By Charmaine Slater
A parliamentary inquiry found that the November 9, 2016, floods were exacerbated by a blockage at one of the culverts.
Six people died as a result of the floods last year.
A culvert is a structure that allows water to flow under a road. The blockage led to water overtopping the embankments and spilling onto the N3.
“This incident is an indictment on the South African Roads Agency Limited (Sanral) which is responsible for the maintenance of the culverts and our highways,” Member of Parliament Mike Waters said.
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“Despite the already poor condition of the culverts, some of them have become living quarters for vagrants and were partitioned off and divided into rooms.
“It is totally unacceptable that the situation was allowed to deteriorate to such an extent that it led to lives being lost,” he said.
Waters called for an investigation into the matter and ensuring that the person(s) responsible for the maintenance of the culverts face criminal charges.
In response to an enquiry by the NEWS, general manager for communication at Sanral, Vusi Mona, said a team of engineers inspected its network in Gauteng following the flash floods on November 9.
“The independent report confirmed that the flood was an exceptional 1:200 year (one-in-200-year) flood,” Mona said.
He also told the NEWS that maintenance of the culverts within Sanral’s jurisdiction is regularly done, but the culvert system is not designed for major floods such as those which occurred.
Findings of the report:
The parliamentary report reflects on the events of November 9, 2016, and explores reasons for the flooding which occurred at specifically three sites:
• R24/N12 interchange.
• Linksfield Road interchange.
• Gillooly’s Interchange.
From the conducted hydrological and hydraulic analyses, the following can be concluded:
• The Linksfield interchange flooding can be attributed to the excessive high rainfall resulting in peak floods exceeding the hydraulic capacity of the drainage systems.
A blockage at one of the culvert inlets further exacerbated the problem, resulting in water overtopping the embankments and spilling onto the N3.
The flow phenomenon was interesting and unexpected. In cases where debris, however, blocks a hydraulic structure, flooding can occur.
• The median barrier in the case of the N3 flooding probably prevented further loss of life, as it prohibited water from crossing the N3, which would have washed vehicles into the Little Jukskei River.
It further resulted in the N3 northbound being accessible during the event and providing an escape route.
• The R24/N12 culvert system is inadequate to handle the recommended design flood (1:80).
The inlet configuration, changes in catchment area and proximity of the commercial developments all played a role in the problems experienced at this site.
• Various scenarios have been analysed to find a workable solution for conveyance of the floods downstream.
The suggested solution would be to provide an additional four culverts underneath the R24/N12 and create a retention/stilling pond upstream, linking the existing channel to the new culvert system.
The existing structure underneath the N12 consists of two 1.2 x 3.1m culverts.
The situation here is that if the capacity of the culverts under the N12 is increased, the houses on the northern side of the N12 are flooded.
A rough estimate of the cost of these works is R30-million to R40-m.
• Increasing of the capacity of stormwater conduits and the inlets at the Gillooly’s Interchange is required to drain water from the freeway.
The existing pipe system is made of 600mm diameter pipes and it is proposed to supplement them with a 900mm pipe.
A rough estimate of the cost is R4-m to R5-m.
