At the time, 1,832m³ of water poured into the dam every second, the equivalent of nearly 110 Olympic-sized swimming pools every minute.
To prevent structural failure, the Department of Water and Sanitation (DWS) opened sluice gates on the Vaal Dam wall, releasing water downstream into the Vaal River at 1,881m³/s.
While this response is in line with the dam’s flood management design, which allows it to hold up to 126% temporarily, it set off a chain reaction: overtopping riverbanks, flooding homes and businesses downstream, and raising questions about how prepared authorities are for the new normal of more frequent, intense rainfall.
“People living within the floodline downstream of the Vaal and Bloemhof dams […] should continue to avoid flooded areas,” the DWS warned. “The river catchments remain oversaturated.”
Managing the Vaal Dam’s capacity
The Vaal Dam and River are not just isolated water bodies but part of the complex Integrated Vaal River System, crucial for water security in South Africa, supporting millions of people and a significant portion of the national economy
Constructed in 1938 to ensure a reliable water supply, the Vaal Dam has undergone enhancements, including the addition of a controlled spillway in the 1950s. Its full supply level is designated as 100%, but the dam can temporarily accommodate approximately 26% additional water above this level, up to 126% capacity, utilising its flood storage zone during periods of heavy rainfall.
Recent heavy rains in the Upper Vaal Catchment last week pushed the dam toward this flood storage zone, requiring controlled water releases to protect the dam and downstream communities.
While these releases are high, they fall within the dam’s flood management design. The dam’s buffer is used to reduce flooding risks downstream.
For context, during the record 1996 flood, the dam managed inflows up to 4,800m³/s – more than double this year’s peak. At that time, the dam was nearly full, leaving little flood buffer and increasing danger. In February 2023, the dam reached 115% capacity, with 12 sluice gates opened to control outflow.
Mike Muller, adjunct professor at Wits University and former director-general of the Department of Water Affairs, cautioned that during prolonged or intense rainfall, especially when upstream catchments are already saturated, releases must be planned so that this flood attenuation space can be overwhelmed.
Read more: Full dams don’t mean water security — Gauteng can’t afford to be complacent
“In such cases, releases must be made to protect the dam’s structural integrity,” says Muller.
These controlled releases can still result in downstream riverbanks overtopping, putting nearby communities at risk if they are within the flood lines.
Impact on communities – Vaal Dam
The DWS warned that controlled releases from the Vaal Dam have caused riverbanks to overtop downstream along the Vaal and Orange rivers, flooding settlements within the one-in-100-year floodline, damaging homes and infrastructure, and forcing some residents to evacuate.
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Permanent residents who live along the Vaal Dam say recent floods are worse than anything they’ve experienced in decades.
“Normally, this time of year, the water is 40 metres from our house,” said one couple, who’ve lived near the Vaal Dam for over 20 years and asked not to be named.
They tried to stop the water with sandbags and towels, but it reached their sliding door. Their house was built according to municipally approved plans to withstand up to the 125% flood line.
“This level of flooding is meant to be a once-in-100-year event. But in recent years, it feels like it’s happening almost annually.”
Kathy Manten, who runs Manten Marina in Deneysville, said her business has been shut for over a month.
“We still need to pay salaries and taxes, but we’re totally unable to work,” Manten said. “After the first flood, DWS dropped the dam to 107%, but the next big rainfall pushed it to 121%. That drop wasn’t necessary.”
South Africa has had lots of rain and most dams are full, but water crisis threat persists
Manten criticised the department for maintaining the dam above 100% capacity.
“If 100% is full, that should be the operating level. By keeping it at 107%, they lose 7% buffer capacity. They can’t respond quickly enough to heavy rain, so everyone downstream and upstream ends up flooded.”
Manten added that the term “one-in-100-year flood” no longer reflects reality. “We see them almost every year – sometimes multiple times a year. That means there’s something wrong with the model, and yet they stick to it.”
When Manten spoke to Daily Maverick on Wednesday, 30 April, the dam was 116% full and her yard was underwater.
“We’re not able to work. And now they’re closing gates. It makes us angry. It’s extremely frustrating. With more rain forecast, we’re just more vulnerable to the next flood.”
Downstream impacts: ‘Catch-22’
Further down the Vaal River, past the Barrage near the town of Parys, other communities are also reeling from repeat floods. But they have the opposite problem: when the gates open, they flood.
Henning Visloo runs Vosrite Adventure, a fishing, camping and hiking adventure business on the banks of the Vaal River near Parys. The farm has been in his family since the late 1980s, and Visloo started the fishing adventure business in 2011 after losing his corporate job.
“After losing my dad, the farm became our livelihood, and the fishing business is how we survive,” he said. “These floods threaten everything we’ve built.”
Like other residents along the Vaal River, Visloo has faced repeated devastation from major floods – in 1996, 2010–2011, and most recently in 2022–2023 rainy season – which have repeatedly damaged his riverfront campsites and cabins. His favourite spot, Mana Pools, has been underwater for months, severely affecting his ability to host guests and earn income.
Visloo acknowledges the risk of operating within the 100-year floodline, but said it’s a necessary trade-off, as fishermen want to be close to the river.
“So where you fish, you sleep, and where you sleep, you fish,” he said. “But the risk was there – if the water comes down, then it will be flooded.”
He added: “We take the risk. That’s all we can do. We take the risk because that same guy that’s complaining that we are dumb and we do not build above the 100-year flood line is the same guy that’s going to moan and groan because he needs to walk a distance to the water to fish. Catch-22, as they call it.”
The flooding, residents say, is worsened by erratic water management. Visloo pointed to poor operational decisions by Rand Water (which manages the Vaal Barrage, while DWS manages the Vaal Dam gates), which he claims open and close sluice gates unpredictably, causing damaging surges downstream.
“The floods are not just natural; there’s human error involved,” he said.
“The dam took too long to open the sluice gates, and then they released too much water at once. Rand Water opens and closes the sluice gates almost eight times a day – open, close, open, close – and it’s devastating downstream.”
Despite the challenges, Henning remains committed to adapting, including building a 4×4 track to diversify income.
Further upstream, near the Vaal Barrage, Graeme Addison, owner of Otters’ Haunt Eco Retreat, had to evacuate his family and cancel a guest booking after rising waters threatened their property. The guest house, which is closer to the river, had water come right up to the patio.
Their house, built in the 1970s, has been affected by major floods before — in 2011, they recall stepping out of their home straight into water. In 2023, the river rose into the house itself, prompting them to raise furniture and belongings on bricks. This year, they did the same and evacuated as a precaution, although the houses didn’t flood.
“You’d lie awake at night thinking, how much more water is going to come? How many more gates are going to open?” said Karen Addison, Graeme’s partner.
“As landowners, we really have to be on the ball.”
What’s causing the flooding?
The DWS attributes flooding downstream of the Vaal and Bloemhof Dams to a combination of factors:
Location within one-in-100-year floodlines: Many homes and businesses are built in known high-risk zones. Urban expansion and informal settlements continue to encroach;
Above-average rainfall: Sustained heavy rains filled catchments and tributaries well beyond normal; and
Dam operations: When inflows exceed what the dam can safely absorb, gates must be opened to protect infrastructure – even if this risks downstream flooding.
What about all this rain?
2025 has been hit with a lot of rainfall, not just in the Vaal catchment area, but countrywide.
From January through April, the South African Weather Service (SAWS) says rainfall was above average, just as it predicted. It wasn’t quite as intense as the crazy floods of 2022/2023, but still enough to keep everyone on their toes.
The Vaal catchment, which sits in the Highveld, usually gets between 450mm and 800mm of summer rain, mostly in December and January. This year, despite some data hiccups caused by a cyberattack, SAWS confirms most places saw near or above-normal rain. Vereeniging’s weather station, the most reliable source, recorded more rain than usual.
Karen Addison, from Otters’ Haunt Eco Retreat, tracks her own rainfall data and said she has already recorded a total of 752mm from January to April 2025. She said in 2023, which also saw significant flooding, she recorded 664mm in the whole year.
While individual weather events can’t be directly linked to climate change without a comprehensive attribution study, SAWS said there is a recognised correlation between global warming and the increasing frequency of extreme weather.
Take the 2022 floods in KwaZulu-Natal, for example. Scientists from the World Weather Attribution group found that the kind of extreme rain that caused those floods now happens about once every 20 years. Before the world warmed by 1.2°C, an event like that would have been expected only once every 40 years. In other words, climate change has doubled the chances of seeing such heavy rainfall.
So, if you live in a flood-prone area, it’s fair to say your chances of seeing floods in your lifetime are climbing. More heat means more intense rain, and that means more floods, something Henning Visloo and many others along the Vaal know all too well.
Climate variability vs climate change
Muller notes that while global warming is unequivocal, its impacts on local rainfall and hydrological systems are less clear-cut.
In Muller’s 2021 study on water security under climate change, he notes that “direct evidence of significant changes in hydrological variables such as river flows is not nearly as strong and consistent as the general global warming trend”.
Muller explains that southern Africa’s climate has always been unpredictable, swinging between droughts and floods, and this natural variability complicates efforts to model risk. For example, flood risk tools like the “one-in-100-year floodline” assume stationarity: the idea that past patterns will continue into the future.
Managing the variability we can see
Instead of waiting for perfect climate models, Muller calls for managing the variability that’s already visible. This includes:
Regularly updating the data fed into hydrological models on which flood risk maps and dam operation rules are based;
Strengthening communication between dam operators, municipalities, and affected communities;.
Investing in both infrastructure (such as storage and flood defences) and institutions and ensuring decision-makers have the authority, data and coordination they need to act quickly; and
Diversifying water sources to reduce over-reliance on any one dam or river system.
“An effective approach is to focus on the management of current climate variability,” Muller says. “This strengthens the ability of communities and countries to foresee, manage, and adapt to the impacts of longer-term climate change.”
