The southwest coast of India is exposed to long-period swells propagated from the South Indian Ocean during pre- and post-monsoon seasons. Although swells from the Southern Ocean and Atlantic Ocean were identified in the North Indian Ocean, their existence and impact along the southwest coast of India were not well investigated. On 19 March 2019, the Valiyathura-Shangumukham coastal stretch along the southwest coast of India experienced an unexpected coastal inundation without having a prompt forecast/warning, and not induced by a storm/cyclone in its vicinity. The present study investigates the causative forces of this inundation and estimates the wave runup and inundation. The study reveals that an unusual swell system was developed in the Indian-Atlantic-Southern Oceans (IASO) interface during 10–12 March and propagated towards the southwest coast of India. The measured wave spectra off Varkala clearly depicts the presence of long-period swells (T_p>18 s), which dominantly occurred as single-peaked. Wave modelling has been carried out to characterize the wave transformation associated with the “IASO interface swells” along the southern Kerala coast. A wave runup of up to 0.93 m height and a coastal inundation of up to 83 m onshore have been estimated during this event.

印度西南海岸在季风季节前后受到南印度洋传播的长期海浪的影响。尽管在北印度洋发现了来自南大洋和大西洋的涌浪，但它们对印度西南海岸的存在和影响尚未得到充分研究。2019 年 3 月 19 日，印度西南海岸的 Valiyathura-Shangumukham 沿海地区在没有及时预报/警告的情况下遭遇了意外的沿海洪水，该洪水并非由附近的风暴/气旋引发。本研究调查了这次洪水的成因并估计了波浪上升和洪水。研究表明，3 月 10 日至 12 日期间，印度-大西洋-南大洋 (IASO) 界面形成了一个不寻常的涌浪系统，并向印度西南海岸传播。瓦卡拉附近测得的波谱清楚地描绘了长周期涌浪的存在（T_p > 18 s)，主要以单峰形式出现。已经进行了波浪建模，以表征与喀拉拉邦南部海岸沿线的“IASO 界面膨胀”相关的波浪变换。据估计，在此事件期间，波浪上升高度高达 0.93 m，海岸淹没深度高达 83 m。