Why must our streets flood even after so much investment?

As heavy monsoon rains once again leave large parts of Bangladesh underwater, the familiar scenes of waterlogging have left many wondering why our cities continue to fail despite massive investments in drainage infrastructure. Why do, for instance, Khulna’s streets remain knee-deep in water even after a Tk 800-crore project was undertaken to prevent it? Khulna city has just witnessed large areas being submerged for the third time in 10 days. The answer to this recurring contradiction lies in an illusion that runs deep within our municipal and development policy circles: that pouring concrete can solve what is, at the core, a hydrological crisis.

Every monsoon, the same cities flood again, and every year the response is the same—more drains, more concrete, more contracts. But the underlying hydrological realities are rarely accounted for. Our cities build drains while simultaneously destroying the natural channels meant to receive excess water. From Khulna to Dhaka to Chattogram, among the cities most battered by the ongoing heavy rainfall, the root causes are strikingly similar, even though each city likes to treat its waterlogging as a local emergency requiring its own emergency response. But none of the situations is unique. It is the same failure repeated in three different regions. And three common reasons can be attributed to this failure.

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First, rapid siltation has raised their surrounding riverbeds, reducing the effectiveness of gravity-fed drainage, particularly during high tide. In Khulna, rivers that once flowed well below the city’s drainage outlets now rise to, or even above, those levels during peak tide, meaning stormwater has nowhere to drain naturally. Water will never flow uphill, no matter how many new pipes are laid to encourage it to try.

Second, natural canals—the arteries that once carried excess water away from residential areas—are being systematically encroached upon, narrowed, and often converted into rigid concrete boxes, drastically reducing their carrying capacity. A natural waterway that once adapted to seasonal variations, expanding during heavy rains and accommodating excess runoff, is replaced by a fixed channel designed for ordinary conditions rather than extreme monsoon events. When rainfall exceeds that limited capacity, the water has nowhere left to go except into streets and people’s homes.

Third, weak municipal management makes it so that these expensive, concrete-lined drains quickly become clogged with plastic waste and sludge, reducing multi-crore infrastructure to little more than lengthy, buried rubbish bins. Without routine de-silting, effective waste management, and meaningful penalties for illegal dumping into drains, even a well-designed drainage channel can lose much of its effectiveness within a few years.

Drains are useless if they have nowhere to empty. When outfall rivers are choked with silt and the low-lying wetlands that once absorbed excess water are paved over for development, that water has nowhere to go except onto our roads. This is the element that most drainage plans seem to ignore: a drain is not a solution by itself; it is only as effective as the river or wetland waiting to receive what it carries. One could build the finest drainage network in South Asia, but if the receiving river is clogged, degraded, or poorly connected, the whole network will fail. 

One can see this pattern behind Khulna’s recurring waterlogging crises in recent years, and it is the same pattern playing out in Dhaka and Chattogram. Authorities keep treating waterlogging as if it is a localised engineering issue—a pipe problem here, a pump problem there—when it is, in fact, a basin-wide failure of hydrological management. Each new drainage project treats the symptom in isolation, while the disease—continued degradation of our network of rivers, canals, and wetlands—is left untreated.

There is also another cost of this approach that is rarely considered: the erosion of public trust. Residents watch hundreds of crores committed to drainage works, endure months of navigating dug-up roads and disrupted traffic, and then watch the very same streets flood the next monsoon. When the promised relief never arrives, they are naturally left questioning the justification behind causing such disruptions, and whether these projects are meant to address the problem at all. Right now, as we are inundated with images of waterlogged streets across Bangladesh’s cities, such scepticism is natural. 

Going forward, authorities should abandon piecemeal pipe-laying in favour of what might be called a “living river” approach, treating urban drainage and natural river systems as a single connected ecosystem rather than separate engineering problems. In practice, this means three things. Wetland protection laws must be strictly enforced rather than routinely waived for development, because every wetland paved over is a retention capacity permanently removed from the system. The narrowing and boxing-in of natural canals must stop, and where it has already happened, canals must be restored to their original carrying capacity. Outfall rivers also need engineered sediment-bypass systems to keep them functioning as gravity-fed drainage outlets, rather than as silt-choked dead ends, so that the water a city’s drains collect has somewhere to go.

None of this is exotic engineering. Sediment management, wetland retention, and canal restoration are well-understood approaches used successfully elsewhere in the region. What is missing in Bangladesh is not technical knowledge but institutional willingness to treat a river’s health as infrastructure in its own right, deserving the same budget line and the same long-term maintenance commitment as a concrete drain.

This also requires coordination across the agencies that currently work in isolation. City corporations lay drains, water development authorities manage rivers, and land administration bodies oversee decisions that often allow the encroachments that narrow canals in the first place—often without speaking to one another. A living-river approach cannot work as long as the agency building a drain, for instance, has no control over the wider system that determines whether it can function effectively. Real reform will require all these agencies to plan and work together, with a basin-level central unit to be held accountable for any unexpected outcomes.

Until the authorities manage urban drains and natural waterways as one connected system, Bangladesh’s multi-crore drainage projects will remain ineffective when they are needed most.

Dr Ahad Chowdhury is a geologist and environmental scientist, currently teaching at Jefferson Community and Technical College in Kentucky, US.

Views expressed in this article are the author's own. 

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