ENVIRONMENTAL ENGINEERING
Kuils River corridor plan
UNLOCKS DEVELOPMENT
The upgrading of a 2 km long section of the Kuils River in Cape Town has transformed a dysfunctional watercourse into a vibrant ecosystem and serves as an excellent example of the execution of the city’s Liveable Urban Waterways Programme in practice.
New gabion drop structure
U
nder taken by Redefine Properties and VDMV Property Holdings, in collaboration with the City of Cape Town, the Kuils River upgrade project paved the way for the Stikland Industrial Precinct development, which is situated within the suburbs of Bellville and Brackenfell. But first a comprehensive River Corridor Plan needed to be developed. Periodic, aggressive clearing of invasive riverine vegetation had contributed to the destabilisation of the river channel, putting sections of the city’s water and sewerage infrastructure at risk. Over the years, adjacent properties had also encroached on the river, with illegal infilling of the floodplain. The subsequent degradation of the river channel resulted in frequent flooding. These and other factors posed a major stumbling block to the future development of the Stikland Industrial Precinct, as this affected section of the Kuils River traverses the precinct site. Therefore, it was in everyone’s interest to implement a sustainable and environmentally beneficial solution. The developers commissioned a multidisciplinary project team that included Zutari (previously Aurecon South Africa) to provide hydraulic engineering design consulting services, together with a freshwater ecologist, as well as environmental, civil and landscaping consultants. The River Corridor Plan was
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IMIESA February 2022
workshopped through several iterations with the relevant Stormwater, Parks, Environmental and Maintenance departments of the City of Cape Town, prior to being approved and adopted for implementation. The river corridor was initially 100 m wide; however, it was reduced in size to 50 m to allow for additional developable area, while also allowing sufficient space for river improvements.
Integrated elements Key features of the river upgrade include: • A 13 m wide, trapezoidal, riprap-lined, low-flow channel, which conveys the oneyear flow. The use of riprap allows for the establishment of aquatic plants and organisms within the river channel, improving biodiversity and water quality. • A 50 m wide, terraced, trapezoidal, grasslined floodplain, which contains the 100year flood. Various species of indigenous vegetation were also strategically positioned and planted on the floodplain. • Buried Reno-mattress erosion protection on the bends of the terraced floodplain, which prevents lateral movement of the river. • A 150 m long and 3.5 m high gabion retaining wall on the west bank to enable reclamation of the floodplain area. • A 50 m long, 1 m high gabion drop structure across the low-flow channel and floodplain,
which protects a concrete-encased sewer pipe crossing the river. The drop structure also serves to reduce the longitudinal grade of the channel and floodplain to keep flow velocities within the limits appropriate for the riprap and grass lining. The stilling basin downstream of the drop structure also functions as a silt trap. • A new road bridge over the low-flow channel and floodplain, conveying the 100-year flood without raising upstream flood levels. • 2.4 ha seasonal and permanently constructed wetlands to compensate for the loss of wetland habitat in the development area. The wetlands are designed to be fed by the river during occasional overtopping of a lowered riverbank in this area. They also serve as stormwater detention ponds and compensating flood storage facilities. • Swales on the floodplain for the treatment of stormwater run-off from the development site. All of the above, including the development of a stormwater management plan for the development site itself, were undertaken in compliance with the City’s Management of Urban Stormwater Impacts and Floodplain and River Corridor Management policies. The river upgrade was split into two contracts. The first entailed the river works, which were designed by Zutari and implemented by contractor Burger & Wallace. The second
