Bengaluru Paradox: Floods go hand in hand with groundwater depletion

The city of Bengaluru is a victim of a paradoxical situation – urban flooding on one hand and depletion of ground water levels on the other, as a recent CAG audit report on Management of Storm Water in Bengaluru Urban Area informs.

The report is an eye-opener in the backdrop of recent floods that the city witnessed.

The audit report for the year 2021 highlighted that there is an urgent need for urban managers to address this issue from the perspectives of water security/environment and urban planning. Rapid increase in frequency of floods in the city over the last few years have lead to destruction of roads, traffic congestion lasting several hours and extensive damage to public property and health.

The performance audit revealed that Bengaluru witnessed large scale encroachment of lakes and drains and depletion of natural drainage systems. The changes in land use such as decreased vegetation cover and open spaces and increased built-up area resulted in loss of inter-connectivity between water bodies, impacting effective recharge of ground water and increase in runoff of storm water.

The CAG audit report referred to a study by Indian Institute of Science which says that the city (covering an area of 741 sq km) had 1,452 water bodies with a total storage capacity of 35 TMC during the early 1800s. By 2016, the number of water bodies in the same area reduced to 194 with a storage capacity of 5 TMC. The current storage capacity which has further declined due to siltation is merely 1.2 TMC. Out of 210 lakes under the jurisdiction of Bruhat Bengaluru Mahanagara Palike (BBMP) as at the end of December 2020, 18 lakes with a total area of 254 acres and 17 guntas were identified as disused lakes, making them vulnerable to encroachment and future conversions.

The report said that a robust policy governing storm water management does not exist. The State Government and BBMP failed to consider urban surface runoff (average annual rainfall being 969 mm during 2013-19) as a water resource despite growing scarcity of water in the state/city. More than 40 per cent of properties under the purview of Bengaluru Water Supply and Sewerage Board (BWSSB) failed to adopt mandatory rain water harvesting structures.

Though a large number of works were abandoned and rescinded due to poor performance of contractors, risk and cost clause were not invoked. This led to extension of undue financial benefit of Rs 35.31 crore to the contractors. BBMP also resorted to payment of Rs 94.93 lakh to an agency without the original records and proper reconciliation under questionable circumstances, it said.

The report highlighted that BBMP failed to prepare a Storm Water Drain (SWD) manual specifying the design, construction and maintenance of the SWD infrastructure of the city.

“It failed to factor in reasons for high intensity rainfall due to rapid urbanisation and did not adhere to the provisions of Indian Road Congress and the guidelines of National Disaster Management Authority while designing and constructing roads/drains. Ground water recharge structures were not taken up due to flow of sewage in SWDs. Water bodies and drains were not inter-connected and linkage between different drains was absent. This affected free flow of storm water leading to frequent flooding in various parts of the city,” said the report.

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