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September 20, 2018

Why urban flooding is a perennial woe for Karachi


September 20, 2018

For Karachi’s residents, the monsoon season is a welcome respite from the ever-present heat of the port city. The cloudy skies, cooler days and breezy evenings signal the arrival of the impending elusive rain that stays clear of the city most of the year. However, during every monsoon, the possibility that a downpour could flood major arteries and localities and paralyse the city also looms large.

Just last year, heavy rains toward the tail end of August left most of the city at a standstill as major localities, including North Nazimabad, North Karachi, Malir and Saddar, were inundated. The water pressure caused a breach in the Thado Dam in Gadap Town causing the Super Highway and its adjacent areas to flood. Many had to wade through waist-high waters to get home, while drivers had to leave their stalled cars behind on the submerged roads.

Over the past few weeks, downpours in the northern parts of the country have caused massive urban flooding in Peshawar and Lahore, causing casualties and damage to infrastructure. Aside from a few drizzles, Karachi has so far been spared a major monsoon deluge.

[Not] going with the flow

Urban flooding occurs when continuous and heavy rainfall over a short duration overwhelms the city’s drainage capacity. There are a number of factors that make Karachi particularly prone to it, according to a study conducted by Karachi University’s Geography department and published in 2012.

These include heavy rainfall over a short duration, which saturates the soil and increases run-off water, constructions and settlements over riverbeds and on flood plains, and unplanned infrastructure growth. City planning experts add that encroachments on drains, the dumping of municipal waste and sewage in them, and the lack of open spaces and parklands also cause the city’s perennial flooding problem.

Although the city government initiates a campaign to clean drains every year ahead of the monsoon, the drive remains largely inefficient because the Karachi Metropolitan Corporation, which is just one of nearly a dozen agencies overseeing municipal affairs in the city, can only clear the drains that come under its jurisdiction.

According to KMC Senior Director Masood Alam, who oversaw this year’s cleaning drive, there are nearly 500 small, medium and large drains in Karachi. Several of these come under the limits of the District Municipal Corporations, various cantonments and development authorities and it is their responsibility to clear them before monsoon.

Speaking about KMC’s efforts, Alam said solid waste and sewage is constantly falling in all drains and there are 30-35 major choking points in them. “We are trying that the places where the garbage has solidified and can stop the flow of water are de-silted and cleared so that the drain’s water carrying capacity can be increased.” He added that they also removed encroachments from drains and widened them in places where they had narrowed.

Alam believed the city is well-prepared to handle any flooding situation if it occurs this year. He pointed out that the flooding depends on the rain’s intensity, duration and the tide, but he was hopeful that solutions designed based on the lessons learnt from previous years will be of great help.

Planning flaws

In the first few decades of Independence, Karachi had an efficient drainage system with scores of naturally-occurring nullahs carrying rainwater into the Lyari and Malir rivers which flow to the sea. However, with rapid growth and haphazard development, these nullahs became the receptacles of garbage and sewage in the absence of a planned sewerage network or a city master plan.

World over flood-risk zones are identified in cities based on the rainfall patterns and drainage channels’ capacity and propensity to overflow. But in Karachi there has no such extensive planning on this, said Farhan Anwar of Sustainable Initiatives.

Anwar is an urban planner and architect with more than 25 years of experience in environmental consulting.

The last major investment made to prevent flooding in the city was the construction of the Malir River embankment which was done after the river overflowed in July 1977 during record rains and the Malir and Korangi industrial areas were inundated.

“Since then, there haven’t been any physical structures made for flood control nor investments made in the drainage system,” said Anwar.

Aside from the low-lying localities like PECHS and downtown areas of Saddar that regularly flood in monsoon rains, underpasses have emerged to be another significant flood zones since they are designed and constructed without keeping drainage in mind, he said.

By the government’s own estimates, some 40 to 60 per cent of solid municipal waste ends up in our drains and so does a lot of sewage, he said.

Weak and inefficient urban infrastructure designs that don’t account for local topography and climate are also a reason why Karachi floods so often, explained Fariha Amjad Ubaid, associate professor at NED University’s Department of Architecture and Planning.

She explained that because of the prevalence of continuous paved surfaces – from sidewalks and roads to lawns in people’s residences – when it rains the water instead of being absorbed by the soil runs off to the drains which are already choked with garbage and sewage.

Moreover, the intermediary drains leading to big nullahs which are themselves far in between also full of garbage or encroached upon, leaving no path for any accumulated water to head to the nullahs.

“All the talk is of rivers and drains, but no one talks about the intermediary channels like Neher-e-Khayyam, which drains into Boat Basin,” she said. “No one is looking into the system in the middle.”

To combat urban flooding you need to clear the channels – the river, the drains and the then the intermediary channels, she said.

Ubaid said leaving open spaces in footpaths for water to be absorbed and being mindful of rainwater drainage needs when designing infrastructure projects would also help in reducing urban flooding.

KMC’s Masood Alam said there is also the need for a complete city master plan for drainage, in the absence of which flooding will remain a persistent problem.

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