Indu Jain

Computation of Expected Total Water Levels along the East Coast of India

Abstract Extreme sea levels generated by strong tangential wind stress and normal atmospheric pressure gradients at the sea surface due to tropical cyclones were studied for the western sector of the Bay of Bengal (the east coast of India). The maritime states along the coast, hit by different intensities of cyclones, are West Bengal, Orissa, Andhra Pradesh, and Tamil Nadu. Based on precise historical data for the period 1891–2007, statistical projections have been made on the probable intensities of tropical cyclones for various return periods. With the help of numerical models developed at Indian Institute of Technology Delhi, maximum probable surges along the coast were simulated. The local tide effect was considered in the computations as rise of sea level would be greater if the cyclone crosses the coast during high tide. The total water elevation is computed by linearly adding the local tide and wave setup to the surge simulated along the coast. In the present study, an assessment of cyclone risk and vulnerability was evolved, which is an important component of the information used to create sustainable local-level development action plans for preparedness and mitigation.

Numerical Modeling of Cyclone's Impact on the Ocean- A Case Study of the Orissa Super Cyclone

Abstract A three-dimensional numerical model is described to study and investigate the impact of the Orissa super cyclone on the ocean. The forcing mechanism in the model is the wind stress derived from moving cyclonic storm/satellite winds. Numerical experiments have been performed using the model in order to understand the dynamics and thermodynamics of the ocean owing to the cyclone crossing the Paradip coast. The model was used to simulate the thermal response of the ocean to study the surface cooling and the surge associated with the cyclone. A net decrease in sea-surface temperature of about 5–6 °C and a peak surge of over 6 m were simulated when the storm moved over the Orissa coast. The model computations were compared with the satellite data (TMI—Tropical Rainfall Measuring Mission [TRMM] Microwave Imager) available during the storm period. In the subsequent experiments, the variation of the oceans response to the changes in the translation speed of the cyclone was examined. We conclude that the speed of the cyclone, which determines the resident time of the cyclone over the ocean, leaves an overwhelming influence on sea-surface cooling and surge generation.

Estimation of Extreme Water Levels Due to Cyclonic Storms: A Case Study for Kalpakkam Coast

Numerical ocean models are considered today as an essential tool to predict spurt in the sea level rise and associated inland extent of flooding that could be generated by a cyclonic storm crossing any coastal stretch. For this purpose, the advanced two-dimensional depth-integrated (ADCIRC-2DDI) circulation model based on finite-element formulation is applied for the simulation of surges and associated water levels off Kalpakkam coast. Using the long term inventory of cyclone database, synthesized tracks are deduced for affected coastal districts of Tamil Nadu, a state bordering the Bay of Bengal encompassing the Kalpakkam region. Return periods are also computed for the intensity and frequency of cyclones at each coastal district of Tamil Nadu. Using the ADCIRC-2DDI model, validation of surges and associated water levels generated by the November 2000 cyclone, which had landfall near Pondicherry coast was initially carried out. The simulation exercise exhibits a good agreement with available observations from post-storm survey reports. Considering the importance of Kalpakkam region, extreme water levels are computed based on a 50-year return period data, for the generation of storm surges, associated water levels and extent of inland inundation. Based on experimental evidence, it is advocated that this region could be inundated from produced water levels when pressure deficit exceeds a threshold value of 66hPa. Also it is noticed that the horizontal extent of inland inundation ranges between 1–1.5 km associated with the peak surge.

Vulnerability Assessment at Village Level Due to Tides, Surges and Wave Setup

An assessment of cyclone risk and vulnerability at the village level has evolved, which is an important component of the information system for local level development action plans for preparedness and mitigation. Here, a case study for the Nellore district along the east coast of India is considered. Using maximum probable surges along the coast, total water level (TWL) due to the combined effect of surge, tide, and wind wave is computed for the most vulnerable coastal villages of the Nellore district due to any tropical cyclones. The computations suggest that the TWL along the Nellore coast varies from 2 m in the south to 4 m in the north.

Numerical Modeling of Suspended Sediment Transport in the Gulf of Kachchh Including Kandla Creek, West Coast of India

A depth-averaged numerical model has been developed to study tidal circulation and suspended sediment transport in the Gulf of Kachchh including Kandla creek, west coast of India. The resolution of the model is taken as 750 m × 750 m, which is found to be adequate for the gulf region. However, this resolution could not produce the realistic circulation pattern and suspended sediment concentration in the Kandla creek region. There is a major seaport at Kandla which serves as the sea gate to northwest India. Therefore, a 2-D fine resolution (75 m × 75 m) model for Kandla creek has been developed and coupled with the coarser gulf model to compute the flow features in the creek region. The model dynamics and basic formulation remain the same for both the gulf model and the creek model. The models are barotropic, based on shallow water equations, and neglect horizontal diffusion and wind stress terms in the momentum equations. The models are fully nonlinear and use a semiexplicit finite difference scheme to solve mass, momentum, and advection-diffusion equations in a horizontal plane. The tide in the gulf is represented in the model by the semidiurnal M2 constituent mainly. In this study, no fresh water discharge conditions have been considered so the results are appropriate for the dry season. Numerical experiments are carried out to study the circulation and suspended sediment concentrations in the gulf and the creek regions. The computed results are validated with the available observations.