As a deficit southwest monsoon has left many parts of Karnataka parched, and concern over the water situation in capital city Bengaluru hit the headlines amidst the Cauvery water sharing row, a new report on Bengaluru’s water balance shows that the total demand for freshwater is 2,632 MLD, a high quantum compared to the city’s current claims over various sources.
The report, ‘How water flows through Bengaluru: Urban water balance report,’ by the WELL (Water, Environment, Land and Livelihoods) Labs, looks at Bengaluru’s contrasting water problems: how borewells and lakes dry up and water tankers ferry water from elsewhere to quench the thirst of neighbourhoods during peak summer, while during the monsoon, large parts of the city face severe flooding.
The authors of the report - Rashmi Kulranjan, Shashank Palur and Muhil Nesi, argue that these problems are interconnected.
“With population growth, the city will not be able to meet its water needs with existing resources. Groundwater caters to nearly 50% of Bengaluru’s water demand, the rest from the Cauvery. In addition to 1,460 MLD of Cauvery water, Bengaluru currently consumes an estimated 1,372 MLD of groundwater. This is worrying because groundwater recharge rates remain significantly lower than extraction rates. Natural groundwater recharge through green spaces and waterbodies is as low as 148 MLD,” said the report, adding that it is critical to maintain lakes and green spaces to recharge shallow aquifers with rainwater during the wet season.
Run-off
The report also speaks about run off, the big seasonal difference and the problem of flooding in Bengaluru. “The total rainfall in wet and dry seasons amounts to 2,149 MLD and 1,322 MLD, respectively. However, utilisable run-offs from the total rainfall is 982 MLD in the wet season and 568 MLD in the dry season,” says the report, adding that approaches such as ‘sponge cities’ must be considered.
“Cities can be planned to ‘make room for the rain’ and allow fallow spaces to become temporary thriving wetlands or even green recreational spaces that can hold excess flood water, while contributing to other benefits such as boosting overall livability and acting as carbon sinks,” said the report.
Importance of lakes
It also emphasised the importance of the city’s lakes: “Lakes receive and store both rainwater and wastewater and store groundwater. The cascading lake systems of Bengaluru play an important role in draining water from the city, especially in the Hebbal and Koramangala-Challaghatta valleys, due to greater undulations in their terrain. Inlets, outlets, and stormwater drains that did exist were either broken or encroached upon by other structures. With the loss of these connections, we found that many lakes have become isolated from the system, causing them to dry out. Flooding is another problem in many parts here since there is no path for the water to flow and reach the next lake.”
As for wastewater, of the total 1,940 MLD produced by the city, around 63% of this wastewater is treated by centralised treatment plants, and 13% by decentralised treatment plants, but 24% goes untreated and a meagre 30% is reused, the report says, adding that there is scope for better utilisation.
