Bengaluru’s interconnected chain of lakes were meant to prevent floods, but have now ended up as the cause, as seen on Thursday when waters of Doddabidarakallu lake breached the bund and flooded as many as 500 homes. Similar incidents took place during the floods in 2016 and 2017 when heavy rain caused lakes to overflow.
The Bruhat Bengaluru Mahanagara Palike wants to install sluice gates – water flow control mechanism – at the outlets of all lakes in the city to manage water levels in anticipation of heavy rainfall and to prevent such flooding in future.
“We cannot control water inflow into the lakes, but we can intelligently manage water levels and outflow. There is a desperate need to prevent such floods in future,” said BBMP Commissioner B.H. Anil Kumar.
The matter was discussed at a recent meeting of Mayor M Gautam Kumar and the heads of all departments of the civic body. Officials of the lakes division have been instructed to prepare an estimate for the project.
Earlier, all lakes in the city had a version of a flood mechanism, but that has now vanished as the purpose of the lakes has changed.
“Water in the lakes was earlier used for agriculture. There was a water outflow mechanism at all lakes to release water into channels for agriculture. This also doubled up as a flood control mechanism, as water was let out into the channels in anticipation of heavy rains. But as agriculture vanished, this mechanism slowly died,” said Harini Nagendra, Professor of Sustainability at Azim Premji University. The city's agencies did not continue with this practice during rejuvenation of lakes, contrary to advice by experts, she added.
Nowadays, lakes only have overflow weirs, which essentially cause floods when there is a large inflow into the lakes. This is something a sluice gate – a mechanical gate usually deployed at barrages and check dams – can correct.
Water conservationist S. Vishwanath pointed out that at present, lakes have only overflow weirs. “Water can be let out only once the level goes above the weir, but not from the lake bed. In the case of a sluice gate, the lake bed can be emptied by letting water into stormwater drains in anticipation of heavy rainfall. This will increase the carrying capacity of lakes and prevent flooding,” he said.
However, sluice gates are not a silver bullet to prevent floods, cautions Ms. Nagendra. “The city's drainage and stormwater drain network needs to be cleared of encroachments to ensure free flow of water,” she said.
