The nation learning to embrace flooding

With future climate change, flooding in Bangladesh is predicted to become more extreme due to cyclonic storm surges and rising sea levels. Under a “moderate” climate change scenario, flooding will become more intense and cover greater areas, with two crucial crops – Aus rice and wheat – declining by 27% and 61% respectively as a result. Much of the nation is exposed, as 80% of Bangladesh is flood plain, with the majority of the country a metre or less above sea level. Sheikh Hasina, Prime Minister of Bangladesh, called sea-level rise a “planetary emergency”, and one of which Bangladesh will bear the brunt.

Troubled waters

Many of the conventional methods to cope with flooding in Bangladesh have tried to defy the flood-prone nature of the delta nation. After the 1987 and 1988 floods, for example, there was a Flood Action Plan of 1990 with at least 26 feasibility studies and pilot projects carried out in an effort to make the country “impregnable” to water.

Shafiul Azam Ahmad, who has been a water and sanitation specialist at the World Bank and a regional consultant for Bangladesh, Sri Lanka and Nepal, describes the period as one of rapid investment into structural interventions. But they didn’t work out as planned. “Serious waterlogging followed,” says Ahmad. “When the rain fell [in Dhaka] it had no place to go. Pumping it out was difficult and expensive.”

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The prospect of fortified walls to contain rivers might seem alluring, but the high-water mark in parts of south-west Bangladesh has been rising faster due in part to the constriction of water flow caused by embankments, putting these areas at a higher risk of flooding. “It’s like stepping on a gardening hose and then releasing it,” says Mohamad Khalequzzaman, a geoscientist and coastal oceanographer at Lock Haven University, Pennsylvania. “The water shoots out.”

Walling off low-lying islands using permanent embankments, or polders, has been another popular intervention. One embankment known as Polder 32 – one of 139 protected low-lying islands – collapsed dramatically during a cyclone in 2009, when floodwaters broke through the defenses. The land within the polder, home to more than 10,000 people, was inundated.

Researchers are finding that polders have a very mixed effect on flooding – while they make monsoon flooding worse, they offer some protection from storm surges. One of the main issues is the way they disrupt sediment flow. In 2015, polders had lost 1-1.5m of elevation compared with surrounding mangrove forests over the past 55 years because they prevent silt and sediment from spreading over the landscape, according to research led by Leslie Wallace Auerbach of Vanderbilt University, Tennessee. The effect of blocking sediment from entering during gradual flooding inadvertently raised the risk of a more sudden one.

For the polder strategy to work in the long term, “you’d have to keep building higher and higher,” says Khalequzzaman. “Ultimately, you’d be living in a castle. What do you do when it crumbles?” As Polder 32 illustrates, when a barrier does fail, the results are catastrophic for those who rely on the barriers. “Embankments inevitably breach,” he says. “Nature’s power is overwhelming. People, lulled into this false sense of security, build closer and closer to flood-prone zones.”

Some researchers argue that structural interventions have also interfered with the "autonomous adjustment" indigenous farmers were accustomed to. The result has been some local hostility to water-management interventions, with some polder residents battling to reverse dykes or cut through embankments.

So, if not reliance on barriers, what is the answer to the more extreme floods that the country will face with climate change?

Indigenous intervention

Traditionally, settlements in Bangladesh favoured higher ground to build, reserving the lower-lying areas for farmland. An area could be raised by digging and elevating the soil, before building – known as the “dig, elevate, dwell” approach. Historically, this allowed homesteads to cope with all but the worst storms. Small ponds next to homes were common, and that water often served as a reservoir for the dry season. “It’s a beautiful system, really,” says Khalequzzaman. “Our ancestors worked with the flood.”

Likewise, today, some roads in Bangladesh are built using materials that can withstand prolonged water immersion. During the rainy season, people often use boats to travel making roads non-essential, until the dry season when the waters recede and the roads emerge. And adaptations of existing defences led by indigenous people – such as controlled breaching of a polder to allow tidal waters and sediment in – have been linked to better food security, flood management and land development. Government tidal river management efforts have also explored similar approaches.

Such resilience, by planning rather than preventing floods has also been urged for settlements. Relief providers such as the Obhizatrik Foundation’s Jami report the efficiency of basic platforms or elevated houses in regions such as Bharisal and Bhola – areas prone to cyclones that fared better in the floods this year. This combination of indigenous knowledge coupled with evidence-based research is an approach many are welcoming.

“Everything we’ve done in the past decades was against nature,” says Khondker Neaz Rahman, who has worked with the Bangladesh government and the United Nations Development Programme on urban and regional planning. “I don’t see a problem with water. I see a problem when we start considering water the enemy.”

But relying on methods that have worked in the past, in a pre-climate-change era, may not be able to stand up to the more intense flooding to come – but preparing for a world without structural defences is going to be the way forward, says Rahman, who worked on the most recent master plan for Dhaka. He is planning settlements as they would exist in the absence of embankments or flood gates. Though shifting away from the conventional approach is a slow process. “Tension between the new understanding of water and the inertia of continued investment is fraught,” he says.

While the idea of containing the formidable rivers and dynamic delta of Bangladesh is proving inefficient, he cautions that demolishing the structures now would likely be even more damaging.

“If you were to destroy all the embankments, the next monsoon – it would be devastating,” says Rahman. With decades of lost sediment and lowered ground levels, removing the protections would inundate the polders – and entire megacities like Dhaka – risking incalculable deaths, injury and loss.

Much like the ever-mutating rivers evading definition and charting their own territory, Bangladesh has a chance to map out a middle way between existing fortifications and wiping the slate clean. The solutions will have to be complex and nuanced, if they are to reflect the duality of Bangladesh’s relationship with water.

After all, as Rahman points out, many families traditionally name their daughter “Bonna” – the Bangla word for flood. It shows how vital floods, in a manageable form, are to the country. “Would you name your daughter drought, famine or earthquake?”

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