Vaal River Swells Third Sluice Dam Gate Opens
The Vaal Dam’s third sluice gate has been reopened amid high inflows due to the continued heavy rainfall in the upper catchment.
The department warned that the controlled and uncontrolled water releases at all these dams will lead to overtopping of riverbanks downstream of the Orange and the Vaal Rivers, resulting in flooding of settlements that are in the lower-lying areas within the 1 in 100-year floodline.
The third sluice gate was reopened on Wednesday at 4pm to manage water outflows at the dam, which operated with two sluice gates since last week, 16 April 2025.
The Department of Water and Sanitation said the opening of the third sluice gate will increase the outflow from 299.59 cubic metres per second (m3/s) to an estimated 400 m3/s.
“The current water inflow is estimated at 943 m3/s and the water level at the dam is at 108.4% as of midday [Wednesday]. There is a possibility that another sluice gate will be opened tomorrow [Thursday] should the inflows continue to increase,” the department said in a statement.
The department has also increased water outflows at Bloemhof Dam, from 500 m3/s to 650 m3/s at 10am, and to 800 m3/s at 12pm on Wednesday, in anticipation of the measured incoming flows upstream.
“People living within the floodline downstream of the Vaal and Bloemhof Dams and have had to evacuate should continue to avoid the flooded areas as the river catchment remains oversaturated.”
The adjustments were necessary to manage the continuous rising inflows and safe operation of the dam, which was at 106.71%.
As of Wednesday afternoon, the inflows into the dam were estimated at 640 m3/s, and the department said the inflows were likely to increase over the next 24 hours, with potential plans to further increase releases on Thursday morning.
“All the sluice gates remain closed at Grootdraai Dam, and the storage capacity is still at 104.92%, with inflows of 32.44 m³/s. The controlled water releases at both the dams have led to overtopping of riverbanks downstream, resulting in flooding that has affected settlements that are in the lower-lying areas within the 1 in 100-year floodline.
With more rainfall predicted in the Upper Vaal Catchment, the department said it will continue to monitor inflow water levels in the Integrated Vaal River System (IVRS), to ensure that necessary precautions are in place in line with dam safety standards and hydrological monitoring systems to safeguard infrastructure and attenuate any flood conditions.
Sluice gates are opened for controlled water releases when dams breach the full capacity mark, to prevent the water resource infrastructure from failing as it may lead to a dam bursting and causing a disaster of unimaginable magnitude.
“The department implements these necessary controlled water releases at the dams as part of dam safety precautions to safeguard the infrastructure and protect human life.”