On the night of July 4, 2025, the Guadalupe River in Texas Hill Country rose about 26 feet in 45 minutes. Camp Mystic, a girls' summer camp on its banks, lost 27 campers, counselors, and its director before dawn. More than 135 people died across the region in that single flood, according to state investigative findings.
What made the event so lethal was not simply how much rain fell. The National Weather Service's own warnings that night cited rainfall rates climbing to several inches an hour, a pace that turned a river into a wall of water before most people even understood a flood was underway.
This is the point that gets lost in most conversations about flooding, in Texas and in Bangladesh alike. The number that matters most in the changing climate is often not the total rainfall for the day, but how fast it arrives.
A given volume of rain spread over 12 hours is manageable. The same volume in 90 minutes can be fatal. Chittagong found this out on its own terms this July, when the city recorded about 410 millimetres of rain in 24 hours, according to a Dhaka Tribune report, the heaviest single-day total the port city had seen in 42 years.
The rain fell hardest while the Karnaphuli River was at high tide, and while runoff from the surrounding hills poured into a drainage network already at its limit.
A city I did not expect to see this in
I grew up in Comilla, and waterlogging is not something I remember from my childhood there. A hard rain meant wet streets that dried out again by the next day. That is no longer true. Comilla now floods most summers, sometimes badly enough that students have had to reach their exam centres by boat.
Comilla has no hills to cut and no tide to fight. What it has, like dozens of other urbanizing cities across Bangladesh and beyond, is a much less dramatic but equally potent sequence: Canal margins and low channels lost to construction, drains left uncleared for years, and a habit, shared by households, markets, and construction sites alike, of treating the nearest drain as the easiest place to get rid of waste.
None of that needed a hill or a coastline. It only needed disregard for the environment and indifferent authorities.
Two cities, two different problems
Dhaka and Chittagong show the same underlying pattern at a larger, more studied scale, each with its own mechanism layered on top.
Dhaka's story is mostly about disappearing land. According to a study on canal encroachment in Dhaka, the city has lost roughly 60% of its wetlands and 65% of its canals over the past 30 years, paved over as construction spread.
Retention ponds that once held monsoon runoff have shrunk sharply in the areas where records exist. That is a loss of natural capacity to absorb water, separate from anything happening in the pipes.
The piped network is its own weak point. A Daily Star investigation found that Dhaka's main drainage authority maintains roughly 370 kilometres of storm drainage pipe, covering only about a fifth of the city's 400 square kilometre area, with seven different agencies each looking after their own section and little coordination between them.
So even where canals are intact, the underground system meant to feed them is often undersized, aging, or simply absent.
Chittagong has, or used to have, a hilly terrain and sits next to a coastline, a perfect combination for compound flooding where bidirectional flow coming from the sea and the land overwhelms the natural and built drainage infrastructure.
Chittagong has also historically seen heavier monsoon rain because of its proximity to the sea. When a hillside is cut for construction, it destroys a delicate hydrologic balance. As in Dhaka, loss of natural drainage to land grabbing compounds the strain on what remains of the natural drainage pattern.
According to a 2023 Daily Star report, the city's own drainage authority now counts 56 canals where 72 once existed, and green space has fallen below 15% of the city's land. Underground drainage fares no better. A recent engineering study found that large parts of the city have no properly connected underground network at all, which means canal restoration alone will not solve the problem even where it succeeds.
Underneath both cities' specific drivers of waterlogging sits a simpler failure that needs no special geography to operate: Neglect.
Drains and canals that are not regularly cleared silt up regardless of how well they were designed, and clearing them depends on maintenance schedules and budgets that routinely lose out to flashier priorities.
An ordinary afternoon shower is often enough to expose a canal that has not been desilted in years, or a drain choked with waste that residents and businesses put there themselves.
This pattern is not confined to Dhaka and Chittagong, or even to Bangladesh.
Wetlands, floodplains, and canal margins disappear first precisely because they look empty between storms. Each time this happens, in any city following the same sequence, the next flood has less capacity to work with than the one before it.
Plans that stop keeping up
Dhaka's current drainage plan, drafted by WASA in 2015, assumed 40% of rainfall would soak naturally into the ground, and its pumping stations were sized to match. That was a reasonable estimate at the time, according to an urban planner quoted in a July 2026 Daily Star report.
As concrete replaced open soil across the city in the years since, actual infiltration fell well below that number, and the plan was never revised. The same report notes that the city's pumps can now handle only about 40% of the current load.
Chittagong's plan is older and carries a different kind of stale assumption. Its Storm Water Drainage and Flood Control Master Plan was drafted between 1993 and 1995. One specific flaw stands out: According to a paper in the Journal of Bangladesh Institute of Planners, drain widths were fixed at 2 to 3 feet regardless of whether the road above them was 20 feet or 60 feet wide, so as development scaled up around them, the drains never did.
Hill cutting, meanwhile, is banned under a separate national law, the Environment Conservation Act of 1995, but enforcement has been too weak to stop it.
Spending has not been the constraint
Chittagong's experience argues against the idea that money is the missing piece. According to a recent statement from the finance minister, four major flood-mitigation projects have been running for close to a decade, with roughly Tk 14,400 crore allocated and about Tk 10,400 crore of it already spent.
A separate Daily Star report found that the largest single project, covering 36 canals, has seen its cost rise from about Tk 5,600 crore to roughly Tk 8,600 crore, with its deadline pushed from 2020 to 2026. Over that same period, according to the same report, the city has lost 47 of its original 104 canals to encroachment and sedimentation.
Money spent building fixed infrastructure to an unrevised design, without enforcement, coordination, or updated assumptions behind it, buys less every year the city keeps changing. A bigger budget applied to the same static approach does not fix that problem. It just makes it more expensive.
What this argues for
None of this argues against having a master plan. It argues against treating one as a document written once and left alone for 20 years.
A better version is a living plan: Built and updated at the scale of individual drainage basins, with lessons from each basin carried into the next. In practice, that means:
Jasim Imran is Professor in the Department of Civil and Environmental Engineering at the University of South Carolina. The opinions expressed here are the author's own. Figures cited in this piece were drawn from publicly available sources.