Coastal morphological changes due to the Nivar cyclone on the East Coast of India

The shoreline and beach profile vary due to various factors like rising sea levels, changes in wave characteristics and littoral drift due to the presence of coastal structures. These coastal morphological changes can be identified through field observations and numerical simulation. A sudden change in the coastal feature is caused due to extreme events like cyclonic storms, tsunamis, hurricanes, or other natural and anthropogenic disasters. An extremely intense cyclonic storm, Nivar caused landfall off the coast of Tamil Nadu in the early hours of the 26 November 2020. The Nivar cyclone brought widespread heavy to very heavy rainfall in the surrounding regions, with a maximum of 246 mm in addition to the storm surge. The study utilises the SWAN (Simulating Waves Nearshore) model for wave propagation in the nearshore and the XBeach model for morphodynamic analysis to investigate the variations in beach profile and shoreline at Thazhanguda village, where the maximum erosion was observed. This study simulates the changes before and after cyclones, and observes a strong correlation between the morphological variations in the littoral zone and the forcing mechanisms acting on the shore. The numerical model calculates the bed level change from the beach dune up to 6 m water depth. The initial beach profiles measured on 20th of November 2020 are considered as the pre-cyclonic input to XBeach with spectral boundary conditions from the SWAN model. The model is validated with the field-collected nearshore bathymetry data. The study findings indicate significant morphological changes, including shoreline erosion and sediment movement in Thazhanguda village following Cyclone Nivar’s landfall on November 26, 2020. These changes are strongly correlated with the dynamic forces exerted by the cyclone on the coast.