A major civil engineering project aims to reshape the management of stormwater close to Cape Town’s northern coastline, protecting residential neighbourhoods and sensitive wetlands in the area.

The multi-year project to upgrade the Bayside Canal in Cape Town’s Blaauwberg area demands large quantities of rock and other materials, and contractor CSV Construction is partnering with AfriSam as its main supplier.

The canal is a single stormwater outlet for a broad catchment that includes Tableview, West Beach, Parklands and Sunningdale. Increased development and years of reed encroachment downstream have placed significant pressure on the existing infrastructure.

“This upgrade really broadens the system’s hydraulic capacity,” explains CSV Construction contracts manager Alex Pospech. “This is critical for preserving the Rietvlei reserve - an important recreational and wildlife resource - while also reducing flood risk in an area that sits very low.”

Pospech explains that an important feature of the project is its balance between engineering and ecological considerations. Stormwater entering Rietvlei currently filters through dense reed beds that naturally trap solids and absorb nutrients. The expanded system must honour this natural treatment function, but on a more controlled and higher-capacity basis.

The redesigned outfall therefore includes two primary sedimentation ponds, each about 140 m long, to allow heavier particles to settle. Downstream, a 460 m secondary treatment canal slows the water further so that finer sediments can separate out.

“These structures give us a controlled way to manage sediment loads before the water reaches the reeds,” Pospech notes. “It is a more resilient version of what the wetland has been doing on its own.”

After passing through these treatment stages, the flow spills over a weir and into a reed-lined section for nutrient absorption and final polishing. To handle high volume storm events, CSV is also constructing a nearly 600 m bypass channel along the R27 road, ensuring major surges can be diverted safely.

The engineering design requires unusually large rock sizes and consistent material availability and AfriSam territory sales manager Ian Trimmel explains that the supply chain has needed careful planning.

To meet the high demand for gabion stone, AfriSam set up a dedicated production plant, shifting from the traditional method of hand-selecting stones to an industrial-scale process tailored for this project.                                                    

Work on upgrading the canal will continue into 2027, as most work can only be conducted during the dry summer seasons. Once completed, about 45 000 m³ of material - much of it reed-choked sludge - will have been removed using long-reach excavators and articulated dump trucks. The cleared footprint is being stabilised with 12 000 m³ of dump rock, followed by about 20 000 m³ of overburden and nearly 15 000 t of gabion stone baskets lining key sections of the canal.