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ENVIRONMENTAL ARTICLE

URBAN RIVERINE Photo by Carol Knoll

RENATURALISATION

Chris Brooker of CBA Specialist Engineers operates in
conjunction with other professionals providing expertise
in surface water management, largely in the urban
environment. Three such projects completed over the
last six years have involved riverine renaturalisation: two
for the City of Johannesburg and two phases of stream
rehabilitation for Fourways Gardens residential estate.

Environmental journalist Carol Knoll interviewed Brooker
on behalf of Landscape SA, and he made the general
comment that urban rivers have largely been treated as
stormwater drains with little attempt to incorporate them
into the urban fabric, both from a social and ecological
perspective. A professional team with the necessary
skills can attempt to correct this through a process of
renaturalisation, as illustrated by the Fourways Stream in
the aforementioned residential estate, the Jukskei River
in Bruma (Lake) Park and the stream running through
Paterson Park.
BY CAROL KNOLL

All photos by Chris Brooker,
unless otherwise stated

rban rivers and streams should be maintenance.
seen as recreational opportunities Boulders in a renaturalised channel need
Uand renaturalised to return plant and to be placed for stability, whereas in a
animal life to areas of urban open space, pristine river, boulders will roll with the
helping to create ecological awareness water. Engineering expertise is required
amongst city dwellers. Creating a near to understand flow regimes: the nature
natural river profile will return functions of stresses that occur on the streambed
such as varied water flow to create and along the banks under different flood
different habitats, erosion control, flood conditions. Reeds, rushes, sedges and
control through absorbent capacities and veldgrasses will tolerate high flooding
filtration of pollutants. if they are rooted firmly. Although such
riparian vegetation will tolerate quite
Brooker points out that the dynamics of high velocities, it will only do so for short
a ‘natural’ river, such as its meanderings periods.
through a floodplain, cannot be managed
in an urban environment and the system Brooker explains that the size of the
needs to be engineered. The urban river boulders to be used in the riverbed should
cannot be allowed to change as it would in be determined by the friction of the
a natural area but has to be a stable course. flowing water. It is possible to calculate Renaturalisation of Fourways Stream
He adds that movement of sediment the size of the boulders needed to create in Fourways Gardens after placement
down a renaturalised river is expected, stability dependent on the variation of of boulders and planting of rushes,
as illustrated by the development of textures (surfaces) along the riverbed. sedges, etc, in 2013. NLA Landscape
sandbanks at Bruma. Some of these will Architects worked with CBA on the
become vegetated and stable while others It is also necessary to consider habitat design while landscape contractor
may remain mobile. Any sandbanks that diversity: the whole range of river life,
cause an increase in flood levels would such as pockets of topsoil worked into Earthforce constructed the renewed
have to be removed as part of normal gaps for planting of marginal species, riverbed and banks.

26 Landscape SA • Issue 91 2019