Coastal flooding by wave, wind, tide interactions and related processes along the southern part of SW coast of India

Occurrences of coastal flash flooding events are not always associated with extreme events, which are often responsible for the high wave activity and ensuing flooding along coastal areas during the rough season. In the present study, the causative factors that led to a flash flood event at Valiyathura, Thiruvananthapuram, located along the southern part of the SW coast of India, during September 2018 have been investigated based on both field observations and numerical model studies. Numerical simulations reveal the presence of high period swells from the Southern Indian Ocean, leading to a rise in wave runup, coinciding with the Perigean Spring Tide (PST), along with the increased wind speed that sustained for more than 6 h, resulting in the piling up of nearshore waters and sudden flooding along the coast. This inference is well reflected in the beach morphology, particularly the sediment characteristics depicting the impact of coastal flooding. Further, field observations confirm that the nearshore wind–wave interaction prior to the event also contributed to the flooding. Thus, the study emphasizes the need for continuous monitoring of nearshore and other contributing factors such as waves, wind, tide, and beach morphological conditions for reliable predicting coastal flooding events and their probable impacts.