An analysis on optimizing the use of sustainable urban drainage systems to provide non-potable water supply in the Isipingo region.

Abstract

Population growth and urbanisation lead to increased water demand and stress on water resources. The increased demand implies an increased water treatment cost, utilities therefore charge higher tariffs consequently reducing consumer affordability and accessibility. Furthermore, many countries experience drought and intermittent water supply, low revenue collections and high operational costs. The National Water Act (Act 36, 1998) endeavours to find a balance between water conservation or demand management, water safety, affordability and accessibility. Potable water in many countries, including South Africa, is being used for non-potable purposes which is wasteful and threatens the exhaustion of potable water reserves. This research looks at sustainable urban drainage systems as a possible solution for providing an alternative water supply. The methodological approach involves setting up a PCSWMM model to investigate the optimal use of SUDS systems in the Isipingo region. Required data such as monthly water supply volume, GIS information for characteristics of the region, water supply pipe network was collected from eThekwini municipality data base. Weather data such as rainfall, temperature and humidity were collected from South African Weather Services. The current System input Volume (SIV) in Isipingo region was estimated as 11 780 000 Kilo Litres per year from logged data between July 2018 and July 2019. The water treatment costs required by the utility for Isipingo baseline volume is R5.33 /KL according to eThekwini municipality’s master plans. A water balance model was constructed to illustrate the existing scenario. Different SUDS controls were then added onto the existing scenario to analyse the SUDS impact on the water balance components such as the baseline supply volume, water treatment cost and non -potable water demand. Results show that the municipal water supply demand reduces by an average of 74% across the use of the different SUDS scenarios. The water treatment costs reduce from R62 787 400 per year to an average of R 25 057 409,59 which is the treatment cost saving due to the SUDS interventions. The challenges with SUDS include initial installation and maintenance costs, the lack of adequate utility planning and design standards. However, SUDS reduce the risk of flooding, water pollutants, stress on potable water supply and contributes to the tourism economic activity through pleasing aesthetics for recreational areas and job creation. Therefore, the use of SUDS in diverting storm water for alternative non-potable usage is a viable option.