AN INVESTIGATION OF THE TREATMENT EFFICACY OF PERMEABLE PAVEMENTS
WITH A VIEW TO HARVESTING STORMWATER FOR USE IN SOUTH AFRICA
Dr Kirsty Carden, Mr Benjamin Biggs & Prof Neil Armitage
INTRODUCTION
South Africa is a water scarce country and the sustainable provision of water to its citizens is becoming an increasing challenge. The demand on
the potable water supply system could potentially be alleviated by substituting it for stormwater in a ‘fit-for-purpose’ manner. Sustainable
Drainage System (SuDS) technologies set out to mitigate the adverse effects of urban stormwater runoff such as increased flood peaks and
poor water quality through a multi-objective approach that includes the reduction of flood peaks, the retention of water for future use and the
improvement of water quality. Permeable pavement systems (PPS) are one of the most widely-adopted SuDS technologies in South Africa.
EXAMPLE IMAGE
Experimental bins
Typical PPS cross-section
Permeable
pavement
systems
Sustainable
drainage
systems
(SuDS)
Stormwater
harvesting
Treatment
efficacy
Fit-forpurpose use
Multiobjective
approaches
Pavement designs with varying base layers
Typical PPS installation
• WRC Project K5/2409 was aimed at providing locally-relevant data on the treatment efficacy
of PPS for possible use in stormwater collection, treatment and storage. A laboratory
experiment comprising four separate units was set up to determine the capability of various
different PPS to reduce selected pollutants.
• Permeable concrete block pavers were laid over four different layer-work options – one in
each unit – using aggregate largely collected from stockpiles used to construct a nearby PPS
in a parking area at UCT.
• In the first phase, clean tap water was applied to each unit over a period of time in
quantities roughly representative of a typical rainy season in Cape Town and the discharge
collected and analysed. The parameters measured were: Orthophosphate, Ammonia,
Suspended solids, Temperature, pH and Electrical Conductivity.
• The results showed that failure to adhere to accepted international practice with respect to
the washing of the aggregate prior to construction – and the prevention of the ingress of dirt
into the pavement layers during construction – have an adverse impact on the treatment
performance of PPS. Further phases will examine water quality of effluent from PPS under
more favourable conditions.
ACKNOWLEDGEMENTS
The Future Water Committee would like to thank and
acknowledge the following sponsors: