Vaal Dam levels drop by 15 percentage points in two months, but ‘not a significant concern’ yet

The Vaal Dam’s water level has plummeted by 15.5 percentage points over just 11 weeks, with an expert weighing in on what the future may hold for the dam.

Forming an essential part of the Integrated Vaal River System (IVRS), the Vaal was at 30.8% of its full storage capacity (FSC) of 2.5 billion cubic metres, last week.

The Department of Water and Sanitation’s comparison report noted that this was down from 31.5% the previous week, and 71.8% last year.

The dam stood at 46.3% on 4 September.

Water expert Carin Bosman explained that while the decrease is substantial, it falls within expected parameters.

“The Vaal Dam falls by around 1-2% percentage points per week if there is no good rain in its upstream catchment, due to evaporation and regular consumption. The drop of 15.5 percentage points over 11 weeks is within the expected margins,” said Bosman.

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Vaal Dam year-on-year comparison and seasonal patterns

The current decline appears more dramatic when compared to the same period last year when the dam level decreased by 13.9%, falling from 85.7% to 71.8% between September and November 2023.

According to Bosman, the rainy season in the upper reaches of the Vaal Dam catchment typically runs from October to early April, peaking in December and January.

“This year, the rainy season started a bit later, around 14 October, and we have not had many big showers yet, but we also have not yet entered the peak of the rainy season,” she noted.

She said she would not consider the drop in levels to be a cause for “significant concern” at this stage, and “from a water security perspective, the backup system we have in the Sterkfontein Dam will cover any potential shortfalls.

“If the levels reach 18%, water from the Sterkfontein Dam will be transferred to the Vaal Dam system,” Bosman explained.

She said at the current rate of decline, the dam level could fall to 18% by the end of March.

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Vaal Dam water December rainfall warning

While the current situation isn’t cause for immediate concern, Bosman has warned it could become dire if rain is further delayed.

“If the low rainfall patterns continue through December, we are in for a rough ride, and for this reason, we need to tighten our belts and make sure that we do everything we can to save water and to fix leaking pipes and washers in our taps.”

Bosman said municipalities must implement responsive leak reporting systems and address identified leaks within 24 hours.

ALSO READ: Vaal Dam level continues to drop: Here’s what it and other reserves below 50% stood at this week

Citizens have been urged to adopt water-saving practices, including taking shorter showers and fixing leaking taps and toilets.

Climate change

Bosman said climate change played a significant role in the region’s changing rainfall patterns.

Data shows that Johannesburg’s mean precipitation declined from 821mm in 1981 to 626mm in 2023, representing a decrease of almost 180mm in annual precipitation.

The area experienced a dramatic shift from 958mm in 2022 – the second-highest rainfall in 25 years – to just 626mm in 2023.

ALSO READ: Water crisis: Gauteng residents told to take 3 min showers and not water gardens until 8pm

Long-term outlook

Looking to the future, Bosman advocated for a fundamental shift in water management.

“We have to start talking about and implementing alternative sanitation solutions that are not water-based,” she stated.

Bosman said water-borne sanitation is not only a colonial legacy but also environmentally problematic, causing damage to river systems through eutrophication and disrupting the natural nitrate cycle.

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