Vaal Dam level surges: Over 5 percentage point increase in 24 hours

The Vaal Dam has experienced a dramatic increase in water levels, rising by 5.82 percentage points in just 24 hours to reach 46.15% capacity on Tuesday, according to the latest data from the Department of Water and Sanitation (DWS).

This marks a significant improvement from earlier this month when the dam sat at just 24.3% before authorities opened two sluice gates at the Grootdraai Dam to release water into the Vaal system. Additionally, rain in the catchment areas has contributed to improvements in the dam’s level.

Rapid rise in Vaal Dam levels

The pace of filling has accelerated considerably since, with data showing the dam level stood at 30.36% on Saturday, January 11, before climbing to 40.33% on Monday.

A 20.65 percentage points increase in just seven days has added more than a fifth of the dam’s total capacity in about a week.

The most recent measurements indicate an inflow of 1093.9m³/s and an outflow of 16.8m³/s, slightly lower than Monday’s inflow of 1268.4m³/s with the same outflow rate.

At the Vaal Barrage, water levels have also increased marginally from 7.4m to 7.6m between Monday and Tuesday, with outflow increasing from 111.3m³/s to 157.0m³/s.

Water temperature has remained relatively stable, rising slightly from 22.2°C to 23.0°C.

Vaal Dam historical outlook and trends

Data shows the Vaal Dam’s water levels fell sharply during 2024, from 70% in January to just 25% by December.

However, in January 2025, there was a sudden increase in water flowing into the dam.

This inflow surge has helped raise the dam’s levels quickly, even while the amount of water being released has stayed steady.

Understanding the Vaal Dam’s decline

The DWS explained last year’s decline.

“The Vaal Dam had been declining by 1.5 weekly until around mid-December. This is primarily due to climatic factors including low inflows owing to lack of rainfall in the Vaal catchment and elevated temperatures (heat waves) which have led to increased evaporation losses.”

The department also highlighted the dam’s structural vulnerability.

“The Vaal Dam is one of the 3 largest dams in the country and its surface area is wide and shallow and is therefore susceptible to high evaporation losses.”

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Grootdraai Dam management

Meanwhile, upstream at the Grootdraai Dam, authorities are carefully managing water releases as the facility operates above capacity.

Information from the department and other sources revealed that as of 14 January, the dam level was recorded at 27.21 meters, equivalent to 103.56% capacity, despite no rainfall in the area over the previous 24 hours.

Two gates are currently open at the Grootdraai Dam, with one at 3 meters and another at 2 meters.

Officials have planned adjustments, with the 2-meter gate scheduled to be increased to 2.5 meters, which will bring the total outflow to approximately 418m³/s.

The Blesbok River, which was previously a concern, has shown a marked decrease in flow from 662m³/s to 40m³/s.

However, the Bloukop River continues to contribute significantly, maintaining an inflow of 448m³/s into the Grootdraai Dam.

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Future outlook

If the current net inflow into the Vaal Dam is maintained, calculations suggest it could reach full capacity by the end of the month.

However, water expert Carin Bosman warns against overly optimistic predictions about the dam’s recovery.

“Nobody can predict whether the Vaal Dam will be full at the end of January. It depends on both the inflows, which in turn depends on the amount of rain that we receive and the run-off that reaches the river upstream from the Vaal Dam and the levels of consumption,” she told The Citizen.

Meanwhile, the DWS noted that “the current filling of Vaal Dam during the rainy season, is not unusual”.

The department added that the current inflow was slightly less than it would have been had the Lesotho Highlands Water Project Tunnel not been closed for ongoing maintenance until the end of March.

Authorities continue to monitor the situation closely, particularly in areas downstream of the dams.

While a Joint Operations Committee (JOC) meeting may not be necessary at this stage, officials emphasise that this decision depends on inflow patterns.

Residents in affected areas are advised to stay informed about changes in dam operations, particularly those living downstream of the facilities.

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