Civil Engineering June 2021 | Vol 29 No 5

Civil Engineering June 2021 11 assessment of potential sites and, in doing so, building up the database of the coun- try’s water infrastructure. TYPES OF HYDROPOWER The different hydropower types, as depicted in Figure 1, are summarised in Table 1. It should be noted that there are other locations (desalination plants, dam release and the mining sector) that can have potential for hydropower generation or energy recovery that do not form part of the initial development of the SAHA. Despite being a water-scarce country, South Africa has numerous river sys- tems, more than 4 500 dams, thousands of weirs, irrigation networks consisting of more than 6 500 km of canals, hun- dreds of water and wastewater treatment works, and thousands of kilometres of water supply and distribution networks with numerous pressure reducing locations, with many of these being untapped resources. EVALUATION FRAMEWORK DEVELOPMENT FOR THE SAHA The evaluation of hydropower potential requires the available head and flow to be known, with the exception of hydrokinetic hydropower where the velocity in the river or channel is the primary driving factor. The limited available data on some of the country’s water infrastructure and rivers provides a major challenge to the evalua- tion of hydropower potential and uptake of hydropower in South Africa. Generic methods to assess the poten- tial available within South African water infrastructure and rivers have been devel- oped for all hydropower types (as listed in Table 1) with the aim of assisting in the quantification of hydropower potential at sites or locations where data limitations pose a challenge. The development of these generic methods allows the assess- ment of more sites, which will in turn in- crease the number of potential sites to be included in the SAHA. A summary of the methodology for developing such generic assessment methods is provided below. Q Q Identification of available data sources from which parameters necessary for hydropower evaluation can be esti- mated. These data sources include the Department of Water and Sanitation (DWS) database, municipal asset reg- isters, digital elevation models, Green Drop reports, etc. The quantified Table 1 Hydropower types included in the SAHA (Bekker et al., 2020)) Hydropower type Description Storage schemes The available pressure or water level and the discharge from the dam can be used to generate hydropower. This hydropower type is often referred to as conventional hydropower. Retrofitting small hydropower schemes onto large dams can reduce the environmental impact that is normally associated with large hydropower dams. Run-of-river schemes Hydropower is generated from these types of schemes through the diversion of either all or a portion of the flow from the river combined with the head difference between the inlet to the diversion structure and the turbine unit(s). Pumped storage schemes Hydropower at these types of schemes is generated by pumping water to an upper dam (during off-peak periods) and releasing the water under gravity conditions to generate electricity. Water treatments works (WTW) Hydropower can be generated at a WTW if the water source for the WTW is located at a higher elevation than the plant. The available head combined with the flow into the WTW provides the opportunity to generate electricity. Wastewater treatment works (WWTW) The opportunity for energy recovery exists at the outflows from the WWTW into the natural river system, given that there is an available head between the WWTW outlet and the river system. Water supply and distibution systems The opportunity for energy recovery exists at the pressure reducing valve (PRV), where excess pressure being dissipated by the PRV can in turn be utilised for energy generation through the installation of a turbine. Irrigation canals and rivers Hydrokinetic installations in rivers and canals are referred to as zero head installations, as energy is generated from kinetic energy in the flowing water. Weirs Hydropower opportunities exist at weirs, where the potential for hydropower exists in the water level difference created by weirs.