Drains in DHA unable to handle storm water, SHC told

The existing storm water drains in DHA are unable to handle rainwater in addition to sewage flow and domestic waste, significantly reducing their design capacity, technical experts informed the Sindh High Court (SHC) on Thursday.

Filing a report on the DHA drains’ situation vetted by NED engineers, the experts said that extreme flooding in 2020 and this year in Karachi in general and in DHA in particular are recent examples of flooding due to a lack of planning and maintenance of the drainage system of a cosmopolitan city.

The report stated that existing road profiles and cross slopes do not support free overland water flow so that it can concentrate and drain into an interceptor drain, while the 2007 sewerage water drain plan, which was the sewerage master plan for DHA to ensure no sewage entered the existing drainage system, was not implemented.

The report also stated that after the August 12 rainfall event, perforations in major drains are clogged with sewer, trash and sediment, and so the drains require maintenance and rehabilitation.

The report further stated that some drains are used as combined sewer and rain drains, which goes against the purpose for which they are designed. The experts said storm water drains are meant to handle only rainwater, so they will likely overflow when they are already handling sewage flow at 50 per cent of their capacity.

The report said that the outfalls of the drains are in a poor hydraulic condition, and that the entire system is in need of rehabilitation and maintenance. In the light of the NED experts’ evaluation, the current storm water drainage network designed by the private evaluator violates the international criteria and guidelines, and the 10-year design return period selected must be at least 50 years.

The experts opined that the existing and proposed design may be inadequate if the storm water drainage system is also handling sewage flow in addition to storm water. They said that it is very important that in future sewage is drained separately to get the maximum benefit of the existing and proposed system.

They suggested that DHA use at least a 50-year return period rainfall intensity for redesigning the storm water drainage system that is also supported by the international design criteria and guidelines.

They said that the major drains that are clogged due to sewage flow, solid waste, etc. require cleaning and maintenance to ensure safe drainage of storm water in future. They also said that Part IV of the 2007 sewerage water drain plan must be implemented by the authorities.

After taking the report on record, an SHC division bench headed by Justice Syed Hasan Azhar Rizvi directed the counsel to examine it and file replies, if any, on the next date of hearing. DHA and Clifton residents had filed a petition seeking an effective infrastructure for the sewerage and drainage system in the area, and compensation for the damages to the lives and properties suffered by the residents during the monsoon rains of 2020.

A counsel for the petitioners also sought the details of the existing drainage infrastructure maps as well as the requisite support and assistance for such purpose. The petitioners — Azar Kalwar, and other DHA and Clifton residents — had maintained in their plea that at least 41 people were killed across Karachi due to the rains on August 27 and 28, 2020.

They said that the city’s people, including DHA and Clifton residents, had to suffer losses worth millions of rupees due to catastrophic flooding after the rains. Their counsels had informed the SHC during previous hearings that heavy rains had wreaked havoc on the city, and the authorities responsible for handling the situation had failed to perform their duties.

They said that there was a complete failure on the part of the Karachi Metropolitan Corporation, the cantonment boards, the Karachi Water & Sewerage Board, the Sindh Solid Waste Management Board, DHA and the Karachi Development Authority.

They pointed out that those authorities had been receiving millions of rupees in taxes under different heads but they had been spending nothing on the drainage infrastructure of the city.

The SHC was told that there should be a complete audit of the amount being received by those civic bodies because nothing was being spent on the maintenance of the sewerage infrastructure.

The petitioners sought the forming of a committee to conduct a comprehensive evaluation in respect of the drainage infrastructure, and directions for the DHA and cantonment boards to take all necessary steps to construct efficient storm water drainage systems in their respective jurisdictions.

The DHA had also filed a contingency plan based on the observations during the heavy rains of August 2020 to deal with any emergency that might arise due to future downpours.