Understanding the differences between the cordon and open approach to flood control.
Bangladesh, a deltaic nation nestled between the Ganges, Brahmaputra, and Meghna rivers, faces an intricate and everlasting perpetual battle with water. As floods increasingly ravage its landscapes due to climate change, the debate over how best to protect communities, infrastructure, and agricultural land has become more urgent. Two primary strategies have emerged in this battle: the cordon approach and the open approach, both of which offer distinct benefits and face significant challenges.
Cordon: Current Practices and Vulnerabilities
Since the 1950s, Bangladesh’s flood control strategy has primarily relied on the cordon approach. This method proposes that certain areas should be cordoned off or barricaded to protect them from flooding. As a result, flood control efforts have shifted toward an emphasis on flood prevention. A classic example of this approach is the Dhaka-Narayanganj-Demra (DND) project. Under this project, a tract of floodplain with Dhaka, Narayanganj, and Demra at the vertices has been sealed off from the adjoining Buriganga and Shitalkhya rivers through the construction of cordons.
The 1988 floods that submerged most of Dhaka city gave momentum to the cordon approach. The Greater Dhaka Embankment Project is a direct result of that flood. The events of 1988 led to the idea of constructing cordons along entire stretches of all major rivers. The idea is to let the river water remain confined only to its channels and pass directly to the sea. Similar cordons have been constructed along various stretches of many other rivers. Such projects include the Gumti Embankment Project, the Meghna-Dhonagoda Project, the Barisal Irrigation Project, and others.
Given Bangladesh’s deltaic conditions, the implementation of the cordon approach simply aims to seal off floodplains from adjoining rivers through broken embankments, creating adverse effects on flooding, draining, soil quality, sanitation, preservation of freshwater fish stock, functioning of waterways, and temperature balance, leaving a big debt burden. The cordons create a false sense of elevation and dryness, prompting the construction of houses without sufficient elevation of land. The cordons do not reduce the total volume of water, instead, the water finds space elsewhere. This increases pressure on neighbouring areas, which now have to experience high tides of floodwater only to be drained artificially through pumps. Thus, a disproportionate amount of national resources are being spent on draining floodwaters.
Open: The Theoretically Better Approach
Hydrologists, engineers, and geographic information systems (GIS) professionals have, on multiple occasions, suggested that Bangladesh needs to work with natural water systems rather than attempting to control or contain them through rigid infrastructure. They have proposed that the open approach, which utilises the natural landscape, will be far more effective in maintaining and restoring natural floodplains, wetlands, and river basins, allowing controlled flooding in designated areas. The open approach can also mitigate five dimensions of climate effect on water bodies – submergence, salinity intrusion, destabilisation of rivers, increase in extreme weather events, and increased risk of diseases. To implement this approach, landscaping is required to re-excavate surface water bodies and widen rivers, canals, and floodplains that have been blocked over time due to natural sedimentation or human activities. Re-excavation, in the framework of the open approach, is consistent with the idea of working with natural systems by strengthening their innate ability to control water and reduce the risk of flooding. Given the high number of river systems in Bangladesh, the open approach to flood control is generally considered better than the cordon approach because it allows for more natural water flow, reduces flood damage, and promotes ecological sustainability.
Re-excavation, in the framework of the open approach, is consistent with the idea of working with natural systems by strengthening their innate ability to control water and reduce the risk of flooding.
High Time for a Transition
Despite the open approach’s benefits, Bangladesh’s continued reliance on the cordon approach is largely due to historical, economic, and social factors. The country has invested heavily in flood control infrastructure over the years, and transitioning to a new approach would require significant resources and planning. Additionally, the cordon approach has provided some level of protection, especially in densely populated areas. However, the long-term sustainability and effectiveness of this strategy are increasingly being questioned, leading to growing calls for a more holistic and adaptable approach.
A path to a resilient future for flood management in Bangladesh lies in integrating both structural and nature-based solutions, combining the strengths of the cordon and open approaches. The use of a hybrid strategy recognises that while hard infrastructure like embankments may be necessary to protect densely populated areas, long-term sustainability depends on embracing natural flood management systems. By fostering resilience through this integrated approach, Bangladesh can slowly ease its way into the open approach, ensuring a future where both its people and environment are better equipped to withstand the increasing challenges of flooding.
