SUMMARYA finite-difference method is described for the numerical integration of the one-dimensional shallow water equations over a sloping shelf that allows for a continuously moving shoreline. An application of the technique is made to the propagation of non-breaking waves towards the shoreline. The results of the computation are compared with an evaluation based upon an exact analytical treatment of the non-linear equations. Excellent agreement is found for both tsunami and tidal scale oscillations.

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.

SUMMARYA numerical model is developed for the simulation of surges generated by a tropical cyclone in the Bay of Bengal. The analysis area extends from approximately 11"N to 22"N and, in the northeastern sector of the Bay, includes a representation of the Ganges-Brahmaputra-Meghna river system in Bangladesh. The extent of the analysis area allows three days of the surge-generating capacity of a cyclone originating in the southern Indian Ocean to be recorded before landfall at the Bangladesh coast. The incorporation of the river system permits a potentially deep inland penetration of surges originating in the Bay. The model is non-linear and this allows a determination of the interactive effect between surge and the astronomical tide. Numerical experiments are described that relate to the change in surge response resulting from a change in the cyclone track during the 24 hours preceding landfall. An account is given of the interaction between surge and tide in the Bay and the river system.

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