Explained | How Did Stormwater Drains Cause Bengaluru Floods & Waterlogging?

Stormwater drains are a key part of Bengaluru's drainage network. But they've been affected by Illegal encroachment.

Stormdrains and drain network failures are the primary cause of Bengaluru's floods, according to urban planners.

(Photo: Namita Chauhan/The Quint)

Bengaluru received the heaviest rainfall it had witnessed in over seven years in late August and early September this year. Several parts of the IT city were waterlogged, flooded, and inaccessible to the residents of the city.

Urban planners and civic planning experts that The Quint spoke to blamed a combination of encroachment on stormwater drains, inefficient drains, and shrinking drain networks for the crisis in Bengaluru.

What exactly is a stormwater drain? What are the problems plaguing Bengaluru's drain networks? And what steps has the Karnataka state government taken to resolve this problem?

Stormwater drains are iron grates and pipes that form a part of the drain network. They are built to drain rain and stormwater from roads and paved areas into lakes and other water bodies.

They form an essential part of stormwater management and flood prevention.

But Bengaluru's drainage network has been fast shrinking since the latter half of the 20th century. Increased construction, illegal encroachment, and building on storm drains, canals, and drains has led to shrinking of the city's drain networks.

For example, in the 1900s, Koramangala had a drain network that extended to 113.2 kilometres. By 2017, this had reduced to just over half, at 62.8 kilometres.

Similarly, Vrushabhavathi which boasted a drain network of 226.3 kilometres in the 1900s, reported just 111.7 kilometres of drain networks in 2017. Both of these numbers were recorded in a 2017 audit by the Comptroller Auditor General.

Bengaluru Floods – A Symptom of Fast-Disappearing Lakes and Water Bodies

On a similar note, according to the CAG's 2017 audit, Bengaluru had 1,452 lakes in the 1800s with a water storage capacity of 35 thousand million cubic (TMC) feet. By 2016, this had dropped to just 194 lakes and a storage capacity of 5 TMC only.

By 2020, 18 more lakes had fallen into disuse.

A fall in the number of lakes and water bodies in the city means that the total rainwater disposal systems in the city also falls.

This is because the drain network is a series of interconnected pipes, with several "checkpoints" through the network in the form of lakes and water bodies.

Water drains from paved areas and roads into these lakes first and then further down.

These water bodies link Bengaluru's drain network to allow for efficient drainage of stormwater.

The disappearance of lakes in this network is like the removal of an essential cog or connecting pipe in a series of pipes. If you remove enough parts of this machine, the drainage network stops working as intended.

This leads to waterlogging and flooding.

What Steps Have Been Taken To Fix Bengaluru's Storm Water Drains?

The Bruhat Bengaluru Mahanagara Palike (BBMP) identified a total of 696 encroachments on storm drains across the city, and on 9 September, a day after the floods began to recede, the state authority began demolishing homes, buildings, and parts of buildings which encroached on or blocked stormwater drains.

The government destroyed encroachments in Marathahalli, Munnekolala, Challaghatta, and Yamaluru. It added that encroachments had also been destroyed near Abbigere lake, Singapura lake, KR Puram lake, Munnekollala lake, and Bellandur lake.

What Next for Bengaluru?

Urban planners have said that this move will help ease the present situation, but add that far more needs to be done. This includes the building of proper drainage networks and maintenance of the same to avoid another similar crisis.

Critics, however, have said the "demolition drive" is simply an eyewash, and that much more needs to be done to prevent similar crises in the future.