A. D. Rao

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.

The simulation of a continuously deforming lateral boundary in problems involving the shallow water equations

A finite-difference method is given for the treatment of a continuously deforming lateral fluid boundary in computer simulations of systems involving the shallow water equations. The technique is described in the context of a numerical storm surge model for the east coast of India. Using a forcing wind-stress distribution representative of the 1977 Andhra cyclone, a comparison is made between simulations using models both with and without inland intrusion of water along the coast of Andhra Pradesh.

Extreme Sea Levels Associated With Severe Tropical Cyclones Hitting Orissa Coast of India

Extreme sea levels associated with severe cyclonic storms are common occurrences along the east coast of India. The coastal districts of Orissa have experienced major surges in the past. The recent Paradip super cyclone is one of the most severe cyclones, causing extensive damage to property and loss of lives. Extreme sea levels are major causes for coastal flooding in this region. Damages can be minimized if the extreme sea levels are forecast well in advance. In the present study, we develop a location specific, fine resolution model for the Orissa coast on the lines similar to that of IIT-D storm surge model (Dube et al. 1994). The model runs on a personal computer. The bathymetry for the model is extracted from very fine resolution naval hydrographic charts for the region extending from the south of Orissa to south of West Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea surface elevations. An attempt was made in this study to simulate extreme sea levels along the Orissa coast using the data of past severe cyclones. The model results reported in the present study are in good agreement with available observations or estimates.Extreme sea levels associated with severe cyclonic storms are common occurrences along the east coast of India. The coastal districts of Orissa have experienced major surges in the past. The recent Paradip super cyclone is one of the most severe cyclones, causing extensive damage to property and loss of lives. Extreme sea levels are major causes for coastal flooding in this region. Damages can be minimized if the extreme sea levels are forecast well in advance. In the present study, we develop a location specific, fine resolution model for the Orissa coast on the lines similar to that of IIT-D storm surge model (Dube et al. 1994). The model runs on a personal computer. The bathymetry for the model is extracted from very fine resolution naval hydrographic charts for the region extending from the south of Orissa to south of West Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea surface elevations. An attempt wa...

Sea Levels and Coastal Inundation Due to Tropical Cyclones in Indian Coastal Regions of Andhra and Orissa

Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding.Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding.

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...

A breadth averaged numerical model for suspended sediment transport in Hooghly estuary, east coast of India

Sedimentation is of vital concern in the conservation, development and utilization ofour soil and water resources. The suspended sediment in estuarine waters is hazardousto navigation in estuaries, which have important ports and harbours. A breadth-averagednumerical model to study circulation and sediment transport is presented in this paper.The model is applied to Hooghly estuary, along the east coast of India. The model is fullynon-linear and uses a semi-explicit finite difference scheme to solve mass, momentum andadvection diffusion equation for suspended sediments in a vertical plane. The erosion anddeposition have been computed by empirically developed source and sink terms in thesuspended sediment equation.

On the occurrence of upwelling along the East Coast of India

A numerical model is applied to simulate the coastal circulation of water off the east-coast of India. The driving mechanisms consist, in general, of wind-stress forcing representative of that applying during the southwest monsoon season, and a forced southward transport of water across a northern open boundary that models the fresh water discharge from the Hugli and Mahanadi rivers. The model predictions (both with and without northern boundary forcing) are compared with recently published data on observations of upwelling along the east coast of India. The simulations provide definitive evidence that, with the simultaneous presence of both a forced fresh water flow and upwelling favourable winds along the east coast of India during the monsoon season, the occurrence of upwelling is confined to latitudes south of Visakhapatnam. To the north of this latitude, it is shown that the local effect of the southward forced transport of fresh water across the northern boundary remains sufficiently strong to inhibit the occurrence of upwelling and, instead, to lead to a sinking that is consistent with the observational data.

On the effect of bathymetry in numerical storm surge simulation experiments

Abstract A numerical model is described for the simulation of storm surges which uses a non-uniform off-shore grid-spacing adjacent to coastal boundaries. This permits an increased resolution near the coast in the models described in[1,2]. Using data on the 1977 Andhra cyclone, which struck the east coast of India, it is shown that the near-coastal bathymetry is critical in determining the coastal surge-induced sea-surface elevation. It is also shown that the coastal surge response is effectively independent of the depth of water in the deepest regions of the analysis area. Conclusions are drawn concerning the selection of an optimum resolution in the numerical scheme together with the proper representation of the bathymetry.

Numerical Simulation of Extreme Sea Levels Using Location Specific High Resolution Model for Gujarat Coast of India

Although the frequency of tropical cyclones is less in the Arabian sea compared to that of the Bay of Bengal, there are several severe tropical cyclones which caused extensive damage along the Gujarat coast. In view of the high tidal range in the funnel-shaped gulfs of the Khambhat and the Kachch, it is very useful to study the surge response in these regions. There is always a possibility of abnormal rise of sea level when the occurrence of surge coincides with high tide, which may eventually cause inundation of vast stretches of shallow coastal areas. In view of this, a location specific fine resolution model is developed for the Gujarat coast. The east-west and north-south grid distances for the model are 5.1 km and 5.2 km, respectively. Several numerical experiments are carried out to compute the extreme sea levels using the wind stress forcings representative of 1982, 1996, and 1998 cyclones, which crossed this region. The model-computed extreme sea levels are in good agreement with the available observations.Although the frequency of tropical cyclones is less in the Arabian sea compared to that of the Bay of Bengal, there are several severe tropical cyclones which caused extensive damage along the Gujarat coast. In view of the high tidal range in the funnel-shaped gulfs of the Khambhat and the Kachch, it is very useful to study the surge response in these regions. There is always a possibility of abnormal rise of sea level when the occurrence of surge coincides with high tide, which may eventually cause inundation of vast stretches of shallow coastal areas. In view of this, a location specific fine resolution model is developed for the Gujarat coast. The east-west and north-south grid distances for the model are 5.1 km and 5.2 km, respectively. Several numerical experiments are carried out to compute the extreme sea levels using the wind stress forcings representative of 1982, 1996, and 1998 cyclones, which crossed this region. The model-computed extreme sea levels are in good agreement with the available obs...