Six years ago, the Visserhoek landfill site in Cape Town was granted authorisation to extend its lifespan to provide an extra six to nine years of landfill capacity. This extension was granted provided the City of Cape Town develop a master plan for the closure and rehabilitation of the site once landfill operations ended.

Rehab conditions

One of the main conditions was to reduce the visual impact of the decommissioned landfill with landscaping and indigenous vegetation.

The City of Cape Town requested a study to determine the necessary requirements to help new plants thrive and to uncover which plant species would be best suited to survive on landfill slopes.

It is foreseen that the site will eventually become a wildlife habitat, due to its proximity to the Blaauwberg Conservation Area, says City of Cape Town spokesperson, Priya Reddy.

A test study was recently done to determine whether this particular rehabilitation process will be effective once the landfill reached maximum capacity.

Test methods undertaken to rehabilitate site

1. A portion of the currently active landfill zone was capped with a clay layer, a common process when decommissioning a landfill site.
2. An impermeable geotextile membrane preventing toxic liquids from seeping into groundwater was established to prevent contamination by waste in the landfill.
3. The area was divided into zones with different soil depths. The main area of interest was to determine whether increased soil depths would sustain a greater number of vegetation species, although many other valuable lessons were learnt.

Major challenge

One of the major rehabilitation challenges, especially in high wind zones, are the high levels of erosion that make it difficult for plants to start growing.

Higher grass content is said to mitigate against potential erosion as these plants are hardy and fast-growing and can also help to create the right conditions for other plants to establish themselves.

The species of grass commonly found in the Vissershok area, which are also endemic to a lowland thicket biome, were selected in order to blend the site into the surroundings as best as possible.

Project results

The project is currently being monitored and the outcomes are being recorded, however initial results confirmed expectations that the pioneer species (i.e. grass and other hardy vegetation) would establish first, and create a stabilised environment in which the slower growing plants could establish themselves. Encouragingly, within a year, some perennial plants will be rooted and tolerate the harsh conditions.

Other recommendations for eventual site rehabilitation:

• Only once the area is stable and there is certainty that the clay capping layer and membrane will not be compromised, should long-term rehabilitation be undertaken, otherwise plant species will die.
• Seeding must occur during the right season for the plant species to ensure successful germination.
• Windbreaks are recommended until vegetation can establish itself.
• Alien vegetation should be suppressed, with the use of fire as a first measure to stimulate endemic fynbos.

‘The lessons that have been learned through this experience will go a long way to ensuring that the site can be returned to nature, first as a wildlife habitat and eventually, once open to the public, to expand our conservation efforts and to enable future generations to enjoy our natural heritage,’ Alderman Ernest Sonnenberg, the City’s Mayoral Committee Member for Utility Services said.