Karachi's storm water drains are covered by "too many encroachments", Chairman of the National Disaster Management Authority, Lt Gen Muhammad Afzal, said on Sunday.
At a press conference in Islamabad, he said that this is compounded by the fact that the sewerage systems are dysfunctional.
He said that on a daily basis, as much as 20,000 tonnes of solid waste is generated in Karachi and has become a bane for the city, whereas in other countries solid waste is utilised for producing electricity.
The widths of most of the nullahs have been narrowed from 400 metres to three to four metres, the NDMA chairman said.
Lt Gen Afzal said that beginning tomorrow (Monday), Frontier Works Organisation will conduct a large-scale operation to clear the drains.
Additionally, local corps of Pakistan Army has also been tasked to provide relief to the people from flash floods.
Prime Minister Imran Khan had, earlier in the week, directed Pakistan Army and the NDMA to assist the local administration in relieving the city of its urban flooding problem.
The NDMA chief expressed regret over the vast damages caused to the city's infrastructure by the recent spells of rain.
He said that he held three meetings with Chief Minister Sindh Murad Ali Shah and the Corps Commander also held meetings with Shah.
Discussions with Governor Sindh Imran Ismail and Mayor Karachi Waseem Akhtar also took place.
He warned that the next wet spell will start from August 7 and last till August 10. Another 1-2 day spell is expected on August 15, however the chances of rain then are 40%.
Furthermore, there is a 60-65% chance for rain from August 24 to 26.
Lt Gen Afzal said efforts have begun to formulate a long-term solution for flash flooding in the city by taking on board all stake holders including federal, provincial, local governments, etc.
"Urgent efforts are being made to minimise the damage in the upcoming spell," he added.