Project context and challenge
Chattogram, Bangladesh’s second largest city and home to some 3.3 million people, floods almost every monsoon. In the Khatunganj and Chaktai area alone, about a tenth of the city, flooding causes an estimated USD 45 million in damage each year.
Two problems lie at the root. More than 70% of the city’s natural water bodies have disappeared under urban growth, leaving little room to store rainwater. At the same time, the city produces around 2,500 tonnes of solid waste per day, and nearly 1,000 tonnes of it is never collected. Much of that waste ends up in canals and drains, where it blocks the flow and clogs the pumps.
The two problems reinforce each other. Clearing canals achieves little if waste keeps flowing in, and better waste collection alone will not create the storage and discharge capacity the city lacks. Tides add to the pressure: high water in the Karnaphuli River blocks gravity drainage for around a fifth of the monsoon, a share that grows as sea levels rise. With funding from the Embassy of the Kingdom of the Netherlands, CDR and SweepSmart were asked to find an integrated and bankable way forward.
CDR’s approach and contribution
The study treated waste and water as one system. The team mapped the full waste chain, from collection and transfer to processing and disposal, alongside the drainage network, flood risk and institutions.
CDR focused on drainage and flood management. After a citywide basin analysis and stakeholder consultation, the densely populated and economically vital Chaktai Khal catchment was selected as case study. CDR built a hydrodynamic flood model capturing the interaction between rainfall, tides, canals and pumps, and ran it for a range of storms, tidal conditions and climate scenarios. The analysis showed that canal capacity falls short at several locations and that pumps can handle only a small fraction of peak canal flow, so the lost storage must be restored.
Building on the principles of delay, store, discharge and divert, CDR developed three concepts. Restore Flow removes waste, silt and bottlenecks and adds missing canal links. Increase Buffer creates new retention areas, ideally combined with green space or urban development. Optimise Control adds pumping capacity and active polder management. These were combined into a minimum and a full package and tested through multi-criteria and cost-benefit analysis.
On the waste side, the study recommended a 500 tonne per day processing facility combining mechanical biological treatment, refuse derived fuel production and anaerobic digestion. For both tracks, the team set out a financing route combining public private partnership with international and government funding.
Result
Chattogram now has a clear, evidence based roadmap to unclog the city. The full drainage package reduces flooding from a storm that occurs once every two years by around 75%, the minimum package by about 33%.
By tackling waste and drainage together, the solutions address the root cause of flooding rather than its symptoms. Chaktai Khal will serve as pilot for the wider city, paving the way for detailed design and implementation.
