Watershed: A video showing damage to the wall of the Bloemhof Dam has gone viral. Photo: PicVoice
The Vaal Dam, boosted by above-average rainfall, surged past more than 97.8% on Wednesday and is now almost full.
The dam, which has an additional flood-absorption capacity of 26%, is being managed in accordance with its operational rules, according to Wisane Mavasa, the spokesperson for the department of water and sanitation.
“The forecasted rainfall and routing model simulations suggest that the Vaal Dam may reach 100%, which is the normal operating rule of the dam, in the next few days,” Mavasa said. “Therefore, controlled increases in the discharge of water from the dam have been activated through control valves.”
These were not the same as sluice gates, she stressed.
“Control valves release certain quantities of water. However, these releases are still very far below safety limits and are unlikely to lead to downstream flooding.”
This week, a viral video revealed collapsing slabs in the wall of the Bloemhof Dam, which is downstream of the Vaal Dam.
On 24 February, in a letter to the deputy water and sanitation minister, Isaac Seitlholo, Naudé Pienaar, the chief executive of Agri North West, said it is a “well-known fact” that the wall of the Bloemhof Dam has been eroded by previous floods.
“It has significant structural damage, especially above the 80% level. We have warned that further damage could be catastrophic and that repairs should be done urgently,” the letter read.
“The dam levels rose by more than 10% yesterday and the dam is already 95% full with more flood water approaching.”
Pienaar requested urgent intervention including lowering levels below the damaged portion and starting immediate repairs to restore the integrity and structure of the dam.
“It is very clear that normal flooding caused severe damage in the past. Damage to the wall will be fatal and cause a crippling effect on the livelihood of all people downstream and on food security in general,” he said.
Mavasa said the department had noted the video, which showed damage to the upstream slope slabs.
“We are aware of the damages of the slabs and would like to advise our stakeholders and the public that, despite these damages, there is no imminent risk of the dam’s failure.”
The perception is that these slabs were damaged by recent or previous floods, “however, we can categorically state that this is not the case”, she said.
“The issue at this moment started a while back when the fine material started leaching through the superficial construction joints opening on the slabs due to wave action … This is joined slabs as the dam was getting constructed and this was, and has been, a progressive action in this particular area.”
All the necessary precautionary stability checks were done during the design stage of the major maintenance work taking place at the dam.
“Based on that assessment, the upstream slopes are still stable [enough] to meet the minimum required factors of dam safety.”
The department was “actively addressing” all the safety concerns and a contractor was on site dealing with this.
The Bloemhof Dam was 100% full and had an additional 16% flood-absorption capacity.
“As such, the department has also started to increase water release in that dam on Wednesday.
“These current releases are via the outlet pipes and not the sluice gates … at the Bloemhof Dam.”
This is because of increased river flow from the upper catchment area, which includes recent rainfall in the Bloemhof Dam’s catchment.
“These releases are to facilitate proper management of the water levels and to keep the dam at, or below, its full capacity.”
Mavasa said the department was closely monitoring the inflows from all the key monitoring stations.
“Water is being released slowly so as not to cause sharp changes in the river flows. If further changes are to be made in the Vaal, or in the Bloemhof, dams stakeholders will be informed in advance via the existing communication channels that we normally use.”
She added that the department was actively monitoring the water levels of both the Vaal and Bloemhof dams to ensure that the water levels did not exceed 100%.
“Should there be an update on the operating procedure to respond to any impending emergency, our stakeholders will be duly informed timeously.
“We further urge members of the public to remain calm and refrain from distribution of misinformation as this exacerbates unnecessary panic during these heavy rains.”