilometers of drains have a width of 0.6 meters or more
only 205 kilometers of drains, you look at this number 6000 kilometers here, we need
6000 kilometers whereas only about 1660, okay 1660 kilometers of storm drains are there
and out of this only 205 kilometers of drains have a width of 0.6 meters or more.
Now storm water drains are provided only for roads with 12 meter width or more, there is
a focus mostly on the macro-drainage, there is not much attention paid to the micro drainage,
and many of the drains are clogged due to solid waste.
I’ll show you some pictures, this is a feeder drain which is clogged with solid waste, definitely
this kind of a drain, this kind of canal or a channel will not be able to drain the area
very easily and will lead to water logging.
This is another one, here you see this is an entry point to the drainage system and
this entry point to the drainage system again is clogged due to lot of solid waste, so how
do we expect during the heavy intense rainfall events the rainwater will actually go through
this into the storm drainage system and then drain off, which also brings to the point
that it’s not just the design and construction of this drains but the maintenance of this
drains is very important.
It’s not only the maintenance of the drains is very important but if we’re trying to
solve the drainage problem or the storm drainage problem of Chennai city then we also need
to solve the problem of the solid waste, without solving the problem of solid waste or without
having a proper solid waste management in practice we’ll find ourselves in this kind
of a situation again.