No more concrete boxes; Bengaluru embraces nature to stave off floods

Bengaluru: City officials are shifting from concrete drains to "nature-based solutions" that help the ground absorb rainwater, aiming to prevent both flooding and summer water shortages.

At a meeting by the Jana Urban Space Foundation on Thursday, officials said the city’s drainage system is failing. Despite sufficient rainfall, too much ground is paved. This prevents rain from soaking into the earth, causing it to flood the streets.

"Despite over 900 mm of annual rainfall, rapid urbanisation has broken natural recharge pathways,” said M Maheshwar Rao, Chief Commissioner, Greater Bengaluru Authority (GBA). He noted the city’s geography should prevent major flooding, but sewage mixing with drains and loss of open ground cause problems.

Rao said sloping areas stay dry, but places like Yelahanka and south Bengaluru face flooding. He proposed bioswales, rain gardens, and permeable pavements to slow water and recharge groundwater.

Box drains 

The city is replacing old concrete “box drains” with new systems.

BS Prahalad, Engineer-in-Chief and and Director (Technical) at B-SMILE, said box drains were often misused for dumping sewage, causing clogs and odours.

So far, 160 kilometres of new drains have been built. The city’s 200 lakes, including Madiwala Lake, will act as storage tanks for storm water.

A Rs 2,000-crore World Bank loan is funding projects like K-100 Valley, aiming for more green spaces and keeping sewage out of the rainwater system. Officials hope to make Bengaluru a model for other cities.

Rao also released the draft working paper, 'Rebuilding Urban Drainage Systems: Learnings from Nallurahalli Nallah Rejuvenation in Bengaluru'. 

How it works 

The city is installing a 'pipe-and-chamber' system.

The new design:

* Keeps sewage separate from rainwater.
* Uses special underground chambers every 45 metres.
* Has 'open bottoms' in these chambers to let water soak back into the ground.