Sinkholes threat to houses in Gauteng

2011-10-05 22:07

Johannesburg - Gauteng authorities have warned of an increasing risk of dolomitic sinkholes opening up around Johannesburg, which has cost 38 lives in the last 50 years.

"The dolomitic situation is satanic," says Gauteng MEC for local government and housing, Humphrey Mmemezi.

"[Residents don't realise] it comes during the night... People can wake up and the section [of the township] is not there."

Greg Heath, an engineering geologist at the Council for Geoscience (CGS), says dolomite forms a loose belt around Johannesburg and makes up a quarter of the province. It stretches from Westonaria in the west to Centurion in the north and Thokoza in the east.

At least 2 600 sinkholes have been recorded.

"The damage they have caused to development and infrastructure is estimated at a very conservative R1.5bn.

Unstable land


"At least 38 people have died as a result of sinkholes and the number will increase if people do not move off unstable land," says Heath.

About 110 informal settlements exist on dolomitic land in Gauteng.

Heath says sinkholes are almost always man-induced and develop when communities move into an area with water-bearing services. In townships and informal settlements, leaking taps or burst pipes could trigger dolomitic erosion, which expands underground cavities.

In areas of mining or farming, dolomitic ground could become unstable through changes in the water table.

Two weeks ago, part of a street in Centurion collapsed as a sinkhole opened up. The 7m x 5m hole stretched over a lane of Jean Avenue, revealing water pipes and a dark depth below.

In Westonaria, an ever-growing sinkhole the size of a small dam and about 100m deep, lies a metre away from a tee-off at the local golf course.

Excuse


In Thembelihle, an informal settlement near Lenasia, protesting residents who want electricity infrastructure were told they need to relocate as the dolomitic land beneath their shacks is unstable.

Many residents are refusing to move, even though new housing developments are available for them at Lehae and Vlakfontein. They believe dolomite is being used as an excuse for removing informal settlements.

Heath says with an increasing population and a limited amount of land, the government will have to review dolomitic areas and assess the risk of erosion.

"We can't always avoid dangerous ground, but [the question is] how can we use it? People have gravitated towards Johannesburg [and surrounding areas]. We have to use what land we've got."

Unpredictable

Geologists can work out where "good" dolomite and "bad" dolomite lies.

"Good" dolomite is more stable and may allow development while "bad" dolomite is filled with voids and should be avoided.

Heath says dolomite is unpredictable over short distances and extensive surveys are needed to map it.

Engineering geologists and geotechnical engineers use a gravity surveying machine to determine the density of underground materials. A team then drills percussion boreholes at small intervals to survey what is up to 100m below.

The downside of this technology is that it is slow and expensive, costing about R250 per metre.

With few other options, the provincial government has mandated the CGS to help with surveys on populated dolomitic land.

Immediate intervention

Besides Thembelihle, seven areas in Gauteng have been prioritised for immediate intervention.

They are Khutsong and Bekkersdal on the West Rand; Bapsfontein informal settlement, Thokoza, Vosloorus, Katlehong on the East Rand; and the Centurion CBD in Tshwane.

Most have been targeted because of leaking and deteriorating infrastructure.

In Bapsfontein, the abstraction of dolomite groundwater by farmers is causing sinkholes. In Centurion, anticipated development in the CBD will increase the risk of dolomitic exposure.

Precautions have been taken for part of the Gautrain, which runs through Centurion, traversing about 16km of dolomitic ground.

The CGS's risk management strategy involves precaution, monitoring and working with property owners and developers.

For established properties, gutters and aprons - a ground covering of concrete or other material surrounding a property - are used to protect underlying dolomite from water erosion.

Water-bearing services are also monitored periodically for leakages. If a leakage is found, it should be repaired quickly.

Mmemezi has urged residents to be responsible with taps, pipes and buckets, or face the consequences.

"If they don't care and ignore our warnings, they'll be buried."

- SAPA

Read more on:    humphrey mmemezi  |  johannesburg  |  environment
NEXT ON NEWS24X

Read News24’s Comments Policy

24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.

Comment on this story
57 comments
Add your comment
Comment 0 characters remaining
 

Inside News24

 
 

Zuma: Pray for peaceful polls

President Jacob Zuma has asked members of the Universal Church of the Kingdom of God to pray for peaceful elections on 7 May.

 
 

Latest elections multimedia

Why Jack Parow wants you to vote on 7 May
The ad the SABC doesn't want to air
Elections 2014 in one cartoon
This year's election posters
 
Traffic
Lottery
 
  • Friday Grabouw - 11:32 AM
    Road name: N2 Eastbound
    DELAYS between Sir Lowrys Pass and Grabouw
  • Friday Cape Town - 10:14 AM
    Road name: M3 Inbound
    EVENT - left lane closed between Rhodes Avenue and UCT
 
More traffic reports...
 

Jobs in Cape Town [change area]

Property [change area]

Travel - Look, Book, Go!

Escape winter, head to Mauritius

Escape winter by spending 7 nights in Mauritius' tropical bliss from R13 215 per person sharing. Includes return flights, airport transfers and accommodation. Book now!

Kalahari.com - shop online today

Get many eggs in one basket!

Gaming bundles: 2 Super Hits games for R99, 3 Disney games for R99 and more + exclusive accessory bundles only available on kalahari.com. While stocks last. Shop now!

25% off bestselling books!

The Real Meal Revolution by Tim Noakes, Jeffrey Archer’s Be Careful What You Wish for, Man’s Search for Meaning by Victor E. Frank and many more titles. Shop now!

Up to 25% off electronics

Buy top electronics and save up to 25%. Such as kalahari.com’s 1# selling product the gobii eReader, Patriot X Porter flash drive, Asus Nexus 7” 3G tablet, Samsung Galaxy SIII, Lenovo G580 Notebook and many more. Shop now!

DStv HD PVR Decoder now R949

The DStv HD PVR Decoder has further revolutionised the television experience with lifelike viewing, sharper images, more vibrant colours and precision picture quality. Now R949, save R550. Offer valid while stocks last. Shop now!

Up to 30% off appliances & homeware

Save up to 30% on appliances and homeware this Easter! Offer valid while stocks last. Shop now.

OLX Free Classifieds [change area]

Samsung Galaxy s4

Mobile, Cell Phones in South Africa, Western Cape, Cape Town. Date October 24

Best bargain in big bay

Real Estate, Houses - Apartments for Sale in South Africa, Western Cape, Cape Town. Date October 25

VW Golf 6, 1.6 Trendline (Excellent condition)

Vehicles, Cars in South Africa, Western Cape, Cape Town. Date October 25

BlackBerry Torch 9810

The BlackBerry Torch 9810 gives you the powerful combination of...

From R2820.00

I'm shopping for:

Horoscopes
Aquarius
Aquarius

You may find yourself putting in that extra effort on looking good and making an impression. ...read more

There are new stories on the homepage. Click here to see them.
 
English
Afrikaans
isiZulu

Hello 

Create Profile

Creating your profile will enable you to submit photos and stories to get published on News24.


Please provide a username for your profile page:

This username must be unique, cannot be edited and will be used in the URL to your profile page across the entire 24.com network.

Settings

Location Settings

News24 allows you to edit the display of certain components based on a location. If you wish to personalise the page based on your preferences, please select a location for each component and click "Submit" in order for the changes to take affect.








Facebook Sign-In

Hi News addict,

Join the News24 Community to be involved in breaking the news.

Log in with Facebook to comment and personalise news, weather and listings.