When Henry Grimes was driving along Heriot Drive in George last March, the last thing he expected was that his SUV would plummet nose-first into the road.
But this was the reality Grimes faced when his vehicle ended up in a sinkhole filled with water and mud.
Grimes escaped the vehicle and swam to safety with his nine-year-old son. His lawyer, Corlia Bester, said she was “still in discussion” with the municipality about their belief that the road should have been cordoned off after a water main burst.
Grimes’s experience might have been unusual, but sinkholes are not. The Council for Geoscience says roughly 200 sinkholes have been reported in SA in the last five years.
The City of Tshwane said it had recorded 41 sinkholes, with Centurion, Laudium, Pretoria west and Atteridgeville the areas worst affected.
“We are planning to execute the repair works, but to repair sinkholes costs millions and, having a tight budget, it becomes more difficult,” said city spokesperson Sipho Stuurman.
Stuurman said that in the 2020/21 financial year five sinkhole repairs had cost R30m, with each taking up to nine months because of the specialised nature of the work. The budget for sinkhole work this year is R28.5m.
He said two sinkholes at the junction of Len Beyers Avenue and Dan Pienaar Road in Pierre van Ryneveld Park, reported in June 2018, were a priority, and repairs on the first were almost complete. Work on the second would start on February 1.
Willem Meintjes, manager of the engineering geology and geohazards department at the Council for Geoscience, said most sinkholes occur in Gauteng's greater Centurion and Carletonville/Khutsong regions.
The latest sinkhole in the province developed at the weekend on the N1 near the Flying Saucer interchange, also in Pierre van Ryneveld Park. The South African National Roads Agency (Sanral) said the sinkhole had opened after heavy rain, forcing the closure of two lanes.
Sanral said engineers and geotechnical specialists were working on a repair plan but it was not yet clear how long the lanes would remain closed.
Meintjes said the Centurion area was prone to sinkholes mainly due to the dolomite rock in the area.
“In Gauteng, but more specifically in the Tshwane region, the primary causes of sinkholes are due to concentrated stormwater ingress — especially after heavy rains — or leaking water-bearing infrastructure,” he said.
Research had shown that sinkholes could be almost eliminated by dolomite risk management, he said.
“This typically includes maintenance of water-bearing infrastructure, upgrading and replacement programmes of ageing infrastructure, stormwater management and control and land-use restrictions, among other things.”
Dolomitic rock underlies about 25% of Gauteng and Meintjes said “active and stringent implementation of risk-management and mitigation measures” are vital if land in the region is developed.
Other sinkholes develop due to mining, he said. “We have a number of these old mines that historically mined quite close to the surface and that can also cause sinkholes to occur.”
There is an example of a mining-related sinkhole in Snake Road, Benoni, east of Johannesburg.
Meintjes said sinkholes are caused by two human-induced triggers: large-scale extraction of groundwater in dolomitic areas or concentrated ingress of water from leaking water and sewer pipes or stormwater runoff.
“This can result in the erosion of surface materials into already cavernous dolomitic sub-terrain, leading to the formation of either a sinkhole or a subsidence at surface,” he said.
“With an increase in ageing water-bearing infrastructure that requires more stringent routine maintenance and monitoring, or ultimately replacement, and densification of development on dolomitic land, the rate at which sinkholes occurs can be expected to increase over time if effective dolomite risk-management systems are not implemented.”
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