Near-shore wave induced setup along Kalpakkam coast during an extreme cyclone event in the Bay of Bengal

An enhanced sea level during an extreme weather event can result from cumulative effects of reduced sea-level pressure, storm surge, tidal effects and wave induced setup. A numerical experiment was conducted to evaluate sensitivity of model resolution and bottom slope on wave induced setup for an arbitrary coast. Further, an assessment of wave setup at coastal Kalpakkam was investigated, in response to passage of a Category-4 cyclone ‘NARGIS’, in the central Bay of Bengal. The sensitivity experiments cover an arbitrary region of 5 km×5 km, with varying horizontal resolutions and beach slopes, and subjected to uniform wind forcing and JONSWAP wave spectra prescribed at the open boundary. The computed wave setup using SWAN model reveals that model resolution is not sensitive for gentle bottom slopes, unlike the case with steep bottom slopes. Findings from sensitivity experiments were then applied to evaluate wave setup at three different locations along Kalpakkam coast, for the Cyclone NARGIS event. The study shows that wave setup was highest for a steep slope (1:20), reducing to almost 50% for gentle slopes (1:80). It is inferred that wave setup is an important parameter that needs to be incorporated in an operational storm surge forecasting system.

► Investigate the sensitivity of model resolution and bottom slope to wave induced setup.
► Investigate wave setup for an extreme event NARGIS in Bay of Bengal.
► Estimation of wave induced setup at coastal Kalpakkam for different beach slopes and model domain size from NARGIS event.