Abstract
Stormwater Harvesting (SWH) to alleviate water scarcity is often hindered by the lack of suitable available storage in urban areas. This research aimed to discover an economically viable strategy of storing runoff in existing stormwater ponds with the assistance of rudimentary Real Time Control (RTC) techniques to increase the effective storage capacity. The Diep River sub-catchment situated in the southern suburbs of Cape Town, South Africa, that has several stormwater ponds that were largely constructed for the purposes of flood mitigation, was used as a case study. Six SWH scenarios utilising three distinct RTC strategies coupled with two alternative water demand alternatives were simulated with the aid of 10 years’ of historical rainfall data with a view to determining the unit cost of supplying selected developments with non-potable water. The use of RTC to increase the effective storage of the ponds was shown to improve the volumetric yield without significantly impairing the flood mitigation provided by the system at a cost that was comparable to what the local residents were already paying for potable water. This finding is important as it suggests a cost-effective way of overcoming one of the greatest limitations associated with stormwater harvesting.
Highlights
South Africa is facing increasing concerns over the security of its water resources as population growth—overwhelmingly concentrated in urban areas—has pushed water demand to the limits of sustainability with the existing, surface-water based systems [1,2,3]
As a water-scarce country, South Africa is looking at augmenting its traditional water supplies with alternative water resources
This study demonstrated that it is possible to secure considerable additional storage capacity within an existing stormwater pond system through the use of rudimentary Real Time Control (RTC) techniques without significantly impairing the existing ponds ability to mitigate downstream flood risks
Summary
South Africa is facing increasing concerns over the security of its water resources as population growth—overwhelmingly concentrated in urban areas—has pushed water demand to the limits of sustainability with the existing, surface-water based systems [1,2,3]. Since stormwater flows are intermittent, SWH systems require facilities that can store large enough volumes of the collected runoff to ensure that they can deliver a reasonably reliable water supply during dry periods [5,6]. Stormwater ponds were constructed to attenuate the stormwater flows associated with large storm events (e.g., 1 in 10 years or larger) by providing temporary storage for runoff [7,8]. Since events of this magnitude seldom occur, they commonly have unutilised storage potential [9,10]
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