The viability of rainwater and stormwater harvesting in the residential areas of the Liesbeek River Catchment, Cape Town
The sustainable provision of water to South African citizens is a significant challenge facing the country. In order to avert a crisis, municipalities will need to reduce their reliance on traditional water sources. Rainwater harvesting (RWH) and stormwater harvesting (SWH) are two alternative water resources that could supplement traditional urban water supplies. To date, the potential benefits of RWH and SWH within an urban setting have not been adequately considered or investigated in South Africa. The only way to quantify the benefits and potential viability of rainwater and stormwater harvesting was to select and model a representative catchment - the Liesbeek River Catchment, Cape Town South Africa was selected. An Urban Rainwater Stormwater Harvesting Model was developed to model the use of RWH and SWH in the catchment. Additionally, a Storm Water Management Model (SWMM) of the catchment was developed to investigate the stormwater management benefits of RWH and SWH. The study found, inter alia, that: RWH was viable for only a minority of property owners; climate change would have limited impact on the performance of RWH systems; and RWH is an unreliable - even for small storm events - means of attenuating peak flows. On the other hand, SWH has the potential to reduce potable water demand in the Liesbeek River Catchment by up to 20%. However, for SWH to be viable there would need to be a high level of adoption by residents, at least for non-potable uses such as flushing toilets and outdoor irrigation. SWH is also of benefit in the attenuation of peak flows during storm events. Finally, the research found that the implementation RWH and SWH together would be unwise, as both are most cost-effective under conditions of maximum demand. The study concluded that SWH could be a viable alternative water resource for urban residential areas in South Africa - depending on the scale at which it is implemented, the end use for which it is utilised, and the population density that drives the water demand. RHW, on the other hand, has limited potential - depending on climatic conditions; it may, for example, be viable in areas with year-round rainfall.
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