Informatics Publishing Limited

Linta Rose ¹, Prasad K. Bhaskaran ¹, Selvin P. Kani ²

Affiliations
1 Department of Ocean Engineering and Naval Architecture, Indian Institute of Technology, Kharagpur 721 302, IN
2 Integrated Coastal Zone Management Project, Institute of Environmental Studies and Wetland Management, Sector-1, Salt Lake City, Kolkata 700 064, IN

Abstract

The Hooghly estuary located in the head Bay of Bengal region is a part of the highly dynamic deltaic environment. Tidal variations are pre-dominant in this estuary, and tides propagate considerable distance through a complex network of various riverine systems, inlets, bays and creeks having vital implications on water mass exchange, reworking of deltaic sediments and the mixing process. The Hooghly River houses two major ports of national importance, viz. Kolkata Dock System and Haldia Dock Complex. Tidal forcing is primarily semi-diurnal in nature and with the presence of complex riverine morphology, the tidal characteristics are substantially modified causing various tidal constituents of compound tides. The present study performs location-specific tidal analysis and prediction utilizing one-hourly tide data with SLPR2 harmonic tidal analysis tool for Gangra situated upstream of the Hooghly River. In a geomorphologic perspective, the water-level elevation at Gangra results from natural tidal flow, as well as refracted effects from cross-flow due to the presence of two natural island barriers, namely Sagar Island situated southward off Gangra and Nayachara in the east. The Hooghly channel comprises of complex bathymetric features and tidal analysis at Gangra reveals the presence of Msf (luni-solar synodic fortnightly) tidal constituent. Very few locations in India have reported on the existence of the Msf tides, and Gangra is one among them. This study also performs a comprehensive validation between the computed monthly tidal prediction from SLPR2 and measured water level at Gangra. The skill level of prediction exhibits a good match. This study also investigates the influence of atmospheric effects on sea-level pressure variations and the resultant water-level elevation from extreme weather events such as depressions and severe cyclonic storms that occurred during 2013. The study signifies the importance of tidal analysis and prediction for operational needs.

Keywords

Estuary, Numerical Models, Tide Prediction and Analysis, Water-Level Elevation.

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Nitika Gupta ¹, Prasad K. Bhaskaran ¹, Mihir K. Dash ²

Affiliations
1 Department of Ocean Engineering and Naval Architecture, Indian Institute of Technology, Kharagpur 721 302, IN
2 Centre for Oceans, Rivers, Atmosphere and Land Sciences, Indian Institute of Technology, Kharagpur 721 302, IN

Abstract

Surface gravity waves play an important role in ocean engineering studies and their influence on the dynamics of the coastal zone is critical. Proper knowledge on wind-wave climatology is an area of immense interest to engineers and climate modellers. Climate change has influenced weather patterns over global oceans and at present is a matter of serious concern, as it can have long-term repercussions. There is a need to understand the recent trends in variability of windwaves for planning operations. To improve climate projections the Intergovernmental Panel on Climate Change report highlights the need and importance for wind-wave climate study. With this motivation, we study the variability of recent trends in maximum wind speed (MWS) and maximum significant wave height (MSWH) exclusively based on altimeter data for the Indian Ocean basin. We use daily data of MWS and MSWH from eight satellite missions covering a period of 21 years (1992-2012). The findings indicate that regions in the Southern Ocean (between 45°S and 55°S) experienced the largest variability in wind-wave climate. Higher MSWH resulting from increased MWS has practical implications on swell generation field that eventually cross the hemisphere influencing wind-waves elsewhere. The study also reveals the impact of wind-wave activity for the Indian Ocean basin in the past decade.

Keywords

Climate, Indian Ocean, Maximum Wave Height, Maximum Wind Speed, Satellite Observations.

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Prasad K. Bhaskaran ¹, Swetha Mangalagiri ², Subbareddy Bonthu ³

Affiliations
1 Department of Ocean Engineering and Naval Architecture Indian Institute of Technology, Kharagpur 721 302, IN
2 Ranbir and Chitra Gupta School of Infrastructure Design and Management, Indian Institute of Technology, Kharagpur 721 302, IN
3 National Centre for Sustainable Coastal Management, Chennai 600 025, IN

Abstract

The present study reports on a systematic procedure and maintenance plan for conducting dredging activity at the Kolkata port located in the Head Bay region, east coast of India. It is one of the oldest riverine ports in the country constructed by the British East India Company. The port comprises two docks, viz. Kolkata Dock Complex and the Haldia Dock System under the administrative control of the Kolkata Port Trust. The navigation channel located in the Hooghly River accommodates sea-going vessels with 200 GRT with pilotage assistance cruising upstream almost 145 km from Sagar Islands located in Hooghly estuary. The navigation channel experiences high rates of sedimentation being a riverine port. This study investigates the sedimentation rate throughout the navigation channel, identifying zones of high sedimentation rate. The behavioural pattern of tides and currents is analysed using the state-of-the-art ADCIRC model, and wave conditions are simulated using SWAN model. The hydrodynamic information obtained from ADCIRC and SWAN is input to the SEDTRANS model. Based on the intensity of sedimentation, the maintenance plan is proposed for three dredging seasons. On the basis of this scientific rationale and seasonal dredging maintenance procedure, it is anticipated that huge investments involved in the maintenance dredging of this channel can be minimized.

Keywords

Dredging Maintenance, Navigation Channel, Ports and Docks, Sedimentation Rate.

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Prasad K. Bhaskaran ¹

Affiliations
1 Department of Ocean Engineering and Naval Architecture, Indian Institute of Technology, Kharagpur 721 302, IN

Abstract

Gas bubbles produced by breaking waves play an important role in acoustic sound transmission. For a wide range of frequencies, the scattering is resonant in nature, and resonant bubbles scatter as well as absorb acoustic energy changing the compressibility of seawater. The present study deals with gas bubbles at the air-sea interface and their role in the attenuation and scattering of underwater sound propagation. This study leads to development of a damping model for gas bubbles as function of their size and acoustic frequency, including their role at resonance frequency covering aspects on damping mechanism due to thermal, viscous and radiation effects. The damping model estimates the variation of attenuation rate at resonance frequency for high wind speeds utilizing input from bubble population model considering geometrical aspects, and parameterizes bubble distribution at different stages of evolution. The study also estimates attenuation of sound speed in the presence of bubbles using climatology fields from the World Ocean Atlas. Finally, to assess the behaviour of random bubbles on sound attenuation, the statistical distribution function signifies that damping characteristics follows a normal distribution.

Keywords

Air-Sea Interface, Attenuation, Damping, Gas Bubbles.

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R. Gayathri ¹, Prasad K. Bhaskaran ¹, Felix Jose ²

Affiliations
1 Department of Ocean Engineering and Naval Architecture, Indian Institute of Technology, Kharagpur 721 302, IN
2 Department of Marine and Ecological Sciences, Florida Gulf Coast University, Fort Myers, FL 33965, US

Abstract

Coastal inundation is the flooding of coastal zone resulting from increased river discharge, spring tides, severe storms, or generation of powerful waves from tectonic activity (tsunami). This article discusses the critical factors that contribute to coastal inundation. Among the probable factors that cause coastal flooding and destruction, storm surge is the most frequent, and hence this article provides a detailed evaluation of the progress made in storm inundation research. Recent advances in coastal inundation modelling include efforts to understand the nonlinear dynamic interaction of near-shore waves, wind and atmospheric pressure with still water sea level and coastal currents, and their combined effects on storm surge along the coast and interaction with coastal morphology. An advanced storm-surge model comprises different modules, viz. an atmospheric component, and two ocean components for surge and wave simulations; these modules are coupled with each other. The nesting of regional coastal model with an ocean-wide model captures the far-field boundary forcing of extreme events that usually originate from the warm open ocean. Even though significant advancements reported on the efficiency and accuracy of storm surge and inundation prediction, further studies are required to understand the nonlinear interaction of storm surge with coastal landforms and their vegetation (land cover). In the context of rising sea level, increased tropical cyclone activity and rapid shoreline change, it is pertinent to evaluate the future flooding risk associated with landfall of tropical cyclones in densely populated coastal cities.

Keywords

Coastal Inundation, Coupled Models, Storm Surge, Tropical Cyclones.

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