Spate of affairs

When 18 lakh cusecs of water were released from the Sardar Sarovar Dam in Gujarat in September 2023 due to a heavy upstream influx, many called it a man-made flood. The dam, which provides water security to parched regions in Gujarat, Rajasthan, Madhya Pradesh and Maharashtra, flooded large parts of Bharuch district, already battered by heavy rainfall. Around 5,700 people were evacuated from the flooded areas, and crops and homes were damaged. 

The same dam, however, had successfully contained the heavy rainwater flow from catchment areas in 2019, preventing flooding in downstream areas. "In these times, when climate change and anthropogenic activities are redefining the occurrence and impact of extreme weather events, traditional methods of managing infrastructure will also need a redefining," says Vimal Mishra, Professor of Civil Engineering at the Indian Institute of Technology (IIT) Gandhinagar, the co-author of a recent study on the role of dams in flood mitigation (bit.ly/india-dam-flood).

The study, which analysed data of 178 dams, noted that in several cases, the very dams which had mitigated floods during some years were responsible for inundation in other years. For instance, a heavy discharge from the Chembarambakkam Dam to the Adyar River caused flooding in Chennai in 2015, but the dam prevented flooding in 2023 under similar rain conditions. The report concludes that the flood mitigation potential of a dam depends more on the amount of water it contains at the time of a heavy rainfall event than on the actual rise in upstream flow due to rain; dams that can store excess water during an extreme rain event can mitigate floods downstream.