Coastal vulnerability due to extreme waves at Kalpakkam based on historical tropical cyclones in the Bay of Bengal

The study reports the development of a coastal vulnerability index (CVI) based on extreme waves for the Tamil Nadu coast. Region of interest is Kalpakkam, a coastal town located approximately 70km south of the metropolis Chennai in Tamil Nadu State, India. The CVI computation performed for a coastal stretch of about 250km that covers ten identified locations, with coastal Kalpakkam as the focal point. The study uses historical records of past cyclone tracks from 1945 to 2009 that had its landfall in Tamil Nadu State. There were 31 best cyclone tracks identified to construct the most probable synthetic/hypothetical track for this region. This synthetic track used to conduct several numerical experiments for cases of medium- and fast-moving cyclones. The extreme waves computed at these locations using a high-resolution Simulating Waves Nearshore (SWAN) wave model particularly tuned for this region. Seven key parameters finally identified in the computation of CVI. These include maximum significant wave height, maximum probable surge estimated from 50-year return period, and other geomorphologic characteristics at all ten stations. This is the metric indicator used in the final estimation of CVI. The study signifies that metropolis Chennai and the adjacent region extending up to 57km northwards is a high-risk prone zone. The risk level due to extreme waves is low at Kalpakkam.