Simulation of storm surge level at a tidal channel due to coastal cyclone along the Bangladesh coast

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. XV 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.