Get a few rooftops and save a lake

Get a few rooftops and save a lake

Alladi Jayasri

All it requires is rain and some rooftops



WATER-STARVED: A file photo of Yediyur Lake in Jayanagar in Bangalore. — Photo: K. Bhagya Prakash

BANGALORE: Yediyur Lake is one of the half-a-dozen water bodies in the city that are considered "live." But with most of its catchment area having been developed into residential localities of Basavanagudi and Jayanagar, citizens fear it is gasping for life.

In 2002, the Bangalore Mahanagara Palike (BMP) spent Rs. 3.25 crore on a jogging track, a waterfront garden and so on around the lake. Yediyur Lake falls in Vrishabhavathi Valley of Arkavathi sub-basin of the Cauvery basin. Its area is around 6.55 hectares, and the water spread 4.67 hectares, with a maximum depth of 2 metres. The catchment area is 55 hectares.

Consultant hydrologist N. Ranganathan, who was an official in the Mines and Geology Department, does not want to be one of those wringing their hands as the lake dries up. He has come up with a plan to save the lake.

The catchment area is fully developed with construction and all the roads are metalled. Owing to this, the runoff from rainwater that reaches the lake is highly polluted. He has calculated that the maximum quantity of water that can be stored in the lake, the depth of which is 1 metre, , is 4.67 million litres.

Now for Mr. Ranganathan's idea: rooftop harvesting of rainwater that will be guided to the lake. All it requires is for residents of buildings around the lake to lend their rooftops. Assuming 60 per cent of the 55 hectares of catchment area is built up, 33 hectares of "rooftop" is potentially available for rainwater harvesting. Again, assuming that there is around 1,000 mm of rainfall annually, the rooftops will yield about 33 million litres of rainwater. Harvesting just 14.5 per cent of this is sufficient to fill the lake, he says.

To increase the capacity, desilting and increasing depth to a uniform 3 metres will add a storage of 14 million litres.