Recovering Bengaluru’s tanks and rain terrain

September 03, 2016 12:00 am | Updated September 22, 2016 04:48 pm IST

Bengaluru’s terrain cannot be defined as being a series of lakes. Instead, it is a terrain of tanks.

Understanding the difference is critical to designing the city’s infrastructure and conceiving its relationship with rain; and more immediately, explains that demolition of ‘lake encroachments’ or ‘drain encroachments’ will do little to save the city.

These encroachments are merely the last nails in the coffin, for the process of altering the terrain started in the 1800s when settlers did not see the need to respect the difference between lakes and tanks. Perhaps, they believed they could engineer their way out of the difference. The consequence is that Bengaluru today is consumed by thinking around its ‘lakes’, instead of thinking around the tanks. And, this is responsible for floods.

Tanks, not lakes

A lake calls attention to a water body appreciated for its scenic nature, recreational possibilities and the habitat it affords birds. Planners see it fitting the land use category of open space and people welcome it as ‘nature in the city’.

They covet the relief it offers from the congestion, filth, kitsch and unsightliness of a city-in-development. Lakes certainly raise the value of properties by giving them a ‘lakefront’; and they build an expectation for seeing water all year round.

A tank (or kere in Kannada), more humbly, draws attention to a bund (i.e., an embankment) built across a low ground . In the city’s gently undulating terrain, this low ground is a concavity between high grounds that are convexities. It begins like a web between fingers and slopes down. Bunds built across it hold rain coming off high ground, not just as ‘rainwater’ but also as wetness in plants, animals, soil and even air.

Bunds were traditionally fitted with two kinds of openings: first, as a plug at the lowest point of a concavity (generally, in the middle); second, was as an overflow weir at one or both ends of a bund, which set the limit of rainwater held and allowed the excess to pass across the bund into a nallah (canal) into the next tank. This nallah also allowed a stretch of low ground to be bypassed in case of heavy rain.

As rainwater in a tank receded – through consumption, evaporation or permeation – the exposed ground was planted, harvested for silt or clay, or used for events. In this way, a bund gathered an area of rain, its own rain-shed. This created a unique and resilient infrastructural system with an ability to absorb excess and scarcity of rain. The system was essential to settlement on the Deccan Plateau where rivers are ‘yet to form’, where there are no ‘natural lakes’, and the only source of water is rain.

Apart from being a terrain of ‘tanks’ and rains, the city cannot be considered as a terrain of rivers. The idea that Arkavati needs to be revived – on the lines of a potential ‘Thames riverfront’ – is entirely misplaced.

Arkavati is instead a reference to a bypass nallah along a series of tanks from Nandi Hills being activated in a moment of heavy rain. Like Vrishabhavathi, Ponnaiyar and other such names, Arkavati refers to a rain terrain rather than a river – a terrain that has been worked by a venerable system of bunds.

From rain to lakes

The undermining of Bengaluru’s ingenious tank/rain terrain and its conversion to a lake/river landscape began in the early 1800s with the filling of the ‘first tank’ of a series, to create the parade ground between Cubbon and Mahatma Gandhi Roads, as the central feature of the British Cantonment. The embankment of this tank is still visible along the north of M.G. Road.

Its plug opened into Rest House Crescent, leading to a second tank impounded by Rest House Road. The constructions south of M.G. Road can then be said to be among the first violations of Bangalore’s low grounds.

Over the decades, this violation would become bolder and more intensive. Often, though, it is not this channel that was made the drain, but the nallah on the side. It required that the nallah be deepened and/or the lowest ground of the tank be filled.

Such interventions disrupted slope, replacing the resilience afforded by the combination of autonomy and community of a tank/rain terrain with a rigid, hierarchical, and vulnerable flow system that acquires its datum from a ‘last tank’, such as Bellandur (and further down from ‘sea level’).

Possible Corrective Measures

If Bengaluru is to overcome its flood problem, it must recover the ability of its low grounds to hold and absorb rain. We suggest beginning with three elements essential to each rain-shed of a bund: roadside gutters; storm water drains that are generally former bypass nallahs ; and the ‘lake’ or in most instances, a vulnerable development in a ‘tank bed’ prone to flood. Each demands a reversal of current policies.

Tanks and tank beds

a) Reverse the drive to turn them into perennial lakes

b) Design them for seasonal water holding, biotic cleansing, de-silting and cultivating

c) Recover, if only in part through surgical interventions, tanks lost to development

d) Reconstruct the ability of other low grounds to hold and absorb rain

Storm water drains

Reconnect drains to tanks. Design them for biotic cleaning, movement of excess rain, and public greenways

Road-side gutters

Do not cover them. Galvanise the community to keep them open and clean

( Dilip da Cunha and Anuradha Mathur are architects and authors of Deccan Traverses: The Making of Bangalore's Terrain )

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