The Indian National Centre for Ocean Information Services (INCOIS), headquartered in Hyderabad, has installed a second Coastal Flood Monitoring System (CFMS) near Kollam Harbour in Kerala to enhance the accuracy of ‘Kallakkadal’ (swell surge) forecasts along India’s southwest coast.

Who are at threat from swell surges?

‘Kallakkadal’ events — sudden and powerful swell surges — pose a significant threat to fishing communities and coastal infrastructure. These surges are typically triggered by long-period swells generated by distant storms in the southern Indian Ocean, nearly 10,000 kilometres from the Indian coastline, said INCOIS Director T.M. Balakrishnan Nair.

Swell surges frequent during pre-monsoon

The first observational evidence of such waves in Indian waters was recorded during the initial deployment of the CFMS at Vizhinjam last year. The system was operated between February and May, covering the pre-monsoon season when these swell surges are most frequent.

Scientists observed that these swells, with periods ranging from 30 to 300 seconds, can substantially elevate coastal water levels. The aim, they said, is to identify patterns in southern ocean swells and refine forecasting models for improved accuracy.

CFMS integrates a coastal automatic weather station with four high-frequency pressure sensors installed in shallow waters at depths of three to seven metres. This configuration enables precise monitoring of nearshore wave transformation processes, providing valuable real-time data.

INCOIS is working to build a comprehensive understanding of the entire chain of processes — from swell generation in the open ocean to wave transformation near the shore and the resulting coastal flooding. This integrated approach is expected to strengthen early warning systems and improve the precision of ‘Kallakkadal’ forecasts.

Scientific basis of swell surge generation

About a decade ago, it had established the scientific basis of swell surge generation in the southern Indian Ocean, demonstrating how distant meteorological systems can produce long-period swells that travel thousands of kilometres before impacting the Indian coast. Subsequent research has linked ‘Kallakkadal’ events to infragravity waves — low-frequency waves formed through interactions among shorter waves in the open ocean.

As these waves approach shallow waters, their energy intensifies due to shoaling — a process in which wave height increases as waves move from deep to shallow regions. Coastal bathymetry, or underwater topography, further amplifies these surges and contributes to sudden coastal flooding, said scientists.

Kollam was chosen for the second system due to its frequent exposure to such events. Following the installation, INCOIS conducted a community awareness programme to improve preparedness and encourage effective use of forecast information, said scientist Praveen Kumar. Through a combination of scientific research, advanced observations, and community outreach, INCOIS aims to strengthen coastal resilience and reduce the risks posed by ‘Kallakkadal’ events.