Sanral to act following last week’s devastating flash floods

Flooding on roads during last week's flash floods.
Flooding on roads during last week’s flash floods.

Many residents have questioned the safety of South African roads following Wednesday’s flash flood tragedy. Following this week’s flash flood chaos on highways and roads throughout Gauteng, the South African National Roads Agency (Sanral) has announced that a team of engineers will be inspecting its network in Gauteng urgently to check for damage.
In addition, the agency will appoint independent, reputable registered professional engineers with extensive experience in floods and storm water systems to investigate the extreme flooding, and to advise on any remedial actions.
Edwin Kruger, Sanral’s Bridge Network Manager, said Sanral’s first infrastructure survey would look for obvious signs of damage to roads and bridges to make sure they are safe for use.
He explained the country’s freeways would have in the past been designed to pass a 1:20 year flood or up to a 1:50 year flood in the case of larger rivers. “This means that in any year there is a 5 percent chance that a flood of this magnitude or greater will occur if the design recurrence period is 20 years. The design standards used in South Africa are very similar to the varying international norms.”
He said Wednesday’s rainfall was so extreme that it was likely to be and was a once-in-a hundred-year occurrence. “Unconfirmed reports indicated that the storm was indeed severe with between 90 mm and 150mm rain falling in a very short period.”
Frequently, floods are not isolated events but can occur within days of each other depending on the type of storm encountered. “It is not possible to guarantee that a road or bridge will never be damaged or over-topped,” said Kruger. “Unfortunately, due to the possible effects of global warming this means that ever increasing extreme events and some flooding of roads can be periodically expected.”
He further explained: “After a severe storm, there is potential for soil erosion (commonly known as scour damage) or sinkholes opening up and these are closely monitored by the roads agency’s Routine Maintenance Contractors. Should problems be observed, the applicable portion of highway is closed at short notice. A further factor that influences floods is also development in the catchment areas which may increase run-off and consequent flows. It is not possible to design for each and every extreme event.”
He said the blocking of storm water pipes, culverts and bridges by homeless people was also increasingly becoming a problem. “Although they are removed on a regular basis the illegal structures blocking the storm water systems are often reconstructed within a day or two of them being removed.”
Alex van Niekerk, Project Manager at the South African National Roads Agency SOC Ltd, gave as an example of Kruger’s statement: “Last week, the maintenance unit came across a homeless man who had used concrete blocks to build a shelter in a culvert at Gillooly’s. They cleared this but it is uncertain if the structure was rebuilt a day or two later.”
Sanral has expressed its condolences to the families of those who lost their lives during the flash floods.