Project context and challenge
Payra Port is set to become the third largest seaport of Bangladesh and a key asset for the national economy. Its location is shaped by the Ganges, Brahmaputra and Meghna rivers, which carry huge volumes of sediment into the Bay of Bengal and have built a wide, shallow platform far offshore. To reach water deep enough for seagoing vessels, the approach channel to the port has to be at least 75 km long, and because sediment keeps settling, it must be dredged and maintained continuously.
The Payra Port Authority contracted the capital and maintenance dredging of the Rabnabad Channel and needed an independent engineer to supervise the works and review the channel design. That design had to work under demanding conditions: strong currents along and across the channel, layers of fluid mud, large seasonal differences in water levels and waves, and future jetties that still had to be built. At the same time, the dredging volume was limited by the contract budget, and part of the work was already under way.
CDR’s approach and contribution
Together with its joint venture partners, CDR supported the Port Authority with contract administration, day to day supervision and quality control of the dredging works, and monitoring of the dredging activities and siltation in the channel.
A key task was the validation of the conceptual channel design. CDR set up a new basis of design following international PIANC guidelines, allowing the channel to serve partially loaded Panamax vessels instead of the smaller ships originally assumed. The team analysed long term data on water levels, waves, currents, salinity and siltation, gathered the experience of local pilots and aligned the channel with existing and planned jetties in the port masterplan.
The design was then tested in real time navigation simulations at HR Wallingford in the United Kingdom, where pilots sailed the channel on a ship bridge simulator, including the effects of fluid mud. A detailed probabilistic under keel clearance study with ship response simulations determined how deep vessels can safely be loaded for every season and tide.
This led to a channel made up of eleven straight sections with widths between 110 and 168 metres, extra width in the bends to cope with drifting vessels, and an optimised depth profile.
Result
The validated channel design accommodates larger vessels than originally planned, while requiring less capital dredging and keeping the same availability for shipping. Navigation safety has improved at the most critical locations, the layout is ready for future port expansion, and unnecessary dredging work was avoided.
The Port Authority also gained a clear method to set the maximum loading draught, from 7.6 to 10.8 metres depending on season and tide, so that it can get the most out of its channel and increase throughput.
