Protecting Dhaka from rain-induced floods

Dhaka has been experiencing heavy downpours over the past few days and in consequence that have left the megacity city non-functional. But why should a heavy downpour be able to completely inundate a modern city and disrupt entire city life altogether? What has happened to its drainage system? Since the experience of life coming to a halt after every heavy rain for a longer period is nothing out of the ordinary in this city, it may sound quite silly to ask such a question in the first place. One would say, as nothing has been done over the decades to stop senseless encroachments of some 50 to 65 canals that that the city was once proud of and which carried their waste and rain waters into the four rivers surrounding the city, there is no point any more asking such a silly question. But how long can we allow this senseless urbanization that has been systematically destroying the sole lifeline of the city's survival? The 'River and Delta Research Centre' says that over the years, some 120km of those canals have been lost to encroachment while some have been used as dumpsites. In a similar fashion, the wetlands, a large number of them, have been lost. Whatever is left is also being sacrificed at the altar of development day in day out. So, it is not really news when we hear that Dhaka is relegated to the 171st out of 173 cities of the world in order of their Liveability Indices on the Economic Intelligence Unit (EIU)'s scale with a score of 42 out of 100. In fact, we are just above war-ravaged Tripoli and Damascus! Worse yet, Dhaka's infrastructure fared worst as one of the lowest-scoring one among its peers. Are we surprised?
Not, really. But, ideally, Dhaka being the capital of a country that straddles the tropic of cancer and experiences a classic tropical monsoon climate characterized by high temperatures, significant humidity, and heavy seasonal rainfall, it should have been like other such tropical cities, say, Singapore. In that case, it should ideally have all the modern technological solutions in place to drain out all the water even after a heavy downpour. Consider that Singapore, which operates a highly advanced stormwater management system. The city features large scale drainage enhancements like the Deep Tunnel Sewerage System and massive underground reservoirs. So, waterlogging after a heavy rain is unknown in that city, as the excess water is routed to collection ponds.
Dhaka's urban environment comes to a standstill during heavy rain as the city's drainage infrastructure is overwhelmed by flash floods. Apart from the loss of natural water bodies and wetlands, widespread solid waste clogging the drainage networks, and a lack of coordination among the city's management agencies are to blame for Dhaka's present misfortune.
Today, concrete surfaces cover over (approx 80 per cent) of the city, forcing rainwater directly onto the streets.
The existing storm-water drainage network is fundamentally inadequate, with many drains only capable of managing about 20 mm to 40 mm of rainfall. Furthermore, these small-capacity drains are often blocked by indiscriminately dumped solid waste, plastic, and silt. Water is unable to flow freely to the surrounding rivers, causing immediate inundation on the roads.
The natural discharge paths of the city, as noted in the foregoing, have been blocked by by illegally built concrete structures. Furthermore, a lack of cohesive coordination between various responsible agencies (like the city corporations and the Dhaka Water Supply and Sewerage Authority - DWASA) often stalls routine maintenance and long-term drainage upgrades. But Dhaka, if it is to be liveable, must transition from its makeshift cleanups to an integrated water management strategy. This involves enforcing the Detailed Area Plan to protect the remaining flood-flow zones, actively reclaim encroached canals (as much as possible), deploy portable pumps at key spots and strictly enforce waste-management regulations. And, last but not least, transfer the city's stormwater drainage responsibilities from DWASA to some dedicated drainage departments under the city corporations.

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