Return period estimates of extreme sea level along the east coast of India from numerical simulations |
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Authors: | B Sindhu A S Unnikrishnan |
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Institution: | (1) National Institute of Oceanography, Council of Scientific and Industrial Research, Dona Paula, Goa, 403004, India;(2) National Institute of Oceanography, Dona Paula, Goa, 403004, India;(3) Present address: COWI Gulf A/S, PO Box 52978, Dubai, UAE |
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Abstract: | Estimates of return periods of extreme sea level events along the coast are useful for impact assessment. In this study, a
vertically integrated 2D model was developed for the simulation of storm surges in the Bay of Bengal. The bathymetry for the
model was derived from an improved ETOPO-5 data set, which was prepared in our earlier work. The meteorological forcing for
the model was obtained from the cyclone model of Holland using the data available for 136 low-pressure systems that occurred
during 1974–2000 in the Bay of Bengal. The simulated total sea level and the surge component were obtained for each event.
The simulated peak levels showed good agreement with the observations available at few stations. The annual maxima of sea
levels, extracted from the simulations, were fitted with Gumbel distribution using r-largest annual maxima method to estimate the 5- and 50-year return periods of extreme events at 26 stations along the east
coast of India. The return periods estimated from simulated sea levels showed good agreement with those obtained from observations.
The 5- and 50-year return levels of total sea level along the east coast of India show a considerable increase from south
to north, with the 50-year return total sea levels being as high as 6.9 and 8.7 m at stations along the north eastern coast
such as Sagar Island and Chandipur, respectively. The high return levels are expected at these stations as the cyclones developed
in the Bay of Bengal generally move north or north-west, producing extreme events in the northern part, and moreover, these
stations are characterized by high tidal ranges. However, at some regions in the southern part such as Surya Lanka and Machilipatnam,
though 50-year return levels of total sea level are not very high (2.98 and 2.97 m, respectively) because of the relatively
lower tidal ranges, high return levels of surges (0.84 and 0.57 m, respectively) are found. In addition to the role of shallow
depths (5.0 and 6.1 m, respectively) at the two stations, the high return levels of surges are attributed to the effect of
geometrical configuration at Surya Lanka and width (100 km) and orientation of continental shelf at Machilipatnam. |
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