Storm-induced sea-level changes at Saugor Island situated in north Bay of Bengal

Abstract

The sea level at Saugor Island is not significantly affected by freshet discharges of the river Hooghly although there are significant changes at a station about 70 miles upstream (Minist. Irrg. Pwr. 1952, 1953). Daily departures of the observed tidal heights at Saugor Island from the values predicted by the tide predicting machine were obtained for selected periods when cyclonic storms affected the north Bay of Bengal and were located 150-250 miles away from Saugor Island. The. monthly mean departure dm was subtracted from the daily departures and the resultant values of (8-dm ) were found to vary between I and 3 ft. On the assumption of (i) a mean  .wind distribution found as the average of a large number of cyclonic storms in the Bay of Bengal, (ii) negligible' static' pressure effect and (iii) a wind stress coefficient of 0.0024 (Sverdrup), the wind pile-up at Saugor Island caused by the wind systems associated with the cyclonic storms, was computed. The depths of the ocean needed for the computation were taken from the Admiralty charts. The computed values of the pile up were found to agree fairly well with the values of (8-dm), the mean percentage deviation being 10 per cent for the six instances studied. This suggests that wind pile-up accounts for nearly 90 per cent of the departure of actual tidal heights from the predicted values. Probably the remaining 10 per cent comes from the mass-transport effects associated with the water currents generated by the wind systems.