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Q&A with Arif Hasan: Why does Karachi flood when it rains?

Explains nullah network, donor agency mistakes

SAMAA | - Posted: Aug 22, 2020 | Last Updated: 6 months ago
Posted: Aug 22, 2020 | Last Updated: 6 months ago

Rain is predicted till Sunday for Karachi, many parts of which are still struggling with the last showers. We spoke to a town planner, architect, and historian Arif Hasan on why the city keeps flooding. 

When it rains, the water naturally ends up in the city’s thousands of little nullahs. These little nullahs feed into 64 big nullahs or natural stormwater channels. And they, in turn, reach the Malir and Lyari rivers which take all the water to the sea. “There is a whole network that comes together and finally it falls into the sea,” Arif Hasan said. “This is all-natural.”

Read more: Rain lashes Karachi for the second consecutive day

The problem is that over time, these tiny, tiny nullahs have disappeared as the city has grown. And the engineering of new works is flawed. “When a road is made, its tender includes drainage,” Hasan explained. “The problem is that the drainage goes nowhere.” It’s built by the roadside, but where the road ends, the drainage ends and is not connected to the bigger network. He gave the example of Shaheed-e-Millat Road.

This is why your roads are converted into nullahs. This is why the city’s roads flood. The water has no other place to go reach the sea.

If you cover up these small or big nullahs, you upset the natural system. In many cases, people have covered up the tiny nullahs with construction.

Usually, when you build a house, say on a five-acre plot, the first thing you do is see where natural water flows for it. And usually, there is a very definite slope to a particular place from where the water goes. The first thing you do is secure that nullah and ensure that you do not build on it. You can also redirect the nullah so that its exit point is undisturbed; the water should not be blocked. “This is normal planning practice and it has not been followed in this city,” he said. “It is the job of the architect planner to see that on their site it is followed and it is the job of the Sindh Building Control Authority.”

Karachi’s exponential growth means that much of these systems have been destroyed.

Related: Karachi witnesses heavy rain with lightning and thunder

After the Karachi Development Authority was formed and in 1958 big housing schemes were started in Gen. Ayub’s era, the drainage and sewage systems were kept separate. These were formal housing schemes (as opposed to katchi abadis) but a big informal sector started to develop. They needed sewage as well and the only place they could send it was Karachi’s natural rain nullahs. So the “slums” started diverting their sewage into these streams because the government did not provide them the infrastructure.

Then, slowly and gradually, even KDA housing schemes began to adopt this method of dumping sewage in stormwater nullahs. They were forced to do this because no drainage system had been developed as separate from a sewage system. “And I think that we can say that 1975-76 is the date when the city’s new neighbourhoods, schemes, flats had no place to put their sewage other than the rain nullahs,” added Arif Hasan. “We did not have trunk sewers that would take that sewage to a treatment plant.”

And so after that, Karachi’s sewage was put in its stormwater drains in a planned fashion. The sewage sludge started to clog up the drains supposed to carry off rainwater. When it rained, the sludge would be washed out but if it didn’t rain for years that sludge would solidify in the nullahs and it could not be cleaned out.

“After this, there was a grand plan with the World Bank in the 1980s, I think,” said Hasan, “and the Asian Development Bank plans that ran into the 1990s.” As far as he remembers, the World Bank project was to reorganise and improve the capacity of the Karachi Water and Sewage Board. 

The ADB had a sewage plan for Karachi and put in trunk sewers by the roadsides. A new treatment plant was successfully added and completed. “But the problem was that the sewage never reached that treatment plant,” said Hasan. “This happened because the trunk sewers stayed empty. No one thought of designing the trunk sewers so that they pick up the sewage from the natural rainwater streams.”

As a result, the sewage kept flowing in the natural drainage system, rainwater nullahs, and the trunk sewers stayed empty. The Asian Development Bank has even mentioned this failure in its reports and accepted it. “This was a great loss for the Government of Pakistan and especially the Sindh government,” said Hasan.

An ADB report said that an estimated 89% of households in Karachi have a flush toilet connected either to the sewerage system or a septic tank. “But the sewerage network suffers from poor connectivity and a large number of undersized and broken sections,” it said.

Watch: Karachi’s Naya Nazimabad still submerged 14 hours after rain

“As a result, most of the wastewater is discharged to the stormwater drainage network and only about 25% of sewage generated finds its way to one of the three functioning sewage treatment plants – which operate at just over 50 percent of their design capacity.”

The Sindh government, NDMA and local authorities are trying to remove encroachments on drains, but in the long run, they will have to be kept clean constantly. This is a mammoth task and will require constant flows of money. This problem is connected to the garbage disposal. When people throw their garbage or solid waste in nullahs, they are also contributing to the problem. The Sindh government will also have to ensure that the Sindh Building Control Authority is strengthened to prevent encroachments from covering up the drainage in the first place as well.

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  1. Ahmed  August 23, 2020 2:44 pm/ Reply

    This is a good time to create public awareness that your houses & streets are flooded because you have thrown the garbage in your nearby nallahs & on roads.
    The nallahs have overflowed because we Karachi ites have filled up the nallahs. If you compare yourselves with the cleanliness of NEW YORK or London or Paris then behave like them re garbage.
    Yes government needs to do much better. But all they do will be of temporary benefit if we dont change the way we manage our garbage.

  2. Nadeem  August 24, 2020 9:56 am/ Reply

    I know many places where severage water is returning back on streets even without rain, this happens 24X7X12

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