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Urban Floods – A case of Bengaluru


The spotlight of media and the public is continuously on the unprecedented flood in the city of Bengaluru in particular and elsewhere in the state of Karnataka and the subsequent damages to property, work shutdown for an extended period, and loss of a few invaluable lives. The soundbites were high due to losses suffered by IT companies in Silicon Valley of India. Illegal waterbody & storm drain encroachments, improper operation & maintenance of water infrastructure, and lackadaisical government departments are being blamed as the reasons for the catastrophe.


People walking in flooded road in Bengaluru after the September of 2022 rains
Flood fury in Bengaluru in the aftermath 131.6 millimeters of rainfall between September 4th and 5th, 2022 (source: freepressjournal)

Social media is awash with emotional appeals and arguments calling other parties for not doing right & enough. Quite naturally under distress fault lines open and we try to pass the buck on one another.

It is the right time for us to sit together, introspect and analyze what has gone wrong and what needs to be done next to save ourselves.

Development at a huge cost:


The panacea for everyone’s livelihood is economic growth, so natural growth of urban centers and hence unpardonable compromise on the equilibrium of nature. It is just not in Bengaluru elsewhere in all parts of the world the compromise beyond tolerable limits has pushed us to a state of brink and we are vulnerable to the impact of climate change. What we are witnessing now is the resulting lack of resilience in the city’s infrastructure to absorb this natural calamity.


Low-impact development:


Let us come to brass-tacks the reasons for recent flooding in Bengaluru is because of a combination of the following. Hitherto the importance of hydrological & hydraulic analysis was not felt by city planners to the desired level and construction and other developmental activities continued to flourish. This resulted in encroachment of erstwhile water bodies & natural drains, deformation of natural contours of the city (topography), and Land use land cover changes with more impervious surfaces resulting in enhanced runoff.


aerial view of flooded roads in Bengaluru
source : gettyimages

The number of lakes in the city is now reduced to 400 from 1400. Add to this, Inadequate maintenance of the drainage system, isolated planning & implementation, insufficient coordination between administrative departments, unprecedented extreme rainfall events of high intensity due to climate change, and public apathy have compounded the sufferings. In nutshell, all developmental activities are pushing Bengaluru towards unsurmountable consequences with a huge impact on nature.


By harvesting the runoff available for the city 17-20 TMCft of water will be available which would more or less make the city self-sufficient in its water requirement.

Opportunity?


Have we reached an irreversible state? Can we not move the wheel back and redeem ourselves? Succor lies in better water management! The benefits of such management are immense to Bengaluru. By harvesting the runoff available for the city 17-20 TMCft of water will be available which would more or less make the city self-sufficient in its water requirement.


Additionally, the dependency on Cauvery water is reduced significantly. Cauvery water supply is coming from a distance of more than 100km with a lift exceeding 500m consuming more than 100MW of energy for pumping besides significant losses on the way. The other major problem is lake water and groundwater pollution which can also be addressed by insulating sewers from storm drains. This arrangement can facilitate decentralized effective wastewater treatment plants amenable to less load and better operation and maintenance.


These acts of better water management will also attenuate the negative impacts of climate change. Finally, revenue generation through aquaculture, recreational & health facilities in and around lakes has the potential to support the water and wastewater infrastructure of the city while ensuring much-needed protection of the environment.


Environmentally benign plan:


The first step in the process of water management is the preparation of a comprehensive water & wastewater plan with emphasis on hydrology, hydrogeology, and hydraulics for the entire city, and start working from head reaches of each of the three valleys of the city (Vrushabavathi, Hebbala, and Koramangala-Challaghatta) deriving appropriate implementations for each micro or mini watershed of each valley.


All implementations should be based on the micro or mini watershed as a hydrological unit (not BBMP wards) of analysis to completely capture the details to arrive at effective implementation strategies. With current-day advances in remote sensing, geographic information systems, and computer applications this can be done better than ever by incorporating the principles of integrated water resources management.


Heat Map - Depth of submergence shown as a result of Inundation patterns
Inundation Pattern Results (green pink is low- high depths of submergence)

The results of such an analysis will provide inundation scenarios for any magnitude/intensity of rainfall and thus in helping compare the floods of past, present, and future for further consideration of necessary care, caution, and interventions. Concurrently it is also possible to assess conjunctive use of water (combination of surface water, groundwater, and wastewater) vis- à-vis capacity enhancement requirements of waterbodies and natural & storm drains.


Graphical Map of Storm Drain Analysis of Areas in Bengaluru
Storm Drain Analysis Results (Red segments of storm drains unable to accommodate the incoming flow)

Single repository or data source:


However, the challenge is in terms of obtaining reliable results because these results depend on input i.e., data which needs to be adequate, accurate, and relevant data is in the custody of various government departments of the state. The data necessary for the purpose relates to rainfall, topography, water bodies, storm drains, natural drains, water supply & sewer networks, land records, BBMP administrative boundaries, and many more. A team consisting of hydrologists, environmentalists, geospatial experts, geologists, and water resources experts will have to work together to arrive at a permanent solution.


Epilogue:


All of these necessary works to bring back normalcy can come at a high cost, but it is justifiable for the redemption of the impaired ecosystem with unmindful anthropogenic activities. With this, the garden city (the earlier tag of the city) known for its salubrious weather & environment, and silicon city (the current tag) representing development can complement each other for improved livelihood. Better late than never!


Check out the urbnpost: Aid Lies in Better Water Management

References:

  1. Geospatial approach for integrated water management – case study of Bengaluru, funded project investigated by the authors of this article, report yet to be published.

  2. Flood Risk Assessment Studies for a client in Kakinada, Andhra Pradesh by Street Matrix.






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