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PROJECT

Stones were packed around the ponds, concealing the plastic liners and
creating a more natural look and feel to the water elements

THESEN ISLAND POND

REHABILITATION

Thesen Island’s five ornamental ponds have been rehabilitated following the

severe droughts of 2016 and 2017, when rainfall plummeted to a mere 370 mm
per annum. Although this has improved over the years (with 2020 having closed at
634 mm), water was still being lost through seepage.

he original ponds were built in the the HDPE and this ‘blanket’ helped to
core contaminated zone of the island Project Team bind the soil, enabling plants to grow and
Tand were not sealed to specification. Client: Barloworld in association protecting the waterproof liner from UV
As the water was not permanent, an with the Thesen Island HOA light.
unsuitable marsh-type situation resulted. Participants: Barloworld Pond 4, with extensive reed beds near
For the rehabilitation work, the client Environmental Consultants, the bird hide, was the final pond completed.
requested TurfWorx to create a natural, Department of Environment, Work on it commenced in June 2021 and
bird friendly water system, not deeper Forestry and Fisheries, Knysna was completed in August 2021.
than 500mm, that would blend into the Municipality, SANParks, Pledge
natural look and feel of Thesen Island. This Nature Reserve, Lakes Bird Club Pond enhancement
had to be done without disturbing the (affiliated to Birdlife SA) The appearance of the ponds has been
sealed off contaminated zone. Landscape Contractor: TurfWorx enhanced by plant material which had
Due to the contaminated soils, it to harvested and propagated on site, as
was imperative that the contaminant most species were not available in local
be contained, with no disturbance. nurseries. Because of the plastic liner, all
Frequent soil samples were taken by the water plants had to be potted and placed in
environmental consultants to ensure that the water. The landscaping was required to
2
the subsoil was not disturbed. The overall pond areas are now 2300 m , be indigenous and bird-friendly. To soften
reduced from the previous size of 3000m . 2 the edges of the exposed plastic, large
Technical aspects Levels required particular attention as stones were packed all the way around the
Work involved the re-sealing and TurfWorx needed to create a natural flow ponds.
landscaping of the existing ponds to fit into between the three major ponds. The drop A stand of black wattles in the reed beds
the island’s environmental plan without between ponds 1 and 2 was 300mm and is presently a nesting site for Black-headed
disturbing the site’s sensitive base. The between ponds 3 and 2, it was only 150mm. Herons and Sacred Ibises; the wattles have
old material and sludge were removed The first process involved laying down been ring-barked and will be removed once
to a maximum depth of 500mm and the metre-wide strips of corrugated plastic to the breeding season is over. Other birds
ponds were lined with a waterproof layer enable the venting of any gaseous ground that have returned include Egyptian Geese,
to prevent ground seepage. In addition, release. The second layer was a 1mm Blacksmith Lapwings, Grey Herons, a Pied
they were made smaller and shallower to thick HDPE (high density polyethylene) Kingfisher and a pair of Water Thick-Knees.
limit water volume as well as evaporation. watertight layer. Bidim cloth was laid over Crabs and frogs have also been sighted.

Landscape SA • Issue 120 2022 9