Modelling tide-driven currents and residual eddies in the Gulf of Kachchh and their seasonal variability: A marine environmental planning perspective
ABSTRACT Tide-driven currents in the Gulf of Kachchh (GoK) have been studied using MIKE21 hydrodynamic model. The results are validated with measured currents for three different periods characterized by different wind fields. Comparison of model results showed very good agreement with the measured currents. The study suggests that though the currents of GoK are predominantly tide-driven, they respond significantly to the seasonally changing wind system. Strong southwesterly winds enhance the flood tidal currents by about 20% but reduce the ebb tidal currents by about 20% during June–July. The currents intensify during NE monsoon period as well as SW monsoon period when the winds become stronger. However, the currents are comparatively weak during pre-monsoon transition. Irregular topography of the western gulf slows down the tidal wave propagation and induces a phase shift. Tidal residual currents computed from the model results exhibit the presence of three eddies in the western gulf. The tide–topography interaction could be responsible for generating eddies in the residual flow field. It is possible that these eddies could effectively decrease the flushing rate of materials discharged in the upstream gulf, and subsequently increase their residence time. The hydrodynamic modelling setup forms a base for future ecological modelling endeavours planned for the gulf in order to reduce stress on the ecosystem especially in the sensitive areas such as the Marine National Park and Marine Sanctuary.
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ABSTRACT: Two-dimensional hydrodynamic and advection-dispersion simulations were carried out to identify the appropriate locations of inlet and outlet for cool seawater discharges from the proposed Liquefied Natural Gas (LNG) terminal using MIKE-21 suites of software. The model simulations were validated by comparing the observed and simulated hydrodynamics in terms of water depths, current speeds and directions. The model is satisfactorily correlated with coefficients 0.98, 0.86 and 0.91 for water depth, current speed and direction, respectively. The validated model was extended to predict the advection-dispersion phenomena for the two scenarios based on positions of inlet and outlet and their discharges. The predicted results of cool water discharges were compared to the existing Environmental Health and Safety, World Bank guidelines for LNG discharge facilities. It was observed that a trade-off is required before taking engineering decisions for selecting an environmentally acceptable and energy efficient option for such cool water discharges from an LNG facility.International Journal of Environmental Research 10/2014; 8(4):953-960. · 1.82 Impact Factor
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ABSTRACT: Current speed often varies with depth, so vertical movements of larvae are expected to have profound effects on dispersal velocity and therefore dispersal potential. Systematic behaviours are expected to have strong effects on dispersal. However, reliable information on the presence of vertical migrations in larvae is scarce, but the few well investigated empirical examples justify a detailed simulation study and an analysis of potential effects. We present a spatially explicit 3D hydrodynamic model that incorporates biological information in the form of active particles advected in a Lagrangian fashion. The set-up is designed to analyze the sensitivity of dispersal distances to variation in vertical behaviour of larvae. We simulated short (4 days) pelagic larval durations (PLDs) to determine whether behaviour might be important over short dispersal periods. We found that sinusoidal behaviours (slow vertical migration) in or out of phase with tides did not significantly change the dispersal patterns compared to those of larvae that remained at the surface. By contrast, a quadratic pattern of behaviour resulting in rapid vertical migration, in or out of phase with tides, had dramatic effects on both distance and direction of dispersal. The resulting dispersal kernels were found to be multimodal due to the interaction between tidal and meteorological components in flow. Incorporating biological information on larval migrations in Lagrangian simulation of dispersal will be important in estimates of connectivity and forecasting marine reserve networks.Marine Ecology 06/2012; 33(2). · 1.84 Impact Factor
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ABSTRACT: Present study is the coastal circulation modelling off Ratnagiri under the influence of winds and tides. A two-dimensional hydrodynamic model MIKE 21HD has been used to simulate tides and currents, and model results are in a good agreement with the measurements. In July, representing the southwest monsoon, wind is relatively strong, onshore current component is more pronounced; but, tidal variations are masked to a great extent by the wind driven circulation. Relatively stronger winds of the order of 8 m/s, persisted for a longer period, and that contributed to the southward flowing coastal current which is more consistent in its direction and magnitude. Meridional current has a prominent southward direction with a maximum alongshore speed of ~0.41 m/s. Zonal current is too weak to have a considerable impact on the circulation pattern. Prominent circulation is southward, irrespective of the seasons.Indian Journal of Geo-Marine Sciences 02/2014; 43(4):481-488. · 0.31 Impact Factor