The water & sanitation department has urged Gauteng water users to actively cut back their water use as dam levels in the integrated Vaal River system (IVRS) dip below their levels of a year ago.
The 14 dams in the IVRS provide water to households and industries in Gauteng, including the economically critical Eskom and Sasol, which rely heavily on the system. The average dam level is at 69.7%, from 73.2% at the same time in 2018.
The system is also under strain from sewage pollution downstream of failing municipal treatment plant. This poses a risk to communities using untreated water directly from the rivers in the system, and to farmers watering stock and irrigating directly from the Vaal River.
Department spokesperson Sputnik Ratau said soaring temperatures in Gauteng are directly linked to abnormally high demand for water. Recent temperature recordings and forecasts by the SA Weather Service show highs consistently more than 30°C over the IVRS catchment area.
This condition is being made worse by higher evaporation rates as a result of the hot weather and by relatively lower rainfall over the catchment. The Vaal Dam, the biggest in the system and the main source to households and industry, is relatively shallow, allowing for a high evaporation rate. This rate is 10 times higher than Lesotho’s Mohale Dam, the upper-most dam in the IVRS.
However, the much deeper if smaller Mohale Dam’s level is at 18.2%, from 21.4% in 2018, and that of the Katse Dam, the next highest in the system and also in Lesotho, is at 40.8%, from 39.2% in 2018, according to the department’s figures.
This is considerably lower than the Vaal Dam’s 75.2% and indicates a greater threat to water security than the levels of the dams lower in the IVRS, according to water-management experts. Best practice is to maintain higher levels in upper dams and lower levels in lower dams to minimise evaporation losses and optimise flood control, they say.
Demand management, however, is not necessarily the ideal way of dealing with supply constraints. Water politics expert Anthony Turton said on Thursday that while demand management was a necessary part of the water-management toolbox, if applied overzealously it would destroy business confidence. To resort to demand management as the primary solution for supply constraints was predicated on water being a stock, which it was not, he said.
“Water must be viewed as being in flux and thus infinitely renewable.”
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