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| Abstract Submission No. | ABS-2022-09-0275 |
| Title of Abstract | Sub-inertial Oscillations and its impact on Flooding in the Tropical Estuary. |
| Authors | Jubin K Thomas*, Anoop T R, Sheela L Nair |
| Organisation | National Centre for Earth Science Studies |
| Address | National Centre for Earth Science Studies, Akkulam Thiruvananthapuram, Kerala, India Pincode: 695011 Mobile: 8779092949 E-mail: jubin.oceanography@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Sub inertial fluctuations of currents and sea level with a period of few days to weeks have been reported along various coasts in the world. Similar observations have been made by the Indian researchers along the west coast and east coast of India. In the present study, an attempt has been made to investigate the influence of coastally trapped waves on the water level fluctuations in the Ashtamudi estuary located along the southern part of the Kerala coast. The study is based on 18 months (January 2020 - July 2021) of water level data at nine locations along the Indian coast. Out of the nine locations, 5 stations namely, Porbandar, Mumbai, Karwar, Mangalore, and Cochin are located along the west coast of India, three are inside the Ashtamudi estuary (one at the mouth (Neendakara) and the other two at distances of 6km (Ashtamudi) & 12km from the estuary mouth (Munroe Island) and the remaining one is located at Tuticorin representing the southeast coast of India. The measured water level data is de-tided using the TASK-2000 software to delineate the intra-seasonal as well as seasonal oscillations along the study area. The de-tided water level is further subjected to Fast Fourier Transform (FFT) analysis, mainly to identify/assess the influence of different frequency bands. The results from all nine stations indicate that the observed long-period oscillations correspond to 3 prominent frequency bands, i.e., 50-, 20-, and 13-day periods. Further detailed analyses using wavelets revealed that the 13-day oscillation was observed during 2020 and 2021 summer monsoon both along the west and southeast coast of India. Inside the estuary, this oscillation was maintaining the same energy level (both at Ashtamudi and Munroe) throughout the estuary whereas the oscillation in 2021 summer monsoon appeared to be more intensify towards upstream. The influence of the second long-period oscillation of 20-day observed during 2020 summer monsoon, maintaining the same energy level throughout the estuary without any intensification. During the summer monsoon of 2021, however, a significant change in the propagation pattern was observed: an oscillation of a 20-day long period wave propagating constantly into the estuary that lasted more than a month. The observation of the third long-period oscillation of 50-day was mostly confined to the southern part of the coast which was confirmed from the data obtained from the Tide Gauge Stations at Tuticorin, Needakara, Cochin, and Mangalore. The Mumbai and Porbandar stations did not exhibit this type of oscillation. Propagation of the 50-day oscillation into the estuarine side was significant during 2020 winter monsoon and this coincides with the high sea level reported along the Kerala coast. From this preliminary study, it can be concluded that the combined effect of the high sea level and the long-period oscillation could be one of the major causative factors for the flooding events reported upstream of the estuary, particularly, the Munroe Island. |