The Vaal Dam is full, now what?

The Vaal Dam has exceeded its full capacity, currently sitting at 102.14%, prompting water authorities to implement measured releases to maintain safe water levels.

As Vaal Dam water levels rise quickly, experts and the Department of Water and Sanitation have clarified whether the dam will overflow, and any potential danger this may pose.

Current Vaal Dam status

According to The Reservoir, a Water Resource Information Centre for the Catchment Management Forums of the Upper Vaal Water Management Area, recent measurements taken on Wednesday showed the dam recording an inflow of 119.9m³/s while maintaining an outflow of 41.7m³/s.

This follows a significant increase in outflow that began on 6 March, when authorities raised the release rate to 60m³/s as the dam approached 100% capacity.

This elevated outflow rate was maintained until early this week.

At the Vaal Barrage downstream, Wednesday’s readings indicated a water level of 7.5m with an outflow of 59.7m³/s. The water temperature was recorded at 21.9°C.

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Vaal Dam management strategy

Department of Water and Sanitation spokesperson Wisane Mavasa explained on Monday that despite reaching full capacity, the dam has additional safeguards in place.

“We will provide another update this week, but as part of our flood management plan to ensure that there is balance between the inflows and outflows at the dam, the department is currently releasing at 61.2 cubic metres per second (mᵌ/s) using five valves at the dam,” Mavasa said.

She clarified the purpose of these controlled releases: “These releases are meant to ensure that the dam’s capacity stays within the range of 100% to 103% at the current inflow levels.”

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Dam infrastructure

The Vaal Dam’s water release system consists of eight valves that manage river outflow.

Under normal conditions, water authorities typically operate just two valves, which release between 16.8m³/s and 17.6m³/s to maintain the natural river flow.

With five valves currently in operation, authorities are demonstrating their commitment to proactive water management during this period of high water levels.

Vaal Dam sluice gates on standby

Water and Sanitation Minister Pemmy Majodina previously assured that the Vaal Dam’s sluice gates are up to standard.

She said the department would warn communities nearby if water needed to be released from the dam to maintain a safe level.

This is a precautionary measure to prevent overflow, which she said could lead to disaster.

Although the dam has been checked and is safe, residents downstream would need to be informed when water is released to avoid panic.

The department of water and sanitation has also provided crucial insights into the dam’s capabilities.

“The Vaal Dam operates with a full supply level of 100%, but it has a flood absorption capacity of 26%, meaning it can accommodate water levels up to 126% before posing a significant structural or operational risk,” the department explained.

As a precautionary measure, they aim to keep the dam’s level below 103% to ensure optimal peak inflow attenuation.

The department employs comprehensive monitoring systems, including real-time flow gauging stations, South African Weather Service rainfall forecasts, and advanced hydrological modeling tools.

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Expert insights on potential overflow

Contrary to public concerns about overflow, officials have emphasised that the Vaal Dam is designed to manage high water levels safely.

Midvaal councillor Pieter Swart clarified, “The Vaal Dam doesn’t ‘overflow’ in the way some other dams will do. It makes use of sluice gates to release water in a controlled manner, once the dam reaches 100%.”

Water expert Carin Bosman reinforced this point, saying that the term “overflow risk” is technically misplaced.

“The dam is designed to overflow so there is no risk associated with the overflow. The risk of overflow is not a risk. The dam is designed to overflow,” Bosman stated.

She explained that overflow events typically occur “towards the middle end of March, beginning of April, and that’s the dams designed to handle overflow”.

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