Impofu barges ready to extract last drops

The low-water extraction barges on the Impofu Dam. On Wednesday, the average combined level of the Bay’s dams was 19.96%
DELVING DEEP: The low-water extraction barges on the Impofu Dam. On Wednesday, the average combined level of the Bay’s dams was 19.96%
Image: EUGENE COETZEE

Two barges capable of extracting precious extra volume from the Impofu Dam are nearly completed and should be commissioned by the end of this week.

Northfield Engineering MD Robert Archibald said on Wednesday his team needed to extend the electrical cables which would link the on-board pumps to a power source in the intake tower.

“The idea is the barges need to be positioned over the deepest point in the dam. It’s 9m deep at that point and about 40m away from the inlet pipe.

“Our cables were slightly short so we’re going to install longer ones today and then hopefully test them properly on the water over the next few days.

“If all goes smoothly then the barges will be finished and ready for use next week.”

Archibald said his team had not worked on an extraction barge project before but had been referred to pipe flotation techniques developed in Canada, and were able to source the latest equipment from Dockpro, another Bay company.

“It was a really interesting project and my guys have been working flat out since we got the contract.”

They had two existing pontoons to work with but they were 12 years old, he said.

“We took them apart, refurbished them and installed new pumps at our workshop in Port Elizabeth and then took them back to site.”

Once the barges are activated, the extracted water will be channelled through the floating reticulation and into the inlet and thereafter to the treatment works and then to the Bay as normal.

The Impofu is the Bay’s biggest dam. On Wednesday, the average combined level of the metro’s dams was 19.96%.  

Nelson Mandela Bay water and sanitation director Barry Martin said in November that the Impofu Dam, then at 16.8%, had fallen below its inlet pipes.

A barge would be repaired and then floated to extract further volumes down to 9% of capacity, he said.

DA member of the provincial legislature Retief Odendaal said on Wednesday his understanding was that the Impofu could be taken down to 8% before the extracted water became too silted up.

“That will give us extract an additional 8,500Ml of water for Nelson Mandela Bay, or 27 days’ worth, going by our March average consumption of 327Ml a day.

“That’s not a lot but we are desperate.

“It will buy us a little time and allow us to reduce the pressure we are putting on the Churchill Dam with the 100Ml a day which we are presently extracting from there.

“The Churchill may be quite full at 62% but it is only a third of the size of the Impofu.

“We also need to take pressure off the Kouga Dam, which is down to 9% and which we should not be using at all.

“So if the barges are nearly ready that’s very good news,” Odendaal said.

The DA called last week for the metro to stop extracting water from the Kouga Dam to allow Gamtoos Valley farmers and the towns of Hankey and Patensie, which relied on the same source, to survive.

DA provincial leader Nqaba Bhanga said the Kouga would be down to 5.6% by the end of June and that included 3.1% dead capacity.

However, Nelson Mandela Bay political head for infrastructure and engineering Andile Lungisa said on Wednesday the metro would not be immediately deploying the Impofu barges.

“Yes, the Churchill is small but it can be taken down to a lower level.

“There are also ecosystems at low levels in the Impofu which we do not want to disturb unless it is necessary,” Lungisa said.

“If a supply problem arises on the western side of the metro then we will float the barges to extract some extra water from the Impofu but not until then.”

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