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Explainer: Flooding of Karachi’s Super Highway near Saadi Town

Lath River flows obstructed by N. Bypass development

SAMAA | - Posted: Aug 11, 2019 | Last Updated: 2 years ago
Posted: Aug 11, 2019 | Last Updated: 2 years ago

The 2016 map shows how the water is obstructed by housing societies at the Northern Bypass.

Karachi’s Super Highway has done the all-important work of connecting the city to the rest of the country since it was commissioned in the early seventies. This is the artery that steadily pumps our exports and imports to Pakistan.

It was built by an Italian company called Salini Impregilo. Initially, it was a single road with two lanes. In 1996, two other lanes were laid so traffic could run two-way. In 2018, the motorway was completed by expanding it to six rows with a separating barrier.

During the construction of the original highway, the planners were careful to factor in hill torrents that ran down the Kirthar Range to cross the road when it rained. Detailed surveys were carried out and waterways were properly siphoned to make way for flooding.

For the last eight to nine years, however, something strange has been happening. When it rains heavily, the hill torrent called Lath River, which originates in Kirthar National Park, inundates the Super Highway at the Northern Bypass interchange near Saadi Town.

The 2016 map shows how the water is obstructed by housing societies at the Northern Bypass.

The raging waters flood the road completely, making it impossible for traffic to pass. It also spreads all through Saadi Town, threatening the lives and properties of its people. The local grid station is flooded and power supplies are cut off. Some people believe that the government has built dams in the mountains, which breach or overflow and cause this flash-flooding.

Fortunately, Google Earth gives us historical images and so you can easily check and compare satellite maps from 1984 to 2016. The maps also come with land surface elevation from the sea and all this helps diagnose this phenomenon.

If you look at satellite images in this case then, you see that the so-called broken dams are not water storage but are actually
retention weirs. Weirs are structures that delay the flow of torrents of water down hills in order to recharge groundwater aquifers. (See diagram). Without them, the flood waters will still run down, just with more speed.

Groundwater dams obstruct the flow of groundwater and store water below ground level and replenish the wells. There are different types of ground water dams also called retention weirs. Image: Freie Universitat Berlin

If you surf the area in Google, the puzzle of the Super Highway flooding can easily be solved. The 1984 imagery shows that the Lath River used to flow down its natural route, which went just beside the Cosy Water Park crossing at the Northern Bypass, behind Gulshan-e-Hadeed and Dream World Resort. It ultimately reaches a catchment of the Lyari River, crossing Arzi Brohi Goth. The Northern Bypass, was proposed in the Karachi Master Plan, 1975–1985 and commissioned in 2004.

The latest map on Google Earth is from 2016. It becomes quite evident that from the surface you see that the construction of the Northern Bypass obstructed the original path of the Lath River. This was followed by the decision to lease lands for residential schemes. There are hundreds of housing schemes on both sides of the bypass. A majority of them have the prefix of Gulshan, some the suffix of lake city and some with scheme numerics. It seems that nobody bothered to undertake topographic or hydraulic contour mapping before giving away permission for housing in this area. 

All these developments obstructed the original flow the Lath River, which now takes a straight route and inundates the Super Highway. A solution seems to be difficult, but it can still be done. In the Global North they have large storm drains to speedily evacuation flood water. The Lath dam scenario needs a proper on-ground survey. The old route of the hill torrent can still be connected to Lyari. We may need to plan and design a large storm water drain on the original river course, with protective dykes. This will not only protect the residents of the Northern Bypass, but will also protect commuters on the Super Highway as well as Saadi Town. The crux of the problem is that when we go about expanding our cities and developing infrastructure, we should make them human friendly as well as disaster resilient.

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karachi, rain, explainer, saadi town, karachi rain, lath dam, lath river, northern bypass, lyari

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