Catchment area in best spot:

Records show infrastructure ideally placed to feed Bay dams

WHILE Nelson Mandela Bay dam levels remain critically low despite some welcome rain this week, a review of whether existing catchment area infrastructure is positioned in the right place shows there is no better location for it.

Although there may be questions over whether dams which supply the Bay are where they need to be or should alternatively be located closer to the city, historical rainfall figures reveal they are indeed in exactly the right spot.

With the help of the South African Weather Service (SAWS), The Herald gathered rainfall figures for the main catchment areas supplying water to the Bay for the last 10 years and compared them with the rainfall received in the city itself.

The results show there is in fact very little difference between the rainfall in the city and the areas around it that supply its water.

In fact, over the last 10 years the average rainfall has been above these regions’ historic averages, and current low dam levels can be attributed to lower than normal rainfall since late 2015 and increased pressure on the supply system.

SAWS Port Elizabeth spokesman Garth Sampson said they had heard all the questions about the dams and catchment areas before, and the bottom line was that there were no better locations for the supply dams.

“We have done the research, and looking at the stats over the last couple of decades we have come to the conclusion that building new dams, or attempting to move the ones we have, will make very little difference,” Sampson said.

“The guys who built the dams knew exactly where to build them, which is quite remarkable when you consider they did not have the technology or the records we have readily available today.”

The Impofu and Churchill dams, built in 1982 and 1943 respectively, fall within the same catchment area in the Langkloof. Historically, this region receives 600mm of rain a year, and the average over the last decade has surpassed that figure by more than 40mm.

The Kouga Dam, near Humansdorp and Patensie, was built in 1970, and over the last 10 years the average rainfall has been nearly 90mm above the historical average of 600mm.

Similarly, the Groendal Dam, near Uitenhage, has seen an average of 465mm since 2007, 15mm above its historical average.

During the same period, Port Elizabeth received 37mm above its historical average of 600mm.

The last time the dams supplying Nelson Mandela Bay were full was in November 2015. Since then, the levels have declined steadily, with not enough rain falling to raise the levels significantly.

Sampson said a catchment area needed at least 50mm of rain at a time for it to have a significant impact on dam levels, and since November 2015 these areas had not had that kind of rainfall.

The Nelson Mandela Bay Municipality said besides the rainfall figures in each dam’s specific region, their locations were also tied to large rivers and the run-off from surrounding landscapes that feed those rivers.

Municipal spokesman Mthubanzi Mniki said it was for this reason that the suggestion of moving catchment area infrastructure was impractical, with the building of new dams being a very costly exercise.

“The last dam built in South Africa was in the Western Cape, and cost the Department of Water and Sanitation in excess of R1-billion,” Mniki said.

Apart from lower-than-expected rainfall in recent months, Sampson said urban development and growing population figures were the main factors impacting on falling dam levels.

“The dams were built to supply a certain number of people, and we are exceeding that amount,” he said.

“For that reason, we want to reiterate the municipality’s cry for people to use water sparingly.”