Coastal towns of Machilipatnam, Surya Lanka, Kavali and Gudur in Andhra Pradesh are sensitive regions with high return levels of sea surge in case of cyclones or tidal waves in the Bay of Bengal

Syed Akbar
Hyderabad: Coastal towns of Machilipatnam, Surya Lanka, Kavali
and Gudur in Andhra Pradesh are sensitive regions with high return
levels of sea surge in case of cyclones or tidal waves in the Bay of
Bengal.

Sea scientists from the National Institute of Oceanography (NIO), Goa,
conducted studies to estimate the return periods of extreme sea level
events along the East coast of India for as many as 26 coastal cities
and towns. The research concentrated on five-year and 50-year return
levels, which will help design marine structures for the protection of
coastal areas.

NIO scientists B Sindhu and AS Unnikrishnan found that Machilipatnam,
Surya Lanka, Kavali and Gudur are sensitive regions as they show
considerably high return levels of surge component due to their
shallow sea floor. The 50-year surge level of 0.8 metres at Surya
Lanka is the highest along the coast of Andhra Pradesh. This is due to
the geometrical configuration of the coastline forming a cove-shaped
bay in the region.

Though Machilipatnam is deeper than Surya Lanka by about one metre,
the 5-year and 50-year return levels (0.6 metres and 0.3 metres)
respectively, are comparable to those at Surya Lanka. It is higher
than that at Kakinada by 40 cm.

“The effect of orientation of coastline on the height of surge
component can be discerned at Kakinada where the return levels are
substantially lower by almost 60 cm than that at Surya Lanka in spite
of its much wide shelf (about 65 km) and similar ocean depth,” the NIO
team pointed out.

The team simulated the studies based on the data of some of the major
super cyclones that occurred in November 1977, May 1979 and November
1989 that hit the AP coast, and the super cyclones of Orissa and West
Bengal in June 1982, April 1991 and October 1999.

 The 5-year and 50-year return levels of total sea level along the
east coast of India show a considerable increase from south to north,
with the 50-year return total sea levels being as high as 6.9 metres
at Sagar Island and 8.7 metres at Chandipur.

The high return levels are expected at these stations as the cyclones
developed in the Bay of Bengal generally move north or north-west,
producing extreme events in the northern part. These places are also
characterized by high tidal ranges.

“The massive destruction and loss of human life associated with a
tropical cyclone can be attributed mainly to the sudden inundation and
flooding of the coastal areas produced by storm surges. Though the
cyclones generated in the Indian Ocean are weaker and smaller than
those generated in Pacific and Atlantic Ocean, the death toll is the
highest,” the NIO scientists said.