Abstract
Mud bank formation during the southwest monsoon along the southwest coast of India remains an enigma to the researchers and coastal community in spite of several earlier studies. The present study attempts to unravel the mystery through a high-frequency, season-long time-series observation at Alappuzha, located at the southern part of the west coast of India, a region of frequent occurrence of mud bank. Using 7-month-long weekly time-series observation, we identified strong winds and high waves associated with onset of the southwest monsoon and subsequent three episodic atmospheric low-pressure events (LPEs).With the help of in situ time-series data, we show that the strong winds and high waves associated with southwest monsoon pre-conditions the near shore bottom sediment to bring it into suspension. The high amplitude waves associated with the southwest monsoon, while propagating from the deep water to shallow water region, interact with the bottom initiating bottom-sediment movement and its suspension due to wave refraction and shoaling. The sporadic occurrence of the atmospheric LPEs enhances the process of suspension of bottom sediment in the near shore region leading to the formation of fluid mud. Simulations with a cohesive sediment transport model yielded realistic estimates of sediment transport, in the presence of an onshore current, a pre-requisite for transporting the fluid mud toward the coast. The prevailing onshore upwelling current during the southwest monsoon provides the favorable pre-requisite conditions for transporting the fluid mud through depression channel network towards the coast. Once sufficient quantity and thickness of fluid mud is accumulated in the near shore region, it acts as a wave damper for subsequent high monsoon waves, as indicated by the time-series wave data, leading to the formation of tranquil mud bank region. Depression channel networks extending from the shelf to the coast off Alappuzha, Kochi, Ponnani, Beypore, and Ullal were found in the bathymetric charts, thus explaining why mud banks occur only at few locations in spite of the prevalence of similar monsoon conditions.
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Change history
13 November 2017
In the original article, V. Samiksha’s family name was incorrect. It is correct as reflect in this erratum. The original article has also been updated.
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Acknowledgements
This forms part of the Alappuzha Mud Bank Process Studies (AMPS), a joint program between CSIR–National Institute of Oceanography (CSIR–NIO), Goa, its Regional Centre (RC) at Kochi, and Central Marine Fisheries Research Institute (CMFRI), Kochi. The authors thank Dr. S. W. A. Naqvi, former Director, CSIR–NIO, for his support in the formulation and execution of this program. We also thank Dr. A. Gopalakrishnan, Director, CMFRI, for his active involvement in this program and providing FV Silver Pompano for data collection. The authors thank Dr. N. Ramaiah, Chairman, Mentor Group for CSIR–NIO RC–Kochi, for his contribution to AMPS. We acknowledge the Indian National Centre for Ocean Information Services (INCOIS), MoES, for providing wave data at Kollam. The authors also thank all the AMPS participants for their active support in the data collection and discussion. This is NIO contribution number 6125.
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Communicated by Mead Allison
The original article has been corrected: V. Samiksha's family name was incorrect as indicated in the erratum.
Highlights:
• Episodic atmospheric low-pressure events superimposed on high southwest monsoon winds and waves trigger the formation of fluid mud at the bottom initiating the formation of mud bank.
• The onshore current associated with the coastal upwelling facilitates the mobilization of the fluid mud toward the coast.
• The existence of a depression channel connecting the shelf to the coast at specific regions explains the occurrence of mud banks only at select locations.
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Muraleedharan, K.R., Dinesh Kumar, P.K., Prasanna Kumar, S. et al. Formation Mechanism of Mud Bank Along the Southwest Coast of India. Estuaries and Coasts 41, 1021–1035 (2018). https://doi.org/10.1007/s12237-017-0340-0
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DOI: https://doi.org/10.1007/s12237-017-0340-0