Hydrodynamic and sediment transport modelling for coastal management in Chittagong, Bangladesh

Hydrodynamic and sediment transport conditions were simulated in the Chittagong region of Bangladesh to provide recommendations on the future management of the coastal zone, and to support the objectives of sustainable economic coastal development, shipping and associated infrastructure.
A fully coupled wave, current and sediment transport model was set up and run in TOMAWAC, TELEMAC 2D, and GAIA for various weather conditions, including three different cyclones and accounting for transport of sand and mud sediments.
The first of these simulated tropical cyclones was selected from the The IBTrACS archive. We searched to recorded storms passing within 500 km of Chittagong since 1979 and selected the strongest cyclone, which was in 1991, making landfall close to Chattogram with estimated wind speeds of approximately 70 m/s leading to a very large surge that coincided with high tide. The flooding arising from the 1991 cyclone was devastating, causing at least 138,000 deaths and catastrophic damage to housing, infrastructure and farmland. The other simulated cyclones modelled were synthetic and of smaller magnitude, but making landfall near relevant infrastructure on the delta of the Karnaphuli River and the Matarbari Port.
For each modelled tropical cyclone, time-evolving wind fields were set up, waves and surge modelling was undertaken, and the hydrodynamics and sediment transport were characterised in order to support in identifying ‘risk’ areas with respect to future infrastructure development. Such risks were defined as places with significant rates of morphological change that would impact proposed infrastructure development. For example, excessive channel migration, coastal erosion or accretion, cyclone surge/wave attack.
The model results helped in the evaluation of the hydrodynamic regime and morphology in the Chittagong region and provided useful data for a high level assessment of the potential risk of coastal flooding due to cyclones. Moreover, they were useful for studying the impact of existing and proposed engineering developments along its coastline.