As Kerala struggles to recover from the monsoon floods that ravaged the state yet again this season, research has highlighted that floods triggered by heavy rain has left reservoirs and dams highly prone to earthquakes.
The state has 43 dams and reservoirs predominantly located in the highly deformed and fractured Western Ghats. Of these 21 are now highly prone to tremors, a phenomenon called reservoir-induced seismicity (RIS), according to the latest geographic information system (GIS) analysis.
RIS occurs in deep reservoirs that have water columns more than 100 metres depth. Such huge water columns increase the stress on the earth crust, the infiltration of water from the reservoir reduces the effective stress. These changes in stress in the underlying rocks lead to RIS.
“The RIS would have occurred during August 2018 flood itself, but this did not happen because all the dams of the overflowing reservoirs during the flood were opened and the water was released, our observations revealed," said S.M. Ramasamy of the Tamil Nadu-based Bharathidasan University, who led the study, which also involved researchers from Alagappa University. The findings were published in the journal Natural Hazards.
Kerala was ravaged by the worst floods of the century last year in August taking a heavy toll on lives and causing massive damage of an estimated $200 billion to infrastructure and property. After the floods, the research team studied the geology of the Western Ghats and found them to be highly deformed with folds and faults caused due to tectonic movements.
“The cracks are very active. With flooding going to become a recurring phenomenon, we need to study the hydro-dynamics of these dams and optimize their storage and water release to avert major disasters," said Ramasamy.
RIS has been known to be disastrous globally. In 1967, 180 people were killed and 1,500 injured due to induced seismicity in Koyna reservoir in Maharashtra.
Researchers found that in the case of Kerala, there are several conditions that can trigger RIS in and around the dams and reservoirs, including faults which are wide open.
The ecologically fragile Western Ghats cover almost half of Kerala, which has been known to be seismically active. The state has been witnessing seismicity of the magnitude of 3–5.5 for centuries. Previous studies have found that most of these seismic episodes occur after torrential rain lashes the region, indicating hydro-seismicity.
The 21 reservoirs that are prone to dam induced tremors include the Parambikulam reservoir, Peringalkuthu dam, Idamalayar dam, Mattupetty dam, Mangalam dam, Siruvani dam, Pothundi dam, Idukki dam, Chulliyar dam, Sagar dam and the Mullaperiyar dam.
“There is urgent need for effective water management strategies, especially for these 21 reservoirs," said Ramasamy.