Illegal mining and leaking infrastructure are causing sinkholes in different parts of Johannesburg, damaging roads and other property.
Dolomitic land is also contributing to the development of these dangerous sinkholes.
Manager of engineering geology and geohazards at the Council for Geoscience, Willem Meintjes, said illegal mining, which has been taking place in Gauteng for more than a century, had left tunnels running underground, some close to the surface.
“Because of the illegal mining activity, those channels are being used. The illegal miners literally go to mine underneath people’s houses and that causes damage to the surface. If the old mine channels stayed as they were and there were not new mining activities, you probably would have not seen as many as you see of these collapses,” Meintjes said.
He said it was difficult for authorities to predict or plan as illegal mining activity moves from one place to another, placing public infrastructure and private property at risk.
Illegal mining has grown substantially in Gauteng and North West, with gangs creating a network of illegal activity that has been difficult to police.
According to Tiaan Ehlers, executive director environment and infrastructure services in Johannesburg, large parts of the western, southern, southwestern and northeastern parts of the country’s economic hub are located on dolomitic land, including areas of intense residential, commercial and industrial development.
Sinkholes form as a result of leaking water-bearing infrastructure, poor stormwater management or the large-scale abstraction of ground water.
But not all dolomitic land is prone to sinkholes.
Ehlers said dolomitic areas in the city include Ivory Park, Braamfischerville, Dobsonville, Dobsonville Gardens, Chiawelo, Doornkop, Protea North and South, Green Village, Meadowlands, Naledi, Nancefield, Lufhereng, Protea Glen, portions of Lenasia South, Eldorado Park, Thembelihle, Lehae, Lehae East, Nancefield, Emdeni and Thulani.
The Council for Geoscience has recorded about 200 sinkholes across Gauteng in the past five years.
Sowetan saw some of the sinkholes.
On the corner of John and Booysens streets in Selby a sinkhole has swallowed part of a second-hand car parts business.
The manager of the business, who did not want to be named, said he first saw the sinkhole in December and had to immediately remove some of the vehicles from the premises.
“It is really a mess here. As you can see, the affected area is bigger than what you see on the surface. My guys went inside the hole to see and it was really scary what they saw. The tunnels underground run as far as 30m to 40m from the intersection,” he said.
Sowetan counted 14 different channels running from the big hole into other parts of the area, including a nearby Bus Rapid Transit System (BRT) depot.
The manager said the municipality had already started bringing in soil to try fill it.
Despite this, the man said he was concerned that things could get worse.
“If we have sustained heavy rains here. I don’t know what will happen,” he said.
The sinkhole along Klipspruit Valley Road in Orlando West, Soweto, developed in May last year, leading to part of the road being cordoned off.
Traffic has been diverted into the oncoming lanes.
Tall grass is growing in the sinkhole.
A stream flows under the hole, which has eaten up two lanes and is about 3m deep.
Percy Lelope, a senior sales executive at a car dealership, said he uses the road because it is the quickest route to his home in Senaoane.
“It is scary to drive next to the sinkhole but I use it because it is the quickest way to work and I save a lot on fuel. The only challenge is that when it rains, you do not know whether the road is just going cave in while you pass there,” Lelope said.
Gloria Hlungwani described driving along the route as “uncomfortable”.
“You do not know what could happen if we can have rains like the ones they had in Durban. I use it because it is the quickest way to Orlando High, where I work,” Hlungwani said.
Another sinkhole has developed on Wemmer Pan Road, which links the inner city with the N17 to Springs on the East Rand.
The entire stretch of this road, which cuts through the woods, has been cordoned off.
Ehlers said most of the sinkholes in the city are not caused by dolomite but “failed infrastructure such as stormwater pipes collapsing or incomplete maintenance work”.
The city has started to develop dolomite risk management by-laws.
“The city will also consider the establishment of a dedicated unit within the city to monitor dolomite risks within the city with the necessary capacity to be able to assist with any trend being detective from monitoring or when an incident does occur.”
Ehlers said all developments were evaluated based on geotechnical conditions.
Meintjes said there are reasons it takes long for the municipality to fix sinkholes.
“It is not as easy as taking up a truck and just filling up the hole. Once the sinkhole forms, there are some immediate risk assessments that have to be done to safeguard infrastructure and ensure that houses are evacuated if needed. Stormwater has to be managed to ensure that it does not go into the hole. Water supply has to be cut off to prevent damage to infrastructure from pouring water into the hole.”
Geoscientific assessment must then be done to see the scope of damage underground before construction begins.
“Once you get to the point of fixing it, it can take between six and nine months to fix one sinkhole.”
Meintjes said research has proven that whenever authorities plan with scientists and engineers to properly monitor dolomitic land and upgrade infrastructure, sinkholes are successfully avoided.
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