Abstract:
This study work has been conducted for simulation of storm surge level at a tidal
channel due to coastal cyclone along the Bangladesh coast. Bay of Bengal
hydrodynamic model (BoB) of IWM has been updated with finer mesh resolution at
Baleshwar channel and it has been calibrated and validated for water level using the
measured data of the year 2017 and 2015 respectively.
Moreover, cyclone model of MIKE-21 maintained by IWM has been calibrated for
measured wind speed at several locations for cyclone 1991, cyclone SIDR (2007) and
cyclone AILA (2009). These two calibrated models (hydrodynamic and cyclone
model) have been coupled together and storm surge model has been developed for
Bangladesh coastline. Finally this storm surge model has been calibrated and validated
using the measured storm surge levels for cyclone SIDR (2007) and cyclone AILA
(2009).
This calibrated and validated storm surge model has been further verified with the
storm surge level during Cyclone SIDR-2007 measured by Japan Society of Civil
Engineers (JSCE) team. Wave model needs to simulate wave height during the
cyclone period. Therefore, both storm surge and wave model has been simulated for
cyclone SIDR-2007. Both storm surge and wave model result has been used to verify
the maximum observed water elevation during cyclone SIDR-2007 at three locations
of Baleshwar river namely Southkhali, Rayenda Bazar and Solombaria. Simulated
storm surge level of calibrated storm surge model (under this research work) shows a
difference of (+)10.7%, (-)11.5% and (-)18.4% at Solombaria, Rayenda Bazar and
Southkhali respectively with the field investigation of JSCE team for cyclone SIDR-
2007. This may happen due to some measurement uncertainty of the JSCE team.
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The model simulated result of storm surge level is then further compared with the
existing storm surge model simulations of IWM. The result shows a little difference
in the surge level compared to the simulation result of IWM. It is to be mentioned that
IWM storm surge model is developed by coupling of calibrated hydrodynamic model
and cyclone model (calibrated with the pattern of satellite image). It is seen that
simulated storm surge level under this study is found to be decreased by a range of 13
to 24 cm at different locations of Baleshwar channel and estuary compared to IWM
model simulation results.
The calibrated and validated storm surge model has been simulated for five different
water level and five different wind speed conditions to see the impacts of water depth
and wind speed on storm surge height at Baleshwar estuary. The simulation result
shows that storm surge height is a power function of wind speed. Storm surge height
increases with the increase of wind speed for constant water depth and cyclone track.
Again, it also found that storm surge height is inversely proportional to water depth
for constant wind speed and cyclone track. These analysis results have been used to
establish a relation between cyclone parameter and storm surge height at Baleshwar
estuary. An equation has been developed for estimating the storm surge height at
Baleshwar estuary which is further verified with the simulated surge height of IWM
and shows good agreement.
