A GIS-based decision support system for rainwater harvesting (RHADESS)

Rainwater harvesting (RWH) is an unconventional water source that is increasingly adopted in South Africa. Its implementation is promoted by non-governmental organisations and government programmes to alleviate temporal and spatial water scarcity for domestic, crop and livestock production and support the overall water resources management. Unreliable water supply is one of the elements central to the poverty level of rural population. As the potential of RWH to improve water access for drinking and other basic human needs is still untapped, the technique will spread further in the coming decades. Studies on the hydrological impacts of RWH are focused on plot scale and very little is known about its impacts at catchment scale. To integrate RWH into the development and management of water resources in South Africa, there is a need to develop tools and methodologies that not only assist planners with the identification of areas suitable but also quantify the associated hydrological impacts of its wide scale adoption. aper presents the rainwater harvesting decision support system (RHADESS) that was built to assist decision makers and stakeholders by indicating the suitability of RWH in any selected part of South Africa and quantifying the potential impacts associated with its adoption at catchment scale. RHADESS is GIS-based and uses ArcView 3.3 as a platform to assess the RWH suitability of any given area of South Africa. Results are thereafter exported into an Excel spreadsheet that contains the hydrological impact, as runoff reduction, of different levels of adoption of RWH assessed by using the Pitman model. The decision support system guides the implementation of the following RWH categories: Infield RWH and ex-field RWH and domestic RWH. RHADESS was tested in two selected quaternary catchments C52A and V13D located in the Upper Orange water management area and the Thukela water management area, respectively.