S. K. Dube

Numerical Modelling of Tide-Surge Interaction in the Bay of Bengal

Numerical models are described for the evaluation of the interaction between tide and surge in the Bay of Bengal. The models are used to simulate the combined tidal and surge response on 3 June 1982 along the Orissa coast of India when the landfall of a tropical cyclone led to severe inland flooding. This is one of the few events for which a reliable tide-gauge reading is available and this enables a direct comparison to be made between the model predictions and the observationally determined sea-surface elevation anomaly. The comparison, although only utilizing limited observational data, appears sufficiently good for us to assert that the principal features of the surge response are correctly reproduced. A model simulation is also made of the surge that occurred along the Andhra coast of India during the period 18—20 November 1977 when there was heavy coastal inundation. Although tide-gauge readings are not available for this event, the predicted surge response agrees well with indirect estimates of the maximum sea-surface level and eyewitness accounts of inland flooding. The principal requirement for the operational use of these models is the availability of accurate data on the surface wind field together with a reliable forecast of the track to be followed by the tropical cyclone.

Numerical modelling of storm surges in the Arabian Sea

Abstract Using the basic hydrodynamic equations governing motion in the sea, a coastal zone numerical model has been developed for the prediction of storm surges along the west coast of India. Numerical experiments were performed with the help of this model to simulate the surge generated by the devastating 1975 Porbandar cyclone. The results of the experiments were in good agreement with the reported values along the Gujarat coast.

Numerical investigation of tide‐surge interaction in Hooghly Estuary, India

This article describes the numerical modeling of the tide‐surge interaction in Hooghly Estuary along the east coast of India. Nonlinear, vertically integrated numerical models are used to simulate the combined tide and surge response. The pure tidal solution developed in Hooghly Estuary provides the initial conditions for the model. The storm‐tide frequency calculation consists of generating surge by a given cyclone at the mouth of the estuary using a numerical model developed for the Bay of Bengal. The computed surge is then combined with the astronomical tide at the entrance of the estuary and the calculation continues within the estuary. However, this study does not include the feedback from the estuary on the surge model, hence the interaction is one way. Numerical experiments are performed involving three cyclonic storms, having landfall points to the south of the estuary, at the mouth of the estuary, and to the northeast of the estuary. The comparison, although utilizing only the observed tidal data...

An application of a wind-driven coastal upwelling model in the western Bay of Bengal

Abstract A three-dimensional numerical model of the type described by Johns et al. [ Quarterly Journal of the Royal Meteorological Society , 109 , 211–224 (1983) ] and further developed by Li (unpublished thesis, 1989) is applied to study the response to local wind-stress forcing of the coastal ocean in the western Bay of Bengal. Limited data on the thermal structure of the ocean off Visakhapatnam are utilized in an attempt to determine whether the observed form of the isotherms may be positively identified as a response to the pattern of local pre-monsoon and monsoon wind-stress forcing associated with periods of south-westerly and north-easterly winds prevailing during the months of March and October. Comparison of the model results with the observational data appears to support such an identification and an account is given of the corresponding computed currents to ascertain both the qualitative and quantitative form of the circulation responsible for the support of the observed thermal pattern. It is shown that south-westerly and north-easterly wind-stress forcing lead, respectively, to circulation patterns characteristic of those to be expected in classic Ekman-divergence-induced upwelling and downwelling processes. Thus, it is positively demonstrated that the changes in the sea-surface temperature and the upwarping and downwarping of the isopycnals observed by Rao et al. (1986) during the months of March and October may be explained in terms of upwelling and downwelling induced by the local winds prevailing during those periods.

Effect of sea level rise on tidal circulation in the Hooghly Estuary, Bay of Bengal

The issue of sea level rise is receiving considerable attention all over the world. Although the Indian stations have shown mixed trends, a positive sea level trend has been noticed in the Hooghly Estuary, situated on the east coast of India. The Hooghly River serves as a navigable waterway to Calcutta and Haldia ports. The river is tidal for nearly 250 km. To study the water levels and tidal currents in the lower part of the Hooghly Estuary, from sea face at Sagar to Hooghly Point, a vertically integrated numerical model has been used. The model is fully nonlinear and uses a semiexplicit finite‐difference scheme to solve the basic hydrodynamic equations on a staggered grid. This model is coupled with a one‐dimensional model, which has been used for the upper estuary from Hooghly Point to Swarupganj, where the flow is unidirectional. The computed water levels and currents are found to be in good agreement with the available observations. This model is applied to study the alterations in tidal circulation ...

FINITE DIFFERENCE TECHNIQUES APPLIED TO THE SIMULATION OF SURGES AND CURRENTS AROUND SRI LANKA AND SOUTHERN INDIAN PENINSULA

SUMMARY A well-known problem in fluid dynamics is the prediction of storm surges. In the present work, a coastal zone numerical model is described using finite difference techniques. The model has been applied to the prediction of storm surges generated by a tropical cyclone along the coasts of Sri Lanka and southern Indian peninsula. Experiments are carried out to simulate the surges associated with a forcing wind-stress distribution representative of the 1964 Rameswaram cyclone and the 1992 Tuticorin cyclone. The simulated surges for both cyclones are in good agreement with the reported counterpart maximum surge values.

A Tidal Flow Model for the Gulf of Kachchh, India

A vertically integrated model has been used to study the tidal circulation and currents in the Gulf of Kachchh along the west coast of India. The model is fully nonlinear and uses a semiexplicit finite difference scheme to solve the basic hydrodynamic equations on a staggered grid. The model is forced by prescribing the tides along the open boundary of the model domain. The flow is simulated both with and without the presence of the proposed tidal barrage across the Hansthal Creek in the Gulf of Kachchh. The results show a considerable change in the behavior of the tidal flow in the presence of the barrage.A vertically integrated model has been used to study the tidal circulation and currents in the Gulf of Kachchh along the west coast of India. The model is fully nonlinear and uses a semiexplicit finite difference scheme to solve the basic hydrodynamic equations on a staggered grid. The model is forced by prescribing the tides along the open boundary of the model domain. The flow is simulated both with and without the presence of the proposed tidal barrage across the Hansthal Creek in the Gulf of Kachchh. The results show a considerable change in the behavior of the tidal flow in the presence of the barrage.

Storm Surges: Worst Coastal Marine Hazard

Storm surges associated with severe tropical cyclones constitute the world’s worst coastal marine hazard. Storm surge disasters cause heavy loss of life and property, damage to the coastal structures and the losses of agriculture which lead to annual economic losses in affected countries. Death and destruction arise directly from the intense winds characteristic of tropical cyclones blowing over a large surface of water, which is bounded by a shallow basin. As a result of these winds the massive piling of the sea water occurs at the coast leading to the sudden inundation and flooding of coastal regions.

Numerical simulation of upwelling off Visakhapatnam on east coast of India during pre-monsoon months

A three-dimensional numerical model of the type described by Johns and coworkers (1992), hereafter referred to as model (J), is applied to study the response of a coastal ocean to pure wind-stress forcing. Conservation equations are applied for mass, momentum, temperature, salinity and turbulence energy. Experiments are performed to investigate the evolution of the thermal structure and upwelling processes along the east coast of India during the pre-monsoon season. A comparison between the computed results and the limited observations on the thermal structure and alongshore currents over the inner-shelf off Visakhapatnam is presented.

Numerical modelling of coastal upwelling in the Bay of Bengal

Abstract A baroclinic numerical model is applied to evolve thermal structure near the coast. The driving mechanism consists of wind-stress forcing representative of that applied during pre-monsoon (May), monsoon (July), and post-monsoon (November) seasons. During the monsoon season, a large quantity of fresh water is expected to be discharged from the Hooghli and Mahanadi rivers. Therefore, the simulations are carried out for July with a combination of wind stress and northern boundary forcing. The simulations show that the May winds are favourable for upwelling processes off Visakhapatnam. The upwelling off Visakhapatnam expected in July in the presence of southwesterly surface wind stress forcing is suppressed by the northern fresh water discharge and replaced by local sinking. The simulations for November indicate that the winds are favourable only for downwelling off Visakhapatnam.