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Water Reconciliation Strategy Study for the Large Bulk Water Supply Systems: Greater Bloemfontein Area 19 5. WATER BALANCE 5.1 The Orange River System The Upper Orange WMA is a component of the extended Orange and Vaal River System. This has been the subject of various water balance and reconciliation studies. The latest water balance from the Orange River system indicated a surplus of 333 million m³/a for the year 2000. This surplus yield reduced to 158 million m³/a in 2003 when Mohale Dam was commissioned, due to the fact that more water could be transferred out of the system to the Upper Vaal WMA. Although the Mohale Dam increased the local yield in the Upper Orange, the increase in yield is transferred to the Upper Vaal WMA and cannot be used in the Upper or Lower Orange WMAs. The effect of Mohale Dam can be seen in that the surplus yield is reduced from 333 million m³/a to 158 million m³/a. When the effect of the 12 000 ha earmarked for resource poor farmers is taken into account, the surplus of 158 million m³/a will reduce further to only 44 million m³/a. This surplus is reserved for the growth in demands in the urban, industrial, and mining sectors in the Upper Orange WMA, the Lower Orange, and the Fish to Tsitsikamma WMAs. The future Polihali Dam site is situated on the Senqu River approximately 1.5 km downstream of the confluence of the Senqu and Khubelu Rivers. Polihali Dam would increase the water delivered from Lesotho Highlands Water Project to the high value industries in the Vaal catchment, but would, in the long term, result in a reduction in the water available at downstream Gariep and Vanderkloof dams. It is envisaged that the Polihali Dam would reduce the yield of the Orange River downstream by approximately 283 million m 3 . This is based on the assumption that overall yield of the system increases by 182 million m 3 /a but an additional 465 million m 3 /a might be transferred to Gauteng, causing a shortfall of 283 million m 3 /a (465 – 182 = 283). Table 5.1 shows a mass water balance of the Upper Orange WMA. Table 5.1: Orange River Water Balance Surplus Yield (million m 3 ) Year 2000 Surplus Yield 333 Less Transfer to Gauteng from Mohale Dam (impact on Orange River) -175 Net available yield 158 Less Allocation for Resource Poor Farmers -114 Net current available yield for growth in urban water requirements 44 Less growth in urban, industrial, and mining sectors in the Upper Orange WMA, the Lower Orange, and the Fish to Tsitsikamma WMAs (NWRS 2025 base case) -90 Net deficit in Yield in 2025 -46 Less Transfer to Gauteng from Polihali Dam (impact on Orange River in 2053) -283 Anticipated net deficit in 2053 (will be higher with additional growth in urban water requirements) -329 The Upper Orange WMA has a large commitment to support the local water requirements and transfers to the Upper Vaal WMA, the Fish to Tsitsikamma WMA, as well as release obligations to the Lower Orange WMA. A number of augmentation interventions have been identified to provide additional yield to the Orange River System to make up the envisaged shortfall caused by transfers from Polihali Dam to the Gauteng area. Some of the interventions identified include: using the lower level storage in Vanderkloof Dam; the construction of Bosberg/Boskraai Dams; and the raising of Gariep Dam. Interventions Report June 2012
Water Reconciliation Strategy Study for the Large Bulk Water Supply Systems: Greater Bloemfontein Area 20 It is the intention of the DWA to initiate a separate reconciliation strategy study on the Orange River System, which will draw on the information from the Greater Bloemfontein Reconciliation Strategy Study. 5.2 The Greater Bloemfontein Area The anticipated surplus yield in the Orange River System (including the Caledon River) is approximately 44 million m³/a. According to the Internal Strategic Perspective for the Upper Orange River WMA, this surplus is reserved for the growth in demands in the urban, industrial, and mining sectors in the Upper Orange WMA, the Lower Orange, and the Fish to Tsitsikamma WMAs. It is not anticipated that there will be any further growth in agricultural water requirements in the Greater Bloemfontein Area (with the exception of the allocation made to the resource poor farmers). As the agricultural sector and urban sector in the Greater Bloemfontein Area and surrounds do not share any yield from a common surface water resource, it is possible to undertake a reconciliation of supply and requirement based on the current urban water requirements and available yield of the surface water schemes serving the Greater Bloemfontein area and surrounds. Figure 5.1 illustrates the comparison of available surface water supply and current water requirements for the High and Low water requirement scenarios in the Greater Bloemfontein Area. The current water requirement (based on 2009 data) is approximately 83 million m 3 /a while the available supply is 84 million m 3 /a (Historical Firm Yield). High Growth Scenario (3%) Figure 5.1: Surface Water Balance for Study Area Low Growth Scenario (1% p.a.) It appears that the 2009 water requirement was in balance with available supply (historical firm yield) and any increase in use (as predicted by the high and low water requirement scenarios) would put the system at risk. The higher the growth in water requirements, the higher the risk would be. It is clear that measures to increase the surety of supply need to be implemented as soon as possible. This includes measures to increase the supply of water as well as WC/WDM measures to reduce the demand. Interventions Report June 2012
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