Residual estuarine circulation in the Mandovi, a monsoonal estuary: A three-dimensional model study

Vijith, V and Shetye, SR and Baetens, K and Luyten, P and Michael, GS (2016) Residual estuarine circulation in the Mandovi, a monsoonal estuary: A three-dimensional model study. In: ESTUARINE COASTAL AND SHELF SCIENCE, 173 . pp. 79-92.

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Abstract

Observations in the Mandovi estuary, located on the central west coast of India, have shown that the salinity field in this estuary is remarkably time-dependent and passes through all possible states of stratification (riverine, highly-stratified, partially-mixed and well-mixed) during a year as the runoff into the estuary varies from high values (similar to 1000 m(3) s(-1)) in the wet season to negligible values (similar to 1 m(3) s(-1)) at end of the dry season. The time-dependence is forced by the Indian Summer Monsoon (ISM) and hence the estuary is referred to as a monsoonal estuary. In this paper, we use a three-dimensional, open source, hydrodynamic, numerical model to reproduce the observed annual salinity field in the Mandovi. We then analyse the model results to define characteristics of residual estuarine circulation in the Mandovi. Our motivation to study this aspect of the Mandovi's dynamics is derived from the following three considerations. First, residual circulation is important to long-term evolution of an estuary; second, we need to understand how this circulation responds to strongly time-dependent runoff forcing experienced by a monsoonal estuary; and third, Mandovi is among the best studied estuaries that come under the influence of ISM, and has observations that can be used to validate the model. Our analysis shows that the residual estuarine circulation in the Mandovi shows four distinct phases during a year: a river like flow that is oriented downstream throughout the estuary; a salt-wedge type circulation, with flow into the estuary near the bottom and out of the estuary near the surface restricted close to the mouth of the estuary; circulation associated with a partially-mixed estuary; and, the circulation associated with a well-mixed estuary. Dimensional analysis of the field of residual circulation helped us to establish the link between strength of residual circulation at a location and magnitude of river runoff and rate of mixing at the location. We then derive an analytical expression that approximates exchange velocity (bottom velocity minus near freshwater velocity at a location) as a function of freshwater velocity and rate of mixing. (C) 2016 Published by Elsevier Ltd.

Item Type:	Journal Article
Publication:	ESTUARINE COASTAL AND SHELF SCIENCE
Publisher:	ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
Additional Information:	Copy right for this article belongs to the ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 24-28 OVAL RD, LONDON NW1 7DX, ENGLAND
Keywords:	Estuaries; Residual circulation; Salinity; Numerical models; Mandovi; India
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	15 Jun 2016 07:23
Last Modified:	15 Jun 2016 07:23
URI:	http://eprints.iisc.ac.in/id/eprint/53957

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