Gauteng’s big sinkhole problem – and how much government is spending to fix it
As part of a recent parliamentary Q&A session minister of public works, Thulas Nxesi, expanded on the risk of buildings built on ‘dolomite’ areas across Gauteng.
Nxesi said that due to a considerable amount of assets built on dolomite land, the department has established a Dolomite Risk Management Unit (DRMU), which is mandated to monitor the dolomitic conditions of these areas.
“The DRMU is, among others, responsible for monitoring the department’s facilities constructed on dolomite land, to classify the dolomitic status for every greenfield and brownfield project and to monitor the designs and construction of projects executed on land underlain by dolomite formations to ensure compliance with standards and specifications,” he said.
Nxesi added that the DRMU has a full-time Dolomite Specialist Consultant appointed for a period of three years, whose tasks comprise of the monitoring and investigation of reported and urgent dolomite incidences.
The consultant is also responsible for surveying and conducting integrity inspections of current infrastructure to ensure that deteriorated infrastructure with a high likelihood of causing subsidence and sinkholes is proactively replaced, he said.
“The Department is also in a process of finalising the appointment of an emergency contractor (after the previous contract had expired in the previous financial year), who will assist in addressing emergency dolomite-related requests.
“In the previous financial year, a total of R2.2 million was spent on dolomite-related professional consultancy fees for monitoring, investigations, and issuing of technical specifications for the repair of already occurred and reported dolomite incidences.
“This represents 93% of the R2.4 million allocation for the 2017/2018 financial year. A total of R118 million was spent on preventative and remedial dolomite capital and maintenance projects. This represents 105% of the R112 million allocation for the 2017/2018 financial year.”
Nxesi said that in the current financial year, a total of R127 million has been allocated for dolomite related projects and services, which include the professional consultancy services for the specialist consultant, emergency construction services, and preventative capital projects.
About R55 million of this allocation has already been spent, he said.
“Most of the preventative projects are concentrated in the City of Tshwane area covering Thaba Tshwane, Centurion, Waterkloof and Swartkop.
“There are however, other projects implemented across the Gauteng Province, which include Lenasia (Westonaria), Katlehong (Ekurhuleni), Olifantsfontein (Ekurhuleni), Carletonville (Merafong), KwaThema (Ekurhuleni), Protea (Johannesburg) and Dobsonville (Johannesburg).
“In the coming financial year of 2018/2019, the department is planning on continuing to strengthen its dolomite risk management programme by, among others, strengthening the DRMU through the recruitment of suitably qualified and experienced persons to carry-out the mandate of the unit, and prioritisation of more preventative capital and maintenance projects with more focus on the Thaba Tshwane and Centurion areas.”
Why building on Dolomite is a risk
A Department of Water Affairs guideline on dolomite may help understand why the government is spending so much money on a risk unit.
According to the document, dolomite rocks make up some of South Africa’s best aquifers. This is because they often support boreholes and springs which yield a lot of good-quality groundwater.
“Although sinkholes and dolines can form naturally, some human activities may increase the risk of these events occurring. For example, water leaks at the surface (from a broken pipe for instance) can erode the soil cover into cavities in the dolomite bedrock which can then result in a sinkhole appearing on surface,” it states
“Excessive pumping of groundwater lowers the underground water level (water table), which can also raise the risk of sinkholes and ground instability. Allowing the water table to fluctuate (move up and down) outside of its natural range also leads to more rock being dissolved, and can increase the risk of sinkholes.
“The maintenance of the original groundwater conditions within an aquifer can therefore be critical to dolomite stability. For these reasons, groundwater management in dolomite areas which are prone to sinkhole risk is important. It is not just a case of managing the water resource for its own sake – groundwater management decisions can affect the stability of the ground and the safety of buildings as well.”
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