Abstract
By 2030 South Africa (SA), a developing country, is predicted to be severely impacted by physical water scarcity. In order to avert a future water crisis, the country needs to find ways to reduce its reliance on conventional surface water schemes based on impoundments on rivers. Rainwater harvesting (RWH) is an alternative water resource. To date, the viability of domestic RWH within an urban setting has not been adequately considered in SA. The purpose of this study was thus to address this omission through the detailed modelling of a representative catchment. The Liesbeek River Catchment in Cape Town – comprising some 6 200 domestic properties in 6 suburbs covering an area of around 1 300 ha – was chosen for this purpose; and a new computational tool, the Urban Rainwater/Stormwater Harvesting model (URSHM), was developed to take best advantage of the available data. The analysis showed that: RWH was only economically viable for a minority of property owners; climate change is likely to have limited impact on the performance of RWH systems; and – contrary to some claims – RWH is an unreliable means of attenuating peak stormwater flows. Keywords : domestic rainwater harvesting, alternative water resources, developing country
Highlights
South Africa (SA) is a water-stressed, developing country facing a range of challenges with respect to water management, inter alia, resource shortages, environmental degradation, fragmented institutional structures and basic services backlogs (Kok and Collinson, 2006; DEA, 2010; Fisher-Jeffes et al, 2012; DWA, 2013)
It indicates that Scenario 1, where rainwater harvesting (RWH) is considered for filling pools, would only reduce the annual potable water demand by a maximum of 1.3% (28 ML/yr), while Scenario 2, which considers RWH for garden irrigation, would only reduce the annual water demand by up to 9.5% (200 ML/yr)
This is generally at the cost of a decreasing volumetric reliability depending on the end uses in question
Summary
South Africa (SA) is a water-stressed, developing country facing a range of challenges with respect to water management, inter alia, resource shortages, environmental degradation, fragmented institutional structures and basic services backlogs (Kok and Collinson, 2006; DEA, 2010; Fisher-Jeffes et al, 2012; DWA, 2013). This includes: total water demand met, volumetric reliability, total runoff, per cent of harvested runoff, and the cost per kilolitre (Neumann et al, 2011; Maheepala et al, 2013) Such an approach, assumes that, inter alia: every RWH system supplies much the same amount of water at much the same time; every RWH system has roughly the same size catchment area (roof area); and rainfall and evaporation are relatively constant in both time and space, etc. A total of 20 scenarios – essentially combinations of contributing roof area and end-uses (Table 2) – were analysed for the Liesbeek River Catchment using the available 10 years of rainfall data in order to assess the likely viability of RWH.
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