S Vishwanath, a civil engineer and urban-regional planner with over three decades of experience in the water and sanitation sector explains what Bengaluru must do to prevent flooding and water-logging.
(Above image courtesy Twitter/Ashwin Mahesh)
Overnight rains in Bengaluru have left “one person dead and 75 localities inundated, displacing residents of nearly 2,000 flooded houses, marooning 10,000 other residences and damaging 20,000 vehicles”, a Times of India report notes. These are astonishing figures for a city like Bengaluru following heavy rainfall.
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The worst affected parts were the eastern, southeastern and northeastern parts of the city. According to the Indian Meteorological Department (IMD), the city recorded 13.16 cm (131.6 mm) of rainfall, most of which fell in less than 12 hours on Sunday night. This was the third heaviest rainfall the city has witnessed in September in the past 75 years.
What we saw on Sunday night is a continuation of heavy rainfall from last month. In August, the city recorded 370 mm, according to IMD. The figures for August 2022 fell a little short of the city’s record of 387.1 of rainfall in August 1998.
Despite unprecedented rains, the reason why parts of the city are horribly inundated, flooded and water-logged is primarily because of man-made factors.
Speaking to The Better India, S Vishwanath, a civil engineer and urban-regional planner with over three decades of experience in the water and sanitation sector, discusses why Bengaluru has witnessed such unprecedented floods and the potential solutions to address them.
Visuals from RBD layout in Sarjapur road. Most residents here were evacuated using boats. There was no electricity for abt 36 hours. Drains remain chocked in the area. Earlier this year the MLA & BBMP officials had met residents & assured to fix flooding. #bengalurufloods pic.twitter.com/TNVKKXkO03— Deepak Bopanna (@dpkBopanna) September 6, 2022
‘Tyranny of small decisions’
In 1966, the American economist Alfred E Kahn wrote an essay explaining a phenomenon he called ‘the tyranny of small decisions’. The essay presents a scenario in which several decisions, individually small and insignificant in size and time perspective, cumulatively result in significant outcomes that are both sub-optimal and undesirable.
Bengaluru, according to S Vishwanath, has reached this juncture of excessive flooding and water-logging because of what he calls ‘the tyranny of small decisions’.
Having worked on policy teams for writing the State (Karnataka) Water Policy, rainwater harvesting policy and bye-laws for Bengaluru and wastewater reuse policy for Karnataka, he says, “Every individual act by a landowner to level a site, encroach on a stormwater drain or fill up debris into a lake doesn’t have an immediate impact. An individual doesn’t think that it’s a problem if they encroach on a drain. But like that one person, 50 others are doing the same thing because of individual decisions taken by the authorities. When you’re suddenly confronted with a 120mm a day rainfall event, you have a massive problem.”
More specifically, however, Vishwanath highlights three key reasons behind recent events:
1) Climate crisis is clearly upon us: We have a distinct increase in rainfall compounded by the urban heat island effect – caused by exponential growth and concretisation – which creates excess heat and thus causes more intense rainfall across shorter durations. Typically, the city would endure a rainfall intensity of 60 mm per hour, but now we are talking about 180-200 mm per hour for short durations. Bengaluru is just not prepared for this sort of rainfall intensity.
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2) Parts of the city worst-affected have relatively flat terrain: These areas used to be old rice paddy fields. When we overlaid infrastructure here, we built roads without any cross-drainage works adequate for this kind of rainfall. These roads have essentially become dams.
3) Underinvestment in critical infrastructure: There are feeder channels that take the water from the surface to a nearby lake or a channel. During agricultural times, these feeder channels used to move about depending on which land was cultivated, which lake was being used and so on.
They have not been identified for modern requirements of runoff. Therefore, governments have underinvested in stormwater drainage infrastructure. To compound that problem, we have inadequate sewage infrastructure, leaving sewage to float about in these drainage channels and lakes.
Why is #bellandur area of #bangalore flooding badly? A clue👇🏽
Agara-Bellandur-Varthur #lakes were connected #wetlands.
Then, built over. See change 2003-2015.
Prolly worse now!#Environment ≠ an “obstacle to clearances”
It’s what we need to pay attention to, to save ourselves pic.twitter.com/OLtwmQCb0B— Arati Kumar-Rao (@AratiKumarRao) August 31, 2022
However, Vishwanath does believe that there are both short and long-term solutions available.
1) Road audit: One of the things we need to do immediately is a road audit for drainage. The authorities need to ask themselves whether all roads have stormwater drains on adjacent sides. Are these drains networked? Most drains today simply stop at a dead end. These drains should go in a hierarchy and empty into a lake or a river. Are the cross drainage works adequate like the box culverts and Hume pipes, and can the water move from one side of the road to the other? This kind of audit has to be done for all roads in the city.
2) Protect stormwater channels: Stormwater channels should be lined with concrete so that they are demarcated and authorities must ensure they are not allowed to be encroached upon. That network should make sure that it disposes of the water finally into a river like Vrishabhavathi.
If a government wants to build a road or metro station, they acquire the land, pay compensation to the previous owners and clear up the space for those purposes.
Similarly, the authorities need to now acquire land for stormwater drains. The city will have to fairly compensate those who lose their land, but then they will have to design the stormwater drains adequately for these climate change rainfall events. This process has to be systematic as a hydrological design which is watershed-based. We’ve not been engaging in the process systematically and instead have been increasing the number of drains on an ad-hoc basis.
3) Invest rapidly in sewage networks: We need to saturate the city with sewage networks so that all sewage is picked up and sent to sewage treatment plants (STPs).
4) Improve our prediction skills: The Karnataka State Natural Disaster Monitoring Centre has 99 automatic weather stations in Bengaluru, which is the largest density of weather stations for any city in India. Now, they are very good at identifying heavy rainfall incidents and sending a signal out to a given area in the city that it can expect floods.
We need to improve their predictive powers to a minimum of three days in advance and make sure that this information is acted upon as soon as possible. This will require more investment in the modelling process and improving the automatic weather stations.
5) What can citizens, communities and apartment complexes do? People must invest heavily in rainwater harvesting. We need to make sure that we collect as much of the rainwater as possible, use that to recharge our aquifers and try to design our plots and apartments and gated communities as zero rainfall discharge areas. The idea is to hold onto the rain and ensure its positive use rather than letting it run about and flood the place.
The rainwater harvesting by-law in Bengaluru states that for every square metre of roof area, you have to create a storage or recharge of 60 litres of water. For every square metre of the paved area around the building, you must create a storage or recharge of 30 litres of water.
Broadly, a one-day rainfall event of 60 mm can be completely managed by even a small house let alone an apartment or large gated communities.
If the law is followed, we’ll be reducing the impact of flood by a factor of three. About 65% of the land use of any particular area is housing or residential. If these residential areas manage rainwater appropriately through rainwater harvesting, there will be no external water to create floods.
6) Design on a watershed basis: Every lake is a micro or mini watershed. Authorities must understand that a watershed is a hydrological unit, understand how water flows and ensure that it’s drained into channels and flows into the lake. When the lake overflows, it connects to the next downstream lake, for which they will need sluice gates that they can operate.
If you anticipate heavy rainfall, you open up sluice gates, allow the water to flow out, and the lake is ready to receive the flood waters and retain it without a problem. Essentially, you prevent flooding by taking precautionary action. If there is a rainfall event which exceeds 60mm, like the ongoing one, that excess water should be drained to reach lakes which are connected to different parts of the city.
Why is fixing Bengaluru’s flood problem a national issue?
For a city like Bengaluru, it takes a special kind of skill to create floods.
“The city has an average elevation of 920 metres and cascades down into valleys and rivers on all sides. Unlike Chennai, Mumbai or Kolkata, this city is on a hill or a ridge line. It calls for great incompetence if the city can create floods,” argues Vishwanath.
Bangalore sits above 2900ft, one have to be master in bad planning to flood a high altitude, rich metro city.
All cities are not made equal, cities like Mumbai & Chennai with their flat terrain, costal tides, heavy rainfall are geographically flood vulnerable. #bangalorerains pic.twitter.com/99nu3WuiDo— Tamil Nadu Geography (@TNGeography) September 5, 2022
“However, the western or southern parts of the city aren’t flooded except for small pockets where stormwater drains or lakes have been encroached on. The flood has particularly affected the eastern part (its southeast side) of the city. And that is a peculiar hydrological construct. It’s a flat terrain with very limited percolation because the clay layer at the bottom doesn’t allow the water to percolate. We must learn that the city isn’t one unit. It comprises many units of rainfall and hydrology and we should design adequate infrastructure for context,” he adds.
One reason why the recent floods in Bengaluru have garnered such media attention is that it struck the Outer Ring Road, which connects the city to all the major software tech and e-commerce offices. “That’s why there is such a massive public hue and cry. Since the floods have directly hit the city’s economic engine, there is all this hullabaloo,” he notes.
Besides all the damage, the ongoing floods have sparked an unusual public discourse online where ‘locals’ have started blaming the influx of migrants for what’s happening in the city.
Vishwanath says, “But this city can provide good employment opportunities to many Indians. This is something everyone from Bengaluru should be proud of. Commensurate with the value the city generates in terms of GDP, both the Centre and State must invest special funds to build up the requisite infrastructure and prevent these floods. It’s not a local-city problem, but a national one and the authorities need to invest a lot more than they’re doing right now.”
Hey. Extreme #rainfall overnight has resulted in flooding across #Bengaluru!
We introduce this important initiative – #LetsMap – aimed at mapping commonly flooding areas in our city.
Webform: https://t.co/zjcnMRiYjy pic.twitter.com/BWxJH1PihM— Citizen Matters (@citizenmatters) September 5, 2022
(Edited by Yoshita Rao)