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 A.S. 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 Odisha 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 massive destruction and loss of human life associated with a tropical cyclone can be attributed to the sudden inundation and flooding of the coastal areas produced by storm surges,” the scientists said.