Bengaluru needs additional 600 km drains to prevent flooding, says Knight Frank report | Bengaluru News – Times of India


BENGALURU: Following a year of multiple incidents of flooding in the city of Bengaluru, Property consultancy Knight Frank has come out with a study based on existing data to find the gaps in the city’s storm water drain infrastructure.
The two month long study, ‘Bengaluru Urban Flood‘ was released at their office in Bengaluru on Wednesday. It is their first report on the topic in India, and they believe a drainage master plan which could take upto a year and half to plan, is among the solutions.
Driven by statistics from IISc and other sources, researchers estimated the city needed to construct approximately 658 kms of primary and secondary drains, in addition to rejuvenating the existing ones. The city has 842 km of current primary and secondary drain length, and based on certain parameters including Total Road length, etc, the deficit was calculated.
As per Knight Frank estimates, the capital expenditure requirement is estimated to be Rs 2,800 crore. About 80 percent of that amount is for developing the additional requirement, and the rest is for maintaining or upgrading the existing infrastructure, said the main author of the study V Shilpashree.
Shantanu Mazumer, executive director, Bengaluru, Knight Frank said the budget allocations and the revenue from real estate was good enough for the plan. Bengaluru has to see how the other cities in India and abroad have worked out models.
Reduced length of SWD
The study highlights that the storm water drains that were 113.2 km in length in the Koramangala valley in the 1900s are now almost half — 62.8 km in 2016-17 as per the CAG 2021 report. A similar reduction for the said years was seen in the stormwater drain lengths in Vrishabhavathi valley where 226.3km of SWD was reduced to 111.7km.
V Shilpashree, who led the study, explained that the SWD in Bengaluru works thus — primary and secondary drains which are interconnected, help transfer excess water ( due to rainfall) collected, from one lake to the other. However, a lot of concrete development has damaged the inter-connectivity of the lakes, thereby reducing the length of the drainages.
Meanwhile, Mazumer added that the interconnecting channels — naalas — are segregated into primary, secondary and tertiary. “Largely the primary naala exists. The problem is with secondary and tertiary which are encroached, re-aligned or vanished over a period of time. Tertiary and secondary naala are where water flows once in 15- 30 years. So if there was no water, and was not part of the village map, the development was allowed and it vanished. That’s how the reduction has taken place. The primary naala continues to exist. There is tampering that has happened there too, but it has not vanished,” he said.
It is not encroachment, but it is also development, he added further on the aspect of reduced storm water drain lengths.
The report estimates the city’s population to go up to 18 million by 2031, and thereby a need to ramp up the existing storm water drainage system commensurate with that.
Mazumer added that the image of brand Bengaluru was taking a hit because of the rains and the flooding issue becoming a redflag even for apartment buyers . It is part of their checklist when buying a property — whether or not a place is in a low lying area. Even real estate buyers have details about whether the property is in a catchment area in the feasibility assessment, he said.
Rajeev Vijay, Executive Director, Government and Infrastructure Advisory at Knight Frank India said that the team suggests the government to have a comprehensive storm water drainage plan, a master plan like other cities. They have to find the ground situation, geotag issues such as encroachments and create models.

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