Karachi Metropolitan Corporation has started work to expand Gujjar Nullah. It is one of three rainwater channels widened to ensure smooth flow of rainwater.
The Sindh government decided to eliminate encroachment around the waterways following the urban floods in August 2020 in the city.
They have commissioned NED University’s Department of Infrastructure Engineering and Urban Development to provide a permanent technical solution to this problem. The NED University team decided to expand Mehmoodabad, Gujjar and Orangi nullah first.
Gujjar Nullah’s recommendation and technical study was submitted to the Sindh government on 31 December 2020. The 12.58 km drain starts from New Karachi near Noorani Muhallah and ends in Liaquatabad near Haji Mureed Goth.
“As per the final plan, around 4,000 houses will be affected on both sides of Gujjar Nullah,” said Dr Adnan Qadir, chairman of the NED’s Department of Infrastructure and Urban Development.
The NED team has completed the survey report together with the hydrological and drain hydraulics analysis.
Hydrological analysis is the study of the transformation of rainfall into runoff, while hydraulic analysis studies the movement of liquids in relation to fluid mechanics and fluid dynamics.
The plan is to expand the Gujjar Nullah to between 35 feet and 120 feet. “We have recommended a width of 35 feet at the zero point and 120 feet at the tipping point,” said Dr Qadir.
The current drain width varies from 15 feet to 87 feet. Average 33 feet.
Channel depth is not an issue, according to NED experts. It will increase another 3 to 4 feet after clearing the drain.
The NED’s Department of Infrastructure Engineering is working on two designs during the technical study of the channel. The designs are Liberal Model and Conservative Model.
The Liberal model allows the drains to withstand up to 270 mm of rain for 12 hours. This means that 270mm of rain will not affect the city in this duration.
The duration was reduced to three hours in the case of the Conservative Model. This means that the waterways will overflow three hours after the rain reaches 270 mm.
The Sindh government chose the Liberal Model in the case of Gujjar Nullah, said Dr Qadir. The NED team has also proposed a 30-foot walk on either side of the sewer to connect with the Lyari Expressway.
KMC has marked houses around Gujjar Nullah for demolition, said KMC Senior Director Katchi Abadi Mazhar Khan. The process will be completed on January 31.
The demolition of these homes and buildings will begin February 3, according to Khan. Soft encroachment will be removed first.
KMC Senior Anti-encroachment Director Bashir Siddiqui said the demolition work around Mehmoodabad Nullah would be completed on Monday. The KMC anti-encroachment team will then proceed to Gujjar Nullah, he added.
There are 41 main rainwater channels in Karachi. Of them, three were selected for technical solutions. The first is Mehmoodabad Nullah. KMC began demolishing buildings along the channel from 4 January. More than 200 houses had to be destroyed in the operation. Gujjar Nullah is the second channel to be expanded.
Orangi Nullah is the third. More than 2,000 homes will be affected in operations around the sewer.