The Impact of Dredging on Salinity in the Amba Estuary, West Coast of India

Authors: Jubin Thomas*, Simhadri Naidu Velamala

Affiliations:

1-CSIR-National Institute of Oceanography, Regional Centre, Lokhandwala Road, Andheri (W), Mumbai  400053, India

2-Environ Software Pvt Ltd, Electronic city, Banglore-560100.

Citation: Jubin Thomas (2019) The Impact of Dredging on Salinity in the Amba Estuary, West Coast of India. Oceanogr Aquacult Res, 1(1);1-8.

ABSTRACT

The effect of dredging carried out in the channel of the Amba estuary on the salinity variation was studied applying a 2D numerical model. The model hydrodynamics were calibrated and verified using observed tide data. Model results show good agreement with the observations. The model was also calibrated for salinity distribution in the estuary. Diffusion coefficients estimated are 20 m²/s and 0.15 m²/s in longitudinal and transverse directions respectively. The salinity distribution was simulated for different scenarios zero discharge, medium discharge and high discharge, in high tide and low tide, for before and after dredging conditions. The results indicate that low salinity is noticed up to Patalaganga mouth during low tide in the monsoon, which is up to Dharamtar in the case of high tide. In the dry season, salinities vary between 36.7 and 36.6 ppt for both the tidal conditions. In the monsoon, sharp salinity gradient is found during high tide in the middle of the estuary due to convergence of freshwater flux and saline tidal waters. During this season, the higher gradients are found at the mouth in low tide. After dredging, a salinity ingress of 6.4 km is found at low tide at Mankhule during dry season. However, at high tide during wet season the ingress is reduced to 0.3 km. The simulation of residual velocities indicates the net higher residual flow which is directed upstream in the places where dredging was carried out. These resultant higher residual velocities are responsible for the salinity ingress in the region.

KEYWORDS

Amba Estuary, Salinity variations, Diffusion coefficients, Residual velocity, 2D Tidal Model, Hydrodynamic

Copyright: Â© 2019, Jubin Thomas, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

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