After seven months of being unable to extract water from the Impofu Dam when it was de-commissioned in January due to extremely low water levels, water levels have since risen sufficiently for it to be re-commissioned.
According to Matthew Hills, Nelson Mandela Bay Municipality water engineer, the Impofu Dam was last at full capacity almost eight years ago, in November 2015. The dam levels then dropped, but hovered around 16 percent since October 2019. In fact, the dam level has not been as high as the current 17.42% since October 2021.
Noticing the gradual decrease in dam levels, Hills said that the municipality initially contracted Northfield Engineering to install barges, a floating platform with pumps and motors placed directly on the water in early 2020 which would enable them to extract low levels of water to supply the Elandsjagt Water Treatment Works Intake Tower.
“The intake tower within the Impofu Dam is unable to extract water below 16 percent and it was therefore necessary for the municipality to arrange for the installation of these barges. The barges enable the municipality to abstract dead storage water when needed,” said Hills.
He further said that a similar system of barges had been utilised at the Impofu Dam during the drought of the late 1980s, when it proved successful.
“Despite this intervention, the Impofu Dam continued to decline faster than it could be replenished from rainfall and reached a level of 7 percent on January 18, which is the lowest level at which the barges could operate,” said Hills.
Thankfully, after much needed recent winter rainfall, the Impofu Dam has risen above 16 percent, and thus the barges initially installed by Northfield Engineering were re-commissioned on August 12 and will now supply the Elandsjagt WTW Inflow Tower with water once more.
“The dam was recommissioned to reduce the risk of supply of water disruptions to the western and south-western part of the metro. The recommissioning allows the metro to more reliably supply water from the Kromme Sub-System which includes Churchill or Impofu Dams,” said Hills.
Marketing manager at Northfield Engineering, Neil Bisseker, said that on August 12 their municipal support team re-installed and primed the suction lines they had built specifically for the purpose of extracting water during periods of low levels at the Impofu Dam.
“Our team then repaired the variable speed drives which control the water flow rate to the tower, and it was go time,” said Bisseker.
When asked what the recommissioning of the dam meant for water users supplied by the dam, Hills said that it would allow the ability to abstract 30 million litres a day from the dam, whilst ensuring adherence to the 70 percent restrictions imposed by the Department of Water and Sanitation on the Kromme Sub-System.
Hills said,
Since the Elandsjagt WTW Inflow Tower only operates when the dam level is above 17 percent, with the gradual increase of dam levels, he said that they are looking forward to using the Inflow Tower soon.
“All consumers need to continue to adhere to restrictions and be water-wise until this extended drought period is broken,” said Hills.
According to the Nelson Mandela Bay Municipality, as of August 21, the dam levels are as follows, Churchill – 76.34 percent, Impofu – 17.42 percent, Loerie – 88.43 percent, Kouga – 59.27 percent and Groendal – 100 percent. The combined percentage is 47.68 percent.
