Then there is another issue of the aggradation of roads due to resurfacing, let’s say originally
the road level is here, the house level is here and then you have drains on both sides
of the road, so whatever the rainfall falling here or here or here it goes to the drains,
it goes to the drains and then it flows of into the drains and then the channel will
drain the rainwater and that will prevent the water logging.
Whenever we are doing the resurfacing of these roads, what normally they do instead of resurfacing
the roads they actually have to chip the road and then do this part of resurfacing, instead
of that we go from this level, this level and then raise the road level, so every time
the roads are re-laid, repaired, the road level is going up.
Now as the road level starts going up naturally whatever the water is falling in these areas
it will not be able to drain into this drain here, and the road start fragmenting the natural
drainage pathways, in fact in the design of drainage system during heavy flooding events
we would like to use the roads as a drainage channels to pass off excess water, with this
kind of a thing it’s not possible because the roads are becoming like mini, mini embankments
which will fragment the natural drainage pathways, this is not good.
And there is a lack of adequate cross drainage works along the roads, what we mean by cross
drainage works is you have a road like this and then water is flowing from this side to
this side, let’s say natural ground slope is like this, so when the rain falls here,
the rain starts coming down, I mean the water starts coming down here and you need to provide
what we call it cross drainage work, if these drains here, these are cross drainage works,
this is a culworths, if they do not have sufficient capacity or if you do not provide sufficient
number of this cross drainage works then the water will not flow from this side to this
side because the road is coming in between and then it stops flowing over the road and
it can cause breaches in the roads.
In 2015 we have seen a lot of these breaches.
Another issue is what we call the compound wall effect, every time there is a developmental
activity or there is a real estate development or some facilities are coming up, this is
like the wall of an establishment, and before we develop our establishment let’s say gated
communities and then things like that, first thing we do is we go and then construct this
compound walls, and this compound walls when you construct them particularly for large
areas and if we do not adequately provide, I mean for flow of natural water and if you
come on its way it will change the flow paths, it will change the local hydrology there and
it can have localized effects in terms of flooding.
As we see in this picture this is the compound wall of an establishment and there is actually
on the other side of the compound wall there is a natural lake, this natural lake a depression
use to take lot of water during the rains, water is, you can see this water like this
the water is flowing like this and there is a lake on the other side, now we have constructed
this wall, water will definitely cannot flow over the wall until it piles up more than
the height of the wall, which means that this wall is going to cause flooding on the upstream
side and that’s what happened in 2015 December, this wall was coming in the way of the water
flowing so there was a village on the upstream side and those villagers were afraid that
if they don’t do something then they’ll get flooded, and there property will get damaged,
so overnight they came in large groups and they actually broke the wall, you can see
that this path here they took one panel out, they took one panel out here, so that water
will flow towards the downstream side and it will not get piled up behind the wall and
there will be prevented from flooding, now this kind of actions do occur during major
floods.
In 2015 floods also it came to our notice that there are many, many lakes there burns
were willfully breached because the upstream people do not want to get inundated, they
go and then breach the lake and then let the water go to the downstream and then probably
the people on the downstream side are not aware of this and they get flooded without
any warning, so when we go and then talk about the drainage systems, when we go and then
talk about the development we have to consider all these things so that the drainage system
is sustainable, so we have to go in for the concept of sustainable drainage system which
we will discuss at length in a different lecture.
Basically in a sustainable drainage system we have philosophy is you go beyond traditional
rainwater harvesting, we try to mimic natural drainage from a site and where possible you
manage water on the surface and you manage runoff very close to the source wherever whichever
the localities which are generating more runoff you try to keep the water there itself, you
try to manage their itself and then you also provide multiple benefits, these are the philosophies
of sustainable drainage system.
And there are different components for this sustainable drainage system, we can use tanks
as a component of modern day sustainable urban drainage systems because we can use this tanks,
this natural tanks I mean naturally if we can use them as retention basins, what this
tanks would do is they reduce the flood volume because they can reduce the flow magnitude,
this detention basins, the concept of detention basins is very similar to the concept of flood
control reservoirs and flood control dams like the Hirakud dam in Orissa which was constructed
to prevent flooding of the coastal cities or the coastal habitation like for example
the flooding in the city of Cuttack to prevent the flooding there they constructed a multipurpose
dam, Hirakud dam what they do is when the water is when there is heavy rainfall and
large water is coming in, they temporarily stored the water in the reservoir and later
on they release it to the downstream slowly and gradually, so one can take this tanks
which we have and then use them as retention basins.
What is the situation in Chennai, what is the current state of most of the tanks?
Either the tanks have totally disappeared in any cases or the inlet to the tank is cutoff,
that means the tank exists but then water cannot flow into the tank it is cutoff from
the rest of the you know catchment area or outlets are nonexistent because when you have
a tank you should have an inlet which will bring the water to the tank and then the water
gets temporarily stored in the tank and then the water flows off from the tank when there
is an excess water, otherwise the tank will overflow and then will cause the breaching
or it will cause the flooding, so outlets are also important, in many cases these outlets
are not existing.
The excess water sluice is not maintained, wherever there is an outlet then you have
sluice gate there and that excess water sluice are not maintained to dispose the flood to
the natural drainage.
Now what are the tangible actions, let’s say this is the scenario, what are the tangible
actions that one can take to prevent the occurrence of huge flooding or water logging, first thing
is proper solid waste management is, I mean one cannot over emphasize this a proper solid
waste management needs to be there, for this community education on waste segregation and
solid waste management is absolutely essential, other day we found in one of the meetings
that even in a Chennai city apparently the segregation of the waste at the source which
we think it should be a common knowledge to many educated people or urbanized people the
segregation is being done only probably 20% of the ones, so we need a community education
on waste segregation and solid waste management, we should have adequate cross drainage works
across streets, roads, and highways, we have to revive the tanks wherever it’s possible,
wherever tanks are lost at least revive the outlet and excess sluice, demarcate flood
lines of rivers, drains and lakes and restrict the activities within these demarcated water
line zones just like they have coastal regulation zones, so we have to restrict activities within
these demarcated water line zones, we cannot let encroachment of flood plains of the rivers.
We have to ensure resurfacing does not result in aggradation of road level, we have to adopt
and implement IRC codes properly, Indian Roads Congress Codes properly.
And in my opinion we should mandate sustainable urban drainage systems for all the new developments,
we have to have a permit system for storm water discharge, whenever there is any development
that is taking place we have to ensure that that development has considered how they development
effects the storm water discharge and how they are taking care of it, then only the
permit should be given.
We have to ensure that urbanization does not necessarily result in higher rates of runoff,
like we need not go and then construct completely impervious parking lots all over the place,
we should not go and then pave the surfaces with concrete and then prevent infiltration.
And then before any new development takes place we have to make sure that macro drainage
is in place, then ensure proper network connectivity and capacity linkage to major canals and small,
small drains they have to be link to the major canals and waterways, that linkage has to
be ensured, and there has to be a maintenance all through the years rather than just before
the monsoons.
And most of the time again this cleaning activity goes on because of various reasons, funds,
lack of man power and so on, only major drains get cleared whereas micro drains which actually
feed this major drains should also be maintained properly.
In this context if you look at the Adyar River basin, there have been many developments and
new proposals, there is a river restoration for improving the water quality and ecology,
new treatment facilities for waste water are being proposed, they have constructed an ecological
park in the estuary, the picture is shown here and they’re proposing 5 check dams
in the upstream region and creation of new storage facilities, thinking of creating new
storage facilities or to solve the flooding problem, they’re also saying that we can
link Adyar River with Palar River and then divert some of the flood waters to the Palar
River.
What I would like to say here is there are certain things which need to be considered
during the planning stage, or some concerns one should raise at the planning stage itself
that is, is there any holistic view taken in the design and implementation of these
projects, what is the effect of implementing any of these individual projects on the whole
system, have we taken any holistic view?
Is the land use plan in the peri-urban areas scientifically link to flood and pollution
problems in the downstream areas, is the river quality restoration plan sustainable?
That is okay you go and then you restore the river today and then after 2 years it goes
back to the same bad situation that we have now.
Is the river quality restoration plan sustainable?
What is the effect of upstream developments on floods, river quality, and ecology?
The next thing is whenever we talk about sustainability we have seen earlier there are the 3 pillars,
one is economy that means the system should be designed at less price, less cost, and
the second one is the preservation of environment and ecology, and the third pillar is of course
this plans should be socially acceptable, so when we design these things individually
have we considered whether this plans are socially acceptable and how do they implement,
resettlement of slum dwellers, is it part of the planning of this projects.
So what is needed is a holistic view of upgradation of treatment facilities, that is capacity
enhancement and technology choice, creating upstream storage facilities for flood control
as well as maintenance of environmental flows to increase the flood way capacity, socially
and politically acceptable ways for removing encroachments.
Now appropriate policy decisions for land use development in upstream reaches, and of
course optimal operation of tanks and storage facilities, here I give you the example of
Chembarambakkam lake, this is actually meant for a drinking water purpose, so it will be
operated as a drinking water reservoir that means as an when the water comes we don’t
want to lose it and so we go and then store all the water, but it is not operated as a
flood control reservoir, the operation of a flood control reservoir is very different
from the operation of a drinking water reservoir, so if you want to go and then utilize Chembarambakkam
lake for controlling the floods in Adyar river then we have to relook at the operational
policy of this particular reservoir, and then whether that is acceptable from the drinking
water supply point of view.
So we have to come up with a sustainable plan for restoring and maintaining Adyar river
quality and ecology, managing domestic sewage in its catchment, and disposal of storm water
without causing floods and probably we can harvest water from Adyar river basin for useful
purposes.
If you look at the water management in any urban area, there is a lot of linkages, for
example we need water for stream water, the stream quality maintenance, we need water
for industry, we need water for drinking water supply, we need water for irrigation in the
upstream areas because crops are growing and then we can supply water to any of these four
needs either through surface water or through ground water sources, and what is replenishing
water in our surface water and ground water bodies, is actually the rainfall, if the amount
of rainfall is not sufficient to replenish the water in surface water bodies and ground
water bodies as we take from the storage for any of the uses then we have to transfer water
from other basins and of course that is costly and then may not be possible always.
And when we talk about the industry and the requirement or when we talk about the drinking
water supplies that demands for this drinking water supply and industry we can control,
let’s say we have a water distribution network where we are losing 30 to 40% of the water
that we put into the network through leakages, if we plug the leakages then certainly the
demand for drinking water will come down, not only that if we have technological interventions
that is we bring in the concept of recycling of treated waste water for many of our purposes
like flushing of the toilets or many non-portable uses, we can use the recycled I mean treated
waste water, we can treat it to a treasury level and then we can use it, so if I do that
technological intervention then certainly the demand for fresh water for the drinking
water supply schemes will come down, what is this technological intervention going to
have in terms of its magnitude, and what are the other side effects that may be having
when you put in this technological interventions, all these things have to be looked into in
a holistic way in a system, in a system sense, it’s all part of the entire system.
I’ll give you an example 2015 we had huge floods and we could not store the water anywhere
and then we’ll let it go to the sea eventually, and then in 2016 and part of 2017 we had a
significant drought, we didn’t have lot of water to drink in the summer, so when I
talk about flooding problem I should not look at only the flooding problem, I should combine
it with the problem of drinking water supply, I should combine it with the problem of maintaining
the stream water quality, I should combine it with the problem of how much of water I
have for irrigation and so on and so forth, I have to take, I have to design, I have to
plan for all these things in a holistic way, otherwise our solutions will be peace mill,
and then I am also sure they will not be economical, so in this context we would say that sustainable
urban drainage systems or to go further we should bring in the concept of water sensitive
urban design, you design the urban spaces in such a way that all of planning, construction,
maintenance, operation everything is water sensitive, this water sensitive urban design
is becoming need of the day, in fact it is practiced in several parts of the world and
we have to bring in that concept to India also, the water sensitive urban design, I’ll
discuss about this water sensitive urban design in another lecture.
Thank you.