Abstract:
Very limited data on cyclonic storm surge heights from coastal areas of Bangladesh
does not permit estimation of design surge heights by making frequency analysis
of observed data. In this study, design surge heights of given return periods
along with confidence intervals have been derived from synthetic data by performing
a statistical simulation. In the simulation, cyclonic storm surges occurred
randomly among three coastal regions. The regions are Ganges Tidal Plain (GTP),
Meghna Deltaic Plain (MDP)and Chittagong Coastal Plain (CCP). The simulation
model consists of three components: generation of annual maximumcyclonic wind
speed, simulation of storm surge occurrence and genration of surge height,
Annual maximumcyclonic wind speed data has been generated randomly from a
. ,.~, Gumbel distribution. Parameters of the distribution have been estimated from
observed data for the period 1960to 1991 using the maximumlikelihood procedure.
The data is continuous for the period 19'7.1to 1991 but discontinuous for the
period 1960 to 1972. The later data has oeen included in order to improve the
reliability of the estimated parameters and the data has been treated as historical
information. Estimators for the parameters of a Gumbel distribution from a sample
with both systematic and historical data have been derived.
A formula which is capable of predicting the maximumsurge height in the landfall
area during a cyclonic storm has been selected. The formula requires maximum
wind speed and length of the continental shelf as input data. A modification in
the formula has been made in order to include the effect of pressure drop as
well as to make it computationaly simple. It gives comparable results when verified
against observed data and reported results from two dimensional numerical
hYdrodynamic model studies of cyclonic storm surges in the Bay of Bengal. A
methodology for determining the average maximumsurge height in a coastal region
has been developed.
Lognormal distribution is found suitable for fitting the distribution of surge
height data while Gumbel distribution has been- found unsuitable. A methodology
that is capable of treating zero values in a sample of surge data has been used
in the frequency analysis of synthetic data using the lognormal distribution with
the maximumlikelihood procedure.
