Seasonal lakes do dry in summer, but it is time to desilt to raise storage capacity Premium

Lakes drying up as the scorching summer heat intensifies. Should this spreading spectacle be a cause for worry or an opportunity for Bengalureans? Reminding that the city’s lakes were never perennially filled right through the year, environmentalists instead see the next two months as critical to de-silt and de-sludge the water bodies, a sure-shot way to keep them alive.

Lakes drying up as the scorching summer heat intensifies. Should this spreading spectacle be a cause for worry or an opportunity for Bengalureans? Reminding that the city’s lakes were never perennially filled right through the year, environmentalists instead see the next two months as critical to de-silt and de-sludge the water bodies, a sure-shot way to keep them alive.

To address the city’s mounting summer-time drinking water demands, lakes were seen as potential storage tanks. But the accumulation of sewage and silt over decades have made most lakes unthinkable as complementing the piped Cauvery water. So, is increasing the capacity of lakes the best option? It is complicated, lake experts say.

Increasing the depth of lake beds uniformly with only capacity upgrade as objective is not the way to go, notes Raghavendra B. Pachhapur, Senior Project Lead with ActionAid Association, a non-government institution. Lake rejuvenation is not only about removal of residual silt but also about building a habitat around the water bodies for birds and wildlife to thrive, he explains.

The foreshore area is where water enters a lake from multiple streams and the rajakaluve. He reminds, “That area will be naturally shallow. The depth increases towards the other end of a lake at the bund region to a maximum of 10-12 ft. This was the usual conservatory lake. But now, they are building bunds around the lake for people to walk, and this means almost a uniform increase in depth.”

This design, dubbed as ‘soup bowl’ to help increase water capacity and suit fisheries, is inevitably hostile to migratory birds that usually flock to shallow areas within a lake. But has the capacity really increased in rejuvenated lakes and in what manner?

Lake water quality monitored by the Karnataka State Pollution Control Board (KSPCB) shows an alarming rise in Fecal Coliform (measured as Most Probable Number (MPN)/100ml) in most city lakes. Fecal Coliform is a bacteria found in human faeces, confirming that the inflow of untreated sewage into lakes is still extremely high.

The National Greens Tribunal (NGT) has mandated that the Fecal Coliform in water flowing out of the Sewage Treatment Plants (STPs) into the lakes should not exceed 230 MPN/100ml, with the desirable at an even lower standard of 100 MPN/100ml. Within lakes, it is expected to be within 300 to 500 MPN / 100ml. But the reality is a different story.