Engineering News and Mining Weekly
Cape Town bulk sewer upgrades making headway
The City of Cape Town started work on the Milnerton and Cape Flats bulk sewer upgrades earlier this year and is on track to complete both by 2025, says City of Cape Town Water and Sanitation MMC Councillor Zahid Badroodien.
The Milnerton project entails the construction of a new bulk sewer in Montague Gardens using innovative micro-tunnelling technology. The City will also extend and connect the Edgemead and Century City bulk sewers into the new infrastructure.
The upgrade includes the installation of a sandtrap and screening facility at the Koeberg Road pumpstation. This is set to improve performance and reduce breakdowns caused by foreign objects entering the pumpstation.
The City completed a condition assessment for the project in 2019 that confirmed the need to start planning the upgrade of the bulk sewer.
“The current Milnerton Bulk Project comes as a result of planning, as well as the fast deterioration of the existing system, which further confirms that it was the correct starting point,” explains Badroodien.
Meanwhile, planning for the Cape Flats Project began in 2015, with the first phase involving the construction of the Cape Flats 3 bulk sewer.
On completion, the next phase will comprise the current Cape Flats 1 and 2 bulk sewer upgrades, which will accommodate some of the flow, thereby making it possible to access the system safely. “Both systems will ensure that new developments in their catchment can proceed and benefit from the growth of the city and associated economy,” Badroodien assures.
Pipe replacement is part of the City’s strategy to decrease sewer spills over time, which includes major bulk sewer upgrades, the proactive cleaning of sewer lines, the resourcing of sewer spill response teams and digital telemetry systems for early warnings on sewer spills.
Based on preliminary data, these interventions have led to a 30% downward trend in reported spills in Cape Town over the past two years.
Over the next three years, the city will invest R1.4-billion in major bulk sewer upgrades to the Cape Flats, Philippi, Milnerton and Gordon’s Bay lines, in the Western Cape.
Hence, Cape Town is ramping up infrastructure investment, with a 223% increase in its water and sanitation infrastructure budget – from R2.3-billion in 2022/23 to R7.8-billion in 2025/26.
New Technology
Spirally wound pipeline technology has been employed for the Cape Flats Project. This trenchless technology is applied through the existing manholes, whereby a continuous liner is formed inside the manhole as it is introduced into the pipe.
This technology has ensured minimal disruption to residents and roads, and is also cost-saving, compared with open-trench conventional construction.
The Milnerton bulk sewer will be constructed using tunnelling equipment, except where open trench or geotechnical conditions are specified or restrict the use of equipment.
Badroodien notes that tunnelling has limited impact on the surface level; therefore, daily activities are not affected.
Moreover, the installed pipe has a highdensity polyurethane lining, which is inert to sewer gas corrosion and provides for a more than 100-year serviceable life.
During the upgrades, the City of Cape Town faced several challenges, including extortion on both sites, which resulted in delays and damage to contractors' equipment.
Material imports for the Cape Flats bulk sewer upgrades were delayed, owing to the Russia-Ukraine war and harbour limitations in South Africa, while hard-rock excavations in Milnerton delayed the anticipated progress.
Despite challenges, the first three work packages were completed at the end of last month, with Badroodien describing this as “the first milestone for the current financial year”.
The remaining work packages are being prepared, with start dates expected in February 2024.
Considering the works are still in the first year and that delays have been properly handled, the contractor has achieved the programmed works up to the percentage progress required.
“The City is working hard to give effect to its Water Strategy to ensure sufficient and highquality drinking water into the future, as well as a reliable wastewater service, thereby ensuring a dignified service to citizens and a healthy environment,” Badroodien concludes.