Decision support system for sustainable rainwater harvesting in South Africa

Abstract

To reconcile its scarce water resources with the ever increasing demand for fresh water, the South African government continues to explore and investigate various demand management and water supply options such as: effluent reuse, interbasin water transfers, rainwater harvesting (RWH), water conservation as well as sea water desalinisation. RWH is an old but underutilised technology that can play a key role in the improvement of rural livelihoods, thus the need to investigate the potential it holds for South Africa. This thesis presents the Rainwater HArvesting Decision Support System (RHADESS) that was developed to facilitate the integration of three streamlined categories of RWH in the management and development of the country’s water resources at the quaternary catchment scale (± 500 km2). Using biophysical and socioeconomic datasets, RHADESS assesses the RWH footprint of any given area of South Africa. Although physical factors are important parameters in the assessment of the RWH suitability of a given area the non‐consideration of ecological and socioeconomic parameters lead to inappropriate targeting of RWH. Once the footprint is determined, the ecohydrological impact of RWH as reduction in river flow can be established. Despite the increasing adoption of RWH, very little is known about its potential ecohydrological impact. This thesis contributes to understanding these impacts for different levels of adoption of RWH at the quaternary catchment scale. Finally, RHADESS sizes the RWH tank per quaternary catchment, assesses its water security and calculates the area of land needed for a household to achieve food security when RWH is implemented. The decision support system was tested in two quaternary catchments which have contrasting rainfall regimes, the semi‐arid C52A and the humid V13D.