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    • Introduction Raw water in South Africa is considered

    2018-11-05

    Introduction Raw water in South Africa is considered a strategic national resource, with the responsibility for its management taking place at three tiers. These are firstly Central Government, secondly Provincial and Regional Governments, including other specified authorities, and thirdly Local Authorities. The way in which the value of water resources is perceived should reflect both societal values, ethics and the specific characteristics of this BMI1 inhibitor complex resource. The ecological integrity, which gives a water resource its resilience, is an essential component of the value of the resource. South Africa manages its water resources using the 22 primary hydrological basins (Fig. 1). The numbers in Fig. 1 show the basins in South Africa. Administratively and economically, the raw water resource is managed as 19 water management areas (Fig. 2). Water management areas (WMAs) and the hydrological basins boundaries do not coincide in many places (Fig. 3). It is important to note that the aforementioned administrative WMA system is unique to South Africa and that the country has a complex water transfer organisational structure and schemes. These support commercial and industrial growth in line with the new Constitution (Act No. 108 1996) and the new Water Act (Act No. 36 of 1998). For South Africa as a developing country that is in transition, the need for economic development is urgent and many people depend on natural resources and agriculture to sustain their livelihoods. The necessity of assessing major implications of dams is needed, given the complexity of water resources systems (Wurbs, 1993). Oliveira and Loucks (1997) stated that defining effective operating rules for a particular water supply system is a challenging decision, especially those that apply to multiple reservoirs, which serve multiple purposes and objectives. While pointing out that, optimisation models are playing a very important but still very minor role in identifying possible real-time reservoir operating rules. More research towards robust models is necessary. In river basin studies, reservoir systems have their unique aspects and a variety of mechanisms are used in defining their operating rules. Most of the water resources optimisation problems involve conflicting objectives (Chang and Chang, 2001). Reservoirs can increase the reliability of water supplies in promoting livelihoods, raising agricultural productivity, and reducing the farmers\' vulnerability to droughts. The frequency and intensity of extreme hydrological events varies highly in South Africa (Ndiritu, 2003), which obviously restricts the effective use of water and causes insufficient water supply. To overcome the problem of insufficient water supply during periods of low flow, attention has been focused on improving water resources management, especially in optimisation of reservoir operations (Chang and Chang, 2001; Chen and Chang, 2007). The majority of research in water resources is devoted to developing ways to meet human water demands, while the explicit inclusion of environmental flow targets has received less attention. Lately, engineers often face criticisms regarding water resources management due to the lack of careful assessments of environmental impacts caused by reservoir operations. In an attempt to minimise these negative impacts, the related environmental aspects must be taken into account in the management of water storage facilities (Gibbins et al., 2001; McCartney et al., 2005; Bauer and Olsson, 2008). In the last decades, the minimum environmental flow target gained the attention of scientists, engineers, and managers (Stalnaker and Arnette, 1976; Tennant, 1976; Pusey, 1998; Adeyemo and Otieno, 2009). The target was designed to maintain the minimum stream flows for sustaining aquatic ecosystem. It provided a single value that could be easily implemented as another objective to be optimised in water management programs. The implementation of a single flow, however, was found to eliminate the flow variability sustaining healthy and diverse aquatic communities. Lately, there has been a great deal of effort devoted to estimating environmental flow requirements and to the identification of the need for maintaining ecological flows to protect freshwater biodiversity (Richter et al., 1996; Poff et al., 1997; Poff et al., 2003). The importance of mimicking components of the natural flow regime as targets for managing flow magnitude, frequency, and timing variables is now better understood (Richter et al., 1996; Poff et al., 2003). The flow regime, however, contains too many variables, which makes it very difficult to implement in water resources management. Moreover, translating general hydrologic-ecological principles and knowledge into specific management rules for particular river basins and reaches has remained a daunting challenge.